熱延高張力鋼板におけるシャー切断面の疲労強度に関する研究

Abstract

For application of the high-strength steel plate to automobile chassis parts, it is important to reserve the fatigue reliability. In the manufacturing of automotive parts from a steel sheet, the shear cutting process with a die is commonly used. Although the process is economic, it has a drawback that fatigue cracks may initiate from the shearing edges. Therefore, in terms of the reliability of parts, it is necessary to evaluate the influence of shearing edges on the fatigue strength. In this paper, fatigue experiments are conducted on the specimen of high-strength steel sheet with the shearing edge and the influence factors such as the residual stress and surface roughness are examined. As a result, the experiments elucidate that the residual stress has a major influence. The fatigue limit of the shearing edge can be estimated using the residual stress re-distributed by fatigue and fatigue limit diagram, and a method for predicting the S-N curve of shear cutting surface is proposed on the basis of the estimation.