The J integral fracture toughness and damage zone morphology in polyethylenes

The J integral analysis of compact tension samples has been used to evaluate plane strain fracture toughness of various polyethylenes at room temperature. Crack propagation commences from a razor notch in high-density polyethylene at J Ic = 1.7 kJ m −2. Plastic deformation is confined to a small craze region (about 300 μm long, 20 μm high) through which the crack subsequently propagates. A tough copolymer of PE3408 material resists crack advance until J Ic = 8.2 kJ m −2. Here again crack propagation is through a craze, though craze length exceeds 1 mm. Toughness is also imparted by the formation of shear bands near the notch tip. Low-density polyethylene does not really fracture under the present test conditions; this material responds by general yielding and blunting of the notch tip.