8th European LS-DYNA Conference

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• 3-Dimensional Forming of Thick Plates - A Comparison of Deep Drawing and an Approach of Rolling and Bending within a Single Process

  Manuel Bojahr, Hannes Prommer, Ralf Tschullik, Patrick Kaeding - University of Rostock

  A variety of industries require certain 3-dimensional formed thick plates, for example in shipbuilding for shell plates. Nowadays the production of curved ship plates is mainly based on the experience of the worker and is performed manually. The results are good and sufficient for the heretofore use in industry, taking into account that the number of curved plates with the same geometry is quite small. Moreover thick plates with a variable thickness are used for instance as so called longitudinal profiles for bridge building. Currently the combination of curved plates with variable thickness does not meet a wide range of applications. But it has high potential in future. In modern shipbuilding this kind of plates offers special applications with a broad scope, e.g. reduction of weight. Renewable energies are another huge market in future. Today, wind turbines are mostly made of glass or carbon fiber. The manufacturing process leads to high precision and quality of the final product. Nevertheless, this fabrication method of rotor blades is very cost intensive and its production technology is not the best in terms of recyclability. In addition to its good reusability, the handling of steel is well known and its fabrication is inexpensive. Due to these facts an idea of rotor blades to be produced from steel arose. However, when desiring a huge output of a product with the same geometry a manual approach is inappropriate. A new process should be repeatable and within a certain accuracy. Deep drawing of the product is a natural choice but is not used for thick plates of enlarged sizes until now. This paper presents a comparison of deep drawing and a new approach. The developed process is based on a superposition of flat rolling and 3-dimensional bending. A major advantage of combining these steps is the opportunity to deliver formed plates with a variable thickness. This paper presents numerical simulations of deep drawing and rolling processes. The results are compared in terms of practicability for the production of rotor blades.

• A constitutive equation for the aging of elastomer and application to dummy impact programs

  William W. Feng, John O. Hallquist, Christoph Maurath - Livermore Software Technology Corp

  A constitutive equation for chronorheologically simple materials that describes the aging and viscoelastic behaviors of elastomer is presented. A simulated numerical uniaxial relaxation test of a material at various aging stages has been performed. The simulated experimental results demonstrate the chronorheological effect and are used further to determine the material property functions in the constitutive equation. A test of an elastomer at various aging stages has been performed. It demonstrated the same effect as the simulated numerical example. The applications of this constitutive equation to dummy impact programs are mentioned.

• A constitutive model for thermoplastics with some applications

  Arild Holm Clausen, Mario Polanco-Loria1, Torodd Berstad and Odd Sture Hopperstad - Norwegian University of Science and Technology

  A constitutive model for thermoplastics is outlined in this paper. The model consists of two parts: A hyperelastic-viscoplastic response due to intermolecular resistance denoted Part A, and an entropic hyperelastic response due to re-orientation of molecular chains called Part B. Both parts are developed within a framework for finite strains. The main constituents are the Neo-Hookean model describing large elastic deformations, the pressure-sensitive Raghava yield function, a non-associated visco-plastic flow potential and Anand’s stress- stretch relation representing the intramolecular stiffness. The 11 non-zero coefficients of the model are identified from uniaxial tension and compression tests on two materials, HDPE and PVC, which are respectively semi-crystalline and amorphous thermoplastics. Subsequently, it is employed in numerical simulations of three-point bending tests on the same materials. The model gives satisfactory predictions when compared to experimental behaviour.

• A modified approach for simulating complex compound structures within early design steps

  Georg Gruber, Daniel Klein,Sandro Wartzack - University of Erlangen-Nuremberg

  Owing to increasing relevance of lightweight design the deployment of compound structures with their beneficial material characteristics becomes more and more important. These growing demands for lightweight design cannot be met by improving constructive details at the end of the development cycle. On the contrary already the early design steps have to be exploited adequately, since these steps offer the highest freedom of design. The present paper shows a modified approach for simulating complex compound structures adapted to the requirements of early design steps. The basic idea is overlapping several basic material models (characterized by a low amount of input parameters) within one finite shell formulation to describe any combination of material effects. The benefit of the approach is a more accurate simulation of complex compound structures with reduced modeling effort. A validation of this phenomenological material superposition approach is performed by opposing the results of virtual material tests to experimental results published in the literature.

• A new advanced visco-elastoplastic eight chain rubber model for LS-DYNA

  Dr. Tobias Olsson and Prof. Larsgunnar Nilsson - Engineering Research Nordic AB

  A new advanced eight chain rubber model has recently been implemented in LS-DYNA. The material is tailored for polymeric materials. The basic theory is taken from Arruda’s thesis from 1993 but it has been enhanced with advanced features such as the Mullins effect, viscoelasticity, plasticity and viscoplasticity. The Mullins effect is described by two different models: the first one is strain based and developed by Boyce in 2004 and the second is energy based and developed by Ogden and Roxburgh in 1999. The viscoelasticity is based on the general Maxwell theory with up to six Maxwell elements (a spring and a dashpot in series). There are three different viscoplasticity models implemented: a Norton model with two parameters, a G’Sell model with six parameters and a strain hardening model with four parameters. The plastic yield strength is based on the eight parameter Hill model. The material model has been used to simulate a compression test with a rubber specimen. The material parameters were obtained from inverse FE analys and parameter fitting using LS-OPT and a force-displacement data set. The result shows that this material model can predict rubber behaviour inline with experimental results.

• A New Method for CrachFEM ‘Damage’ Parameter Calculation & Transfer from Autoform to LS-Dyna

  Michael Buckley - Jaguar Land Rover, Mike Selig - Autoform Development GmbH, Martin Oehm - MATFEM

• A novel transversely-isotropic 3D elastic-viscoplastic constitutive law for modeling fiber matrix composites

  M. Vogler, R. Rolfes - Leibniz University Hannover, F.X.C. Andrade - University of Porto, J.Schöpfer - Daimler AG, S. Kolling - German Institute for Polymers (DKI)

  A transversely isotropic elastic-viscoplastic constitutive law with a novel 3D failure crite- rion is presented, addressing high pressure effects, strain rate sensitivity in yielding and failure and volumetric plastic strain. The constitutive equations are derived in the frame- work of transversely-isotropic invariants, which allow for a coordinate system independent formulation and an easy parameter identification. Triaxiality dependent non-linearities are taken into account and entirely different yielding behavior under uniaxial/biaxial compression, uniaxial/biaxial tension and under in-plane/transverse shear stress states is addressed. Hardening curves for each loading state can easily be input either via tabu- lated data or optionally by use of a three parameter power law. Lateral plastic straining due to volumetric plastic compression and dilatation is load path dependent as well. In order to control the lateral plastic straining in each stress state, a non-associated flow rule, assuming a plastic potential which gives the direction of the plastic flow is introduced. The applicability of this novel material law is shown by two examples.The first one is a short fiber reinforced thermoplastic PA6GF60, the second one adresses off-axis tensile and compression tests of a unidirectional carbon-epoxy IM7-8552, which is widely used in aircraft industry. For PA6GF60, a complete test setup for characterizing the novel transversely isotropic yield surface is used for validation. All test cases are simulated and compared with these experiments. The sensitivity of the plastic Poisson coefficient and the influence on the simulated load displacement curves are discussed. Strain rate effects are obtained from dynamic uniaxial tensile tests and are considered by a viscoplas- tic approach. Unidirectional carbon-epoxy IM7-8552 reveal pronounced yielding under combined shear- compression loadings as it is observed in off-axis compression tests. Fur- thermore, the glass transition temperature of epoxy resin drops from above 200◦ C to operating temperature in the presence of high pressures. This results in a change of me- chanical properties, effecting the elastic parameters as well as the yielding behavior.This change of mechanical properties and the pronounced non-linear behavior in the presence of high pressure due to matrix yielding can be modeled properly with this new approach.

• A pregnant woman model to study injury mechanisms in car crashes

  Jérémie Pérès, Michel Behr, Lionel Thollon - IFSTTAR, Kambiz Kayvantash - CADLM

  Based on statistical analysis it has been estimated that 3 to 7% of pregnant women experience trauma, 2 third of those trauma are caused by car accidents. According to one epidemiologic study, the frequency of foetal losses could exceed the death frequency of children aged 0 to 4. Some numerical and experimental tools have recently been developed so as to better understand injury mechanisms leading to foetal losses, nevertheless shortcomings regarding the anatomy of the models must be outlined. Indeed they lack internal organs whereas there is a direct interaction with the uterine wall. Moreover the simplified amniotic fluid model (lagrangian) often implemented is not validated. To fulfil the need of an anatomically precise pregnant woman model, a first finite element model of a 9 month pregnant woman has been developed and validated via a PMHS experimental approach. This model was based on the Humos 50th centile male model and a simplified model of the amniotic fluid was used (Lagrangian). This paper will present the development and validation of the second generation of this model using the LS Dyna software. The geometry of the Humos 50th centile male model was adapted to the anatomy of a 50th centile woman using scaling techniques with a special focus on the pelvis. The model integrates the uterine wall, the foetus, the placenta and an Euler model for the amniotic fluid and represents the anatomy of a 7 month pregnant woman. The uterus is surrounded with main internal organs and bones. An improved PMHS approach was used for validation purpose. Some belt loading of the abdomen and crash tests were realized and compared to the numerical response of the model in similar loading conditions. The pregnant numerical model exhibited a response in agreement with the PMHS tests and will be used to investigate mechanisms leading to fetal losses. A study on parameters influencing the risk of fetal loss is also projected and could ultimately lead to specific safety systems designs.

• About Isogeometric Analysis and the new NURBS-based Finite Elements in LS-DYNA

  Stefan Hartmann , David Lorenz - DYNAmore GmbH, David J. Benson - University of California

  In the context of isogeometric analysis many research activities have focused on the use of Non- Uniform Rational B-Splines (NURBS). These NURBS-based finite elements have been studied in depth and it has been shown, that they are particularly well suited for computational analysis leading to qualitatively more accurate results in comparison with standard finite elements based on Lagrange polynomials. Due to these motivating results, NURBS-based finite elements are currently implemented into LS-DYNA. This work outlines the basic ideas of isogeometric analysis and gives a short introduction into NURBS basis functions. The new keyword *ELEMENT_NURBS_PATCH_2D available in LS-DYNA is presented together with various possible options, like shell theories with and without rotational degrees of freedom. Preliminary results on the performance of these new elements are studied by means of a sheet metal forming example discussed in the Numisheet conference 2005.

• ALE Incompressible Fluid in LS-DYNA

  Nicolas Aquelet - LSTC Livermore, Mhamed Souli - University of Lille

  The computation of fluid forces acting on a rigid or deformable structure constitutes a major problem in fluid- structure interaction. However, the majority of numerical tests consists in using two different codes to separately solve pressure of the fluid and structural displacements. In this paper, a monolithic with an ALE formulation approach is used to implicitly calculate the pressure of an incompressible fluid applied to the structure. The projection method proposed by Gresho is used to decouple the velocity and pressure

• An airbag application for the ALAR incidences for the Passenger Aircrafts

  Vailore Anandan

  The airbag system can be designed to reduce the damage on the fuselage during an Approach and Landing Accident Reduction (ALAR) situations as well as ditching in the water for the transcontinental flights. Minimum hull damage protects the passengers in deep waters. A preliminary investigation for this end is performed in this paper. A simple model under 10000 elements is used to investigate the problem. The findings of the LS-DYNA finite element simulation are reported in this paper. It also shows a filtering effect on the impact pulse on the structure. The spikes on the deceleration pulse can create injury to the occupants. The airbag filters the pulse thus reducing various injuries to the occupant apart from hull protection. The most useful feature is its automatic deployment at the most critical moment. This is also useful for the small and mid-size aircrafts to survive various ALAR incidences. It saves life as well as property in case of the small crafts.

• An Approach to capture the Ejection Mitigation Requirements of FMVSS 226 with Finite Element Simulations

  André Haufe, George Dimitru - DYNAmore GmbH, Andreas Hirth - Daimler AG, Robert Kirchner - Friedmann & Kirchner

• An Effective Curve Matching Metric for Parameter Identification using Partial Mapping

  Katharina Witowski - DYNAmore GmbH, Markus Feucht - Daimler AG, Nielen Stander - Livermore Software Technology Corporation

  This paper describes a new method for curve matching essential to the solution of inverse problems represented by system parameter identification. Hysteretic response curves are specifically addressed as a general class. The method is based on Partial Curve Mapping (PCM) of the experiment curve onto the computed curve. This methodology involves a curve matching metric which is computed using the volume between the test curve and the computed curve section. A number of examples are presented to demonstrate the capability. These examples represent hysteretic curves which are impossible to match without mapping.

