喷丸残余应力对TC4钛合金疲劳寿命的影响及其松弛行为

Effect of Shot-peening Residual Stress on Fatigue Life and Relaxation of TC4

喷丸强化残余应力场可以提高钛合金材料的疲劳寿命,但在工作载荷作用下,残余应力场会发生松弛,对于喷丸残余应力对TC4钛合金疲劳寿命影响及残余应力本身的松弛行为研究较少。为研究喷丸残余应力对疲劳寿命的影响以及残余应力变化松弛规律,以TC4钛合金试件为研究对象建立疲劳寿命仿真模型,分析不同喷丸残余应力场下疲劳寿命的变化规律及其影响,开展疲劳寿命试验,对仿真模型结果进行验证。在此基础上以载荷水平和循环次数为因素,对残余应力松弛的影响规律进行试验研究。结果表明:不同喷丸强度的残余压应力大小对TC4钛合金疲劳寿命在一定范围内具有较大影响,残余压应力过小或者过大都会对钛合金疲劳寿命产生负面影响,表面残余压应力为−750 MPa时疲劳寿命大幅度提升;随着循环次数的增加,残余应力会逐渐发生松弛,尤其是当循环次数达到10^(4)次时,残余应力会明显松弛,应力松弛量平均约为23.64%,之后逐渐趋于稳定状态,残余应力也会随着载荷强度的增加逐渐发生松弛,且松弛量不断增大。研究结果可为喷丸残余应力的松弛变化规律研究及工程中提高TC4钛合金使用性能、合理高效的预估疲劳寿命提供借鉴参考。

TC4 titanium alloy is an important material used in the aerospace industry for the development of engine blades,turbine disks,and other aerospace components.However,under actual operating conditions,blades are subjected to high centrifugal,aerodynamic,and other vibratory loads during operation and are highly susceptible to fatigue failure or even fracture.Shot peening(SP)can introduce a residual compressive-stress field on the surface of the workpiece to counteract external loads,thereby significantly improving the fatigue resistance of the component.To date,the effects of SP residual stresses on the fatigue life of TC4 titanium alloys and the relaxation behavior of residual stresses have been sparsely investigated.In this study,the effect of residual stress on the fatigue life of TC4 titanium alloy and the relaxation change in shot-peening residual stress were studied.To study the effect of SP residual stress on fatigue life and the relaxation law of residual stress change,a finite-element model of a TC4 titanium alloy specimen was established using ABAQUS,and a fatigue life simulation was performed.The results of the static analysis were imported into FE-SAFE for fatigue life prediction.The fatigue life change rule and its influence under different shot-peening residual stress fields were studied.Shot-peening experiments were conducted at different shot-peening intensities.The residual stresses of the specimens were determined using an X-ray residual stress diffractometer.In addition,the number of cycles of the fatigue specimens under different surface residual compressive stresses was obtained,and the results of the simulation model were verified.On this basis,the influence law of the residual stress relaxation was experimentally investigated with the load level and number of cycles as factors.The residual stresses of the specimens after cyclic loading with a stress ratio of 0.1 and a frequency of 10 Hz were measured.The changes in the effects of different cycles and load intensities on the relaxation of residual stresses in SP were compared.The results showed that the fatigue life of TC4 specimens with load intensities between 600 and 700 MPa was close to the critical value.The magnitude of the residual compressive stress at different shot-peening intensities had a large influence on the fatigue life of the TC4 titanium alloy within a certain range.Moreover,the fatigue life of the specimen with a surface residual compressive stress of−750 MPa at a load intensity of 600 MPa was substantially better than that of the specimen at other stress levels.Under the experimental conditions used in this study,the amount of residual stress relaxation of SP showed an increasing trend and then gradually stabilized with an increase in the number of cycles.When the number of cycles was increased to 104,the residual stress relaxation was particularly evident,and the average stress relaxation was approximately 23.64%.In the range of 105–107 cycles,the residual stress relaxation tended to stabilize,and the average stress relaxation was approximately 19.68%.With an increase in the load intensity,the residual stress relaxation was evident,and with an increase in the cycle time,the effect of the load intensity gradually decreased.However,the surface residual compressive stress remained high.This provides a reference for improving the performance of TC4 titanium alloy in production and predicting the fatigue life in a reasonable and efficient manner.