Validation of a direct method to predict the strength of adhesively bonded joints

Cohesive zone models (CZM) are a powerful tool for the design of bonded structures, but they require careful estimation of the cohesive laws for reliable results. This work experimentally evaluates by the J-integral/direct method the tensile and shear CZM laws of three adhesives with distinct ductility. Additionally, by the direct method, the precise shape of the cohesive law in tension and shear of the adhesives is defined. The double-cantilever beam (DCB) and end-notched flexure (ENF) specimens were considered to obtain the tensile and shear CZM laws of the adhesives, respectively. After obtaining the tensile and shear CZM laws, triangular, exponential and trapezoidal CZM laws were built to reproduce their behaviour. Validation of these CZM laws was undertaken with a mixed-mode geometry (double-lap joint) considering the same three adhesives and varying overlap lengths (L_O). The strength prediction by this technique revealed accurate predictions for a given CZM law shape, depending on the adhesive ductility, although all CZM law shapes were moderately accurate.