Application of the crack layer theory to modeling of slow crack growth in polyethylene

A crack and a domain of highly fibrillated and stretched material ahead of the crack (process zone), commonly observed in polyethylene, are considered as a system called the crack layer. Slow crack layer growth is assumed to be a result of interactions between the crack, process zone and the rest of the body, as well as of degradation of the process zone material. The energy balance for process zone formation and crack layer advance is presented. The equations governing crack layer propagation are formulated and numerically solved. The proposed mechanism of fracture process models the discontinuous crack growth often observed in polyethylene, and predicts the relationship between the crack growth rate and the stress intensity factor consistent with the experimental one. The dependence of the lifetime on load is discussed.