The strain rate dependence of deformation and fracture behaviour of acrylonitrile-butadiene-styrene (ABS) copolymer in impact test

The impact properties and fracture characteristics of acrylonitride-butadiene-styrene (ABS) copolymer are investigated by using a servo-hydraulic machine and a compressive split-Hopkinson bar at room temperature over a strain-rate range of 10 ^-3 s ^-1 to 4×10 ³ s ^-1 . The effects of strain rate on the stress-strain response, Young's modulus, strain-rate sensitivity and thermal activation volume are evaluated. Scanning electron micrographs (SEM) of the fractured specimens are presented to illustrate the damage initiation and fracture mechanisms. It is found that the deformation and fracture behaviour of ABS are very sensitive to the applied strain rate. There is a significant increase in Young's modulus, flow stress and yield strength as the strain rate increases. By contrast, increasing strain rates lead to decreasing fracture strains. It is also found that the strain-rate sensitivity increases with an increasing range of strain rate, but decreases with strain in large strain-rate ranges due to the development of deformation heat. An inverse phenomenon is observed for activation volume. SEM examination reveals that damage is a complex process and occurs initially at two separate sites: 1) as microvoids and microcracks radiating from the center of the specimen; 2) as microcracks parallel to the specimen axis, starting at the equatorial midline of the cylindrical wall. Rapid microcracking as well as microvoid formation, growth and coalescence lead to final failure. The damaged specimens twist in a catastrophic manner as high strain-rate impact loadings are imposed.