Elastic-viscoplasticity modeling of the thermo-mechanical behavior of chalcogenide glass for aspheric lens molding

Chalcogenide glass (ChG), as an alternative material in place of single-crystal germanium, is increasingly used in thermal imaging, night vision, and infrared guidance systems, etc., owing to their excellent formability through precision glass molding (PGM). The deformation mechanisms of these glasses at the molding temperature involve elasticity, plasticity, and viscous flow, which call for a new theoretical model to assist the design of PGM process. This paper investigates the thermo-mechanical properties of Ge ₂₂Se ₅₈As ₂₀ at the temperature above its softening point and establishes a new elastic-viscoplasticity model to describe its thermo-mechanical behaviors. After determining the model parameters through cylindrical compression tests, the new constitutive model is implemented in finite element method (FEM) of PGM to form an aspheric ChG lens. And the agreement of displacement-time curves between experimental and simulation results exhibit the validity of the proposed elastic-viscoplastic constitutive model.