• An Overview of User Defined Interfaces in LS-DYNA

  Tobias Erhart - Dynamore GmbH

  The user-defined features in LS-DYNA are powerful tools that allow users in academia or industry to verify research results in the context of general and complicated finite element applications. Implementation work concerns only the special field of interest, and there is no need for the comprehensive task of developing and maintaining the complete finite element software. The most popular user interface is for material modeling. But there also exist user interfaces for structural elements, airbag sensors, solution control, friction, interface control, weld failure, loads, output control, adaptivity, thermal contact, and others. An overview of current user-defined interfaces in LS-DYNA version 971 R5.0 will be presented. The aim of this contribution is to bring together the possibilities to add own numerical models and algorithms to the code. Therefore, each interface is described in its functionality. It will be explained, how to activate the particular interface in the input, where to find the corresponding subroutine, and which input/output arguments can be used.

• Analysis of a single stage compressed gas launcher behaviour : from breech opening to sabot separation

  F. Plassard, J. Mespoulet, P. Hereil - Thiot-Ingenierie

  Single stage compressed gas guns are used in Shock Physics laboratory to perform characterization experiments and ballistic events. The main advantage of this kind of launcher is that impact conditions are well defined (impact obliquity, impact velocity). In order to achieve high quality in ballistic performance, it is essential to understand the behaviour of the projectile in the barrel of the gun. This paper is devoted to the simulation of the whole behaviour of a laboratory gun, from breech opening up to the muzzle blast sabot separation due to air drag forces. LSDYNA was used as a numerical tool for the improvement of the launched package behaviour which consists in sabots and projectile. The simulation needs to reproduce the in-bore operations of a launcher taking into account gases which act on both sides of the projectile: very high pressures release at the base as well as pressure built-up and the gas thrown out from the tube at the front. There is also a need to predict perfectly the sabots behaviour when the projectile is released from the tube so as to control the impact conditions on the target. The Fluid / Stucture Interaction (FSI) capability of LSDYNA is used as a numerical tool to increase the knowledge in this field. The challenge is to obtain a simulation recreating the effect of gases on the projectile at both high pressures and high velocities. High speed and ultra high speed video cameras set up in our facility allow us to make correlation between calculations and experiments and so validate the simulation. This work gives to our Laboratory a real tool for optimizing the sabots design in terms of material, shape, dimensions and thus increases the quality and reliability of ballistic experiments.

• Analysis of Fibre Orientation using μCT Data

  Sebastian Mönnich, Robert Glöckner , Florian Becker - German Institute for Polymers (DKI)

  Integrative simulations are based on a calculated bre orientation from which the local material properties can be derived in several ways. For instance the micro-mechanical model proposed by Tandon and Weng may be used coupled with an orientation averaging approach to include the bre orientation. This approach then gives the elastic properties of the bre matrix compound with a strong dependency, of e.g. the elastic modulus, on the bre orientation. Modeling failure for nite element simulations, e.g. crash, also requires knowledge of the bre orientation, because the failure strains and energy dissipation also depend on the orientation of the bres [1, 2]. The accuracy of the calculated bre orientation depends on several simulation input parameters, which are not necessarily physical properties. The most important example is the bre interaction coecient (c). This parameter allows the user to modify the calculated bre orientation from isotropic to transversely isotropic [3]. In this paper a new experimental method to determine the bre interaction coecient is presented. The classical approach to validate the calculated bre orientation would be the usage of optical microscope images of cut surfaces of the specimen and the calculation of the bre orientation by measuring the cut ellipsis dimensions. This method is very time consuming and with respective to the necessary magnication not very accurate, because not all bres can be accounted for. The new method is using a model based algorithm to analyze three-dimensional micro computer tomography measurements. This enables the identication of up to 90% of the bres within the specimen and calculate a second order orientation tensor and the bre length distribution in any arbitrary space. Due to the fact that a model based algorithm is used, the bre detection can also be performed, if the density of the matrix polymer is near to the density of the bre material. This is a novelty to existing bre orientation measurements with computer tomography. To obtain reliable data which can be directly compared with injection moulding simulations, several steps had to be taken. First of all a representative volume must be dened, in which the bre orientation will be evaluated. This representative volume must be the same in the injection moulding simulation and the μCT measurement. As the injection moulding model is already discretized, the representative volume is set as a stack of nite elements over the part thickness. To calculate the second order orientation tensor in exactly the same geometrical space and the same coordinate system as in the injection moulding simulation, it was necessary to develop a method which allows a reconstruction of the original part from which the μCT specimen was taken. A special painting and evaluation procedure were implemented into the existing method to recalculate the original position and orientation of the specimen, enabling us to achieve the desired measurements. At the moment the determination of the bre interaction coecient requires still many injection moulding simulations, which then are compared to the measured values. This allows for a more realistic bre coecient in comparison to the default parameter. The next steps are to automate the described procedure and to correlate the measured bre orientations directly with the bre interaction coecient to avoid unnecessary simulations.

• Analysis of formability of advanced high strength steel sheets with phenomenologically based failure criteria with separate treatment of instability, shear and normal fracture

  K. Isik, C. Soyarslan, A.E. Tekkaya - Technical University of Dortmund, H. Richter - ThyssenKrupp Steel Europe AG

  Despite their wide application in sheet metal forming analysis, Forming Limit Diagrams cannot supply reliable results for the cases involving non-proportional strain paths or material classes with reduced ductility such as advanced high strength steels (AHSS). Fracture criteria appear as complimentary tools for assessment of formability in these cases. CrachFEM, as an advanced failure model, merges an instability criterion that includes strain hardening and yield loci effects with fracture criteria which monitor damage accumulation for ductile normal fracture and ductile shear fracture separately where stress triaxiality ratio and maximum shear stress dependence are taken into account, respectively. In the present study, rectangular deep drawing of two AHSS classes is studied both experimentally and numerically. Blanks with different rolling directions and blank orientations with respect to the punch are taken into account. Simulations are conducted using CrachFEM failure model and LS-DYNA where texture of the sheet due to rolling is modeled with Hill’48 type anisotropic yield locus. Experimental studies reveal that the failure occurs mainly due to instability with necking whereas in- plane shear stress state in drawing zone seems to be insufficient to create shear fracture. Numerical results show not only the predictive capability of CrachFEM but also regarding weaknesses which needs improvement for better predictions.

• Application of LS-DYNA SPH Formulation to Model Semi- Solid Metal Casting

  F. Pineau, G. D’Amours - National Research Council Canada, Aluminium Technology Centre

  Semisolid metal alloys have a special microstructure of globular grains suspended in a liquid metal matrix. This particular physical state of the matter can be exploited to produce near-net-shape parts with improved mechanical properties. Indeed, semi-solid processes take advantage of a much higher apparent viscosity of the die cast materials by limiting the risk of oxide formed on the free surfaces to become incorporated into the casting when the material is injected into the die. Semi-solid processes that use billets as feedstock material are however tied up with an additional type of surface contamination. During the injection phase, the external-skin on the periphery of the billet, which has been in contact with air and lubricant during the transfer in the shot sleeve may be incorporated into the casting. This can be an important cause of reject for most structural parts in the automotive industry. In order to predict and control the occurrence of skin inclusion into cast parts during the injection phase of semi- solid processes, Lagrangian methods are appropriate. Indeed, the skin, composed of contaminated or even partially solidified metal, has different mechanical properties compared to the core of semi-solid aluminum. Abitrary- Lagrangian-Eulerian formulations, which can account for the coupling between the “solid” skin and the flow of “semi-solid” aluminum are promising but still necessitate a huge amount of computer power. On the other hand, particle based Smoothed Particle Hydrodynamics (SPH) approaches are particularly well suited to this kind of flows involving complex flow behavior and solidification. These methods are able to track accurately free surface flows with fragmentation and break up as well as to follow the advection of oxides through the flow. In this paper, a first analysis is performed in order to investigate the potential of the SPH solver of LS-DYNA to deal with the problem of skin inclusion in semi-solid die casting processes. Preliminary results show that the SPH approach is a very promising simulation tool to follow the skins during semi-solid injection casting.

• Behaviour model for semi-crystalline polymer, application to crashworthiness simulations

  R.Balieu, F.Lauro, B.Bennani, B.Bourel - Univ Lille Nord de France, K.Nakaya, E.Haran - TOYOTA MOTOR EUROPE

  Today polymer materials are frequently used in the transport domain with more severe specification requirements. The behaviour modeling and failure prediction have consequently become a priority. In this paper, an elasto- viscoplastic behaviour model is presented, with non associated plasticity, damage and strain rate effect, which represents the observed behaviours of a semi-crystalline polymer under dynamic loading.

• BEM Methods For acoustic and vibroacoustic problems in LS-DYNA

  Yun Huang - Livermore Software Technology Corporation, Mhamed Souli - University of Lille, Rongfeng Liu - JSOL Corporation

  This paper presents the new developments of finite element methods and boundary element methods for solving vibro-acoustic problems in LS-DYNA. The formulation for a frequency domain finite element method based on Helmholtz equation is described and the solution for an example of a simplified compartment model is presented. For boundary element method, the theory basis is reviewed. A benchmark example of a plate is solved by boundary element method, Kirchhoff method and Rayleigh method and the results are compared. A dual boundary element method based on Burton-Miller formulation is developed for solving exterior acoustic problems which were bothered by the irregular frequency difficulty. Application of the boundary element method for performing panel contribution analysis is discussed. These acoustic finite element and boundary element methods have important application in automotive, naval and civil industries, and many other industries where noise control is a concern.

• bjective evaluation of the quality of the FAT ES-2 dummy model

  Christian Gehre - PDB, Sebastian Stahlschmidt - DYNAmore GmbH, Matthias Walz - DAIMLER AG

  The numerical simulation is an essential part of the development of the passive safety of vehicles. Robust and predictable computational models are the base of the successful application of those simulations. Crash test dummies and their virtual counterparts are measuring tools to evaluate the injury risks to occupants in car crashes. The progress of those dummy models was remarkable over the past years. By increasing the quality, the potential of further significant improvements declines. Hence, the assessment of im- provements and their impact on the overall quality of simulations is getting more complex. Major improvements of sub-parts do not necessarily improve the overall performance of a model. There- fore, a standardised objective evaluation of models could ease the definition of priorities of model updates. Objective rating tools could help to solve this problem. These tools are calculating the level of correlation between two signals, usually coming from test and simulation. All signal ratings can be merged to global ratings. However, the analysis of only one loading case is not sufficient to calcu- late a reliable and a robust quality score of a dummy model. A more comprehensive approach is required to provide a valid rating for all relevant loading conditions. Furthermore, it must distin- guish between good and poor models and should correlate with user experiences. This paper presents results of a study to assess the quality of the LS-DYNA FAT ES-2. The data set comprises results of dummy certification tests as well as results of various component and sled tests. The extraction of the most relevant dummy responses was an essential part of the evaluation too. Finally, all scenarios were applied to different releases of the FAT ES-2. The cal- culated quality scores were verified with the experiences of users of the model. The findings of this study are limited to the FAT ES-2 model but can be transferred to another dummy model. However, the selection of loading cases and signals must be adjusted to each dummy.

• Comparison of material models for crash simulation - experimental and simulation work

  S. Mönnich, F. Becker - German Institute for Polymers (DKI), B. Fellner - MAGNA STEYR Fahrzeugtechnik

• Complexity based design robustness analysis

  Damien BORDET, Kambiz KAYVANTASH - CADLM

  Application to mechatronic component (vehicle hatchback )

• Computational simulations of aluminum foam projectile behavior

  M. Borovinsek, M. Vesenjak, Z. Ren - University of Maribor, S. Itoh - Kumamoto University

  The results of experimental tests and computer simulations of open-cell aluminum foam behavior under high deformation rates are presented. Experimental Taylor impact tests showed, that the open-cell foam projectile deforms already during its acceleration in the Taylor barrel. This behavior was investigated further by use of computer simulations with the LS-DYNA. The simulations confirmed very high sensitivity of open-cell foam projectile to the acceleration.

• Cowper-Symonds material deformation law application in material cutting process using LS-DYNA FE code: turning and milling

  Virginija Gyliene, Vytautas Ostasevicius - Kaunas University of Technology

  Finite element modeling becomes the huge support in understanding technological process. Besides, there are no so much milling process studies, or these studies are simplified to, as orthogonal cutting process. This paper presents experiences results from orthogonal turning and face milling process. These results were taken for FE model validation and material deformation law constants prediction. In both cases some cutting process simplifications were taken, in order to define contact interaction - to execute meso-scale FE analysis. Concerning FE modeling, calculation scheme is presented in order to evaluate removing material load to cutting tool. Secondly, material behaviour characteristics were evaluated, assuming high speed deformation and material failure. Thirdly, cutting tool path is modeled in order to evaluate his influence on chip formation.

