Thermal residual stress analysis of epoxy bi-material laminates and bonded joints

Abstract

Finite element analysis (FEA) and continuum mechanics techniques have been used to model the thermal residual stress distribution in bonded joints and assess the suitability of using two-dimensional (2D) analysis methods. The methods are first employed to investigate stresses in metal-epoxy bi-material strip samples. The change in curvature of two bi-material strip systems during heating and cooling in a dry atmosphere were measured and this behaviour was successfully modelled using both FEA and continuum mechanics techniques. 2D and 3D FEA analyses were compared with the experimental results to determine the most accurate and efficient method of predicting the thermal residual stresses. It was found that none of the analytical solutions or 2D FEA approximations were fully able to describe the 3D stress state in the strip. The incorporation of geometric and material non-linearity into the models was also found to be necessary to obtain accurate results. The effects of creep were also considered, but the analyses showed that the thermal residual stresses in the bi-material strips were too low for significant relaxation due to creep. The validated computational methods were then used to predict the thermal residual stresses in bonded single lap joints and double lap joints. The thermal stresses were found to be highest in joints with dissimilar adherends. Measurements of thermal strains in the joints with dissimilar adherends using neutron diffraction were compared with the finite element predictions and good agreement was observed, providing further validation of the computational predictive methods.