Experimental Studies of Stiffness Degradation and Dissipated Energy in Glass Fibre Reinforced Polymer Composite under Fatigue Loading

In this work, tensile and compressive properties and fatigue performances of laminated glass fibre-reinforced polymer (GFRP) composite under constant amplitude sinusoidal load control at frequency of 5 Hz and at room temperature were investigated for three different types of loading: tension-tension at R=0.1 and 0.5, reverse loading tension-compression at R=-1 and compression-compression at R=2 and 10 in the fibre and normal-to-fibre directions. From these series of tests, the corresponding S-N diagrams were obtained. The dynamic stiffness during fatigue loading showed classical degradation of the GFRP laminates. It was observed that the dynamic modulus decreased with time, and the hysteresis loop area changed with some distortion according to the loading conditions. Finally hysteresis loops throughout fatigue testing were examined, and the variation of energy dissipated per cycle throughout the specimen lifetime was quantified. It was demonstrated that the dissipated energy during the fatigue lifetime is dependent on R-ratio and fibre orientation. However, in majority of the cases, the energy dissipated per cycle near the end of the fatigue lifetime increases as a result of an increase in the area captured by hysteresis loops.