• Crashworthiness and Sensitivity Analysis of Structural Composite Inserts in Vehicle Structure

  Chung-Kyu Park, Cing-Dao Kan, Pradeep K. Mohan - The George Washington University, Steven W. Reagan - L & L Products Inc., Balachandra R. Deshpande - SimaFore Inc.

  This study is focused on identifying influential parameters in numerical analysis of structural composite inserts in vehicle structure. A 3-point bending test of a simplified steel-composite beam structure is conducted to evaluate the crashworthiness of composite insert in steel structure. Empty sections of the beam structure are filled with composite insert and foam filler. From physical 3-point bending tests, it is identified that the two critical behaviors of composite insert and foam filler greatly affect the strength level of steel-composite beam structure. Some influential parameters to achieve an accurate simulation model are studied. Finally, future steps of research work are indicated.

• Crashworthiness of an Electric Prototype Vehicle Series

  F. Huberth, S. Sinz, S. Herb, J. Lienhard, M. Jung, K. Thoma - Fraunhofer EMI, Freiburg, K. Hochberg, C. J. Fleig - University of Applied Sciences Offenburg

  The Shell Eco-marathon (SEM) is a challenge for student teams to develop energy-efficient vehicles and demonstrate the fuel efficiency of their prototypes. In Europe, this takes place at the Lausitz Ring in Germany. Since 2009, the Schluckspecht team has taken part in the Urban Concept category of the SEM. The specification of the vehicles which start in the Urban Concept Group requires resemblance to roadworthy cars. In the last quarter of 2009, the University of Applied Sciences Offenburg (FHO) where the team is located and the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI, Freiburg, set up a cooperation to improve safety of the prototype Schluckspecht City. Fraunhofer EMI deals with physical-technical aspects of high-speed, mechanical, and fluid-dynamic processes. This includes experimental and numerical analyses of crash, impact and penetration processes in a broad range of speeds from 10 m/s to 10,000 m/s, the response of structures to shock loads, dynamic material response and vehicle safety.

• Deep drawing simulation of α-titanium alloys using LS-Dyna

  Sebastijan Jurendić - University of Ljubljana, Silvia Gaiani - University of Modena and Reggio Emilia

  Titanium alloys have excellent properties for their target applications; however their use is still limited by high price and formability issues. To avoid extensive on-site trials and to cut development costs, a numerical simulation method is developed for the deep drawing process of α-titanium (hexagonal close packed) alloy sheet using LS-Dyna. The Barlat 1989 material model is adopted for modelling the plastic response of the material and the necessary input data is examined. It is found that in order to adequately capture the plastic properties of HCP titanium, load curves are needed both for strain hardening and to capture the strain dependency of the plastic strain ratio. A procedure for determining the material input data from the tensile test results is developed and an exemplary data set is given. To identify a suitable value of the Barlat flow potential exponent m a parametric analysis is carried out using a simulation of the Erichsen cupping test. Forming limit diagrams are adopted for failure prediction, the forming limit curves are determined using the Nakajima method and a simplified procedure for obtaining limiting shear strains on a tensile testing machine is presented. To confirm the method an example of a deep drawn end-cap for a motorcycle exhaust muffler is presented and the simulation compared to the physical forming process with good results.

• Development and verification of a material model for prediction of containment safety of exhaust turbochargers

  Dieter Memhard , Florence Andrieux , Dong-Zhi Sun - Fraunhofer Institute for Mechanics of Materials IWM, R. Häcker - Bundesanstalt für Materialforschung und –prüfung BAM

  For predicting the containment safety of turbochargers against failure of rotors at elevated temperatures and dynamic loading the complex deformation and damage behaviour of the respective materials has to be determined by appropriate experiments and on the other hand the temperature and strain rate dependency has to be described by a material model to simulate the component behaviour under these complex loading conditions. The investigations focus on the cast iron alloy EN-GJS-400 with nodular graphite. Its mechanical behaviour under uniaxial and multiaxial tension as well as under compression and shear loading has been investigated for a variety of loading rates and temperatures. For the numerical modelling of the containment safety of turbochargers a material model has been developed with the capability to describe the specific deformation behaviour of casting materials, e.g. different properties under tension and compression, temperature and strain rate dependence. The deformation behaviour was described with a model for thermally activated flow and the damage behaviour with a Johnson-Cook type model and an extended failure model (bi-failure model) respectively. The material model has been verified by numerical simulations of penetration tests under highly dynamic impact loading conditions. Also a containment test on a turbocharger was simulated.

• Development of a thorax finite element model for thoracic injury assessment

  Nestor N. Nsiampa, C. Robbe, A. Papy - Royal Military Academy, Belgium

  Kinetic energy non-lethal weapons (KE-NLW) are now widely used by law enforcement, by military forces, by the police in situations where the use of lethal arms is not required or suitable. Unfortunately, their effects are still not well known. Therefore, there is a need to better understand the injury mechanism induced by such projectiles for a better prediction of the risk of injury. This may be beneficial for the manufacturer, the deciders or the end-users. Numerical simulations are being increasingly used for that purpose. This paper describes first steps in the development of finite element model for thoracic impacts. All the simulations were performed with Ls-Dyna code. For validation purpose, the results were compared to the results of tests made on Post-Mortem Human Subjects (PMHS) published in literature. The sensitivity of contact option and the use of two sets of parameters for the lung material model were examined.

• Development of a water filled fender system for off-shore installations

  Sean Duvall - AMEC

  In order to extend the life and productivity of an off-shore oil and gas platform an new installation has been proposed to provide a compression unit. The existing platform is already extensively occupied, having been in existence for over 25 years, and a new approach was required to facilitate the compression unit. This additional facility is an addition outside the existing envelope of the platform and in line with requirements it must withstand a direct ship impact of given mass and velocity. It has been proposed that a fender system be designed that will absorb the energy from the ship impact allowing time to facilitate repair of the platform extension without the need to stop production from the platform. LS-DYNA has been used to model the platform, the proposed extension and the fender system to determine the effects of the ship impact. As with all projects the requirements have changed during the investigation and this paper only represents some of the investigation in to suitability and design of a proposed fender system

• Development of Advanced Finite Element Models of Q Child Crash Test Dummies

  Stephen Fu, Christian Kleessen, Zaifei Zhou, Karl Koschdon, Robert Kant - Humanetics

• Development of an improved screw model at faurecia

  M. Meyer - Faurecia Autositze

  Some years ago Faurecia used a very simple screw model. In this model the screw holes are filled by a rigid body and the screw shaft is modeld by a simple spring beam with an unrealistic stiffness. But this model doesn’t represent the behavior of screws in real test. With this simple model it was not possible to get the peeling effect of the holes. And the deformation of the part and the screw was unrealistic. Also the forces inside the screw were too high. Due to the goal to reduce the time to market and the number of prototypes to develop a new product it was necessary to develop a better screw model. At the end of 2008 a new keyword was available in LS-Dyna with which it was easy to implement a defined preforce on a beam element. This was the point to start with an improved screw model.

• Development of Detailed AF05%ile Hybrid III Dummy FE Model

  Yoichiro Ohnishi, Mariko Mohri, Hayato Kaneko, Tatsuya Komamura, Tsuyoshi Yasuki

  This paper describes a development of the Hybrid III AF05%ile dummy FE model to be used for frontal crash simulations. The precise geometries of the dummy were measured at a pitch of 1.0 mm using X-ray CT scans. The material properties and the mechanical responses of the components were measured in static and dynamic tests and were used for the model validation. The FE model results showed a good correlation with the kinematics and injury index values to those in the sled impact test.

• Development of Frequency Domain Dynamic and Acoustic Capabilities in LS-DYNA

  Yun Huang, Mhamed Souli, Cleve Ashcraft, Roger Grimes, Jason Wang - Livermore Software Technology Corporation, Mostafa Rassaian, Jung-Chuan Lee - The Boeing Company

  A set of new features for frequency domain dynamic and acoustic computation have been implemented in LS- ® DYNA . They include random vibration and high-cycle fatigue analysis, frequency response functions, steady state dynamics, response spectrum analysis, and acoustic analysis based on boundary element methods or finite element ® methods. The objective of introducing these new features is to add capabilities to LS-DYNA to solve frequency domain vibration and noise radiation problems. This class of problems is very common in auto and aerospace industries and many other industries. The paper provides a brief introduction of the new features. Keywords for the features are introduced. Areas of applications are discussed. Some examples are given to illustrate how to use these features.

• Efficient nonlinear multi-scale modeling of composite structures

  Thibault Villette, Jan Seyfarth, Roger Assaker, Laurent Adam - e-Xstream engineering

• Efficient Processing of Multiple Contacts in MPP-DYNA

  Brian Wainscott - Livermore Software Technology Corporation

  Complex models often contain more than just a few contact interfaces. The decomposition of such a model can result in an uneven distribution of these contacts among the available processors. Some contacts may lie wholly on a single processor, while others will be distributed across many or all of the processors. Some processors may have many contacts to handle, and others may have none. This variability can cause inefficiencies which adversely impact scalability. I will show recent work on contact algorithms in MPP-DYNA which addresses some of these issues.

• Failure modeling of a self piercing riveted joint using LS-DYNA

  Silke Sommer - Fraunhofer Institute for Mechanics of Materials IWM, Johannes Maier - LuK GmbH & Co. KG

  Besides the basic product requirements, the aspect of energy efficiency is in the center of automobile engineering. A mixture of different light weight materials like aluminium and higher strength steels, called multi-material mix, is used increasingly to fulfill these requirements and reduce the weight of the vehicles. Hence the challenges for the joining technique are increasing. Mechanical joining techniques like self piercing riveting have great potential to fulfill this challenge. In particular the joints are the highest loaded parts during crash loading and overloading situations and have to be modeled in crash simulations. Joints are modeled with simplified elements in crash simulations due to efficiency. The simplified models should be able to reproduce the deformation and failure behavior as well as the energy absorption of the joints with less computational cost but with adequate accuracy. In this paper the modeling possibilities in LS-Dyna are investigated for a self piercing riveted joint of aluminium sheets. Beams, eight-noded hexahedrons, hexahedron clusters and constrained elements have been used for a simplified modeling of the riveted connection. The material models MAT_SPOTWELD, MAT_SPOTWELD_DAIMLER, MAT_ARUP_ADHESIVE, MAT_COHESIVE_ MIXED_MODE_ELASTOPLASTIC_RATE and the constrained models CONSTRAINED_SPR2 and _SPR3 have been tested with the simplified rivet model. The failure models are based on forces and moments, on normal, shear and bending stresses, on stresses and fracture energies and on forces and displacements for the constrained SPR models. The model parameters were determined by simulation of specimen tests under tension, lap-shear, peel and combined loading and by fitting the measured force vs. displacement curves. The different numerical results are compared concerning the measured load bearing capacities and energy absorption. The comparison showed that the hexahedron element with MAT_COHESIVE_MIXED_MODE_ELASTOPLASTIC is the most promising model for self piercing riveted joints in aluminium sheets because of the good description of the measured force vs. displacement curves and energy absorption under tension and lap-shear loading. The weakness of this model is the insufficient modeling of the peel loading and the lack of a possibility to control mixed mode loading. The paper gives a recommendation for further developments of modeling self piercing riveted joints.

• FEM study of metal rolling in grooved rolls

  D.V. Shevchenko, D.Yu. Saraev - Siemens Corporate Technology, A.I. Borovkov, D.L. Nesterenko - St. Petersburg State Polytechnical University

  LS-DYNA was used to model the rolling process in grooved rolls. One-pass and two-pass (with rotation of the metal sheet at 90° a fter first pass) rolling in grooved rolls, as well as four-pass rolling in plain rolls and various combinations of these two types of rolling were simulated. With the help of finite-element analysis we estimated the influence of the areas of deformation hardening on the stress-strain state of metal sheet. The developed finite-element model allows analyzing stress-strain state of the system caused by variation of parameters, such as: geometry (design), rolling speed, physical- mechanical properties of materials, temperature and friction coefficient. Process parameters can be fine-tuned to achive the desired improvement of physical-mechanical properties of the rolled metal .

