Block loading fatigue of adhesively bonded pultruded GFRP joints

The effect of loading sequence on the fatigue behavior of adhesively-bonded pultruded GFRP double-lap joints was experimentally investigated by applying different tensile and compressive block loading patterns. The observed failure modes were consistent with failure modes under constant amplitude loading. A significant load sequence effect was observed for both tensile and compressive loading. Under tensile loading the transition from low to high load cycles in a two-block loading was more damaging than the high to low sequence. The inverse was observed for compression loading. This behavior was associated with the crack propagation rates and their dependence on loading type. The effect of the number of load transitions in a multi-block loading spectrum was also studied by using different loading sequences. The influence of this loading parameter was found to be more dominant than the sequence effect, which is diminished by increasing the number of transitions.