Numerical Fracture Analysis Considering Forming Effect and Element Size Regularization for Automotive Seat Structures

The aim of this paper is to apply an advanced fracture model and to evaluate its applicability in automotive seat structures. A Generalized Incremental Stress-State dependent damage Model (GISSMO), which was one of the advanced fracture models implemented in LS-DYNA, was adopted as a fracture model. A description of the damage parameter identification process with material tests was introduced in this study. The GISSMO adopts most of the fracture factors, and was introduced in previous works. In order to evaluate the fracture strain in various stress states, uniaxial tension, simple shear-tension, notched-tension, and biaxial tension tests were carried out. The GISSMO damage parameters were calculated and identified using reverse analysis method and theoretical equations with some numerical fitting techniques. The results were compared with material test results, and it was evaluated that the values might be applicable to the seat frame model. In addition, it was found that the effects of element size and manufacturing (forming) are large with regard to fracture behavior. In particular, the seat rail has a residual stress owing to the bending process in the forming step. From these simulation results, the material parameters were applied to the full seat structure. Various models showed good agreement with the experimental fracture strength and crack propagation.