• Finite element analysis of localised impact loading on short glass fibre- reinforced polyamide engine oil pan subjected to low velocity impact from flying projectiles

  Zakaria Mouti, James Njuguna - Cranfield University, Keith Westwood, Darren Long - Eaton, Automotive Group

  This paper investigates low velocity impact involving a glass fibre-reinforced polyamide engine oil pan as part of a complete new development of thermoplastic components. The assessment of the impact resistance has driven the need to employ LS DYNA for finite element modelling in order to virtually benchmark and predict the strength and fracture behaviour of stressed plastic parts. In order to develop a reliable predictive capability and to validate simulations, complete components were manufactured by injection moulding techniques for the experimental samples. Low velocity impact investigations were carried out using a gas gun and a falling weight tester in order to simulate impact events to which the oil pan is subjected whilst in operational service. This was intended to point out damage tolerance and failure mechanisms likely to occur in the structure. The study results show the significant contribution of the design in terms of shock absorption. Specific oil pan design with protective ribbing combined with a superior material considerably improves the impact resistance. The paper provides results and discussions on experimental and finite element analysis investigations before concluding with some remarks.

• Finite element dynamic simulation of whole rallying car structure: Towards better understanding of structural dynamics during side impacts

  E. Nassiopoulos and J. Njuguna - School of Applied Sciences, Cranfield University

  Side impact accidents against a tree or pole remain the most dangerous accident scenarios in rally cars. Statistical data shows that 52% of the fatalities between 2004 and 2009 concern crashes against a rigid pole by the track sides, whilst among those more than 60% were side impacts. Despite the present scientific efforts, rallying cars side impacts are still among the least understood primarily due to limited space between the occupant and door sill, evolving safety regulations and vehicle dynamics. In this study, finite element dynamic characteristics of the whole car were studied. The finite element model consisted of the whole car structure and 241 parts including the engines, tyres and the suspension members with 4 different element types and 7 material models. All structural parts were modelled as low-carbon steel with the piecewise-linear-plasticity material model (mat 24). The tyres were modelled with the Blatz-Ko rubber material (mat 07) whilst also rigid and other materials (mat 020, 01, 09, S01 and S02) were used to represent different parts of the model, as the suspension members, suspension links and the engine. A rollcage and two racing seats were modelled with four-node shell elements and the use of piecewise-linear-plasticity and composite-damage materials respectively. A semi-cylindrical pole of 200mm diameter was also designed and modelled as a rigid body. The model was used to first investigate the dynamics of the crash, and later run a wide range of simulations and parametric studies in the cage, the car’s floor and the seats. The important findings from the study are presented, conclusions drawn and scope for further development outlined.

• Hail Impact Simulation on CFC Covers of a Transport Aircraft

  P. Starke, F. Mayer - EADS Deutschland GmbH

  Due to increasing weight saving requirements in new aircraft, structures traditionally built from aluminium alloys are increasingly replaced by carbon fibre reinforced Composites (CFC). For the preliminary flight clearance hail imact si- mulations were perfomed on CFC covers. For the composite material the authors applied a user- defined material. Behaviour of ice / hail stone was modeled through fitting of parameters for the Johnson–Cook material model to appropriate test data. While the precision of simulations was sufficient for a preliminary assessment, further tests will be necessary for permanent approval as well as for refinement of numerical models.

• How to Use LS-OPT for Parameter Estimation – hot stamping and quenching applications

  Arthur Shapiro - LSTC

  The “direct” heat transfer problem is one in which material properties and boundary conditions are specified, and LS-DYNA [1] is used to calculate the temperature response of the nodes in the mesh. The “inverse” heat transfer problem is one in which the temperature response of a node point in the mesh (e.g., a surface node) is specified from experimental measurements, and the objective is to calculate material properties and boundary conditions that cause this temperature response. This paper describes how to use LS-OPT [2] to solve the “inverse” heat transfer problem. Applications include: - calculating material parameters for austenite-to-martensite phase change kinetics, fitting material properties to experimental data - calculating contact heat transfer coefficients as a function of temperature and pressure during hot stamping, fitting a function to experimental data - calculating boiling heat transfer coefficients for quenching in liquids , fitting a load curve to experimental data

• Hypervelocity impact of aluminium sphere against aluminium plate : experiment and LS-DYNA correlation

  F. Plassard, J. Mespoulet, P. Hereil - Thiot Ingenierie

  High velocity impact of 3 mm diameter aluminium sphere against thin aluminium target plate has been performed at impact velocity of about 4000 m/s with the two stage light gas gun HERMES at Thiot Ingenierie laboratory. Impacts at normal incidence and with a 32° angle generate debris clouds that were collected by an aluminium witness plate. The visualization of the debris clouds generated after the impact has been realized by using an ultra high speed framing camera. LSDYNA 3D Smooth Particle Hydrodynamics and 2D&3D Multi- Material ALE solvers (MMALE) were used to reproduce debris clouds generation and expansion in the two angle configuration. Agreement between simulations and experimental frames are discussed.

• Impact Simulations on Concrete Slabs : LS-OPT Fitting Approach

  Nicolas VAN DORSSELAER, Vincent LAPOUJADE - Alliance Services Plus, Georges NAHAS, François TARALLO, Jean-Mathieu RAMBACH - Institut de Radioprotection et de Sûreté Nucléaire, Fontenay-aux-roses

  This paper is based on a work realized for an international OECD benchmark initiated by IRSN and CNSC. The main goal of IRIS_2010 Benchmark was to evaluate the ability of simulation to reproduce experimental tests of impacts on concrete slabs for two different deformation modes: bending (flexural) and punching. LS-DYNA® has been chosen by IRSN as their main explicit code for simulating such high speed impacts on concrete. Most LS-DYNA® concrete laws include two sets of physical parameters, a first one related to basic concrete parameters (Compressive strength, Poisson ratio), a second one related to each concrete model (Damage, strain rate effects). LS-DYNA® provides an automatic generation capability for the second set of parameters (based only on the Compressive strength) which leads to an acceptable level of accuracy for the majority of cases. However, this automatic set of parameters can usually be optimized to better fit experimental results. For each benchmark case, we performed an advanced 3 steps fitting approach using LS- OPT®. A Monte Carlo analysis was done first on several model parameters to study sensitivities and correlations and identify which ones can affect the slab damage and may improve the results. Then, an Optimization of identified parameters was realized to fit the experimental results. Finally, a complementary Monte Carlo analysis on physical parameters (Concrete resistances, Poisson’s ratio...) was used to evaluate the robustness of our optimal solution and to integrate in our calculation process uncertainty and variations of material data.

• Implementation of a Strain Rate Dependent Human Bone Model

  Zahra Asgharpour, Erich Schuller, Steffen Peldschus - Institut für Rechtsmedizin der Universität München, Dirk Fressmann - Dynamore GmbH

  Strain rate dependency of mechanical properties of cortical bone has been well demonstrated in literature studies. Nevertheless, the majority of these studies have been done on nonhuman bone and at lower magnitudes of strain rates. The need for a mathematical model which can describe the mechanical behavior of bone at lower strain rates as well as higher ones is essential. A human finite element model THUMS (Total Human Model for Safety) [1], developed by Toyota R&D Labs and the Wayne State University, USA has been applied for this study. This work proposes an isotropic elastic-plastic material model of cortical bone where rate effects have also been considered.

• Improving the Prediction of LS-DYNA Calculations with Rhodia Data and Digimat

  Cécile DEMAIN - Lyon Research and Technology Center

• imulation of the flow around a Vertical Axis Wind Turbine : LS-DYNA v980

  Iñaki CALDICHOURY, Vincent LAPOUJADE - Alliance Services Plus, Hervé LE SOURNE, Abdelhaq ABDELQARI - Institut Catholique d’Arts et Métiers, Facundo DEL PIN - LSTC

  The future 980 version of LS-DYNA® will include Computational Fluid Dynamics (CFD) solvers. The main objective of these new solvers will be to perform fluid structure interactions by directly solving the Navier-Stokes equations and by using any LS-DYNA® Lagrangian model for the solid part. In the process of evaluating the new possibilities offered by these new solvers, in particular concerning fluid structure interaction, AS+ has worked in partnership with both industrial and academic clients on the case of a vertical axe wind turbine which was used in the French around the world boat race “Vendée Globe”. The final objective of these simulations is to test various turbine shapes and airfoils in order to determine which one would offer the best aerodynamic behavior without any compromise to its structural behavior. Tests were therefore first conducted on static or oscillating airfoils. Then, 2D simulations of various turbine shapes were performed before aiming for the complete 3D simulation of the problem. This paper aims to highlight the main features of the new incompressible solver by presenting the results obtained on one of the first industrial cases that use the new v980 version.

• Incompressible CFD Results Using LS-DYNA. For High Reynolds Number Flow Around Bluff Bodies

  I. CALDICHOURY, F. DEL PIN - LSTC, V. LAPOUJADE - AS+

  This report will provide some insight on the new incompressible CFD solver that will be available in version 980 of LS-DYNA. Several test cases were performed by AS+ in order to evaluate the capabilities of these new solvers. These studies were conducted in cooperation with LSTC’s CFD developers. Among the various test cases, the airflow over the Ahmed body, a simplified car model will be presented. The flow around this body reproduces the basic aerodynamic features of cars on a well defined basic geometry in order to study the complex interactions associated with vortex wakes and boundary layer separation/reattachment zones. Results were compared to experimental data extracted from reference papers. The results shown here are all part of the global validation process of the incompressible CFD solver.

• Influence of HE shape on blast profile

  J. Mespoulet, F. Plassard, P. Hereil - Thiot-Ingenierie, A. Lefrançois - CEA

  This paper is concerned by the effect of HE geometry on the shape of the blast wave. The aim of this work is to increase the knowledge on pressure profile generated by blast wave so as to optimize the design of explosion chambers. These facilities are commonly designed for spherical HE but most of the customer charges have other geometry (line, plate, cylinder ...). Numerical simulations performed with Multi Materials Arbitrary Eulerian solver in LSDYNA were used to simulate hemispherical and rectangular shape HE events detonated on the ground. Pressure records in front of the charge (reflected pressure) and on lateral positions at different locations (incident pressure) are compared to experiments performed at CEA / Gramat. High speed video has also been used to visualize the shape of the fireball and the shock wave in air. It is confirmed numerically that the shape of explosive generates different shape of blast wave and so will change the way of designing new chambers.

• Integrating plastics molding and structure dynamics analysis by leveraging LS-DYNA, MOLDEX3D and PRESYS

  Allen Y. Peng, Emily Wu, C.T. Huang - CoreTech System (Moldex3D) Co.

  An increasing number of automotive or consumer electronics parts are made of engineering plastic for its low cost and superior material properties. The traditional structure analysis for injection-molded plastics part is to perform CAE analysis based on the assumption of one or several isotropic materials. However, the material characteristic of plastic part is extremely dependent on molding process. The process-induced properties, such as fiber-induced anisotropic mechanical properties or weld-line defects, might not be favorable to the structural requirement of final products. Besides, the mesh requirement for different analysis purposes might not be the same, either. In this topic, we integrate the CAE analysis of structure and plastics molding through the integration of LS-DYNA, Moldex3D, and PreSys. This approach shows the effects of mutually dependent analyses have been successfully examined in some injection-molded parts.

• Investigation and Application of Multi-Disciplinary Optimization for Automotive Body-in-White Development

  Allen Sheldon, Edward Helwig - Honda R&D Americas, Yong-Bae Cho - CSM Software

  A process has been created for applying multi-disciplinary optimization (MDO) during the development of an automotive body-in-white (BIW) structure. The initial phase evaluated the performance of several different optimization algorithms when applied to structural MDO problems. From this testing, two algorithms were chosen for further study, one of these being sequential metamodeling with domain reduction (SRSM) found within LS-OPT. To use the LS-OPT optimization software effectively within a production environment, adaptations were made to integrate it into an established CAE infrastructure. This involved developing a LS-OPT server and architecture for the parallel job submission and queuing required in the MDO process. This enabled LS- OPT to act as an integral part of the enterprise CAE architecture as opposed to a standalone tool. Within this integrated environment, the SRSM method has been applied to an MDO process that combines 7 load cases and takes into account crash and NVH requirements. The objective of the MDO was to minimize mass while constraints enforced the performance requirements of each load case. The thicknesses of 35 parts were considered in this MDO. The application of the SRSM MDO strategy resulted in an optimized design with a 6% weight reduction for the portion of the BIW considered. The optimized design was determined with reasonable computational resources and time considering the computational intensity of the analysis.

