On sizes and contour stresses of crack tip crazes in thermoplastics

The finite element method is applied to contours of craze zones in front of crack tips in Poly(methyl methacrylate) (PMMA) and Poly(vinyl chloride) (PVC) during fatigue crack propagation (FCP) measured by interferometry. Stress distributions along the craze contours at different rates and cycle numbers are computed for both, continuous and retarded FCP. Differences in rate dependence and magnitude of the stresses are found but, in the explanation of the difference in FCP mode, the critical extension ratio of the craze fibrils may be more significant. (IWM