Automotive T1-1

A Path Towards Including Batteries in Electric or Hybrid Car Crash Simulations with LS-DYNA®
Pierre L’Eplattenier, Iñaki Çaldichoury (Livermore Software Technology, LLC)

Safety is an important functional requirement in the development of large-format, energy-dense, lithium-ion (Li-ion) batteries used in electrified vehicles. Many automakers have dealt with this issue by enclosing the batteries into protective cases to prevent any penetration and deformation during the car crash. But with the range of electric vehicle increasing and thus the size of the batteries, a more detailed understanding of a battery behavior under abuse becomes necessary. Computer aided engineering (CAE) tools that predict the response of a Li-ion battery pack to various abusive conditions can support analysis during the design phase and reduce the need for physical testing. In particular, simulations of the multi-physics response of external or internal short circuits can lead to optimized system designs for automotive crash scenarios. The physics under such simulations is quite complex, though, coupling structural, thermal, electrical and electrochemical. Moreover, it spans length scales with orders of magnitude differences between critical events such as internal shorts happening at the millimeter level, triggering catastrophic events like the thermal runaway of the full battery. The time scales also are quite different between the car crash happening in milliseconds and the discharge of the battery and temperature surge taking minutes to hours. A so called “distributed Randles circuit” model was introduced in LS-DYNA in order to mimic the complex electrochemistry happening in the electrodes and separator of lithium ion batteries [1][2][3]. This model is based on electrical circuits linking the positive and negative current collectors reproducing the voltage jump, internal resistance and dumping effects occurring in the active materials. These circuits are coupled with the Electromagnetics (EM) resistive solver to solve for the potentials and current flow in the current collectors and the rest of the conductors (connectors, busses, and so forth). The EM is coupled with the thermal solver to which the joule heating is sent as an extra heat source, and from which the EM gets back the temperature to adapt the electrical conductivity of the conductors as well as the parameters of the Randles circuits [1]. One of the advantages of the Randles circuit model is the relative easiness to introduce internal short circuits by just replacing the Randles circuits in the affected area by a short resistance [1][3]. The Randles circuit model also is coupled with the mechanical solver of LS-DYNA where the deformations due to a battery crush allow the definition of criteria to initiate internal shorts [1]. The Randles circuit model can be used either on a solid element mesh that include all the layers of a cell [1][2][3], or using composite Tshells [4][5]. In the second case, the mechanics is solved on the composite Tshell, but an underlying solid mesh with all the layers still has to be built to solve the EM and the thermal. This implies very large meshes and hence simulation times when dealing with many cells, let alone modules, packs or a full battery. This new Battery Macro (BatMac) model allows simulating a cell with very few layers of elements (down to one). Two fields exist at each node of the mesh, representing the potential at the positive and negative current collectors. These two fields are connected by a Randles circuit at each node. It still is possible to include external and internal shorts. The internal shorts can be locally created depending on local values of different mechanical, thermal or EM parameters. The Joule Heating generated by the current leaking through the short resistance is sent to the thermal solver.
An Approach for Modeling Shock Propagation Through a Bolted Joint Structure
Pouya Shojaei, Mohamed Trabia, Brendan O'Toole, Jed Higdon (University of Nevada, Las Vegas)

Impact loading is typically characterized by a relatively large load happening over an extremely short duration and inducing broad range of vibration frequencies. Standard design approaches of bolted joints based on static or quasi-static criteria may not be effective under these conditions. This study focused on simulating a drop-weight tower experiment where a free-falling mass impacted a target plate, which was bolted to a cylindrical structure. An accelerometer was used to record transmitted acceleration to the cylindrical structure. An approach for simulating the shock propagation was proposed using LS-DYNA® Explicit finite element code. To reduce computational time, thread was not included. Instead, bolts were represented as cylinders with cross-sectional areas equal to the tensile stress area of the bolts. The results showed good agreement between the finite element and experimental results.
An Engineering Approach of an X-Ray Car Crash Under Reverse Small Overlap Configuration
Y. Leost, P. Bösl, I. Butz, T. Soot, M. Kurfiß, S. Moser (Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI), A. Nakata, F. Kase, T. Hashimoto, S. Shibata (Honda R&D Co., Ltd.)

During a crash event, conventional optical measuring systems provide information about the deformation of parts that are directly visible. The new measuring method called X-Ray Car Crash (XCC) developed at Fraunhofer EMI allows accessing the crash kinematic of specific parts inside the vehicle. This method provides precious information that is currently not accessible in a crash test and allows for better comparison with FEM simulations. The present paper describes a preliminary study performed in collaboration with Honda R&D Co., Ltd. The load case under consideration is a reverse variant of the IIHS Small Overlap with integrated X-Ray technology. Fraunhofer EMI Research Crash Center aims at developing new measurement methods to investigate non-standard high-speed dynamics safety issues. Most of these specific requests are coming from car manufacturers. In order to achieve maximum test reproducibility and simplify boundary conditions, the facility is equipped with a propelled sled system on rails. Thus, it enables to perform impactor to vehicle scenarios with moving barriers up to 3000 kg by 22 m/s. The standard Small Overlap at 64 km/h belongs to the vehicle to barrier scenario and requires some preliminary computations to adapt it for the EMI Crash test facility. Special consideration was given to energy balance in order to determine the right barrier velocity and mass to achieve a similar intrusion in the car to in the standard configuration. Numerical simulations were required at each step to meet the different challenges of this study. This paper describes first the numerical assessment of the validity of the reverse scenario. FEM simulations were then used extensively for developing a special moving barrier presenting maximal structural robustness, well-balanced dynamic behavior and allowing on-sled measurement technics and braking system. Then, LS-DYNA® simulations provided necessary data to perform ray tracing simulations and thus finding the right placement for X-ray source and X-ray detector. Finally, numerical simulations played an important role for an enhanced test setup, by finding the best balance between appropriate mechanical robustness of supporting structures (so called Pit-cover) and low X-ray attenuation.
Automatic Analysis of Crash Simulations with Dimensionality Reduction Algorithms such as PCA and t-SNE
David Kracker (Dr. Ing. h.c. F. Porsche AG), Jochen Garcke (Fraunhofer SCAI), Axel Schumacher University of Wuppertal, Pit Schwanitz (University of Wuppertal)

