Plasticity induced anisotropic damage modeling for forming processes

Stringent carbon emission targets and consumer demands for highly fuel efficient and safe vehicles are driving most of the innovations in the automotive industry. In the present era, the prime technological goal of the automotive industry is to design and manufacture commercially viable lightweight vehicles while maintaining the structural performance of the vehicles at the same time. Development of Advanced High Strength Steels (AHSS) is an important step forward in this context. However, plastic deformation induces damage in AHSS. Damage development during the forming process renders the classical failure prediction techniques ineffective, which poses difficulties in designing the forming process. Therefore damage development in these steels has been studied and incorporated in numerical simulations for accurate failure predictions in forming processes and for determination of the product properties after forming. Damage development is anisotropic by nature and shall be considered anisotropic for accurate failure predictions. In this research, anisotropy in damage has been classified into two categories; Material Induced Anisotropy in Damage (MIAD) and Load Induced Anisotropy in Damage (LIAD). MIAD is related to the anisotropy in distribution and shape of second phase particles or impurities and is governed by void/crack nucleation. LIAD is related to the loading direction of the material. The phenomenon of MIAD was discovered during this research. This is the first research showing the occurrence of MIAD in AHSS. The standard Lemaitre anisotropic damage model was modified to incorporate: lower damage evolution under compression, strain rate dependency in damage and Material Induced Anisotropic Damage (MIAD). Viscoplastic regularization of damage models was revisited. This technique proved to be effective in removing the pathological mesh dependence of local damage models. The damage model parameters for the same grade of DP600 were determined. The Modified Lemaitre’s (ML) anisotropic damage model was validated with experiments.