Shear cohesive law estimation of adhesive layers by digital image correlation

Modern and competitive structures are sought to be strong, reliable and lightweight, which increased the industrial and research interest in adhesive bonding. With this joining technique, design can be oriented towards lighter structures. The large-scale application of a given joint technique supposes that reliable tools for design and failure prediction are available. Cohesive Zone Models (CZM) are a powerful tool, although the CZM laws of the adhesive bond in tension and shear are required as input in the models. This work evaluated the value of shear fracture toughness (G_IIC) and CZM laws of bonded joints. The experimental work consisted on the shear fracture characterization of the bond by a conventional and the J-integral techniques. Additionally, by the J-integral technique, the precise shape of the cohesive law is defined. For the J-integral, a digital image correlation method is used for the evaluation of the adhesive layer shear displacement at the crack tip (δ_s) during the test, coupled to a Matlab^® sub-routine for extraction of this parameter automatically. As output of this work, fracture data is provided in shear for the selected adhesive, allowing the subsequent strength prediction of bonded joints.