<p>This study aims to investigate the effect of strap length and pre-embedded geometrical discontinuities on the mechanical properties of adhesively bonded Single Strap Joints (SSJs) and Double Strap Joints (DSJs) with epoxy adhesive using aluminium (Al-6061) flat metal adherends and Glass Fibre Reinforced Polymer (GFRP) composite adherends. Experimental tests were conducted on joints with varying strap lengths (20–50&#xa0;mm) to evaluate ultimate strength and failure modes. Results showed that strength increased with strap length up to a certain point, beyond which it plateaued. Failure modes varied with adherend type and joint configuration. Additional DSJ specimens were prepared with circular and square through-holes filled with adhesive, simulating manufacturing artefacts or embedded sensor cavities. Nonlinear 3D finite element analysis (FEA) was performed on joints with and without these discontinuities to evaluate interfacial stress distributions. The results reveal that defect geometry significantly alters local stress fields, with larger defects increasing peak peel stress near defect boundaries, especially at the strap–adhesive interface. While no explicit failure model is used, qualitative correlation is observed between predicted high-stress zones and experimentally identified fracture initiation sites. Fractographic analysis shows mixed-mode failure, reflecting the complexity of real bonding scenarios. The findings support defect-tolerant design principles and suggest directions for future work involving cohesive failure modelling and fracture energy-based criteria.</p> Graphical abstract <p></p>