Effect of adhesive thickness on fatigue and fracture of toughened epoxy joints - Part I: Experiments

The effect of bondline thickness, from 130 μm to 790 μm, on the fatigue and quasi-static fracture behavior of aluminum joints bonded using a toughened epoxy adhesive was studied experimentally under mode-I (DCB) and mixed-mode (ADCB) loading. Under mode-I loading, it was found that the fatigue threshold energy release rate, Gth, decreased for very thin bondlines, while under mixed-mode loading, the Gth changed very little with bondline thickness. In both cases, the effect of bondline thickness was more pronounced at higher crack growth rates. For quasi-static fracture, the effect of adhesive thickness on the energy release rate for the onset of fracture from the fatigue threshold, Gc0, was similar to that found for the fatigue threshold; however, the steady-state energy release rate, Gcs, increased linearly with increasing bondline thickness.