Numerical and experimental investigation of three-dimensional strains in adhesively bonded joints

Strain distributions within adhesively bonded double-lap shear joints under tensile load have been investigated experimentally using the complementary experimental techniques of neutron diffraction (ND) and moire interferometry (MI). ND provides three-dimensional strain values within the samples, whereas MI gives high-resolution maps of the in-plane strain components at the surface. The resulting comprehensive datasets obtained from both aluminium and steel joints were compared against finite element (FE) predictions. The importance of a range of factors (e.g. two-dimensional versus three-dimensional geometry, sample asymmetry, residual strains) was assessed through development of the FE model and detailed comparison with the experimental data. The main conclusions were that FEA can be used accurately to predict strains in the adherends of bonded lap joints and that many of the simplifications of the joints commonly used in the analysis of bonded joints are justified as including them results in relatively small differences compared with sample-to-sample variation and the safety factors used in designing bonded joints.