高应力水平下表面裂纹疲劳扩展规律的实验研究

多次错误操作或水锤现象等可能引起结构部件承受高应力水平下的疲劳载荷作用。在前人的研究工作中，含表面裂纹板疲劳试验的远场应力水平绝大多数不超过０．６σｙ，。本文通过应力水平为０．８５～０．９５σｙ，的１６ＭｎＲ钢合表面裂纹板的疲劳实验研究，来回答在Ｐａｒｉｓ、Ｃｈｅｌｌ（考虑最大应力的影响）和Ｆｏｒｅｍａｎ（考虑平均应力的影响）等公式中，在这样高的应力水平下究竟哪一个模型更适合描述表面裂纹疲劳扩展速率。实验结果分析表明：对于高韧性材料而言，即使在接近屈服的高应力水平下，Ｐａｒｉｓ公式仍不失为诸多应力疲劳扩展速率描述公式中最有效的。此外，还仔细观察了表面裂纹疲劳扩展的客观几何形貌和微观断裂特征。

Fatigue Growth Law of Surface Crack under High Stress Level

Repeated false operation or water hammer could make structural components to be subjected to fatigue loading under high stress level. In previousresearch works, the remote stress level, which is applied to most fatigue testspecimens containing surface crack, is usually less than 0.6. In this paper, byexperimental studies on the fatigue growth of 16MnR steel specimens containing surface crack under remote stress level of 0.85-0.95, it is determined that whether Paris's formula, Chell's (with the effect of maximum stress into account)or Foreman's (with the effect of mean stress into account) is more acceptable to .express the fatigue growth rate of surface crack under such high stress level. The result is evident that for high toughness material even if the maximum stress of cyclic loading is near to yield point, the Paris's formula is still proved to be the most effectiye one among all mathematical expressions concerning stress fatigue growth rate. In addtion, the geometric features of propagation and their microfracture characteristics of surface crack during fatigue growth process are carefully observed and recorded.