激光冲击强化提高外物打伤TC4钛合金疲劳强度的试验研究

Experimental Research on Improving Fatigue Strength of Wounded TC4 Titanium Alloy by Laser Shock Peening

采用激光冲击强化(LSP)技术对TC4钛合金试件进行表面处理,利用空气炮试验系统对试件边缘进行外物冲击模拟,对外物打伤(FOD)试件进行拉-拉疲劳试验。结果表明,激光冲击强化有效提高了外物打伤TC4钛合金试件的疲劳强度;未强化试件疲劳裂纹源萌生在缺口根部靠近上表面的位置,强化试件的裂纹源萌生位置在材料内部,与缺口根部有一段距离,且裂纹萌生难度增大。数值应力分析结果表明,强化后试件凹坑的最大拉应力值为668.90 MPa,比强化前的1076.21 MPa减小了37.85%;强化后试件凹坑中心的残余拉应力比强化前平均减小了350 MPa;加载拉应力后,强化前后试件凹坑最大应力分别增大到1542.36 MPa和1124.37 MPa,强化后比强化前试件应力减小了30.22%,说明压应力对裂纹的萌生有明显的延缓作用。残余压应力的引入是激光冲击强化提高打伤试件疲劳强度的主要原因之一。

TC4 titanium alloy surface is treated firstly by laser shock peening （LSP）, then the shock of foreign object on the specimen edge is simulated by means of a gas gun test system, and finally the tensiowtension fatigue experiment is applied to the foreign object damaged （FOD） specimen. The experimental results indicate that LSP can effectively improve the fatigue strength of FOD TC4 titanium alloy. The fatigue crack initiation （FCI） of FOD specimen without LSP locates in the notch root near the upper surface, while the FCI of FOD specimen with LSP transfers to the inside of material with a certain distance from the notch root, which makes it more difficult for crack to initiate. Numerical stress analysis results indicate that the maximum tensile stress decreases by 37.85% from 1076.2 MPa to 668.9 MPa as a result of LSP treatment. In addition, the residual tensile stress in the notch center of FOD specimen with LSP decreases by an average of 350 MPa compared with that of FOD specimen without LSP. With the loading of tension stress, in the notch of the FOD specimen with LSP, the maximum stress increases to1124.37 MPa, in contrast, the maximum stress in FOD specimen without LSP increases to 1542.36 MPa. The former is reduced by 30.22% compared with the latter, which indicates the stress can slow the crack initiation obviously. The introduction of residual stress is one of the main reasons why LSP can improve the fatigue strength of the FOD specimen.