Fracture mechanics approach to stress singularities in composite adhesive joints

Structural design has significantly changed over the years driven by a weight reduction goal. In that sense, composite materials established themselves as the material of excellence in most engineering areas, replacing wood, steel and aluminium. Connection processes also experienced a transformation, with adhesive bonding standing out. Those new materials and techniques require deep research until they could be applied to structures. These studies led to the appearance of different methods for evaluating material and bond performance. Fracture mechanics is an approach based on material discontinuities or defects. Recently, a new fracture mechanics based technique arose called Intensity of Singular Stress Fields (ISSF). It hinges on the Stress Intensity Factors (SIF) approach but does not require an initial crack. This investigation aims to evaluate the applicability of this technique to composite materials. For that, Single-Lap Joints (SLJ) made from Carbon Fibre Reinforced Polymer (CFRP) bonded with a brittle adhesive and eight different overlap lengths (LO) are analysed. The numerical simulations and strength predictions are performed through the Finite Element Method (FEM) and MATLAB software. Finally, the numerical predictions are compared to the experimental data. It can be concluded that the ISSF is applicable to orthotropic materials.