Brittle fracture in glassy polymers

Abstract

The brittle fracture behavior of round-notched poly(methyl methacrylate), poly(vinyl chloride), and polystyrene bars has been studied at varying temperatures and bending rates. Brittle fracture originating from internal crazes occurs in a restricted range of temperature. When the plastic deformation zone at the tip of the notch reached a certain size, which decreased with decreasing temperature or increasing bending rate, the internal crazes nucleated at the elastic-plastic boundary. The extrapolation of the position of internal craze nucleation versus temperature plots showed that the nucleation of well defined internal crazes developed above the temperature of the 3 loss peak in each glassy polymer. The mechanism of the ductile-brittle fracture transition at the β-transition temperature in glassy polymers can be understood in terms of variation of the position of internal craze nucleation with temperature and/or strain rate.