An analytical, finite element and experimental study of single-lap joints bonded with epoxy adhesive

This paper investigates the stress distribution in tensile-loaded single-lap joints made of aluminum and bonded with an epoxy adhesive using analytical modeling, finite element analysis (FEM), and experimental testing. The analytical framework is developed for joints with varying material properties, adherend and adhesive thicknesses, and overlap lengths, assuming a constant joint width and a thin adhesive layer. The analysis is based on elasticity theory and the principle of stationary potential energy. Three closed-form solutions are derived. Solutions I and II describe shear stress transfer at the interface, neglecting and including transverse deformability of the adhesive, respectively. Solution III further extends the formulation by accounting for joint bending induced by load eccentricity, enabling the evaluation of both shear and peel stresses. The proposed solutions are validated against classical analytical models (Goland & Reissner, Hart-Smith), FEM simulations (Abaqus), and experimental results. Owing to the adopted representation of the adhesive layer, the stresses predicted by Solution III should be interpreted as effective structural stresses rather than exact local adhesive stresses, particularly near the overlap edges, where the stress field is influenced by the combined effect of geometric features and material mismatch, leading to a singularity. In this region, not only the stress magnitude but also the precise location of extreme values becomes inherently ambiguous and method-dependent. Despite these limitations, Solution III provides a physically consistent representation of the stress state in the joint, accurately capturing the global stress distribution and providing reliable estimates of extreme stress levels.