Analysis of a compressive shear test for adhesion between elastomeric polymers and rigid substrates

Abstract

A compressive shear test for investigating adhesion between an elastomeric polymer and a rigid substrate has been studied. The test consists of loading a specimen comprising of a 3-ply laminate: substrate/polymer/ substrate, in compression and shear at a specified angle to the loading direction. Under displacement control and when adhesion is sufficiently low, an interfacial crack nucleates at one interface early during loading and propagates stably up to a critical load at which unstable propagation with an associated load drop ensues. The case of an isothennal hyperelastic material has been analyzed by computing the energy release rate for an interfacial crack as a function of crack length. The analysis shows that for a range of initial crack size interfacial crack propagation is stable until crack length reaches a critical size at which unstable propagation ensues. The energy release rate at this instability is relatively insensitive to angle of loading, strain, and hyperelastic parameters, which allows one to extract an interfacial toughness, Γ0, from overall measurement of stress and strain. The analysis has been extended to consider combined hyperelasticity and viscoelasticity by using a cohesive zone model for crack propagation implemented as a cohesive finite element. The energy release rate and cohesive zone analyses give identical results for an hyperelastic material. For a viscoelastic-hyperelastic material, the cohesive zone approach allows the viscous losses in the bulk polymer to be estimated separately from the value of interfacial fracture toughness. Both analyses have been applied to experiments on glass/polyvinyl butyral (Butacite®)/glass laminate specimens. The ‘intrinsic’ interfacial toughness, consisting of contributions from bond rupture and a near-tip process zone, is found to be rate-dependent and lies in the range 50–200 J m−2.