• Investigation of Failure Criterion in Dynamic Torsion Tests with Solid Cylindrical Specimens

  Pavel A. Mossakovsky, Fedor K. Antonov, Lilia A. Kostyreva - Moscow State University

  When investigating the limiting states of materials under dynamic loading conditions, it’s important to specify the dependency of plastic failure strain on the stress state. Usually, such dependence is build upon the experimental data obtained from dynamic tests in tension and compression of solid cylindrical specimens with different working part geometry, followed by a monotonic extrapolation. In the recent studies [1] the existence of complex, non-monotonic dependence of failure strain on the stress state parameters is shown for a number of materials. In these cases, a mentioned set of tests is not enough to construct a reliable criterion relations. In statics, one of the most informative experiments for the failure criterion construction is a torsion test on solid or thick-walled cylindrical specimens. Although a nonuniform stress state arises in the sample in this case, effective methods of its interpretation are developed [2,3]. The theory of this experiment conformably to the dynamic processes at large plastic strains has not yet been developed. Using the LS-DYNA implemented virtual test bench, the experimental setup for the solid cylinder torsion test with high strain rates and methods of its stress state identification are discussed. It is shown that for the strain rate range of 102-104 1/s the kinematic hypotheses that are taken in the quasi-static torsion are valid, that allows the effective use of known methods of the sample’s stress state decoding.

• LS-DYNA application to develop a package for air transportation of fissile materials

  A.V. Abramov, O.V. Voykina, E. Yu. Emelyanova, D. Yu. Karpov, I. A. Kochura, I.V. Minaev - Zababakhin FSUE RFNC-VNIITF

  Object of computer study is a package for FM storage and transportation based on a container AT-400R [1]. Shock and fire resistant container AT-400R was designed at Sandia National Laboratories (USA) and was tested by US and Russian specialists in compliance with the IAEA regulations [2], including cases of flooding, falling of a slab with mass 500 kg from the height of 9 m, container dropping from the height of 1 m onto the pin 150 mm in diameter. In the frames of the ISTC projects # 1216 and 1449, performed computation proved that the IAEA regulations to safe transportation of FM are met. Besides, computation determined limited loading, when 500 kg slab falls from the height of 50 m and freefall of the container from the height of 50 m. When this limited value of loading is outranged, inner containment vessel looses tightness. The objective of this work is to develop a package, based on this container, for FM air transportation, which will provide FM pressure-sealing in conditions that are regulated by up- to-date IAEA requirements – package collision with a target at a velocity 90 m/s.

• Material Data Determination and Crash Simulation of Fiber Reinforced Plastic Components

  Florian Becker - German Institute for Polymers (DKI, Stefan Kolling - Institute of Materials and Applied Mechanics, THM, Julian Schöpfer - Daimler AG

  The quality of the mechanical simulation of reinforced thermoplastics depends on very com­ plex input parameters regarding the complex material behaviour. At the beginning of the sim­ ulation chain the material data has to be determined in different mechanical tests (tension, compression and shear, different fibre orientation to load direction, etc.). After the injection moulding simulation the calculated fibre orientation has to be mapped to the structural FE mesh. For the structural simulation a combination of the material model MAT108 and MAT54 was used to simulate the orthotropic, load case sensitive material behaviour.

• Mechanical Characterization of Talc Particle Filled Thermoplastics

  Frank Kunkel, Florian Becker - German Institute for Polymers (DKI), Stefan Kolling - THM

  In this paper, we present the experimental part of the development for an integrative simulation with Moldex3D and LS-DYNA for talc particle lled polypropylene. The properties of thermoplastic polymers considerably depend on the process of moulding irre- spective of the geometry of the part and the raw polymer used. Both, the polymer structure resulting from moulding and formation of weld lines may show a large inuence on mechanical properties. For analysing the inuence of injection moulding on the resulting structural part properties, plates with dierent processing conditions were fabricated with Hostacom XBR169G, a polypropy- lene (PP) lled with rubber and talc. Afterwards, dierent test samples, longitudinal and lateral to ow direction, were milled out from the fabricated plates. Using this extracted test samples, the true deformation and failure behaviour were measured by uniaxial tensile tests and shear tests at small and high strain rates. The complex deformation behaviour was determined by grey-scale correlation strain measurement. The analysis of quasistatic uniaxial tensile tests shows anisotropic eects depending on the prepa- ration direction of the specimen in stress behaviour as well as in Poisson's ratio. This also can be seen at dierent testing temperatures and at high strain rates. The reason of the anisotropic eects might be an orientation of the talc particles. In all experiments, the strain at failure is not inuenced by testing direction. The measured data provide the basis for a material model, which is implemented in LS-DYNA. The model is validated by a three-point bending test.

• Modeling of Cone Penetration Test Using SPH and MM-ALE Approaches

  Ronald F. Kulak, Cezary Bojanowski - Argonne National Laboratory

  The American Society of Association Executives (ASAE) Soil Cone Penetrometer Standard (S313.2) is designed to characterize general soil mechanical conditions. Its results are used predominantly for comparative purposes. Variations of this test are used for in-situ determination of the geotechnical engineering properties of soils and delineating soil stratigraphy. This paper presents a comparison between experimentally obtained results of cone penetration test with results from LS-DYNA®/MPP simulations performed on a high performance cluster computer. The previously reported experiments (conducted by USDA-ARS National Soil Dynamics Laboratory, Auburn, AL, USA) were performed on Norfolk Sand. These experiments show the variation in results for test conducted under identical conditions. In the LS-DYNA simulations, the soil was modeled using the material model MAT_005 Soil and Crushable Foam. Two approaches were used to represent the soil: a hybrid approach that combined Lagrange and Smoothed Particle Hydrodynamic (SPH) methods and the Multi Material Arbitrary Lagrangian - Eulerian (MM-ALE) method. The vertical resistance force versus penetration distance of the penetrometer cone was compared to the experimental results. A close match between numerical results and experimental data was obtained in the study for the Norfork Sand. The response simulated using the two numerical approaches were almost identical. A sensitivity study revealed that the penetrometer force was most sensitive to the soil density followed by sensitivity to a failure surface parameter.

• MPP Execution of Implicit Mechanics with 10M or More Elements

  Dr. C. Cleve Ashcraft, Roger G. Grimes, and Dr. Robert F. Lucas - LSTC

  LS-DYNA models for Implicit Mechanics are getting larger and more complex. We are continually seeing models where the linear algebra problems in Implicit Mechanics have 3 to 5 million elements and know of at least one that is nearly 30M elements. It is these very large linear algebra problems that distinguish the computer requirements for Implicit Mechanics. This paper will present a study of the performance of the MPP implementation of implicit mechanics in LS-DYNA examining such issues as performance, speed-up, and requirements for computer configuration.

• Multi-scale Approach for CFRP Composite Simulation by JSTAMP/NV and DIGIMAT

  Noriyo Ichinose - JSOL Corporation

• Numerical Simulation of Consequences of Passenger Aircraft Tyre Damage

  Dr. Alexander Ryabov , Dr. Vladimir Romanov , Sergey S. Kukanov , Dr. Andrey Kudryavtsev , Anatoliy Botvinkin - Sarov Engineering Center, Maxim Litvinov , Vladislav Gubin , Dmitry Egorov - CJSC Sukhoi Civil Aircrafts

  All new-designed passenger aircrafts have to meet strict national and international safety requirements in accidents. One of the accidents is pneumatic tyre failure (a tyre burst). Because of that the tyre can be fragmented. An air stream from the tyre and some tyre pieces under the air stream can impact on vitally important aircraft system elements in the landing gear box and disable or break them. In this case a designer has to provide a documentary evidence of system assembly reliability in possible accident cases considered. The problem solution by means of direct full-scale tests is too much expensive. Therefore the experimental-numerical method based on the optimal combination of a detailed computer simulation and model experiments for the computer simulation verification can be used. Numerical simulation and some experimental results of dynamic elastic-plastic deformation researches of some aircraft system subjected to the air flow pressure and the tyre piece impact are presented in the paper. The numerical investigations are performed by means of gas-dynamics and structural strength conjugate problem solution on the basis of STAR-CCM+ and LS-DYNA® software.

• Numerical simulation of spiral-strand cables subjected to high velocity fragment impact

  R. Judge, Z. Yang, S.W. Jones - University of Liverpool, G. Beattie - Arup

  This paper presents the results of a numerical study carried out to evaluate the response of high-strength steel spiral-strand cables, when subjected to high velocity fragment impact. A detailed numerical model of a 60 mm diameter spiral-strand cable subjected to impact from a 20 mm fragment simulating projectile has been developed for analysis in LS-DYNA. Detailed consideration was given to the complex geometry of the cable, wire-to-wire contact and friction, cable-end boundary conditions and appropriate material modelling. Fragment velocities between 200 and 1400 m/s were modelled to assess the penetration and perforation resistance of the cable and to study the magnitude of localised cross-sectional cable damage. The numerical results were validated against initial laboratory tests. In both the tests and numerical simulations none of the cables were perforated by the fragments and good agreement was seen in the damage area, the fragment penetration depth and the wire splay phenomenon.

• Numerical Simulation of the Ice-Structure Interaction in LS-DYNA

  Hamid Daiyan and Bjørnar Sand - Northern Research Institute (NORUT Narvik)

  Design of offshore structures in Arctic waters is strongly dependent on local and global ice loads. These loadings are, in general, contact forces transmitted to the structures during interaction with ice floes, ice ridges or icebergs. The prediction of ice forces on structures relies heavily on a thorough understanding of mechanical behavior of sea ice as well as on in-depth knowledge of interaction between ice features and structures. Sloping, or conical shaped structures are commonly used structures for arctic oil and gas exploration and production due to the fact that these structural shapes induce ice bending failure on the structure slope, so that the horizontal ice loads on the structure can be reduced compared to a crushing type of failure, which occurs when ice floes interacting with vertical structures. As an ice sheet advances toward a conical or sloping structure, the ice load increases until the drifting ice sheet fails by bending and forms ice blocks. Following the failure of the ice cover, the failed ice blocks are pushed up the sloping structure or forms ice rubble in front of the structure. Predicting the correct failure modes (crushing, bending, and splitting or combined modes of failure) is desirable as well as the global force on the structure. However, this is not straightforward due to the complexity of the mechanical behavior of ice. It is facing some challenges such as, anisotropy (ice can be considered as a transversally isotropic material), inhomogeneity, and strain rate and pressure dependent response. Some of these key behaviors are considered on this study as a preliminary start for the further investigations as a part of the ColdTech project.

• ODB-10M New Topcrunch Benchmark Data

  Mitsuhiro Makino and Shota Yamada - DYNAPOWER corp

  New Benchmark model ODB-10M is 10 million elements model, which consist of refined NCAC Taurus model and LSTC shell ODB barrier model. Refined NCAC Taurus model is 9 million elements of type16 shell elements and type2 solid elements, and *CONSTRAINED_SPOTWELD is changed to *CONTACT_SPOTWELD with beam. In LSTC shell barrier, type10 shell element is changed to type16 shell element in order to avoid negative hourglass energy. We also discuss about the domain decomposition.

• On Fracture Criterion of Titanium Alloy under Dynamic Loading Conditions

  Pavel A. Mossakovsky, Fedor K. Antonov - Moscow State University, Anatoly M. Bragov, Alexander Yu. Konstantinov - State University of Nizhni Novgorod, Mikhail E. Kolotnikov, Lilia A. Kostyreva - FSUE "Gas Turbine Engineering Researh and Production Center-Salut"

  One of the most important factors in ensuring the adequacy of the mathematical modeling of limiting states of structures is the choice of the material local fracture criterion and accurate determination of its parameters. The paper discusses some traditional approaches to the construction of local failure criteria of metals under dynamic loading, methods of their parameters identification, as well as the development of these approaches on the example of impact penetration problem. The work focuses on the possibility of modeling viscous and brittle types of fracture within a single deformation type criterion, while the dependence of fracture strain on the stress triaxiality ratio can became complicated and nonmonotonic. The quality of the considered criteria is determined by comparing the results of virtual simulation with the data of full-scale experiments that implement various types of stress state and failure mechanisms. The results of full-scale and virtual compression, tension and penetration dynamic tests of the titanium alloy samples are given. Virtual experiments were conducted using nonlinear LS-DYNA code.

• Optimizing Thermoplastic Parts in Crash Applications - Status and Vision

  Andreas Wüst, Dr. Stefan Glaser – BASF SE, Dr. Steffen Frik - Opel AG

• Orion space craft water and land landing system simulation; An injury case study

  Ala Tabiei - The University of Cincinnati, Chuck Lawrence - NASA Glenn Research Center

  NASA’s return to moon program had kept the NESC (NASA Engineering and Safety Center) busy for the past several years. The NESC was charged to come up with a safe landing for the Orion capsule. Water and land landing is considered for the Orion capsule. The NESC took major initiative to come up with recommendation to the program. Part of this initiative is to come up with Injury criteria recommendation during the landing of the Orion capsule. Impact simulation is used to assess the injury and pulse responses of the Orion during landing. Major tasks were under taken to validate the steps of the impact simulations. The models used in water landing, soil landing, and the finite element dummies were validated through experimental testing. In here some of the validation is presented. The paper finally compares the injury values of the astronauts during water and land landing.

