Fatigue strength degradation of E-glass FRP composites and carbon FRP composites

For civil engineering structures subject to cyclic loading, one important limit state in design is fatigue. Previous reviews of existing fatigue data from aerospace, marine, and mechanical applications determined the applicability to civil engineering structures. The objective: to assist in recognizing the fatigue potential of E-glass composite and CFRP composite as an independent structural material for infrastructure application. This comparison will focus on tension-tension axial fatigue without environmental concerns. Test and material parameters which define the data are identified as R ratio, test frequency, load control, specimen shape, type of reinforcement, and resin. Fatigue life diagrams for tension-tension axial fatigue data show normalized stress (maximum fatigue stress divided by ultimate tensile strength) vs. log of fatigue life. These plots, according to fiber reinforcement and resin, reveal distinct lower bounds to the data band, regardless of parameter combination. However, the E-glass FRP composite fatigue data show lower fatigue life for the same normalized maximum stress than the CFRP composite fatigue data. Generally, the lower bounds previously defined can be used in designing both E-glass FRP and CFRP composites as independent structural materials for infrastructure application conservatively estimating tension-tension axial fatigue strength. These lower bounds may be used until further studies refine the effects of individual parameters on fatigue life. (C) 1998 Elsevier Science Ltd. All rights reserved.