Influence of viscoelastic property of adhesive material on evaluation of peel strength

Abstract

Peel test is widely used to evaluate interfacial strength of adhesive tape. The interface strength is usually obtained by subtracting energy consumed for plastic deformation of substrate film from external work for peeling. Deformation of substrate results from interface strength generated in adhesive layer, whose mechanical property is regarded as elastic when substrate is thick enough. It is also convenient to calculate deformation of substrate with assuming elastic behavior of adhesive layer. However, substrates thinner than 100 μm may be affected by viscoelastic property of adhesive layer since thickness of adhesive layer is no longer negligible. It is indispensable to investigate the influence of viscoelastic behavior of adhesive layer on evaluating interface strength of particularly thin adhesive film. In this study, 90° peel test was conducted and the interface strength was evaluated by modifying conventional elastic model to consider viscoelastic behavior of adhesive layer. Stress in adhesive layer caused from displacement of substrate is a function of strain and strain rate, and the corresponding deformation of substrate was computed by finite element method. The shape of substrate deformation was compared with one obtained from conventional elastic model in terms of thickness of substrate and peel speed. The interface strength was also obtained from directly observing peel shape using high speed camera to validate the proposed model. As a result, it was found that the substrate shapes were similar regardless of models when substrate was thick, but proposed model more accurately reflected the influence of peel speed in the thin substrate.