Fatigue Life of Pultruded and Hand Lay-Up GFRP Exposed to Different Environmental Conditions.

The use of unidirectional Glass Fiber Reinforced Polymer (GFRP) composites to reinforce glulam beams in tension has been proven by researchers at University of Maine and others to improve both allowable strength and ductility. The addition of 3% E-glass FRP has been shown to increase the allowable flexural strength by as much as 100%. These promising findings can be used in practice only if the GFRP will maintain a major proportion of its strengthfstiffness mechanical properties over the life of the structure. This study focuses on the fatigue life of two types of E-glasslphenolic GFRP (hand lay-up and pultruded) with special emphasis on the effect of environmental degradation on the fatigue life of pultruded GFRP. Fatigue life of pultruded GFRP was evaluated after treatment in salt water, hot water, freezethaw, and UV weathering. Static tests indicate that hot water (45°C) causes the higher reduction in tensile strength. The Young's modulus did not change significantly for any of the exposed specimens. Fatigue tests were conducted at constant amplitude at a frequency of 20H2, and S-N curves were developed for each exposure group. The results show that except for UV weathering, the fatigue life of all the exposed specimens exhibited slight statistically significant improvement for low stress fatigue tests. Residual strength tests conducted at 10% of ultimate strength exhibited no statistically significant (a=0.05) reduction in tensile strength or modulus at 3 million cycles of fatigue. The fatigue data was plotted using S-N diagrams and modeled using Loglinear equations. From the models, allowable strength for design purposes was recommended using statistical analysis. One-sided lower 95% tolerance limit for 95% of the population (5% LTL) were developed for pultruded control and hand lay-up specimens.