Effect of the quenching temperature on the fields of thermal stresses and on the mechanical and thermal properties of PMMA

This study explores the photoelasticimetry as a means to investigate factors affecting the residual stresses, particularly the thermal stresses, in polymethyl methacrylate (PMMA). The aim was to study the effect of quenching temperature in three different media: air, water, and ethylene glycol, on the impact strength and thermal properties of PMMA. These temperatures varied from a fixed value of 120°C to various values below Tg and the fields of distribution of cooling stresses have been obtained using a charge-coupled device (CCD) camera. It was observed that the quenching in water at 20°C gives rise to an important density of tensile stresses. However, in the ethylene glycol at 110°C this density has a tendency to disappear. An approximate evaluation of these stresses in a point near the specimen center has been assessed, and it was found that the distribution profile of the fields of tensile stresses was much closer to a parabolic form. Notched Izod impact strength and heat deflection temperature (HDT) were measured, and were found to be particularly sensitive to thermal stresses.