Peel of elastomers of various thicknesses and widths

We peel a highly stretchable silicone (Ecoflex), thickness H and width B, sandwiched between two inextensible films. When the peel front advances steadily in the elastomer, the peel force reaches a plateau F_ss, and the ratio 2F_ss/B is commonly reported as the toughness of the elastomer. Our data show that this “peel toughness” is not always a material constant, but can depend on the thickness H and width B. We interpret the data in terms of two fundamental ideas in fracture mechanics. First, as the ratio B/H increases, the deformation in the elastomer changes from the plane stress to the plane strain conditions, so that the stress state ahead the peel front changes from biaxial to triaxial tension. We show that the elastomer under triaxial tension reaches higher stress and damages more than the elastomer under biaxial tension. Second, when the inelastic zone around a peel front is not much smaller than H, peel is under large-scale inelasticity conditions, and the material ahead the peel front deforms in nearly a homogeneous state. We show our data measured using various thicknesses collapse into a single curve on the plane with axes Γ∕H and B/H.