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

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 degrees 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.