Observation and analysis of process zone–crack interaction in crack layer during fatigue crack propagation in polypropylene

Abstract : Fatigue crack propagation in polypropylene, despite its significance in a wide range of structural applications, has not been sufficiently researched because of the complex interaction between the crack tip and process zone ahead of the crack tip. In this study, the crack-layer evolution during fatigue-crack growth in polypropylene was observed using an anti-buckling jig. The lengths of the crack and process zone, damage density, and morphology of the process zone were quantified using image analysis. This enabled the characterization of the process zone–crack interaction in polypropylene (PP), in which process zone damage densified until an instability condition was satisfied, resulting in discontinuous crack growth. A numerical simulation of the theoretical crack layer model reproduced the discontinuous crack growth of polypropylene in experimental observations during fatigue loading and predicted the final cycles leading to fracture with 7.29% error. The simulation results demonstrated that numerically implementing the developed theoretical crack layer model can reproduce crack layer morphology and fatigue crack growth behavior, strongly correlating with the experimental results. Applying the developed crack layer model enabled various geometrical and environmental factors to be considered in predicting the residual lifetime of structural components based on polypropylene.