Modeling of large-aperture bonded mirrors with nonlinear mechanical behaviors

Large-aperture precision opto-mechanical mirrors are usually joined by adhesive bonding. However, the temperature/curing-dependent stresses and viscoelastic properties of adhesives not only lead to surface figure distortion of mirrors, but also degrade the long-term stability of the opto-mechanical products. Herein, we proposed a comprehensive model, using the Schapery model to characterize the nonlinear mechanical behaviors of the adhesive, to investigate the influence of adhesive bonding on the surface figure of a large-aperture mirror. A temperature/curing-coupled three-dimensional nonlinear viscoelastic constitutive model for finite element implementation was derived and developed. Stress relaxation experiments at different temperatures and strain levels as well as cure shrinkage experiments, were carried out to determine the temperature/DOC-dependent shift factors and nonlinear viscoelastic parameters. The mirror bonding experiments and numerical modeling were conducted to verify the comprehensive model. In addition, the mechanisms of curing temperature and cooling rate on the accuracy and stability of large-aperture bonded mirrors were further revealed and discussed.