Fractography of injection molded polycarbonate acrylonitrile‐butadiene‐styrene terpolymer blends

Fractography has been used in the post‐failure analysis of single edge notched specimens of injection molded blends of polycarbonate (PC) and acrylonitrile‐butadiene‐styrene terpolymer (ABS). The mode of ductile tensile fracture of single edge notched specimens depended on comosition. 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 almot 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. Herringbone fracture, a plane strain mode characterized by discontinuous crack growth, was observed when ABS was the continuous phase, PC/ABS 30/70 to 10/90. An S‐shaped relationship was observed between the ductile‐to‐brittle transition temperature and the composition. Addition of ABS to PC increased ductility up to PC/ABS 70/30 and 60/40, which were the most ductile compositions. Further addition of ABS decreased the ductility, and the least ductile compositions were PC/ABS 30/70 and 10/90.