激光冲击强化 TC17 钛合金叶片高周疲劳强度评估模型

Fan and compressor blades are the critical components of aircraft engines. The surface strengthening treatment process is widely used in blade manufacturing. It is important to predict the high cycle fatigue strength of blades after surface strengthening for blade manufacturing. However, the irregular geometric shape of the blades and the complex surface state and microstructure such as hardness and residual stress after surface strengthening pose challenges for the fatigue performance evaluation of surface strengthened blades. This work aims to study the fatigue strength evaluation of surface laser shock peened TC17 titanium alloy blades. Firstly, the microhardness and residual stress distribution of the blade surface after strengthening were tested. Then, surface strengthened blade fatigue tests were carried out to test the fatigue strength and analyze the evolution law of microhardness and residual stress. Based on the internal fatigue limit theory and critical distance theory, a surface strengthened blade fatigue limit prediction model considering surface integrity was established. Combined with finite element modal numerical simulation, the high cycle fatigue strength of surface laser shock peened titanium alloy blades was predicted, which provided theoretical guidance for the fatigue performance evaluation of surface strengthened blades. The surface laser shock peening could improve the high cycle fatigue limit of TC17 titanium alloy material and simulated blades. The tensile fatigue test results of the plate-like tensile specimen showed that the fatigue limit increased by 13.41% after surface strengthening. The fatigue test results of simulated blade bending vibration showed that the fatigue limit increased by 7.77% after surface strengthening. The microhardness results showed that the microhardness of TC17 substrate before laser shock peening was 353HV0.2. After laser shock peening, the surface microhardness of TC17 increased to 394.5HV0.2, and the depth of the affected layer was 800 μm. After fatigue loading, the surface microhardness decreased to 374.8HV0.2, and the depth of the affected layer also decreased from 800 μm to 100 μm. The residual stress results showed that the affected depth of laser shock peening on the residual stress of TC17 titanium alloy was about 300 μm. After cyclic loading, the residual stress on the surface of specimen relaxed and the residual compressive stress layer became shallower. At a depth of about 100 μm, the residual stress value was about –70 MPa, which was equivalent to the initial residual stress value of the substrate, and the influence depth after relaxation was about 120 μm. Based on the internal fatigue limit theory and critical distance theory, a surface strengthened blade fatigue limit prediction model considering surface integrity was established with 7 steps, with a prediction accuracy error of no more than 15%. This study can provide theoretical guidance for evaluating the fatigue performance of surface strengthened components with complex geometric structures and various strengthening methods, such as shot peening, laser shock peening, laser shock peening and shot peening compound strengthening.