The influence of morphology and structure on the crack growth of linear polyethylene

Abstract

For the examination of relationships between structure and crack growth behaviour, different high-density polyethylenes were used. The morphology of the polyethylenes was throughly investigated by different methods such as DSC, TEM and WAXS. Results were supported by calculations of the lamellar thickness and the tie molecule density. An instrumented Charpy impact tester was used for the measurements, and load-deflection diagrams were registered. Different fracture mechanics methods were applied to determine geometry-independent fracture mechanics values as resistance against unstable and stable crack growth on single edge notched specimens. Considering the tough material behaviour of high-density polyethylene the concepts of the elastic-plastic fracture mechanics (i.e. the J -integral and the crack opening displacement) were used for the evaluation of the experiments. The influence of the structure on the crack initiation and the crack propagation in high-density polyethyelenes was studied. Tie molecules density and crystallinity, especially the long period, proved to be important parameters for the energy dissipation of the observed polyethylenes.