Abstract
The fracture behavior of a PMMA toughened by small (0.2 μm diameter) rubber particles was investigated over a wide range of rubber particle volume fractions. Crack tip morphology, material toughness, and fracture surfaces were studied. Whereas isolated particles have no effect, interactions between particles strongly modify the fracture behavior. Interactions occur via two different mechanisms: (i) an overlap of the stress enhancements due to particles, which is a function of the ratio of the distance between particles versus particle diameter; (ii) a geometrical “sifter” effect, which occurs when the distance between particles is less than the craze thickness.