EFFECT OF PHYSICAL AGING ON THE FRACTURE-BEHAVIOR OF CROSS-LINKED EPOXIES

The effect of physical aging on the fracture behavior, crack opening displacement, and plastic deformation zone of unmodified and rubber-modified epoxies was determined at two aging temperatures and different displacement rates. The strain energy release rate decreases to between 40 and 50% (for rubber modified and unmodified samples, respectively) of the unaged values after 35 days aging. Systematic dependence of the decrease in fracture toughness by aging on the rubber content is not apparent. The increased yield stress after physical aging is the main factor contributing to the reduction in fracture toughness, crack opening displacement, and plastic deformation zone. Physical aging suppresses the crack blunting mechanisms in epoxies.