Particle-tear energy contribution to the toughness of rubber-modified epoxies

A previously developed model for the toughening effect of rubber particles in rubber-modified epoxies is tested. The model predicts a correlation between toughness of rubber-modified epoxies and tear energy of the dispersed rubber phase. Particulate tear energies are obtained from tear strains of the particles measured in-situ during crack propagation through the composite. Two types of rubber-modified epoxy which had been exposed to various levels of gamma radiation are used to determine the effect of radiation-induced crosslinking on tear energy of the rubber particles. The toughness data of the irradiated composites only partially follow the trend predicted by the particle tear energy model. The toughness of the rubber-modified epoxies increases to a maximum and then decreases at high radiation levels whereas the predicted values increase monotonically with radiation level. Tearing rate and viscoelastic effects on tear energy and particle debonding are believed to cause the discrepancies between the predicted and measured behavior. 7 figures