混合モード負荷を受ける切欠きからの延性き裂発生挙動に関する研究

Abstract

The behavior of ductile crack initiation from a notch under mixed mode loading has been investigated on a structural steel SM41A. Experiments and large deformation finite element analyses were carried out on the single edge notched specimens under various mixed mode loading conditions which were achieved by loading the appropriate positions in three-point bend tests and four-point shear tests. The profile of the notch tips deformed under mixed mode loading consisted of a sharpened part and a blunted part, and the latter part showed the highest void volume fraction in the notch tip region. The ductile cracks initiated from the mixed mode notch were of two types-fibrous type and shear type-depending on the loading mode. In the notch under mode I predominant-mixed mode loading, the fibrous type crack was initiated by coalescence of voids at the blunted part of the notch tip. On the other hand, in the notch under mode II predominant-mixed mode loading, the shear type crack initiation occurred by large shear deformation at its sharpened part. The initiation of the fibrous type crack from the mixed mode notch can be predicted by the critical void volume fraction at the notch tip. However, the shear type crack initiation is controlled by another criterion. Further study is needed to predict the initiation of the shear type crack from the mixed mode notch.