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Evaluation of energies for crack initiation and propagation is performed on isotropic low density polyethylene (LDPE) and polypropylene (PP). Loading-unloading loops were used to calculate the energies involved during cracking. For PP, an uncracked sample shows necking upon stretching and exhibits high toughness. It was found that, when loaded, the cracked PP sample also showed necking from the crack tip. As a consequence, a crack propagated inside the fully plastic deformed domain. While uncracked LDPE undergoes uniform deformation with strain hardening upon loading, no necking phenomenon was observed at the crack tip of the cracked sample. As the crack propagated, it had to go through the ligament. We suggest that the ligament area is an important fracture parameter in evaluating the fracture energy. In both cases, energies were divided by the ligament area before being related to the crack length increment. Thus, the potential necessary to create unit crack propagation is represented as energy per unit ligament area. As our results show, the fracture resistance of PP is higher than that of LDPE and this is related to the difference in toughness of these two materials.

Посилання на статтю:

Fracture energy analysis of single-edge-cracked isotropic ductile polyolefins / Min-Diaw Wang, E. Nakanishi*, Y. Hashizume and S. Hibi // Polymer. – 1992. – Vol 33. – P. 3408-3414.

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