Evaluating the localised through-thickness load transfer and damage initiation in a composite joint using digital image correlation

Experimental analysis of the stresses and strains in a glass fibre polymer composite double butt strap joint using digital image correlation (DIC) is described in the paper. Initially the strain fields through the thickness of the joint are derived from DIC measurements, capturing the effect of the initiation and development of cracks in the joint up to failure. It is demonstrated that the relatively small strains developed in the through-thickness direction are critical in the development of damage in the joint at the geometric discontinuity between the adherends. An experimental methodology is established to perform DIC at the mesoscopic scale, enabling accurate, high spatial resolution analysis of the small through-thickness strains around the discontinuity. The DIC enables the strains to be evaluated, their development monitored and hence establish their contribution to the failure process. To determine the full-field stresses in the joint experimentally derived materials properties are used. From component stress maps principal stresses maps are derived, which clearly show where the damage is initiating and its subsequent growth in the composite adherends until final failure of the joint.