Tensile fatigue performance of pultruded glass fiber reinforced polymer profiles

Axial tension–tension fatigue experiments were performed on pultruded glass fiber reinforced polymer (GFRP) plates in a laboratory environment. Different full-scale specimen shapes were examined: plate strips as-delivered, plate strips with tabs and plates in tapered form. Experiments were performed up to ten million loading cycles with different frequencies up to 12 Hz. It was observed that the specimen temperature could increase during fatigue test. This increase was dependent on the loading frequency and the loading range. S–N fatigue life curves were determined. Tapered specimens showed a higher fatigue life than as-delivered specimens; and as-delivered specimens showed higher fatigue lives than tabbed specimens. A degradation rate of 3–5% of the single-cycle ultimate tension strength (UTS) per decade of fatigue cycles was observed. This observation is not consistent with a characteristic slope of 10% UTS/decade as shown from many previous studies. A loss of specimen stiffness up to 50% during the fatigue experiments was observed and can only be explained by considerable fiber failures. This finding is consistent with results from previous studies showing that fatigue failure of fiber-reinforced polymer composites is basically fiber dominated. The fatigue behavior of the plates was compared with the fatigue behavior of adhesively bonded double-lap joints made from the same plates. Plates and joints showed converging fatigue life curves and the same fatigue limit at approximately 25% of the single-cycle failure load at ten million cycles. Keywords