| description abstract | One promising polymer replacement to conventional petroleum-derived resins in fiber-reinforced polymers (FRPs) is furfuryl alcohol (FA) resin, which is a thermosetting resin derived from agricultural byproducts. In this study, 120 carbon FRP (CFRP) coupons were tested in tension to examine the fatigue behavior of FRPs with this resin, as compared to epoxy. Test parameters were the type of resin, the number of fiber layers, the manufacturing method, and the stress amplitude, ranging from 65% to 85% of ultimate strength. All specimens were tested in tension–tension with stress ratio R = 0, at a rate of 2.5 Hz. Fatigue life and stiffness degradation were monitored. As per ASTM E739 [ASTM. 2015. Standard practice for statistical analysis of linear or linearized stress-life (S–N) and strain-life (ɛ–N) fatigue data. West Conshohocken, PA: ASTM], a minimum of 75% replicates was used in this study. The normal life distribution, ASTM, and Whitney’s pooling scheme methods were used to determine reliability-based S–N curves. The phenomenological model by Whitworth was used to predict stiffness degradation. With an expected design fatigue life of 2,000,000 cycles, the allowable stress amplitude is predicted at 59% tensile strength using the ASTM method. Based on the Whitney model, this resulted in a stiffness retention of 80% for epoxy-based CFRP and 65% for FA-based CFRP at the end of life. Imaging was also used to assess the damage of the CFRP postcyclic loading. Epoxy-based CFRP showed transverse and longitudinal cracks in the matrix, whereas there was no visible damage on FA-based CFRP; however, environmental scanning electron microscopy showed that FA resin and carbon fiber had poor interfacial bonding. | |
