인터기어 열간단조의 정밀 유한요소해석 및 금형의 저주기 피로파괴 수명의 정성적 예측

Abstract

A typical case of die failure owing to low-cycle fatigue fracture during hot forging of a complicated auto-part is presented. The reason for the fracture is revealed through precise rigid-thermoviscoplastic finite element analysis of the three-stage hot forging process and die structural analysis. The fracture occurred not at the very corner, where stress concentration may occur, but near the corner, a little apart from the very corner. The experiment shows that several cracks occur in parallel, indicating the die fracture is owing to the cyclic loading. The FE prediction shows that the high principal stress band coincides with the crack and that the maximum principal axis is perpendicular to the crack. The cycle of maximum principal stress is traced to investigate the low-cycle fatigue fracture, showing that the amplitude of stress cycle and mean stress at the maximum principal stress point in the fracture region back up the low-cycle fatigue fracture.