Numerical prediction of ductile fracture during the partial heating roll forming process of DP980

Abstract

Automotive and construction industries demand for roll-formed high strength Dual-Phase steels due to their excellent structural performances and attractive appearances have increased dramatically over the last decade. However, their compromised ductility gives rise to problems and faces numerous manufacturing issues. These problems pertain to ductile fracture defect, which is often observed on tight radii during roll forming. The partial heating roll forming method is a recently proposed roll forming method alternative to the conventional cold roll forming method, aimed at reducing ductile fracture by partially heating only the bend areas. In this paper, the ductile fracture during the partial heating roll forming processes of DP980 high strength steel is evaluated by implementing the phenomenological Generalized Incremental Stress State Dependent Damage (GISSMO) model using the FE code LS-DYNA. To this aim, instability and fracture strains from the uniaxial, plane-strain, and shear tensile tests at different temperatures were evaluated. The basic tensile test results are in good agreement with the experimental results found in the literature. Subsequently, the instability and plastics strain at fracture from basic tensile tests were calibrated to numerical simulations of roll forming processes for ductile fracture predictions. Based on the results, the instability and fracture strain increase as the material’s temperature increases. Moreover, the ductile fracture investigation of DP980 during the cold roll forming process showed that fractures were observed on the profile's bend areas. However, no visible cracks were observed on the partial heated roll-formed profile.