Predicting the nonlinearity onset load of adhesives considering the microstructure

Abstract

The lack of understanding of the bond failure behavior of adhesives has discouraged their use in primary structural members. This study focused on the macroscopic and microscopic failure behaviors of single-lap joints (SLJs) bonded with an adhesive to predict the load at which nonlinear behavior begins, which was defined as the nonlinearity onset load Fnl. Bulk test pieces (TPs) of the adhesive were fabricated, and the microstructure was observed using X-ray microfocus computed tomography. The results of tensile tests and finite element analysis were used to construct a macroscopic model that simulated the tensile behavior of the TP. A representative volume element (RVE) model was constructed based on the microstructural observations and was embedded in the macroscopic model. A stress analysis method was developed, where the failure criterion f was defined according to the volume ratio of RVEs that have experienced microstresses exceeding the yield point of the TP, which can then be used to predict Fnl. When the method was applied to an SLJ, the predicted Fnl had an error of less than 10% when compared with the experimental value.