Loading conditions constrained wrinkling behaviors of thin-walled sheet/tube parts during metal forming

With the increasing usages of high strength and lightweight materials, how to accurately predict and fully understand the wrinkling instability of thin-walled parts forming under various loading conditions, viz. stress states and normal constraints, is still a challenge for free-defect design and manufacturing. In this study, taking tension-compression stress state w/wo normal constraints (Yoshida test and deep drawing of sheets) and compression stress state w/wo normal constraints (axial compression and rotary draw bending of tubes) as the comparative cases, two kinds of geometric imperfections (GI), viz., random thickness imperfection (RTI) and geometric deflection imperfection (GDI) are introuduced and implemented into dynamic explicit finite element (FE) models to realize more sensitive prediction of the wrinkling instability. And then, a systematic comparative study on the critical wrinkling behavior and final wrinkling morphology under varous loading conditions has been studied. It is found that the wrinkling is more prone to occur under tension-compression stress state, and the wrinkling of the processes without normal constraint are severer than those with normal constraints. Furthermore, the effects of material parameters on the wrinkling are inconsistent in different processes, the reason proved to be the different loading conditions. When the degree of normal constraint increases, the influence of material properties becomes negligible. Combining the geometric and material parameters, the key issues affecting the wrinkling of thin-walled parts from the perspective of loading condition have been expounded, laying the foundation and theoretical guidance for the study of wrinkling behavior under different mechanical states.