Yield behavior and energy absorbing characteristics of rubber‐modified epoxies subjected to biaxial stress states

Abstract Hollow cylinders of aromatic‐amine cured epoxies, modified with 0%, 10%, and 20% CTBN rubber by weight were tested in stress states ranging from uniaxial compression to biaxial tension. Our results showed that rubber particles decrease the yield strength uniformly over all stress states and suppress brittle fracture in the more demanding stress states. Particle size has no effect on yield strength. Samples were also biaxially loaded and unloaded to varying stress levels to monitor and study their dissipative characteristics. From these tests, a threshold stress was observed where the stiffness of the rubber‐modified resin decreases and the deformation becomes increasingly irreversible. By comparing the changes in damage morphology with the change in loading path, we determined that a significant amount of energy is absorbed in the rubber‐modified samples prior to macroscopic yield. Additionally, this irreversibility does not appear to be associated with rubber particle cavitation or inelastic void growth.