Variable amplitude fatigue of adhesively-bonded pultruded GFRP joints

• Variable amplitude fatigue of bonded pultruded GFRP joints was investigated.
• Significant load sequence effects on the fatigue life were observed.
• Crack propagation rate was accelerated by overloads in the applied loading spectrum.
• A life prediction methodology was proposed to take into account the load interaction effects.

The fatigue behavior of adhesively-bonded pultruded GFRP joints subjected to variable amplitude loading patterns was experimentally investigated. The failure mode of the examined joints was found to be similar to that under constant amplitude loading. The acceleration or retardation of the crack propagation rate due to the load interaction effects was thoroughly investigated by monitoring crack propagation during the variable amplitude loading. The fatigue life of the joints was predicted using classic fatigue life prediction methodology. Existing models for characterizing the fatigue behavior of the examined joints were employed together with the linear Palmgren–Miner’s rule for the prediction of fatigue life. A simple modification was incorporated into the applied methodology to take into account the load interaction effects introduced under the variable amplitude loading. Comparison of the life predictions to experimental data proved that the introduced modification can significantly improve the accuracy of the classic life prediction methodology.