Fatigue response of fabric-reinforced polymeric composites

Mechanical fatigue response of fiber-reinforced polymeric (FRP) composites is essential to better understand the durability of composite materials systems and to develop design specifications. Currently, the fatigue response of multidirectional glass composite materials is not well-understood and much needs to be done to understand their behavior under fatigue loading. In this study, three glass fabric FRP composite material coupons and systems are tested at constant low-amplitude fatigue loading. Experimental results show that for a given FRP material and load configuration, the energy loss per cycle due to fatigue damage is linear from about 10-90% of the fatigue life of the FRP composite material. The energy loss per cycle is determined to be a characteristic value of the constituent materials, and is found to vary with the induced fatigue strain levels by a power law. Based on the experimental results, a fatigue life prediction model is proposed, with internal strain energy as damage metric, to predict the useful life of FRP composites. The experimental and predicted fatigue lives at various strain levels are compared (S-N curves) and the model is found to be conservative.