The Effect of Specimen Thickness on the Tearing Energy of a Gum Vulcanizate

Abstract

Abstract We have examined the effect of thickness on the critical tearing energy of a simple gum vulcanizate of SBR in pure shear. Laboratory experiments and finite-element calculations agree that the tearing energy that is measured with a pure-shear specimen increases with the thickness of the specimen. Laboratory measurements indicate that the deformation for crack growth in a pure-shear specimen increases with the thickness of the specimen. Finite-element calculations show that the energy available for release at a given deformation also increases with thickness in the range from t=1.4 mm to t=14 mm. Experiments show that the crtical tearing energy varies linearly with thickness in the range t=0.7 mm to t=2.7 mm. The effect of thickness on the tearing energy was also studied by calculating the J-integral at various points of the crack through the thickness of the pure-shear specimen. In general, the J-integral calculated at the surface of the specimen can be higher than the J-integral calculated at the center of the specimen for specimens that are sufficiently thick. The thickness effect measured in this work suggests that the “critical tearing energy” obtained from standard laboratory specimens may not be a true material property. For this reason, critical tearing energy that is measured on standard specimens may not be generally applied to predict failure in arbitrary elastomeric components.