Finite element model of thermal stress effects on stress distributions in rubber modified glassy polymers. Part 1 - Single particle model

A single particle finite element model has been used to analyse the effects of thermal stresses on the stress distributions near the interface between the rubber particle and the matrix in rubber modified polymers. The thermal stresses are due to the mismatch of thermal contraction between the rubber particle and the matrix during cooling. The study is to determine whether the thermal stresses are significant enough to affect the distribution of normal stress and von Mises stress at the particle/matrix interface. Results from the single particle model show that a temperature decrease of 60 K, i.e. from 100 to 40°C, can generate a circumferential compressive stress at the particle/matrix interface, which is the same magnitude as the tensile stress required to cause failure in most of the glassy polymers. Although the effect on the circumferential normal stress is significant, its effect on the von Mises stress is very small. The results also show that when the cavitation occurs in the rubber particle, the thermal stress effect is drastically reduced. This study provides encouraging evidence for the importance of thermal stresses in determining the stress distributions in rubber modified polymers and suggests that thermal stresses should be considered in the deformation analysis of these materials.