Sustainability plays an increasingly important role in the automotive industry. In order to reduce the ecological footprint, the suitability of alternative bio-based materials like wood is investigated within the project WoodC.A.R. In order for wood to be used as an engineering material for structural components or even crash relevant structures, it has to fulfill high mechanical demands. The material behavior has to be predictable and describable in a numerical simulation. Therefore, two material models *Mat_58 (*Mat_Laminated_Composite_Fabric) and *Mat_143 (*Mat_Wood) were compared and validated against quasi-static tension and compression tests in all its six anatomical directions but also against three-point bending tests with the wood fibers oriented parallel to the beam’s axis. So called “clear wood” samples, i.e. specimens without any growing features, were tested covering the different load levels: linear elasticity, strain-hardening, strain-softening and rupture. While *Mat_58 is an orthotropic material model, *Mat_143 is transversally isotropic which means there is no possibility to distinguish between the radial and the tangential direction of the material. Therefore, a trade-off for both directions has to be found. On the other hand, the material law *Mat_143 is able to consider influences like temperature, moisture content or even the quality respectively sorting degree of the wood. Both material models show that some simplifications considering the hardening and softening behavior, especially in compression have to be taken into account in multi-element specimens. While wood shows softening at longitudinal compression, there is a pronounced hardening in perpendicular direction. The strengths and weaknesses of both material models are discussed.
Wood is a natural and highly anisotropic material. Therefore, mechanical characteristics of the material depend on the direction and type of the load (e.g. deformation behavior of wood is ductile in compression and brittle in tension). The mechanical behavior of crash elements made of wood material was investigated experimentally and numerically at quasi-static and dynamic strain rates for load-carrying and energy absorption characteristics. For detailed investigations on the mechanical properties of wood, specimens were modeled and *MAT_WOOD (*MAT_143) was selected in LS-DYNA. The process of parameter identification for the *MAT_143 was clarified. In the scope of the experimental studies, quasi-static compression, tension and bending tests as well as dynamic drop tower tests were performed to characterize the material at low and medium strain rates, respectively. It was found that the investigated wood material is highly strain rate sensitive what can be captured by enhancing *MAT_143 by strain rate dependent fracture energy parameters. All material model parameters used in numerical studies were validated according to the experimental results for the *MAT_143. Since wood is a natural composite material, it was modeled with 2D shell element formulation and analyzed with single element simulations by composite material models by referring to material parameters used in *MAT_143. The investigated material models are *MAT_54, *MAT_58 and *MAT_261. The aim is to present a base study to enlighten the damage mechanism of wood for further investigations on the potential of wood-based structural automotive components.
Automotive seat cushions contribute considerably to static and dynamic comfort of the drivers. Design of a cushion is highly challenging due to its highly nonlinear viscoelastic behavior that is dependent on the seated body mass, and magnitude and rate of the vibration excitation. In this study, a dynamic seat cushion model is developed in the LS DYNA platform to determine its static and dynamic properties. The material model *MAT_FU_CHANG_FOAM_DAMAGE_DECAY (083_1) was used, which showed capability to predict nonlinear dynamic cushion behavior under different preloads, and excitation frequencies and amplitudes. This material model, available in the LS DYNA library, permitted evaluations of the nonlinear rate-dependent viscoelastic behavior of the cushion. The effectiveness of the model in predicting static and dynamic responses is demonstrated by comparing the simulation results with the laboratory-measured data in terms of force-deflection characteristics. The comparisons revealed reasonably good agreements between the simulation and measured responses. Contact pressure distribution on the seat cushion was further obtained, which also showed good qualitative agreement with the reported measured data.
Comparison of Different Material Models in LS-DYNA (58, 143) for Modelling Solid Birch Wood