During collisions, base metals may incur ductile fracture without evident defects under complex stress conditions. Herein, we propose a test method for evaluating the initiation behavior of internal ductile cracks in metals under shear stress conditions. The applicability of the developed specimen to the evaluation of ductile crack initiation condition was discussed based on the results of tensile fracture tests and finite element analyses. It is found that the critical equivalent plastic strain for crack initiation was lower in the shear stress state than the tensile stress state under equivalent stress triaxiality conditions.