Finite element modelling of stress relaxation in glass lens moulding using measured, temperature-dependent elastic modulus and viscosity data of glass

Abstract

Cylindrical compression experiments were performed on two different grades of optical glasses to measure their stress response to the applied strain at lens moulding temperatures. The temperature dependence of elastic (Young's) modulus of the two glasses was measured using the technique of Brillouin light-scattering, from ambient temperature to approximately 250 °C above the glass transition temperature. The measured high temperature material data were used as input to finite element method simulation of cylindrical compression as well as to the precision lens moulding process.Good agreement was obtained between stress relaxation patterns predicted from cylinder compression simulations and analytical models. The close agreement between predicted and experimental loads during lens moulding validates the viscoelastic material model.

Final Shape of Precision Molded Optics: Part I—Computational Approach, Material Definitions and the Effect of Lens Shape

“…Jain and Yi [10] modeled the pressing stage of lens molding for BK7 glass using displacement control. The cooling stage was not modeled in this study, which would involve the complex phenomenon of structural relaxation.…”

“…The approach for the creep data was similar to that of Jain and Yi [10] and Arai et al [17], except that these authors used solid disks and assumed that glass is incompressible. In the current study compressibility was taken into account so that a sensitivity analysis could be performed on the effect of the hydrostatic relaxation (4).…”

Glass material model for the forming stage of the glass molding process

“…not only focused on the measurement of the viscosity of glass at the molding temperature but also utilized FE analysis for the glass molding process; this study regarded glass as a viscoelastic material Jain et al, 2006). When discussing the bottle formation of glass at a high temperature, glass is regarded as behaving as a Newtonian fluid, where the viscosity is temperature-dependent, and the material model is rigid-viscoplastic (Hyre, 2002;MSC, 2005).…”

Temperature effect on the deformation and optical quality of moulded glass lenses in precision glass moulding

“…Tarkes et al established a thermal boundary condition model of glass‐N 2 gas to analyze N 2 flow temperature distribution in a PGM machine during the cooling stage. Jain and Yi et al used cylindrical compression tests to determine the parameters of high‐temperature viscosity, and the Brillouin light‐scattering technique to obtain the temperature dependence of the elastic modulus of the glass. Moreover, high temperature glass material data were used in the numerical simulations to analyze PGM.…”