Crack propagation in poly(2,6-dimethyl-1,4-phenylene oxide), polystyrene,and their blends

Cracks have been propagated in double-cantilever beam specimens of poly(2,6-dimethyl-1,4-phenylene oxide), polystyrene, and their blends. The plane-strain crack propagation energy varies with crack speed, distance from crack arrest following an instability, molecular weight, and blend composition. Auxiliary measurements of moduli, yield properties, and craze initiation resistances at crack tips were carried out together with microscopic studies of the crack-tip plastic zone. Fracture instabilities are rationalized in terms of the interplay of shear deformation with crazing in the crack-tip plastic zone. Negative deviations from ideal behavior in the crack propagation resistance of the blends are rationalized in terms of the concurrent negative deviation in crazing resistance which in turn is thought to be related to positive deviations in shear resistance and thus to negative volumes and heats of mixing.