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Advanced High Strength Steel (AHSS) with high strength and deformation resistance is applied to automotive components and plays an important role in protecting passengers in the event of a crash, as well as contributing to fuel economy improvement by reducing the weight of the car body. However, due to the low ductility of the AHSS, there is an issue about the occurrence of fracture during a vehicle crash. In order to cope with these problems from the early design stage, preliminary verification is made through crash CAE analysis, but a high level of material property definition is required for fracture prediction. To predict fracture, many tests are required to secure the base data for parameter calculation of a complex fracture model, and a lot of physical time is required to verify the model. This paper aimed to semi-automate the material parameter calculation and verification process for efficient and reliable fracture prediction of AHSS.

To prepare for the future car market, concept cars based on eco-friendly vehicles with autonomous driving systems are being developed, such as BEV (battery electric vehicle) and HFCEV (hydrogen fuel cell electric vehicle). These concept cars adopt a new body structure to improve passenger convenience, and the CTR-PLRless (center pillarless) body structure is one of the key structures that can improve the passenger convenience. However, the CTR-PLRless body structure has a disadvantage in that it cannot connect the load between the upper parts and the lower parts of the body structure, as well as that it provides limited protection to the passengers from the occurrence of a side collision because the main members on the side of the body are removed.

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.