• Parametric Modelling of Simplified Car Models for Assessment of Frontal Impact Compatibility

  Mathias Stein, Darius Friedemann, Alexander Eisenach, Heiko Johannsen - Technische Universität Berlin, Hans Zimmer - SFE GmbH

  The aim of the FIMCAR project (co-funded by the European Commission within the 7th Framework Programme) is to develop and validate a frontal impact assessment approach that considers self and partner protection. In order to assess the influence of different test procedures and metrics on car- to-car compatibility a huge simulation programme is envisaged. However, car-to-car simulations with models of different car manufacturers are almost impossible because of confidentiality. In addition the detailed models of the car manufacturers are complicated to optimise for different assessment procedures and are consuming considerable computational efforts. In order to overcome these problems, parametric car models were built allowing fast modifications. By simplifying the models, computational efforts are reduced. Due to the rapid increase of the calculation power the level of detail in car models has reached a very high level. At the same time the number of discretised parts drops and smaller structures are considered in the meshing process. However, only a few structures are mainly responsible for the frontal crash behaviour of the vehicle. A high variability of mounting positions, connections and stiffness of parts of a car’s front–end offers a big potential in investigations of frontal impact vehicle structures. However, the modification of these criteria is time consuming, especially the modification of a given FE-mesh or geometry model. The software SFE CONCEPTTM offers the possibility to establish an implicit parametric car model in an easy and fast way. A variable geometric model is created by the specification of base lines and cross sections for the different parts. The modification of a structure with respect to connected parts is one of the advantages of SFE CONCEPTTM. Through manipulation of the implicit parameters, new structure concepts and /or small variations of a part’s dimensions can be established. After all the software is able to mesh the geometry and export the data for different solvers like LS-Dyna. In that way it is possible to generate a manifold number of structures, in a fast and certain way which is necessary for the investigations of the influence of these structures in frontal impact compatibility. The set up of the FE model is adapted to the export data structure of SFE CONCEPTTM. This way the models can be simulated directly after modification without further post-editing.

• Performance Benefits of NVIDIA GPUs for LS-DYNA

  Stan Posey, Srinivas Kodiyalam - NVIDIA Corporation

  This work examines the performance characteristics of LS-DYNA for the latest CPU and GPU technologies available. The results are provided for system configurations of workstations for finite element models that are relevant to current industry practice. The motivation for these studies was to quantify the parallel performance benefits of LS-DYNA for the latest generation GPU from NVIDIA, the Tesla 20-series (codenamed Fermi) for implicit finite element models with 100K and greater DOFs, and for static and dynamic response load conditions.

• Performance of Large Scale Implicit Crash Analysis on Multicore Processor Systems

  Yih-Yih Lin, PhD

• Phenomenological driven Modeling of Joints

  Matthias Bier, Herbert Klamser - Dr. Ing. h.c. F. Porsche AG, Andre Haufe DYNAmore GmbH

  In the construction of automobiles different technologies are used to join sheets. Today the most common method for connections is resistant spot welding. There are thousands of spot welds in body-in-whites, which are determining the behavior of the structure under crash conditions. New research is striving after replacing these thermal joints by adhesives or rivets for optimization of the production process. It is essential to ensure a cost saving and time optimized car development to reduce the required number of experiments by using precise simulations. For the quality of such simulation models accurate reproduction of the mechanical joint behavior is necessary. Because of the fact that the element size is bound by the time step in explicit finite elements schemes, a detailed model for the joints is not applicable in typical body-in-white simulations under crash conditions. For this reason simplified models using beam or solid elements have to be used to represent the connection. In the majority of load cases current modeling strategies do not show the required accuracy needed for design decisions. Therefore new ways of spot weld modeling and approaches for rivets modeling should be investigated. For spot welds several strategies of modeling exist. They all are based on the effort to reproduce the spot weld behavior by using specially adopted constitutive or structural models. For these models parameters have to be determined by comparing the maximum load under tensile, shear and peel conditions with corresponding numerical investigations. In the present paper it will be shown that a model with a relative small number of elements driven by a rigorous phenomenological approach can achieve better results. The quality of the proposed model will be evaluated by comparison of tests with KS2-specimen. In the field of self-piercing rivets an established modeling technique doesn’t exist. In this paper firstly capabilities of several modeling techniques will be investigated and secondly they will be compared with a model based on the aforementioned approach.

• Prediction of failure on high strength steel in seat mechanisms simulation

  M. CHAUFFRAY, G. DELATTRE, L. GUERIN - Faurecia Automotive seating

  Tracks are the mechanisms which enable to translate the seat; they are key contributors in occupant safety as link between seat and car. With the current evolution of ecologic legislation, one of major automotive industry priorities is to decrease the product mass. To reach this objective, the use of high strength steels appears as a good solution with the drawback to be more brittle. In parallel, FEA models have to be more and more predictive in order to reduce the validation cost. In this context, rupture risk prediction appears as a strong need from design office and usual post-processing methods are not accurate enough to bring sufficient support to design teams. The solution chosen is a coupling between Ls-Dyna and the failure criteria crachFEM developed by MatFem Company. The evaluation of this risk is based on plastic strain evolution and stress state of the element. The methodology requires a specific characterization of the material to get information about the failure for different stress states. First application has been launched on ultimate strength subsystem on track. With dual- phase material, primary track failure mode is generally a profile rupture. First results highlighted correctly the area of rupture, but the ultimate strength was generally higher in FEA model than in the hard-test. This gap can be explained by the difference of scale between characterization of failure, which is a very local phenomenon, and the evolution of strain in simulation which is dependant of mesh size. Industrial crash model requirement (best compromise between accuracy and computation time: around 3mm mesh size) doesn’t permit to use mesh size needed for accurate rupture prediction. So “hybrid” modeling has been developed in order to have mesh size appropriate to MatFem analysis in useable computation time. With this approach the ruptures are well identified in term of areas, kinematics & ultimate strengths. Nowadays we are able, on this product, to predict with accuracy a risk of rupture on subsystem or on complete seat crash test.

• Prediction of structural response of FRP composites for conceptual design of vehicles under impact loading

  Sivakumara, K. Krishnamoorthy, Johannes Höptner, Gundolf Kopp, Prof. Dr.-Ing. H.E. Friedrich - German Aerospace Center (DLR e.V.)

  For the predictability of composite material behaviour under highly dynamic loads like crash, there is a need for better models reproducing the exact physics of failure mechanisms (matrix cracking, delamination, heat dissipation etc.). This belongs to the state-of-the-art research topics in numerical modelling. The conceptual design of vehicle structures however requires a qualitative understanding of the load-displacement characteristics, absorbed energy and the load distribution in other structural components and therefore may not necessarily demand a precise modelling of the physical behaviour. From the results of material testing of a variety of composite specimens, the necessary parameters for different LS-DYNA specific constitutive material laws are identified. After that, the modelling and simulation of simplified part samples have been carried out with dynamic loading conditions. The results are then compared with experimental testing of these part samples; hence the suitable parameters for composite design are identified. The scope, drawback and opportunities for numerical prediction using the considered constitutive laws and modelling schemes are then discussed based on the verification of the results.

• Process development for multi-disciplinary spot weld optimization with CAX-LOCO, LS-OPT and ANSA

  Dr. Gordon Geißler - DYNAmore GmbH, Thomas Hahn - Audi AG

  The number of connection entities in modern car constructions is growing continuously. From that point of view, the identification of the most suitable structural behaviour of various car body configurations with respect to the number and the arrangement of connections becomes a challenge in automotive development. A standard simulation and optimization process was developed and established in a common project with the Audi AG and DYNAmore GmbH. The simulation model assembly process consists of a car body without any connection entities, a structured data format that describe the connections in detail and an automated process that realizes the connections using ANSA. All of these components are administrated and provided through the AUDI specific simulation data management tool CAx Load Case Composer (LoCo). This software is developed by DYNAmore and provides, among other innovative features, the possibility to parameterize components of the simulation model. With that ability at hand, it becomes possible to introduce parameters for the number of spot welds on a specified line. With the automated assembly process, the simulation engineer becomes able to investigate a number of spot weld configurations with a minimal amount of time and specific process knowledge. Connecting this parameterized assembly process with a structural optimization software like LS-OPT, provides the possibility to set up a systematic investigation of spot weld configurations with respect to any simulation response representing structural performance. The reduction of the total amount of connections under consideration of constraints can be one goal of such an investigation. Also the adjustment of a desired structural stiffness or the control of the deformation behaviour by the connection setup might be possible objectives in that context.

• Progress on GPU Implementation for LS-DYNA Implicit Mechanics

  Roger G. Grimes, Dr. Robert F. Lucas, and Gene Wagenbreth - Livermore Software Technology Corporation

  Graphics processing units (GPUs) are ubiquitous devices designed to improve the end-user experience in mass market arenas such as gaming. High-end GPUs have an order of magnitude more computing power than their hosts, and are thus attractive candidates for accelerating compute bound applications such as MCAE. This talk will present how we have extended LS-DYNA to utilize Nvidia Tesla GPUs for implicit mechanics. We will describe the target environment along with performance results on a range of benchmark problems. The performance results will illustrate when it makes sense today to utilize the GPU, and when it does not.

• Qualification of *Constrained_Lagrange_In_Solid command for steel/concrete interface modeling

  L. MOUTOUSSAMY, G. HERVE, F. BARBIER - Tractebel Engineering France

  Modeling reinforced concrete is an important requirement for civil engineering calculation. Particularly, engineers need to have information about both rebar and concrete. The need for modeling them separately comes obviously to allow local and global analysis of a reinforced concrete structure. This paper focuses on the validation of modeling of reinforced concrete with the CSCM material and Constrained Lagrange In Solid to tie the rebar. The interest for this method is the possibility to mesh separately concrete and rebar and to avoid overmeshing caused by the concordance between concrete and rebar nodes. This coupling is commonly used to model Eurocodode 2 compatible reinforced concrete. In order to validate the method, a comparison between analytical and numerical results is presented for simple civil engineering frames (beam and portal frame). This first study is made with a pseudo-dynamic loading. First, a four points bending test is presented for different case of steel rate in order to validate that momentum in a section is correctly represented when the concrete is at the maximum damage rate. Then, in a second step, a bending test on a common framework is presented to confirm that the momentum is correctly transmitted in articulation. A particular attention is accorded to the formation of plastic hinges.

• Recent Enhancements to the GISSMO Failure Model in LS-DYNA

  André Haufe - DYNAmore GmbH, Markus Feucht, Frieder Neukamm - Daimler AG, Paul DuBois - Consultant

• Roof Crush Resistance and Rollover Strength of a Paratransit Bus

  Cezary Bojanowski Transportation Research and Analysis Computing Center, Argonne National Laboratory, Bronislaw Gepner, Christopher Rawl, Jerry Wekezer - FAMU-FSU College of Engineering, Leslaw Kwasniewski - Warsaw University of Technology, Faculty of Civil Engineering

  Paratransit buses constitute a special group of vehicles in the US due to their smaller size, two-step assembly process, and their use for complementary services to the regular scheduled transit routes. Due to their uniqueness these buses lack national crashworthiness standards specifically dedicated to the paratransit fleet. Several states in the US adopted the quasi-static symmetric roof loading procedure according to the standard FMVSS 220 for testing the integrity of the paratransit buses. However, as many researchers point out, the dynamic rollover test according to UN-ECE Regulation 66 (ECE-R66), which was approved by more than forty countries in the world, (excluding the US), may provide more realistic assessment of the bus strength.

• Session7_Paper2_Abstract.pdf
• Shock Wave Effect on Aluminium Foam

  M. Vesenjak, M. Borovinšek, Z. Ren - University of Maribor, Slovenia, S. Irie - Kumamoto University, S. Itoh - Okinawa National College of Technology

  The behaviour of aluminium foam under impact loading conditions and especially the shock wave propagation are still not well understood. The shock wave propagation through the cellular material structure under impact loading conditions has a significant effect on its deformation mechanism and therefore it is imperative to understand its effects thoroughly. The goal of this research was to investigate and examine the effects of shock wave propagation on aluminium foam. Additionally, the material and structural properties of pore- filled aluminium foam under impact loading conditions with particular interest in shock wave propagation and its effects on cellular material deformation have been studied. For this purpose experimental tests and explicit computational simulations of aluminium foam specimens inside a water tank subjected to explosive charge have been performed. Comparison of the results shows a good correlation between the experimental and simulation results.

