The determination of adhesive fracture toughness for laminates by the use of different test geometry and consideration of plastic energy correction factors

Abstract

ABSTRACT Fixed arm peel and T-peel test procedures are used to measure peel strength for flexible laminates. Analysis of the contributions from elastic and plastic deformations of the peel arms during these tests enables the energy contribution from plastic effects to be subtracted from the energy required to peel the laminate. In this way, the adhesive fracture toughness is determined. Seven independent laboratories have conducted these procedures (through the ESIS TC4 group) on a flexible polypropylene laminate system. Experiments for fixed arm peel have been conducted at a common peel angle (90°) and also for multiple angles (60°-160°) in order to determine the adhesive fracture toughness. These laboratories also conducted measurements with a T-peel geometry. Similar values were obtained for the adhesive fracture toughness demonstrating that with careful thought to the various energy contributions in the peel tests that a geometry independent value can be derived. The corrections for plastic deformation have been further analysed for metallic substrate laminates, using these two test geometries. A method is suggested for monitoring the correction. It is believed that corrections up to about 70% can be accommodated by the test protocols. Moreover, by investigating the temperature dependence of adhesive fracture toughness for the metallic substrate system, even larger plastic corrections may be tackled (greater than 80%). However, the accuracy of the ensuing results becomes more doubtful.