【作者】 李欣；

【导师】 汪海； 张晓晶；

【作者基本信息】 上海交通大学 ， 飞行器设计， 2014， 硕士

【摘要】 喷丸强化工艺作为表面处理的主要手段之一，能显著改善材料的疲劳性能，已经广泛地应用于航空航天等领域。喷丸强化的主要机制在于引入了表面残余应力场，其对疲劳源萌生位置及疲劳裂纹扩展速率都有着重要影响。因此，定量得到喷丸后的残余应力场以及喷丸后裂纹应力强度因子和疲劳寿命，对喷丸工艺的控制以及应用都有着显著意义。本文首先针对多种材料体系，评估了经验方程、解析模型以及所提出的单弹丸与多弹丸冲击结合的有限元模型等五种方法对喷丸残余应力场四个特征参量的预测能力。与已有文献中的实验数据比较，结果表明：Yao的经验方程适用于40Cr钢和其他与40Cr钢性能相近或相似的钢材料；Wang的经验方程可适用于多种金属材料；解析方法更适用于预测强度和硬化能力适中的材料。单弹丸模型计算弹痕直径和多弹丸模型计算残余应力场的有限元模型可有效预测多种材料体系和覆盖率的喷丸残余应力场。同时，工程中确定了喷丸条件和靶材性能后，对喷丸残余应力场的预测往往需要这五种方案中的几种结合。为了研究裂纹萌生于次表面时，残余应力场对次表面裂纹应力强度因子的影响，本文基于三维权函数理论，将次表面裂纹体处理为三维内埋椭圆裂纹，并将其分解为基本片为共线中心裂纹和弹簧片为偏心裂纹的两组片条，得到了次表面裂纹的三维权函数。在已知喷丸引入的残余应力场基础上，利用三维次表面内埋椭圆裂纹的权函数，得到了40Cr钢在一定喷丸条件下，裂纹萌生于次表面时的三维椭圆裂纹的应力强度因子。与裂纹萌生于表面时的三维应力强度因子的解比较，在残余应力场的影响下，裂纹萌生于次表面时的应力强度因子在数值上要小于表面裂纹的应力强度因子，即残余应力场对萌生于材料表面的裂纹扩展速率的影响更为明显。次表面裂纹靠近有限边界的前缘对应力变化以及距离边界的尺寸的变化更为敏感。更多还原

【Abstract】 As the most useful method to improve the surface conditions andincrease the fatigue life for materials and structures, shot-peening has beenwidely used in the design of aerospace and automobile components. Themain mechanism of shot-peening is the introduction of residual compressivestress field, which can change the crack initiation locations and decrease thecrack propagation rate. Thus, quantitative study of the residual stresses andthe stress intensity factors after shot-peening has been an important subjectin theoretical and practical field.Firstly, with the comparison between the predictions and test results ofvarious shot-peened metals, the capability of five solutions includingempirical equations, theoretical models and FEM models for predicting thecharacteristic parameters of residual stress field was proved. The empiricalequations of Yao had good predictions for40Cr steel and other similarsteels，and the empirical equations of Wang were capable of various metalswhile theoretical models were suitable for metals with medium strength andhardening rate. The predicting results of single-shot FEM models forcalculating the peening dents diameters and multi-shot FEM models forcalculating the residual stress field were in good agreement with test resultsof various metals with different shot-peening coverage. In practice，combinations of these methods were needed.Secondly, to study the behavior and the three dimensional stressintensity factors of subsurface cracks, the crack body was considered aselliptical crack and decomposed into two kinds of slips, that is the fundamental slips with multi-collinear cracks features and the elastic-springslips with eccentric cracks features. Based on the three dimensional weightfunction theory, the three dimensional weight functions of the subsurfaceelliptical cracks were achieved.Finally, on the basis of the three dimensional subsurface weightfunctions, the stress intensity factors of the40Cr steel after shot-peeningwere achieved. The results showed that the stress intensity factor ofsubsurface cracks under the residual stress was less than that of surfacecracks. Thus，the effect on decreasing the propagation of surface cracksafter shot-peening was better than that of the subsurface cracks. And thefront which was closer to the limited boundary was more sensitive to thedistance from the boundary and loads than remote front of the subsurfacecracks.更多还原