冲击波动态传播特性对激光喷丸残余应力场的影响

Influences of Shock Wave Transient Transmission on Laser Peened Residual Stress Fields

以TC4钛合金为研究对象,基于Johnson-Cook本构模型,分析了高应变率效应对激光喷丸过程中塑性波波速的影响。通过三维有限元方法模拟了不同作用参数激光喷丸诱导冲击波的传播过程,探讨了多次激光喷丸作用后残余压应力饱和现象的产生机理及利用该效应获得均匀表面残余压应力的方法。结果表明:高应变率效应对激光喷丸作用过程中塑性波速度有显著影响,塑性波的速度与所产生的塑性应变呈反比关系。功率密度越大,初始产生的塑性应变越大,塑性波速度越小,冲击波能量衰减越快,冲击波压力幅值降低越快;相同激光喷丸功率密度,随着作用次数的增加,产生的塑性应变逐渐减小,塑性波速度增大,冲击波压力衰减变缓,使激光喷丸诱导的残余压应力逐渐增大;作用次数达到3~4次时,衰减过程基本相似,诱导的残余压应力增幅不大,作用效果基本达到饱和。利用多次激光喷丸作用产生的饱和效应,当激光光斑搭接率超过50%时,即可使搭接区域作用次数达到3次及以上,使激光喷丸作用效果达到饱和,可获得均匀的表面残余压应力。

Taking TC4 Titanium alloy as the object, the effect of high strain rate on the velocity of plastic shock wave was analyzed based on the Johnson-Cook constitutive model. First, the transient transmission of shock wave with different laser shock peening parameters was investigated through three-dimensional finite element method. Second, the mechanism of saturation phenomenon with multiple laser peening was analyzed. Finally, the method of obtain uniform surface residual stress was obtained. Results show that the plastic shock wave velocity during laser peening process is significantly affected by high strain rate effects. Furthermore, the plastic shock wave velocity is inversely proportional to the plastic strain. In the initial stage, the plastic strain increases, and plastic shock wave velocity decreases with increasing laser power density, and thus attenuation gradient of shock wave pressure increases. When the power density keeps constant, the plastic strain and attenuation gradient of laser shock wave decreases with increasing laser peening times, and the residual compressive stress induced by laser shock peening increases. When the impact times increase up to 3 or 4, the attenuation rate is similar and the residual compressive stress will not increase, indicating that the effects of laser shock peening reach saturation. The uniform surface residual stress field can be obtained with the saturation effects when overlapping rate during laser peening process is more than 50%.