THE PEELING OF FLEXIBLE LAMINATES

The present work has defined an adhesive fracture energy G(a) for the peel testing of flexible laminates. The value of G(a) characterises th e fracture of the laminate and is considered to be a 'geometry-indepen dent' parameter which reflects (i) the energy to break the interfacial bonding forces and (ii) the energy dissipated locally ahead of the pe el front in the plastic or viscoelastic zone. We have shown that in or der to determine this true adhesive fracture energy G(a) that the foll owing energy terms must be considered: (i) the stored strain-energy in the peeling arm, (ii) the energy dissipated during tensile deformatio n of the peeling arm, and (iii) the energy dissipated due to bending o f the peeling arm. The analysis proposed yields quantitative expressio ns for these various energy dissipation terms and, in particular, cons iders the energy dissipated due to bending of the peeling arm. Another important feature of the analysis is the modelling of the region belo w the peel front as an elastic beam on an elastic foundation; such tha t the peeling arm does not act as a truly built-in beam and root rotat ion at the peel front is allowed. The analysis described in the presen t paper has been employed for four different laminates. The values of the local angle theta0 at the peel front from the theoretical calculat ions have been shown to be in excellent agreement with the experimenta lly measured values; a small-scale peel test rig having been built so that the peel test, as a function of applied peel angle theta, thickne ss h of peeling arm and rate of test, could be observed and photograph ed using a stereo-optical microscope. The value of the adhesive fractu re energy G(a) (i.e. the 'fully corrected' value) for each laminate is indeed shown to be a 'material parameter'.