Mechanics of peeling of rubbery materials. II. Initiation and propagation of peeling

The peel strength of a joint with flexible materials bonded by an elastic adhesive was evaluated in relation to the fracture mechanism. It was found that initiation and propagation of peeling are governed by different mechanisms. Initiation (the formation of an initial crack) occurs when the maximum stress in the adhesive layer reaches a definite value. In this case, the strength fi in a trousers-type peeling is given by 2fi = y0σbϵb, where y0 is the half-thickness of the adhesive layer, σb is the tensile strength, and ϵb is the tensile elongation of the adhesive. On the other hand, propagation is governed by the surface energy of the adhesive. In this case, the peeling strength fs is determined by a balance of energies. For trousers-type peeling it is given by 2fs = Γ, where Γ is twice the surface energy. These results were verified experimentally.