一、前言 大量的工程实践表明,机械及结构物的破坏,大多是疲劳造成的。一般情况下,在零件或结构物的局部,由于应力或应变集中,在循环载荷的作用下,就会产生局部塑性变形的累积,从而形成了微观疲劳裂纹,在循环载荷的连续作用下,裂纹会不断扩展至宏观裂纹,最终达到临界尺寸,导致破坏。疲劳破坏大致可以分成四个阶段:疲劳成核、微观裂纹形成、宏观裂纹扩展、最后断裂。一般把前二个阶段统称为疲劳的无裂纹寿命阶段,把后二个阶段统称为疲劳的有裂纹寿命阶段。 断裂力学的发展,对宏观疲劳裂纹扩展的研究起了很大的推动作用,现在已经可以用断裂力学的方法定量地计算有裂纹阶段的疲劳寿 I. INTRODUCTION A large number of engineering practices have shown that the destruction of machinery and structures is mostly caused by fatigue. In general, parts of the structure or parts of the structure, due to stress or strain concentration, under the action of cyclic loading, there will be the accumulation of local plastic deformation, resulting in micro-fatigue crack, under the continuous action of cyclic load, the crack Will continue to expand to the macro-cracks, eventually reaching the critical size, leading to destruction. Fatigue failure can be roughly divided into four stages: fatigue nucleation, micro-crack formation, macroscopic crack propagation, and finally fracture. The first two phases are generally referred to as the fatigue-free crack-free life stage, and the latter two phases are collectively referred to as the fatigue-cracked life-stage. The development of fracture mechanics plays a very important role in the study of macro-fatigue crack propagation. It is now possible to quantitatively calculate the fatigue life of a cracked phase using the method of fracture mechanics