FEM-based thermal deformation analysis of large Fine Cordierite mirrors induced by CTE inhomogeneity

Le résumé fourni par la source

Fine Cordierite® has attracted attention as a candidate material for large astronomical mirrors because it combines a low coefficient of thermal expansion (CTE) with high Young’s modulus and high thermal conductivity compared to low-expansion glass and glass ceramics. Isoyama et al. (2024) measured the spatial CTE inhomogeneity of Fine Cordierite and quantified its statistical characteristics using a structure function. In this study, three-dimensional CTE distributions were generated based on the measured structure function and introduced into finite element method (FEM) mirror models. Thermal deformation analyses were performed to evaluate the influence of spatial CTE inhomogeneity on mirror surface deformation. In addition, a bulk mirror model and lightweight mirror models with triangular and hexagonal backside rib structures were analyzed to compare the effectiveness of rib structures in suppressing CTE-induced surface deformation. The results show that appropriate rib structures can reduce the peak-to-valley and root-mean-square surface deformation compared with the bulk model, and that the deformation depends strongly on rib pitch and face-sheet thickness. This work provides a framework for evaluating and designing lightweight mirror structures while considering material-specific CTE inhomogeneity.

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