Cohesive Zone Models and the Plastically-Deforming Peel Test

The peel test is a popular test method for measuring the peeling energy between flexible laminates. However, when plastic deformation occurs in the peel arm(s) the determination of the true adhesive fracture energy, Gc, from the measured peel load is far from straightforward. Two different methods of approaching this problem have been reported in recently published papers, namely: (a) a simple linear-elastic stiffness approach, and (b) a critical, limiting maximum stress, σmax, approach. In the present paper, these approaches will be explored and contrasted. Our aims include trying to identify the physical meaning, if any, of the parameter σmax and deciding which is the better approach for defining fracture, when suitable definitive experiments are undertaken.