Delayed yielding of epoxy resin under tension,compression, and flexure. I. Behavior under constant strain rate

Series of loading tests were carried out on epoxy resin specimens, at varying constant strain rates, under tension, compression, and flexure. The stress–strain relationship revealed a distinct yielding stage followed shortly by a post-yielding region of decreasing load. In all cases, results indicate linearity between yield stress and log strain rate, in accordance with Eyring's theory of viscous flow. For specimens unloaded close to the yield point, photoelastic observations revealed a residual pattern parallel to the theoretical principal shear stresses. These results, supported by additional data from other works, indicate a viscoplastic deviatoric stress-biased diffusional mechanism as the dominant factor in the yielding of an amorphous crosslinked epoxy system.