Analysis and test for effect of structural adhesive shrinkage during curing on mirror surface

In the field of space remote sensing,adhesive bonding technology for mounting optical components is increasingly favored by opto-mechanical engineers.In contrast to mechanical methods,adhesive bonding method usually results in lighter weight,lower costs and easier assembly.Most structural adhesives will shrink during curing process,the shrinkage may cause internal stress,which will lead to deformation of optical surfaces,and affect the imaging quality.To simulate this process using finite element analysis(FEA),a concept of equivalent linear expansion is proposed.In this method,the linear shrinkage of structural adhesive is equivalent to the coefficient of linear expansion,so the shrink of the adhesive during curing can be thought of a process of contraction resulted from drop of temperature while doing thermal elastic analysis.Analysis results show that:with circular bonding,the smaller the bonding area is,the lower the error of mirror surface is,the farther the bonding location is,the lower the error of mirror surface is.Experiments are conducted to verify the analysis,and the results show that:1)The variable quantify of surface figure error is 0.64~1.10λPV while the distance between centroid of bonding layer and mirror surface is 20.5mm and the width of bonding layer is 15 ~25mm;2)The variable quantify of surface figure error is 1.08~0.40λPV while the width is 15mm and the distance is15.5~25.5mm;3)The variable quantify of surface figure error is 0.38~0.88λPV while the distance is 25.5mm,the width is 25mm,and circular distribution angle of bonding layer is 40°~80°.The method proposed here and the results of analysis and experiments may guide the engineering design of mirrors.