Environmental Crack and Craze Growth Phenomena in Polymers

The nature of slow crack and craze propagation in polymers and crack propagation in inorganic glass has been considered in terms of time dependent processes. By using a fracture mechanics analysis together with time dependent material parameters, equations have been derived to describe crack and craze propagation in both inert and active environments. Experimental data from a range of materials suggest that a crack opening displacement (c. o. d. ) criterion governs the crack propagation behaviour. Incorporation of a simple fluid flow model into the c. o. d. analysis has allowed the failure processes in liquid environments to be described. The data on organic polymers and inorganic glass suggest that when there are no problems of maintaining the environmental supply, the crack growth behaviour is controlled by relaxation processes in the material. At high crack speeds a transition from relaxation to fluid flow control occurs when the time scale is too short for the liquid flow to be maintained. The flow of an environment in long crazes can be shown to influence their behaviour in a similar manner, while under other conditions relaxation controlled craze growth can occur.