• Simulation of charge and structural behaviour in an tumbling mill

  Pär Jonsén, Hans-Åke Häggblad, Bertil I. Pålsson - Luleå University of Technology, Kent Tano - LKAB, Andreas Berggren - Boliden Minerals

  For a long time discrete element methods (DEM) has been used as simulation tools to gain insight into particulate flow processes. Such a process may be grinding in tumbling mills, where the mechanical behaviour is complex. To include all phenomena that occur in a mill in a single numerical model is today not possible. Therefore, a common approach is to model milling charges using the DEM assuming a rigid mill structure. To close the gap between reality and numerical models in milling, more physically realistic methods must be used. In this work, the finite element method (FEM) and the smoothed particle hydrodynamic (SPH) method are used together to model a ball mill charge in a tumbling mill. The mesh free formulation and the adaptive nature of the SPH method result in a method that handles extremely large deformations and thereby suits for modelling of grinding charges. The mill structure consists of rubber lifter and liners and a mantel made of solid steel. It is modelled with the finite element method. For the elastic behaviour of the rubber, a Blatz-Ko hyper-elastic model is used. The supplier of the lining provided experimental data for the rubber. The deflection profile of the lifters obtained from SPH-FEM simulation shows a reasonably good correspondence to pilot mill measurements as measured by an embedded strain gauge sensor. This computational model makes it possible to predict charge pressure and shear stresses within the charge. It is also possible to predict contact forces for varying mill dimensions and liner combinations.

• Simulation of ice action loads on off shore structures

  Dr. Daniel Hilding , Dr. Jimmy Forsberg - Engineering Research Nordic AB, Dr. Arne Gürtner - Statoil ASA

  During the last years, there has been an increasing amount of work published regarding simulation of ice action on structures using finite element models of the ice. The effect of ice fracture is in these models approximated using cohesive elements. In this article we give an overview of the cohesive element method for ice modelling including recent improvements made by the authors. A description is given of the implementation of the cohesive element method for modelling floating ice sheets in LS- DYNA including effects such as buoyancy. To demonstrate the performance and robustness of the implementation, numerical results are presented from a full scale simulation of an ice sheet impacting an offshore structure.

• Simulation of shock absorbers behavior during a 9m drop test

  Fabien Collin - TN International

  TN International designs, manufactures and licenses packages for the transportation of radioactive materials. To justify the leaktightness and then insure the safety of a package during an accident event, a 9m drop test onto an unyielding target has to be considered. The corresponding kinetic energy is generally absorbed by shock absorbers filled with wooden blocks. In order to improve the numerical simulation of those shock absorbers, a benchmark has been performed using a specific drop test exhibiting an important crushing. This study has led to the improvement of the wood material law, including shear damage effect. The welds failure was also implemented to improve results. This paper will show the main results of this study.

• Simulation of Shock Wave Mitigation in Granular Materials by Pressure and Impulse Characterization

  C. Guéders, J. Van Roey, J. Gallant, F. Coghe - Royal Military Academy, Brussels

  The detonation of an explosive charge has two major effects, blast wave generation and fragmentation. New technologies of energy dissipation, based on granular materials, seem to have good shock attenuation capabilities. Plastic deformation, brittle fracture and comminution are different mechanisms of dissipation which can take place in granular media, allowing blast energy absorption and reduction of dynamic solicitation applied on structures. Dynamic solicitation of structures is determined by the reflected pressure in a quasi-static loading case or by the reflected impulse in an impulsive loading case. Blast pressure and impulse damping represent in a macroscopic way the effects of energy dissipation mechanisms appearing in granular materials. Material efficiency can be determined by the study of the attenuation of these two parameters. Vermiculite, a porous crushable material and CRUSHMAT®, a ceramic granular material made of alumina have been tested. Blast impulse amplification has been observed with thin layers of vermiculite while with CRUSHMAT® only attenuation has been observed. Efficiency stagnation has also been noticed for thick layers of CRUSHMAT® in which pressure and impulse, after being passed through the sample’s upper part, seem to be too low for further attenuation in the lower part of the layer. LS-DYNA has been used to simulate the experimental setup in which reflected pressure and impulse measurements have been realized on the different samples. The simulation model has been developed for a better understanding of pressure and impulse decrease, dissipation mechanisms and macroscopic behaviour of granular materials when they are subjected to blast. The CRUSHMAT® stress-strain curve has been optimized with LS-OPT trying to allow a better correlation between simulations and experimental observations.

• Statistical Analysis of Process Chains : Novel PRO-CHAIN Components

  Daniela Steffes-lai. Tanja Clees - Fraunhofer Institute for Algorithms and Scientific Computing SCAI

  The robustness of production processes and the quality of resulting products suffer from variations in important material and process parameters, geometry and external influences, which can have substantial and critical influences. Therefore these variations have to be analyzed and transferred over process steps in order to achieve considerably better forecasting quality. We developed the PRO-CHAIN strategy for statistical analysis of sensitivity and stability as well as multi-objective robust design-parameter optimization of whole process chains, even for simulation results on highly resolved grids. PRO-CHAIN constructs an ensemble of simulation results; this data base reflects local variations of functionals. Newly developed PRO-CHAIN components deal with transforming and ensemble compression of the data base via a fast principal component analysis with user-controlled accuracy. Essential features are the classification of design parameters into importance and nonlinearity classes in order to reduce the design space and to get an adequate accuracy for an efficient optimization. In this paper we address the importance of this classification and appropriate kinds of classification measures. Another main novel PRO-CHAIN component is the fast and accurate interpolation of new designs on the whole grid. This interpolation works also for nonlinear applications like crash if the design of experiments is adequate for a high-quality metamodel. The interpolation is based on a nonlinear metamodel with radial basis functions accelerated by a specialized principal component decomposition. Summarized, PRO-CHAIN is now able to fully locally analyze a chain consisting of several process steps with regard to sensitivity and robustness and to predict new designs with user-controlled accuracy. In each step, the influence of parameters onto criteria is classified and sensitivity is measured. PRO-CHAIN is able to propagate the essential scatter due to parameter uncertainty locally over the steps, keeping the necessary number of simulation runs small. Additionally, PRO-CHAIN allows for predicting new designs fully locally, allowing for immediate answers to what-if scenarios, without additional time-spending simulation runs. Thus PRO-CHAIN is a very efficient strategy for statistical analysis of process chains, involving parameter uncertainties, in order to get a robustly optimized solution. Recently, we integrated the efficient interpolation method described into DesParO along with LS- DYNA d3plot readers/writers: on one hand, as a so-called “mixing functionality” for constructing and dumping interpolated results, on the other hand into the novel DesParO Geometry Viewer. Now, DesParO allows for an interactive exploration of the design space, connected with direct interpolation and visualization of the new design and its functionals, like thickness, effective plastic strains and damages as well as statistical measures, locally on the whole grid. Results are presented for the forming-to-crash process chain for a ZStE340 metal blank of a B-pillar. In detail, results of importance and nonlinearity classifications in each process step are shown as well as the prediction of new designs by means of DesParO.

• The ACP Process Applied to the FutureSteelVehicle Project: The Future of Product Design and Development

  Akbar Farahani, Paul Dolan, Hamed Sharifi - ETA Inc., Jody Shaw - U. S. Steel, Marc Lambriks - Tata Steel

  WorldAutoSteel launched Phase 2 of its FutureSteelVehicle programme (FSV) with the aim to help automakers optimise steel body structures for electrified vehicles. The Phase 2 objective is to develop detailed design concepts and fully optimise a radically different body structure for a compact Battery Electric Vehicle (BEV) in production in the 2015-2020 timeframe. This paper will provide an overview of the product design methodology and how it was applied to WorldAutoSteel FutureSteelVehicle (FSV) program and result in 35% BIW mass reduction and how it has continued to evolve with each application. The Accelerated Concept to Product (ACP) ProcessTM was applied in this project. The ACP ProcessTM is a proprietary, performance-driven, holistic product design development method, which is based on design optimization. ACP incorporates the use of multiple CAE tools in a systematic process to generate the optimal design solution. The ACP ProcessTM is a methodology that provides solutions, which address the challenges facing the modern product development environment. It achieves this by synchronizing the individual facets of the product development process, resulting in an overall reduction in development costs and time to market. Material selection and utilization, product performance requirements and manufacturing and assembly processes are all considered as early as possible in the design cycle. The resulting design offers a robust and highly efficient solution; which when combined with the strength and design flexibility of Advanced High Strength Steel (AHSS) or other materials; facilitates significant mass reduction for the final design. For the development of a vehicle structure, the methodology offers four key benefits, including a demonstrated capability to reduce product development costs by 40%, reduce product mass by 25% and more, improve product performance (stiffness, durability, NVH, crash/safety, durability) as well as improve fuel efficiency based on the mass reduction results. The paper will further disclose the results of the FSV programme, detailing steel body structure concepts for the aforementioned vehicles that meet aggressive mass targets of 190 kg, while meeting 2015-2020 crash performance objectives as well as total life cycle Greenhouse Gas emissions targets. FSV’s steel portfolio, including over 20 different AHSS grades representing materials expected to be commercially available in the 2015 – 2020 technology horizon, is utilised during the material selection process with the aid of full vehicle analysis to determine material grade and thickness optimisation. Achievement of such aggressive weight reduction with steel will set a new standard for vehicle design approaches for the future. Radically different powertrains, such as the BEV and the PHEV proposed for FutureSteelVehicle, and their related systems make new demands for increasingly efficient body components to handle the new loads. This will require innovative use of AHSS grades and steel technologies to develop structures that are stronger, leaner, greener and affordable. The presentation will explain the “state of the future” design optimisation process used and feature the aggressive steel concepts for structural subsystems incorporated into the FSV structure.

• The Effect of MPI Collective Operations and MPI Collective Offloads on LS-DYNA Performance

  Gilad Shainer, Tong Liu, Pak Lui - Mellanox Technologies, Dave Field - Hewlett-Packard

  From concept to engineering, and from design to test and manufacturing, the automotive industry relies on powerful virtual development solutions. CFD and crash simulations are performed in an effort to secure quality and accelerate the development process. The recent trends in cluster environments, such as multi-core CPUs, GPUs, cluster file systems and new interconnect speeds and offloading capabilities are changing the dynamics of clustered- based simulations. Software applications are being reshaped for higher parallelism and hardware configuration for solving the new emerging bottlenecks, in order to maintain high scalability and efficiency. In this paper we cover new hardware based accelerations and offloads for MPI collectives communications and how is affect LS-DYNA performance and productivity.

• The RHT concrete model in LS-DYNA

  Dr. Thomas Borrvall - Engineering Research Nordic AB, Dr. Werner Riedel - Fraunhofer Institut fur Kurzzeitdynamik

  The RHT concrete model is implemented in LS-DYNA. It is a macro-scale material model that incorporates features that are necessary for a correct dynamic strength description of concrete at impact relevant strain rates and pressures. The shear strength of the model is described by means of three limit surfaces; the inelastic yield surface, the failure surface and the residual surface, all dependent on the pressure. The post-yield and post-failure behaviors are characterized by strain hardening and damage, respectively, and strain rate effects is an important ingredient in this context. Furthermore, the pressure is governed by the Mie-Gruneisen equation of state together with a p-α model to describe the pore compaction hardening effects and thus give a realistic response in the high pressure regime. Validations have been performed on smaller test examples and a contact detonation application is presented to illustrate the performance of the proposed model.

• The use of different CSF representations in a numerical head model and their effect on the results of FE head impact analyses

  K. Baeck, J. Vander Sloten, J. Goffin - K.U.Leuven

  To gain better insight in the mechanopathogenesis of brain and skull lesions and to improve the design of protective devices like helmets, finite element (FE) head models are used. Current FE head models have a detailed geometrical description of the anatomical components of the head but often lack an accurate description of the behavior of the cerebrospinal fluid (CSF). Different material properties, mesh resolutions and numerical implementations are used to represent the CSF in those head models. To examine the effect of those different CSF representations on the brain mechanical responses such as strain energy, Von Mises stress, strain and intracranial pressure, this paper starts with the development of a simplified head model and small adaptations are made to the representation of the CSF, both in mesh resolution and constitutive modeling. From this study it follows that depending on which material definition is used for modeling the CSF, the mesh resolution of the CSF can have an important effect on the brain mechanical responses. The study also highlights the need for a more accurate description of CSF material, since the CSF material properties, both material definition and property values, have a significant effect on the results of a head impact analysis.

