Stress state in tempered glass plate and determination of heat-transfer rate

Thermal tempering is widely used to manufacture safety glass for economic as well as for certain safety measures. Laboratory investigations of the tempering process and the resultant strengthening effect are generally limited to rectangular specimens. Results are, therefore, appropriate for this particular geometry. This paper describes a simple stress-state model of a tempered flat glass specimen. the model, developed using photoelastic equations to determine the three-dimensional stress components, was used to predict the transient birefringence in a rectangular glass specimen subjected to uniform and symmetrical heat-transfer conditions, at a temperature where glass behaves as a perfect elastic material with no stress relaxation within the experimental time. A method of determining the coefficient of heat-transfer rate was then developed based on the analysis of the transient birefringence. This technique uses the glass specimen as an optical transducer, and does not affect, in any way, the natural flow of heat by forced convection or contact cooling.