Characterization, analysis and prediction of damage onset in adhesively bonded joints using fracture mechanics and acoustic emission monitoring technique

This study presents a new method for predicting the fatigue life of aluminum adhesive-bonded joints. The approach involves experimental tests to establish fatigue failure criteria using acoustic emission monitoring to detect damage onset, along with a finite element (FE) model to analyse changes in energy release rate at the embedded crack tip. The proposed method comprises three key steps. In the initial stage, a 3D failure surface criterion is experimentally generated, connecting the maximum total energy release rate (GT) and the mixed mode ratio (GII/GT) to the number of cycles (N) required for initiating the crack propagation. In the second step, the total energy release rate (GT) and the corresponding mixed mode ratio (GII/GT) at the crack tip of a single lap joint under different external loads are numerically determined utilizing the virtual crack closure technique. Mathematical equations linking the applied load (P) to the associated values of GTmax and GII/GT are established. Ultimately, once the energy release rate and mixed mode ratio for a given load are determined, the number of cycles required for initiation of crack growth can be extracted from the experimentally derived failure surface in the initial step. The predictive model shows excellent correlation with experimental data, depending solely on the adhesive system rather than joint design.