Determination of Mode I cohesive law of structural adhesives using the direct method

The Mode I fracture behaviour of adhesive joints, bonded with two different epoxies, was evaluated applying the direct method to obtain the tensile cohesive law, together with Digital Image Correlation (DIC) analysis. The Double Cantilever Beam (DCB) test was performed, and the fracture toughness was attained by applying the J-integral. The DIC measurements were analysed resorting to a Python script, that was used as a post-processing tool, able to minimize the data noise stemming from the experimental results. This tool proved to be of utmost importance to guarantee acceptable results. Finally, the direct method could predict the main features of the cohesive law. Also, the law was used to simulate the fracture behaviour in a different test specimen, to evaluate the influence of the specimen geometry on the results. The obtained data indicates that the direct method is dependent on the joint geometry and the constraining condition of the adhesive.