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Fractography has been used in the post-failure analysis of single edge notched specimens of injection molded blends of polycarbonate (PC) and acrylonitrilebutadiene-styrene terpolymer (ABS). The mode of ductile tensile fracture of single edge notched specimens depended on composition. Plane stress shear tearing was observed in the composition range PC/ABS 90, ' 10 to 70/30 by weight where PC was the continuous phase. Intermediate compositions, PC/ABS 60/40 to 40/60, had a co-continuous or almost co-continuous phase morphology; these blends fractured by mixed mode pop-in, where a tunneling center crack relieved the triaxiality and permitted plane stress shear lips to form near the edges. Hemngbone fracture, a plane strain mode characterized by discontinuous crack growth, was observed when Al3S was the continuous phase, PC/Al3S 30/70 to 10/90. An S-shaped relationship was observed between the ductile-to-brittle transition temperature and the composition. Addition of AI3S to PC increased ductility up to PC/AI3S 70/30 and 60/40, which were the most ductile compositions. Further addition of Al3S decreased the ductility, and the least ductile compositions were PC/AT3S 30/70 and 10/90.

Fatigue behavior in a blend of natural rubber (NR) and polybutadiene rubber (BR) has been investigated. The energy release rates measured from load-displacement curves recorded during the fatigue test could be used to characterize the fatigue crack propagation (FCP) history of NR/BR blend. Crack propagation kinetics showed an initial low slope “ozone crack regime” with an S-shaped “mechanico-oxidative cut growth regime”. The blend has a mechanical fatigue limit of 2.4 kJ/m2. The crack initiation constituted 25% of the total fatigue life and the low slope stage comprised 40% of the crack propagation life. Examination of the fracture profile and the fracture surface revealed that microcracks and crack tip roughening were two damage mechanisms controlling the resistance to crack propagation in the “mechanico-oxidative cut growth regime”, while the reverse herringbone pattern near the notch corresponded to the “ozone crack regime”.