Fracture behaviour of polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) under mixed‐mode loading conditions was studied for several weight fractions of PC and ABS. Mode I and mixed‐mode fracture tests were carried out by using compact–tension–shear specimens. At a certain value of mixed‐mode loading ratio KII /KI  a crack of the shear type will initiates at the initial crack tip. Fracture toughness increases under mixed‐mode loading with an increase in the mode II component, whereas it reduces with the appearance of a shear‐type fracture. Fracture toughness and the appearance of a shear‐type fracture depends on the blending ratio of PC and ABS. The transition to shear‐type fracture occurs at lower value of KII /KI for resins with higher fracture toughness.

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ABSTRACT:The effect of moisture absorption on fracture behaviors of acrylonitrilebutadiene-styrene (ABS) resin has been studied. For comparison, polystyrene (PS) and styrene-acrylonitrile (SAN) resin have been tested. The fracture toughness of PS and SAN resins is determined by the ASTM standard test method for brittle polymers. The fracture toughness of ABS resin is obtained on the basis of the multiple specimens method. The fracture toughness of PS and SAN resin decreases with the increase in moisture absorption. On the other hand, the fracture toughness of ABS resin slightly decreases despite enormous moisture absorption. On the specimens absorbing moisture, a bright whitening region and a milky coloring region are distinguished in the stress-whitening region, and the milky coloring region expands around the bright whitening region at the crack tip. From the transmission electron microscopic observation, the precraze formation can be recognized in this region. The crack-tip shielding effect induced by this formation compensates the fracture toughness decrease due to moisture absorption.

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