The increasing number of crash simulations and the growing complexity of the models require an efficiently designed evaluation of the simulation results. Nowadays a full vehicle model consists of approximately 10 million shell elements. Each of them contains various evaluation variables that describe the physical behavior of the element. Therefore, the simulation models are very high dimensional. During vehicle development, a large number of models is created that differ in geometry, wall thicknesses and other properties. These model changes lead to different physical behavior during a vehicle crash. This behavior is to be analyzed and evaluated automatically. In this article, potentials of several algorithms for dimensionality reduction are investigated. The linear Principal Component Analysis (PCA) is compared to the non-linear t-distributed stochastic neighbor embedding (t-SNE) algorithm. For those algorithms, it is necessary that the input data always has an identical feature space. Geometrical modifications of the model lead to changes of finite element meshes and therefore to different data representations. Therefore, several 2D and 3D discretization approaches are considered and evaluated (sphere, voxel). In order to assess the quality of the results, a scale-independent quality criterion is used for the discretization and the subsequent dimensionality reduction. The simulations used in this paper are carried out with LS-DYNA®. The aim of the presented study is to develop an efficient process for the investigation of different data transformation approaches, dimensionality reduction algorithms, and physical evaluation quantities. The resulting evaluation method should represent physically relevant effects in the existing simulations in a low-dimensional space without human interaction and thus support the engineer in the evaluation of the results.
Modeling Plastic Clips in LS-DYNA® for Low-Energy Impact Analyses
Kenneth E. Freeman, Alexander Gromer (DYNAmore Corporation), Brian O’Hara, Cameron O’Keeffe (Honda R&D Americas, Inc.)

Through several different low-energy automotive impact simulations, it was discovered that capturing plastic clip behavior played a substantial role in predicting the system response. Therefore, a methodology for modeling plastic push-in rivets and snap-fit clip connections was developed in LS-DYNA for use in these low-energy automotive impact analyses. The required geometric discretization, contact definitions, material models and constraints that make up the models are discussed in detail. Pull-out force data was utilized to correlate the response and failure modes of the clip models. In addition, three different levels of clip model complexity were compared with respect to their suitability for different load cases. Simple clip model approaches were easy to pre-process and sufficiently captured most of pull-out failure modes. However, these did not capture shear or off-angle failure. More complex clip models sufficiently captured shear and off-angle failure, but come at a greater pre-processing and development effort. Lastly, some pre-processing methods are discussed to demonstrate how hundreds of clips can be incorporated in a model in very little time.
Side Curtain Airbag Folding Methodology
Pablo Alberto Rodríguez Calzada, Hector Hernández Hernández, Alejandro García Pérez, Carlos Gómez González (Ford Motor Company)

In recent years, CAE simulations have been substantially improved as a result of the growing need to achieve full vehicle developments in a shorter time span while also attending the demand of cost reduction in such developments. One of the most critical components regarding the passive safety systems of a vehicle is the Side Curtain Airbag, therefore the necessity to involve this critical component in an agile product development process becomes compulsory. Consequently, when the validation using numerical methods of such component is performed, a full deployment of the airbag is needed to be evaluated and analyzed, having as a key objective the monitoring of its dynamic behavior caused by the effect of interacting with nearby components. In view of the foregoing, the folding process of the airbag plays a key factor in its whole operation. This study describes a hybrid methodology to fold a Side Curtain Airbag by means of a geometrical and simulation-based routine, which can be defined entirely on LS-PrePost®, using the embedded tools in the occupant safety applications. This work aims to englobe the tools and steps followed in order to obtain, within a short period of time, a LS-DYNA® CAE model of the airbag, capable of representing efficiently and accurately a deployment, which might be used in early stages of numerical analysis for areas such as Interior Trim integrity and safe interaction. Using this CAE methodology, a new scope of problem-solving techniques originates. Applying the novel approach described in the preceding paragraph, a folding scenario could be useful to control the dynamics of the airbag in order to achieve a faster deployment in a certain zone, to avoid an undesired interaction with the interior trim of the vehicle, or to simply evaluate the aperture time of the system overall. All this adds up to a feasible cost reduction alternative to the most common techniques that involve modifying and adapting geometries including supplementary components, that impact directly in the prime cost of a vehicle.