薄膜残余应力和表面杂质对变形镜疲劳寿命的影响

Influence of thin-film residual stress and surface impurities on fatigue life of deformable mirror

文中综合考虑变形镜(DM)薄膜残余应力和表面杂质的影响,采用ANSYS有限元分析软件建立了镀高反射膜系的变形镜应力分析模型,进而基于应力-寿命(S-N)曲线和Miner累积损伤理论,分析了波前校正过程中变形镜的疲劳损伤特性,并详细讨论了变形镜薄膜残余应力和不同尺寸的表面杂质对变形镜疲劳寿命的影响。研究结果表明,在热-机械耦合作用下,热效应的存在会加速变形镜的疲劳损伤。对于给定的待校正畸变波前,随着变形镜薄膜残余应力的增大,变形镜承受的动态循环载荷越强,其疲劳寿命越短,且残余应力主要对变形镜镜面疲劳寿命影响较大;而当变形镜薄膜残余应力一定时,畸变波前PV值越大,其表面应力越大,致使疲劳寿命也随之缩短。在强激光连续辐照下,当表面杂质大于一定尺寸时,变形镜疲劳寿命随着杂质粒子尺寸的增大而减小,而当杂质粒子尺寸较小时,则对变形镜的疲劳寿命影响不大。此外,薄膜残余应力的存在将进一步加剧表面杂质对变形镜的疲劳损伤。

Considering the influence of the thin-film residual stress and surface impurities of deformable mirrors(DMs),the stress analysis model of the DM with high reflectivity films was built up by the use of the finite element analysis software ANSYS.The fatigue damage characteristics of the DM for wavefront correction process were analyzed based on the stress-cycle(S-N)curve and the Miner cumulative damage theory,and the influence of the thin-film residual stress and the surface impurity size on the fatigue life of the DM was discussed in detail as well.The results indicate that,under the condition of the thermal-mechanical coupling,the fatigue damage of the DM tends to speed up due to the thermal effect.For a given distortion wavefront to be corrected,the dynamic cyclic load of the DM is stronger with the increasing thin-film residual stress of the DM,and the fatigue life is shorter simultaneously.Besides,the residual stress mainly affects the fatigue life on the surface of the DM.For the given thin-film residual stress of the DM,the fatigue life also decreases due to larger surface stress caused by the increasing PV value of the distortion wavefront.When the surface impurities are irradiated by the high-power continuous laser,and are above a certain size,the fatigue life of the DM decreases with the increasing impurity size.However,the fatigue life of the DM is rarely affected when the sizes of the impurities are smaller enough.Furthermore,the thin-film residual stress will further increase the fatigue damage of the DM caused by surface impurities.