균열형상비가 다른 구조부재의 피로수명에 미치는 과대하중의 영향

Abstract

Many studies have reported the retardation in crack growth on the structural members and its principle. Until now, much research has been studied the change in the rate of crack growth by overstress. However, there are no studies on the fatigue life of machines and structures considering the size of the plastic zone due to overstress. Therefore, this study assumed semi-elliptical surface cracks with different aspect ratios (As) to evaluate the infinite life of four types of structural member due to overstress. As a result of the evaluation, infinite life is possible in most cases with appropriate overstress. The crack growth pattern according to the AS is determined by the surface crack (c) for the infinite life of As=1.0. In the case of As=0.6 and 0.3, it was determined from surface cracks and (c) and crack depth (a), but there were some differences depending on the material. When As= 0.1, it was determined only by the crack depth (a). The infinite life of fatigue cracks due to overstress is mostly affected by the crack size, design stress, and As, but crack size (a, c) has the greatest effect. Therefore, it is necessary to accurately measure the crack size (a, c) for the infinite life of the structure due to overstress.