Effects of curing temperature and CFRP/Invar bases on the surface figure of adhesive-bonded mirrors

Adhesive bonding technology is widely used to join optical mirrors and their supporting components in precision optomechanical products. However, the curing stresses of optical adhesives often cause mirror distortion, which in turn degrades optical precision. This paper presents a method for analyzing the curing stresses and improving the surface accuracy of a bonded mirror. The approach employs a comprehensive finite-element model that integrates a cure kinetics equation, calibrated with differential scanning calorimetry (DSC) data, and a viscoelastic material model for the adhesive. The viscoelastic model is enhanced through nonlinear time–temperature/degree of cure (DOC) superposition principles, which are determined by stress relaxation tests at varying DOCs and temperatures. The gel point and effective chemical shrinkage strain of the adhesive are quantified using a fiber Bragg grating (FBG) technique. The model is validated experimentally using a bonded planar mirror, elucidating the evolution of surface figure with DOC and temperature. The influences of base materials (carbon fibre-reinforced polymer (CFRP) and Invar) and bonding structure on surface distortion were further examined, and an optimized design for the CFRP base was proposed.