单向加载,平均应力下的疲劳短裂纹生长

SHORT FATIGUE CRACK GROWTH UNDER MEAN STRESS, UNIAXIAL LOADING

本文报道单向加载下平均应力和交变应力对疲劳短裂纹生长的影响。采用一种1.99%NiCrMo钢,在平均应力和交变应力不同组合的应力控制条件下进行室温疲劳试验,将疲劳过程划分为3个阶段:塑性局部化,微观组织短裂纹(MSC)生长和物理短裂纹(PSC)生长,研究了平均应力对上述3个阶段的影响并得到一组关系式,这些关系式可预测多种平均应力和交变应力组合条件下短裂纹的初始阶段和生长行为。获得了不同平均应力下疲劳承载曲线的满意的预测结果。本研究为仍依赖于传统的Goodman疲劳图的设计人员提供了一种以疲劳过程物理机制为基础的方法。

An investigation of the effects of mean and alternating stresses on short fatigue crack growth under uniaxial loading is reported. Tests under stresscontrolled conditions with different combinations of mean and alternating stresses were conducted at room temperature using a 1.99% NiCrMo steel. The fatigue process was divided into three phases: Plasticity Localization, Microstructural Short Crack (MSC) growth, and Physically Short Crack (PSC) growth. The effect of mean stress on the above three phases is studied and a set of equations is obtained which can predict the early stage and growth behaviour of short cracks under various mean and alternating stresses. Satisfactory predictions of fatigue endurance curves at different mean stresses have been achieved. This approach provides an alternative method, based on the physics of the fatigue process, for use by designers who currently rely on conventional Goodman-type diagrams.