Abstract
The initiation, evolution, and breakdown of the craze ahead of the crack tip is known to control the onset of slow crack growth in polyethylene. Extensive craze zones and large specimen deformations in tough polymers render conventional fracture mechanics approaches incapable of achieving a valid toughness characterisation for these materials. This paper describes a novel experimental method for measuring the local work of separation in tough polyethylene, using tensile specimens with deep circumferential notches, which provide a high level of constraint. The traction–separation behaviour of the material within the constrained ligament is measured directly in situ, yielding a rate dependent cohesive law, which is believed to provide a physically based material description of the damage zone that precedes crack growth. Measurements indicate that both the local work of separation and the cohesive strength are strongly rate dependent, allowing quantification of the fracture behaviour over a wide range of test speeds and discrimination between the stress crack performances of different grades of polyethylene.
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