An application of viscoelastic fracture criteria to steady crack propagation in a polymeric material under fixed deformation

Tensile stress relaxation and stable crack growth under fixed tensile deformation over an extended range of crack speeds were measured on a flexible thermosetting epoxy resin. The experimental results are analysed and compared with the predictions of two theoretical models of fracture kinetics in viscoelastic media, based on different approaches: one theory, developed by Schapery, postulates a criterion of material failure local to the crack tip; the second theory, evolved by Christensen, extends the overall statement of the conservation of energy to systems that dissipate energy due to viscoelastic effects. The observed behaviour is in qualitative agreement with the theoretical predictions. Quantitative discrepancies, however, call for further theoretical refinements