When researching the effect of rubber toughening in acrylonitrile-butadiene-styrene (ABS) copolymer and high-impact polystyrene (HIPS) and also toughening methods used in other materials, then, often comparisons are needed between materials with and without the toughening agents over the full crack velocity range. This is from the threshold stress to just maintain crack propagation up to the limiting crack velocity conditions. However, the toughening of materials can change other material properties including, for example, the onset of yield in the material under static stress. The result can be that a crack velocity versus stress curve cannot be obtained by experiment over the full crack velocity range for some toughened materials. However, as used in this study, combined experimental and computer simulations can provide for a meaningful and informative comparison between crack velocity versus stress curves for materials with and without toughening agents over the full crack velocity range. (C) 2003 Kluwer Academic Publishers.