Application of a rate-dependent peel fracture cohesive zone model to simulate mixed-mode I+III fracture mechanics experiments on flexible adhesive layers

Abstract

A recently developed cohesive zone model for pure peel loading is generalized and extended to arbitrary mixed-mode I+III loading conditions in this paper. The mixed-mode I+III extension is governed by an energy-based interpolation between pure peel and shear. The implementation generally allows for the input of different single mode cohesive laws and the corresponding model parameters are defined separately for peel and shear. The resulting mixed-mode cohesive zone model depends on the strain rate prior to crack propagation and the ratio of thickness to width as the initial geometry of the adhesive layer. The model was implemented into an user-defined subroutine of a commercial finite element code and used to successfully describe mixed-mode I+III fracture mechanics experiments at various mixed-mode ratios and strain rates on an elastomeric, flexible adhesive. It was found that there was a significant difference between peel mode I and shear mode III only in the shape of the cohesive law and the initial stiffness, while the fracture energy and the cohesive strength were largely independent of the loading mode. This fact supports the assumption that the fracture process is similar in crack opening modes I and III and peel always dominates under large deformations that occur in elastomeric thick adhesive layers. Therefore, calibrating the mixed-mode model using only peel tests can be a permissible simplification in this case, especially regarding industrial applications.