Comparison of different testing approaches to describe the fracture behaviour of AHSS sheets using experimental and numerical investigations

Abstract

The damage behaviour of Advanced High Strength Steel (AHSS) differs from conventional deep-drawing steels due to their microstructure. For example, shear fracture can occur unexpectedly without prior necking, leading to inaccuracies using Forming Limit Diagram (FLD). An improvement of failure prediction can be obtained by the use of stress state dependent damage models, which have to be parametrised by tests at different stress states for which a wide range of methods exists. Research is still needed regarding the choice of specimen, evaluation methodology and model accuracy. For that purpose, in this study two different experimental approaches are compared to analyse the fracture behaviour depending on the stress state of the complex phase steel CP800. Therefore, tensile specimens of various geometries are used on the one hand and butterfly tests in different orientations on the other. Subsequently, the modified Mohr-Coulomb (MMC) damage model is parametrised with the determined characteristic fracture values of the respective experimental methods. For additional comparison, also an FLD is determined. The different approaches are finally compared regarding their suitability for the parameterisation of stress state dependent damage models.