Effect of the cohesive law shape on the modelling of adhesive joints bonded with brittle and ductile adhesives

Cohesive Zone Models (CZMs) have been increasingly used for the fracture prediction of adhesively bonded joints. In order to better understand the relation between the fracture behaviors of the different geometry/adhesive combinations and the shape of CZMs, the butt-joint uniaxial tension, shear and the double cantilever beam (DCB) fracture experiments were conducted using two distinct adhesives, an epoxy-based brittle adhesive and a VHBTM tape ductile adhesive. Three shapes of CZMs were adopted, including the exponential, bilinear, and trapezoidal models, to numerically predict the experimental performance. The comparisons between the numerical predictions and the experiments results demonstrated that the bilinear CZM is suitable for modelling the brittle adhesive bonding butt-joints in the uniaxial tensile and shear fracture processes, and the exponential CZM is suitable for modelling the ductile adhesive bonding ones. The critical stresses, the fracture energy and the shape of the CZMs have significant effects on the numerical results of the butt-joints uniaxial tension and shear for the two types of adhesives. In addition, for the DCB specimen fracture processes, it is shown that the bilinear CZM and the trapezoidal CZM predicted the brittle adhesive bonding joints better, and the trapezoidal CZM fitted the experimental data best for the two types of adhesives bonding joints. The overall results demonstrate that the selection of the shapes of CZM depend on the properties of the adhesive to obtain an accurate fracture processes prediction.