Robust characterization of anisotropic shear fracture strains with constant triaxiality using shape optimization of torsional twin bridge specimen

In-plane torsion test has been drawing attention as an effective strategy to obtain good shear properties. Herein, a framework of shape optimization for a twin bridge specimen is presented to improve the performance while ensuring better machinability. The framework includes the consideration of material anisotropy and the determination of design variables. In this study, TRIP1180 sheet was employed as a target material. The optimized design was verified by an actual in-plane torsion test. The experimental results demonstrate that the proposed framework can optimize the shape of the twin bridge for maintaining zero triaxiality up to fracture occurrence.