曲げ試験と切欠付丸棒引張試験を用いた冷間据込み加工の表面割れ予測

抄録

In this study, we develop a method for identifying the ductile fracture limit in a stress triaxial range corresponding to surface cracks, such as upsetting in cold forging. A series of fracture tests including 4 types of notched round bar tensile tests and 3 types of 3-point bending tests are carried out experimentally and numerically. All investigation is conducted using carbon steel S45C. The loading path of stress triaxiality at the fracture point of the specimens is identified by finite element analysis (FEA), and the parameters of the exponential ductile fracture model are determined. Critical compression ratios of upsetting tests are predicted using the ductile fracture model taking into account the positive stress triaxiality. Furthermore, the fracture surface of each specimen is observed by scanning electron microscopy (SEM), and the diameter distribution of the dimples is investigated.