Fracture problems of rubbers:: J-integral estimation based upon η factors and an investigation on the strain energy density distribution as a local criterion

This paper dealing with the fracture of rubber-like materials is a continuation of our previous works (Ait Hocine et al., 1996, 1998). Single specimen methods for measuring the J-integral and, so, its critical value J(c) (fracture surface energy) are investigated combining experimental data and finite elements analysis. It shown that the formula of J established by Rivlin et al. in the case of the SENT geometry can be extended to the DENT specimen containing small crack lengths (a/w less than or equal to 0.3). Moreover, considering DENT and pure-shear (PS) specimens, alternative expressions of this parameter, based on the eta factor, are proposed and a good agreement is obtained between the numerical calculations and the experimental data whenever available. The critical values of J are found constant for the two tested materials. Finally, it's pointed out that, at the onset of crack growth, the strain energy density along the crack axis is independent on both the crack length and the specimen geometry.