Characterising the behaviour of composite single lap bonded joints using digital image correlation

Three-dimensional and two-dimensional Digital Image Correlation (DIC) have been used to evaluate the evolution of deformation and strain in composite single lap bonded joints prior to failure. In general, composite components are increasingly being joined using structural adhesives for aerospace and other safety critical applications. Reliable design requires that the mechanical behaviour of composite bonded joints is well understood. In this respect, experimental tests are crucial to (a) characterise the deformation and strains induced under load and (b) develop and validate realistic numerical models. Although modern numerical models contain many degrees of freedom, only a few degrees of freedom are typically measured using conventional instrumentation such as strain gauges and extensometers. However, 3D DIC provides an opportunity to measure full-field deformations and surface strains. In the current study, 3D DIC was successfully used to measure full-field in-plane surface strains and out-of-plane surface deformations for composite single lap bonded joints (adherends manufactured from both fibre preimpregnated resin (pre-preg) and resin infused non-crimp-fabric (NCF)). Moreover, strategically located strain gauges were used to validate the strains measured by 3D DIC. Finally, 3D DIC measurements may be useful in detecting subcritical damage as shown in the case of the pre-preg joint. The specific location and magnitude of the maximum principal strain in the adhesive fillet region were determined using high magnification 2D DIC.