应力水平对激光冲击强化圆角疲劳寿命的影响

Effect of laser shock processing on fatigue life of fillet structures under different stress levels

为了研究不同应力水平(疲劳试验过程中应力最大值)下,激光冲击强化对圆角结构疲劳寿命的影响,对半径为3mm的TC4-DT钛合金圆角试样进行了激光冲击试验,接着对试样进行拉-拉疲劳试验,在疲劳试验过程中采用的两种应力水平分别为385MPa和423MPa,应力比r=0.1,并通过扫描电子显微镜对疲劳断口进行分析。结果表明,激光冲击强化后,疲劳源从圆角表面向内部移动,且疲劳辉纹宽度减小,圆角结构疲劳寿命得到提高;当应力水平从385MPa增大至423MPa时,圆角疲劳寿命增益由246.2%减小至111.8%;激光冲击强化后,圆角结构表面形成一定深度的参与压应力,疲劳性能得到提高;但随着应力水平增大,激光冲击强化对圆角结构疲劳寿命的增益减小。该结果为针对薄弱区域强化而抑制疲劳裂纹萌生的研究具有指导意义。

In order to study effect of laser shock processing(LSP)on the fatigue life of fillet structures under different stress levels(the maximum stress during fatigue test),TC4-DT titanium alloy samples were subjected to laser shock processing,and then tensile stress test was carried out.The stress levels were 385MPa and 423MPa respectively,and the stress ratio r was 0.1.The fatigue fracture was analyzed by means of a scanning electron microscope(SEM).The results show that after laser shock processing,the fatigue crack initiation is moved from the fillet surface to the inside,the width of fatigue striation decreases,and the fatigue life of fillet structure is improved.With the increase of stress level,the gain of the fatigue life of the fillet treated by laser shock processing is reduced.When the stress level increases from 385MPa to 423MPa,the fatigue life gain of fillet structure decreases from 246.2%to 111.8%.After LSP,the surface of the fillet has a certain degree of compressive stress,and the fatigue life is improved.However,with the increase of the stress level,thefatigue life gain of the fillet structure is reduced.This result has guiding significance for the study on suppressing fatigue crack initiation by strengthening weak region.