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

Abstract

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 Ge22Se58As20 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.

Testing Rigidity Transitions in Glass and Crystal Forming Dense Liquids: Viscoelasticity and Dynamical Gaps

“…For organic glasses, there are some early works concerning the study of flexible and rigid polymer models and how this is related with relaxation (Bartenev, 1970;Picu and Weiner, 1998;Picu et al, 1999). For inorganic glasses, this area is still open in many important aspects (Scopigno et al, 2007;Gueguen et al, 2015;Zhou et al, 2017;Zhu et al, 2018;Sen et al, 2019). In this article we will concentrate on how to test rigidity in simple fluids by using the information concerning transversal waves.…”

A Review of the Precision Glass Molding of Chalcogenide Glass (ChG) for Infrared Optics

“…The true strain and stress of the ChG are calculated by measuring the displacement curve of the upper mold. Figure 6 [ 49 ] shows the displacement w of the upper mold under different pressing forces in which the w is defined as w (t) = y (t) − y (0), and y (t) is the position of the upper mold.…”

“…Both stress and strain should be negative in compression but are taken as absolute values in the following figures for convenience. The changes of strain with time during deformation under different pressing forces are shown in Figure 7 [ 49 ].…”

“…The true stress σ ( t ) can be derived by Equation (2): in which F is the molding force, and ρ 0 is the radius of ChG preform. The changes of stress with time under different pressing forces are shown in Figure 8 [ 49 ]. It is noted that the stress decreases more rapidly under higher pressing force.…”

“…Considering the small strain scenario, the first order Taylor expansion of Equation (2) leads to in which is a constant. Substituting Equation (7) into Equation (6), and considering the cases of σ ≥ σ f, results in [ 49 ]: in which , , , and is the initial stress when the upper mold just contacts the ChG surface and is the stress rate at t = 0. The values of and can be obtained from Figure 8 , and they can be utilized in Equation (8) to determine the constitutive model parameters from compression tests mentioned above.…”