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The fracture behaviour of a 50/50 blend of poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene has been studied. The crack propagation behaviour is strongly influenced by the temperature, crack driving force and the nature of the crack tip craze zone. A fracture map outlining the regions of stable crack growth as a function of temperature, crack velocity and crack driving force has been determined. At high temperatures and low crack growth velocities, stable crack propagation proceeds through a single-craze crack tip damage zone, while at lower temperatures and high crack velocities, a multiple-craze crack tip zone is observed. Corresponding behaviour can be observed under fatigue loading conditions. An instability leading to very high-speed fracture occurs at a critical crack velocity, thus limiting the stable crack propagation regime to lower velocities. The various reported measures of fracture toughness, such as those based on crack initiation, peak load and the onset of crack instability, are discussed.

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