A large-strain intrinsic default-based fracture criterion for polymers: assessment in biaxial loading and application to ageing

In this contribution, we attempt to give a general methodology allowing the fracture prediction of polymers under biaxial monotonic loading. Using the intrinsic defect concept, we assume that fracture at a macroscopic level is the consequence of the presence of defects at lower scales. We also assume that the fracture is governed by a macroscopic parameter, the strain energy release rate or the J-integral. Intrinsic defect size, constitutive response and fracture toughness being the criterion inputs; the principal stretches at break can be therefore estimated for any biaxial and monotonic loading path. The proposed methodology includes the estimation of the J-integral for any biaxial loading using a unified expression of this parameter which is a generalised form of that developed in the literature for uniaxial tension. Using different set of experimental data obtained in our team, the methodology is then successfully applied to various kinds of polymers: a natural rubber, a styrene-butadiene rubber, a polyurethane, a thermoplastic elastomer and a high-density polyethylene. We show also that such a methodology can be applied to predict the ageing effects on the stretches at break.