CRACK PROPAGATION IN MODEL POLYETHYLENES.

Crack propagation was investigated in polyethylenes varying in molecular weight and short chain branching. Thin, single-edge notched specimens were examined under macroscopic strains in the range e equals 0 to e equals 0. 3. A definite correlation was found between the amount of plastic deformation at the crack tip, which leads to crack advance and fracture, and the strain hardening rate of the polymer as determined by tensile testing. Polyethylenes with large strain hardening rates resist both crack blunting and crack advance; strain hardening is seen to stabilize the crack. Experiments have shown that this important strain hardening parameter is enhanced in polyethylenes having high molecular weight and low crystallinity.