• The use of Generic Entities for Multidisciplinary preprocessing. A simple but powerful pattern in ANSA

  Yianni Kolokythas, Lambros Rorris - BETA CAE

  Today’s multidisciplinary CAE environment demands for rapid FE Model development cycles, thus the efficient processing of repetitive and complex modeling tasks is vital. This creates a need for highly automated processing steps and effective data sharing between the different CAE disciplines. BETA CAE Systems SA, in order to meet the above requirement, came up with a series of technologies, integrated within its preprocessor ANSA. These technologies allow the handling of the preprocessing environment in the engineering entities level rather in the solver entities level, making possible the treatment of model data as generic engineering data and not as specific FE solver entities. For simple tasks, such as the spotweld connection modeling, to more complex ones, such as a seatbelt or that of a stamping result mapping, there are ANSA entities that hold all the engineering data needed for its realization to the respective e.g. LS-DYNA entities. All the different types of those Generic Entities are similar in their definition and realization. At realization time the generalized entities, automatically adapt to the solver-specific FE (e.g. LS- DYNA). Thus making it straightforward to master the ANSA model-build-up capabilities and share and re-use the engineering data among different disciplines. This technology essentially creates a single, generic, pattern that is re-used throughout ANSA modeling tasks. This pattern driven technology provides a very practical and powerful solution for recurring modeling processes where the engineering data and the solver’s data are kept separately, and associated as required. This paper on ANSA’s Generic Entities presents the latest advances in model build-up technologies in the specific areas of connections and connectors, mass trimming, results mapping, dummy positioning and restraining, pedestrian and FMVSS 201U model set-up. As it is demonstrated, the exploitation of this modeling approach makes the LS-DYNA model built up process more time, effort and cost efficient.

• The Winfrith Concrete Model : Beauty or Beast ? Insights into the Winfrith Concrete Model

  Len Schwer - Schwer Engineering & Consulting Services

  The so called Winfrith concrete model in LS-DYNA (MAT084 and MAT085) provides: • A basic plasticity model that includes the third stress invariant for consistently treating both triaxial compression and triaxial extension, e.g. Mohr-Coulomb like behavior, • Uses radial return which omits material dilation, and thus violates Drucker’s Postulate for a stable material, • Includes strain softening in tension with an attempt at regularization via crack opening width or fracture energy, • Optional strain rate effects: MAT084 includes rate effects and MAT085 does not, • Concrete tensile cracking with up to three orthogonal crack planes per element; crack viewing is also possible via an auxiliary post-processing file, • Optional inclusion of so called ‘smeared reinforcement.’ This introductory document describes the basic plasticity model, the strain rate formulations and tensile cracking options. The *MAT_WINFRITH_CONCRETE model is another of the so called LS-DYNA ‘simple input’ concrete models, that include the *MAT_PSEUDO_TENSOR (MAT016), *MAT_CONCRETE_DAMAGE_REL3 (MAT072R3) and *MAT_CSCM_CONCRETE (MAT159). The Winfrith model requires the user to specify the unconfined compression and tensile strength. A note on sign convention: in geomechanics compression is usually considered as positive, since most stress states of interest are compressive. However, the Winfrith model uses the standard engineering mechanics convention of compression as negative.

• Topology Design using LS-TaSCTM Version 2 and LS-DYNA

  Willem Roux - Livermore Software Technology Corporation

  This paper gives an overview of LS-TaSC version 2, a topology optimization tool using LS-DYNA for the analysis of nonlinear structural behavior. The focus is on its capabilities, current development directions, and integration into an industrial design environment. Examples of using the new developments such as global constraints, geometric definitions such as symmetry and casting directions, and shells are given.

• Usage of fully detailed CAE models for concept design with the ANSA Morphing Tool

  George Korbetis - BETA CAE

  During the concept phase of product development, simplified CAD and CAE models are used to retain model versatility and minimize the set up time and the analysis complexity. However, this process often leads to simplified calculations with inaccurate results diverting from a realistic solution. Additionally, considerable time is spent to convert the simplified CAE models to full detailed ones at a later stage. This paper describes a recommended process for the usage of full detailed CAE models during the concept design phase. The resulting models are ready to run in LS-DYNA and their results are validated. This process is accomplished by the functionality of the ANSA Morphing Tool. The engineer is able to use former versions of full detailed CAE models or even CAE models of similar product versions and transform them according to the new layout within a few work days. Using this process the engineer is able to run the first analysis without the need to add feature details and solver specific entities to the concept model.

• User-Defined Nonlocal Models in LS-DYNA

  F.X.C. Andrade, J.M.A. Cesar de Sa , F.M. Andrade Pires - University of Porto, M. Vogler - Leibniz Universität Hannover

  In this paper, we present an implementation technique that aims to easily incor- porate the benefits of a nonlocal formulation to existing local constitutive models. In order to avoid pathological mesh dependency, an approximation of the nonlocal strategy is adopted. The technique is designed in such manner that the nonlocal extension of previously existing local models is carried out straightforwardly, requiring only minor modifications in the local routines. The implementation in LS-DYNA is depicted in detail for which a FORTRAN code excerpt is provided. In order to validate the proposed nonlocal scheme, we have considered two different constitutive models: one of them intended for the description of ductile materials, the other one suitable for the simulation of fiber-reinforced composites. The numerical analysis of different specimens shows that the proposed nonlocal strategy is able to eliminate spurious mesh dependency under different stress states and using different material models.

• Using CAE to evalute a structural foam design for increasing roof strength

  Sameer Gupta - Honda R&D

  In recent years, there has been increased discussion of the strength of vehicle roofs in rollover crashes. NHTSA recently revised the federal roof strength requirement and the IIHS has published an even more stringent roof strength goal. While working to increase roof strength, automakers are also working to reduce vehicle mass for improved fuel economy and other benefits. Developing technology to achieve both of these goals is challenging. This paper investigates the use of CAE to evaluate the addition of structural foam to an existing design to maintain or increase roof strength. A concept solution that combines nylon and structural foam material was developed and analyzed using an explicit finite element model and later tested on a body-in-white to evaluate the CAE predictions. The main evaluation method was the FMVSS 216 test procedure. Through CAE analysis and actual testing, the modifications were found to have increased roof strength. A performance target was set and a conceptual steel-only assembly was created in CAE to meet this target. The foam/steel assembly met the performance target but at a reduced weight compared to the steel-only assembly. These analyses demonstrated that CAE is useful for predicting the performance of foam/steel assemblies and that foam/steel assemblies can yield greater strength with lower mass than a steel-only assembly. Questions regarding field performance and the feasibility of mass-production must still be addressed.

• Using LS-DYNA MM-ALE capabilities to help design a wall mitigating accidental blast effects

  Julien Lacambre, Laurent Delmas - Alyotech TS&I

  A solution had to be found in order to protect buildings neighboring an industrial site from the blast effects of possible accidental explosions on the site. One of the main issues was that the point of detonation would occur relatively close to the endangered buildings. A possible answer was to build a blast-mitigating wall between the buildings and possible blasts. The MM-ALE features of LS-DYNA provided a way to evaluate the effects of the wall on the pressure waves around the building. As the amount of explosive was rather small when compared to the distances involved, the new 2D to 3D and 3D to 3D re-mapping methods came in handy to avoid the use of an impractically large numerical model. After a first series of computation showed that the proposed solution was indeed promising, a series of simulation runs enabled the design of a wall tall enough to achieve the desired mitigation effect on the pressure waves experienced by the building’s walls and roof.

• Using LS-OPT for meta-model based global sensitivity analysis

  Uwe Reuter, Zeeshan Mehmood, Clemens Gebhardt - TU Dresden, Martin Liebscher, Heiner Müllerschön, Ingolf Lepenies - DYNAmore GmbH

  Popular sensitivity analysis methods such as ANOVA and SOBOL indices are widely used in LS-OPT in order to measure the importance of different input variables with respect to the model response. These methods are applied using meta-models in LS-OPT. In contrast, sensitivity information can be directly extracted from the meta-models using weight-based and derivative-based approaches. Meta-models capture the non-linear relationship of the underlying input parameters to the design response. In this paper, powerful sampling and pre-processing capabilities of LS-OPT are coupled with a user-defined neural network based meta-model in order to perform weight based and derivative based sensitivity analysis. The results of these sensitivity measures are compared with the default SOBOL approach by using an analytical as well as an industry relevant crash analysis example.

• Validation and Material Modelling of Plastics

  A. Haufe , V. Effinger - DYNAmore GmbH, P. Reithofer , M. Rollant , M. Fritz - 4a engineering GmbH

  The virtual estimation of physical product properties is only as good as the virtual description of the behaviour of its material. On the one hand there are well known material cards like *MAT_PIECEWISE_LINEAR_PLASTICITY in LS-DYNA© developed to describe a simplified behaviour of metallic materials. The reduced complexity of these material cards makes it possible to determine its parameters with less effort in actual material testing. Main advantages are high numerical stability and less machine time. On the other hand complex material models like *MAT-SAMP-1 can also handle varying compression and tension behaviours by defining a load case dependent yield surface as well as unloading by using damage functions. With the exception of visco-elasticity the description of visco-plasticity fulfills many requirements to describe a realistic behaviour of thermoplastics. For acceptable use of the above mentioned models a higher amount of load cases like tension, compression, shear have to be carried out to determine the material parameters and to represent the thermoplastic characteristics in crashworthiness simulations. At the moment there is no standardized method to determine material card properties for arbitrary material models from basic (i.e. tension, compression or shear) test setups. 4a impetus represents a standardized method, an efficient and reliable process starting with realistic test scenarios and finally ending up with a validated material card. The method of reverse engineering is used behind this process to generate material cards like *MAT_PIECEWISE_LINEAR_PLASTICITY as well as more complex *MAT_PLASTICITY_COMPRESSION_TENSION with regard to easy and favourable testing. We have compared different ways to determine and validate material cards with the example of PA6. Limits and opportunities of different test methods and material card implementations are shown and compared to each other especially focused on typical polymer behaviour.

• Warm Forming Simulation of 7075 Aluminium Alloy Tubes Using LS-DYNA

  G. D’Amours, J.F. Béland - National Research Council Canada

  The demand for lightweight tubular products, designed specifically for transportation and recreational applications, is currently on the rise. In general, performance increase and energy cost reduction are the main reasons justifying the need for these specialty products. Hence, to reach these goals, both industries are turning to complex-shaped tubes for various types of applications. However, high performance aluminium tubes, such as 7075 alloy, provide very low formability characteristics at ambient temperature and do not have the ductility needed for hydroforming-based applications. A 1,000-ton hydroforming press, located at the Aluminium Technology Centre, was equipped with a + 600 oC heating die designed for such tube and sheet forming applications. The die has 10 separate heating zones that can be adjusted independently. The first application was employed to form a tubular bicycle component. To achieve this, a thermo-mechanical model was developed using LS-DYNA to determine the tube temperature distribution around the heating zones. To this end, conduction, convection, radiation and contact heat transfer conductance were the physical phenomena considered in the thermal model. Prior to developing the mechanical model, a heating chamber was designed and fabricated. Tube samples underwent in-chamber testing using a servo-hydraulic system at various temperatures and strain rates. With the results, an elastic viscoplastic temperature-dependent material constitutive law was used to properly predict tube strains and stresses. The finite-element model can predict the necessary tube temperature and gas pressure during the heat-based forming process, thus enabling to obtain optimum formability of 7075 aluminium alloy tubes.

• Wood-steel structure for vehicle restraint systems

  C. Goubel, M. Massenzio, S. Ronel - Université de Lyon

  Certain roadside safety barriers are structures made of steel and wood. This kind of structure is currently in fashion in location where the safety equipments need to be discreet (mountains, countryside). In Europe, to be installed on the roadside, the vehicle restraint systems have to pass two crash tests, as defined in the European standard EN1317. Our aim is to develop a dynamic model of the multi material structure in order to understand and optimize the safety barriers i.e. to define the best association of the mechanical properties of both materials. The first part of this paper concerns three point bending experimental tests at different energy levels. These laboratory tests were used as a basis for the evaluation of a material constitutive law. Then, a numerical parametric study which takes into account the variation of moisture content and temperature, as observed in the experiment, will be exposed. After that, a model of a roadside safety barrier and a procedure based on variation of failure modes analysis will be presented in order to correlate the numerical model to the real crash test results. Finally, a parametric study, concerning wood mechanical properties, will be performed in order to check the effect of this variation on the device performances.