A note on the role of dilatation in the fracture of viscoelastic elastomer

Abstract

Fracture models addressing crack propagation in viscoelastic materials typically draw on cohesive force distributions coupled with a linearly viscoelastic constitutive material description. While the resulting formulation of the crack speed as a function of applied loads provides good agreement with measurements on polyurethane rubber as well as three other rubbery solids studied by A. N. Gent on the more global scale, the size of the cohesive zone required to match theory and measurements is unreasonably small. Although this glaring discrepancy has not deterred the use of the theory for viscoelastic fracture, it has remained a troublesome question on the wider applications to polymer fracture. The present note revisits this issue and draws on results developed during the past decade to explain this discrepancy via the effect of stress-induced dilatation on the relaxation or retardation times of viscoelastic solids.