A unified strain energy-based fatigue life prediction methodology for composite and metal adhesive joints: Effects of adhesive, geometry and, environment

Ensuring the efficiency and safety of bonded structures across diverse engineering sectors requires a robust fatigue model for adhesive joints in both composite and metal substrates. This study presents a unified fatigue life prediction methodology for similar and dissimilar composite and metal adhesive joints. The proposed model integrates hydrostatic and deviatoric strain energy density components with the theory of critical distances. The model has been validated against diverse experimental data from different joint geometries, loading conditions, and different environments. The linear-elastic assumption is sufficient for toughened epoxies, whereas an elastoplastic model is necessary for ductile methacrylate adhesives. Calibration based on a single fatigue test yields the highest accuracy, while quasi-static test calibration is also satisfactory. The methodology addresses diverse loading conditions and environmental factors, showing a strong correlation with experimental results. It advances the performance, design, and reliability of similar and dissimilar composite to metal adhesive joints.