Plane strain fracture toughness of polyethylene pipe materials

The plane strain fracture toughness of medium density polyethylene pipe materials has been investigated over a range of test temperatures and rates. Conditions are defined under which valid fracture toughness values can be obtained; at higher temperatures the material is notch‐insensitive. Fracture surface morphology is described, and features are compared with predictions from the Dugdale model. The toughness derives from a band of fibrillar, drawn morphology associated with crack initiation or slow growth. The plane strain fracture toughness correlates with percent crystallinity according to the same relationship whether the crystallinity is varied by thermal treatment, comonomer content, or molecular weight.