Crack initiation behavior of ABS resin under mode I and mixed mode loading

Mode I and mixed mode loading testing of ABS resin were carried out by using compact tension shear specimens. Two types of ABS resin were examined. The first one (ABS-1) has a butadiene rubber content of 18 wt % in the form of small particles of diameter of about 200 nm. The second one (ABS-2) has the same overall butadiene rubber content but a bimodal particle distribution with diameters of 200 nm and 500 nm. Crack initiation behavior was observed by using a video microscope. The fracture toughness of ABS-2 obtained by mode I testing is larger than that of ABS-1. The fracture angle for both materials under mixed mode loading coincides with the values predicted by the maximum hoop stress criterion. On the contrary, at crack initiation under mixed mode loading, the critical values of K-I and K-II are larger than those estimated by the maximum hoop stress criterion. The increase in the critical values of K-I and K-II under mixed mode loading for ABS-2 is higher than those for ABS-1. The bimodal type distribution of rubber particle size produces better fracture resistance.