Tensile fracture characterization of adhesive joints by standard and optical techniques

• Estimation of GIC of adhesive joints by a J-integral-based innovative optical method.
• Accurate GIC results comparing with standard techniques for wide range of adhesives.
• Numerical algorithm for parameter estimation enabled the quick calculation of GIC.
• Direct estimation of the cohesive laws showed the different behaviour of the adhesives.
• Full CZM data was made available for strength prediction in tension of adhesive joints.

The use of adhesive joints has increased in recent decades due to its competitive features compared with traditional methods. This work aims to estimate the tensile critical strain energy release rate (GIC) of adhesive joints by the Double-Cantilever Beam (DCB) test. The J-integral is used since it enables obtaining the tensile Cohesive Zone Model (CZM) law. An optical measuring method was developed for assessing the crack tip opening (δn) and adherends rotation (θo). The proposed CZM laws were best approximated by a triangular shape for the brittle adhesive and a trapezoidal shape for the two ductile adhesives.