Stability of crack propagation in epoxy resins

The propagation of cracks in epoxy resins has been studied using a linear elastic fracture mechanics approach and a double torsion testing geometry. Under constant crosshead displacement rate conditions cracks are found to propagate in an unstable ‘stick-slip’ manner at high temperatures and with low rates of testing whereas at lower temperatures and using higher rates of loading propagation is more stable and cracks propagate in a continuous manner. The presence of liquid water tends to cause a transition from stable to unstable propagation at room temperature. The influence of specimen geometry upon crack stability is also discussed.