Application of the Caustic Method to an Environmental Crack-Craze Growth Problem

Abstract

The stress intensity factor K_I(c) is a controlling parameter for craze initiation and growth at crack tips of linear glassy polymers in environmental liquids (Marshall 1970). However, as the craze grows larger than the one which the Dugdale model (Dugdale 1960) assumes, linear fracture mechanics fails to describe the craze growth behavior. The caustic method is applied to a study of the environmental crack-craze stress field in poly(methyl methacrylate)(PMMA). The change of the caustic shape and size reflecting the nonuniform stress state along a craze is experimentally correlated with the craze growth behavior (Abo-El-Ezz). The caustic method was originally based on an elastic assumption (Mannog 1966; Theocaris 1970) and later was applied to materials displaying a large amount of plasticity and strain-hardening (Theocaris 1973, 1974). The two-step stress distribution model along a craze is introduced for a quantitative analysis by the elasto-plastic caustic theory (Takeda). The theoretical caustic shape and size based on this model is then compared with the experimental results.