The effects of laser shock peening (LSP) on the fatigue life of AA7075-T651 were investigated. The combined influence of surface imperfections (i.e. pits and intermetallics), compressive residual stresses (CRS) and the applied stress on crack initiation sites (surface or subsurface) and the associated fatigue life were investigated. Critical surface imperfections were found to significantly reduce the benefits of LSP in life improvement, by promoting surface crack initiation despite the resisting effects of CRS. To facilitate quantifying the effects of LSP on fatigue life, a finite element (FE) model was developed to simulate residual stress distribution induced by LSP, as well as its redistribution caused by the formation of surface pits. Based on the FE results, a method identifying whether the specified surfaces pits and intermetallics are critical to lead to surface cracking at given stress conditions was proposed, based on the Smith-Watson-Topper method and the Murakami’s model respectively. The interaction between surface imperfections, CRS and the applied loads were taken into account in this method. In addition, a fatigue life assessment framework was proposed based on the prediction of crack initiation sites, which was validated to be reliable in efficiently evaluating the efficacy of the applied LSP in improving fatigue life.

研究了激光冲击强化 (LSP) 对 AA7075-T651 疲劳寿命的影响。研究了表面缺陷（即凹坑和金属间化合物）、残余压缩应力 (CRS) 和施加在裂纹萌生部位（表面或次表面）上的应力以及相关的疲劳寿命的综合影响。尽管 CRS 具有抵抗作用，但通过促进表面裂纹萌生，发现临界表面缺陷会显着降低 LSP 在改善寿命方面的优势。为了便于量化 LSP 对疲劳寿命的影响，开发了一个有限元 (FE) 模型来模拟由 LSP 引起的残余应力分布，以及由表面凹坑形成引起的重新分布。根据有限元结果，分别基于 Smith-Watson-Topper 方法和 Murakami 模型，提出了一种确定特定表面凹坑和金属间化合物在给定应力条件下是否对导致表面开裂至关重要的方法。该方法考虑了表面缺陷、CRS 和外加载荷之间的相互作用。此外，基于裂纹萌生位置的预测提出了疲劳寿命评估框架，该框架在有效评估应用 LSP 提高疲劳寿命的功效方面被证实是可靠的。