Environmental fatigue behavior and life prediction of unidirectional glass-carbon/epoxy hybrid composites

Unidirectional glass fiber reinforced and glass-carbon fiber reinforced epoxy matrix composite specimens were subjected to tension-tension fatigue in air and in distilled water at 25 °C. While no significant change in fatigue life was observed for both types of specimens tested in air and in water when cyclically tested at 85% of average ultimate tensile strength (UTS), the detrimental effect of water becomes apparent at lower stress levels of 65 and 45% UTS. Compared to specimens tested in air, cyclic loading in water results in shorter fatigue lives for both glass and hybrid specimens. While all of the glass fiber specimens did not survive to 10⁶ cycles when cyclically loaded in water, hybrid specimens (with 25% carbon fiber (by volume), 75% glass fiber (by volume), 30% total fiber volume fraction) showed better retention in structural integrity under environmental fatigue, for fatigue lives up to 10⁷ cycles, a consequence of the corrosion resistant of carbon fiber. Thus it is shown, by incorporating appropriate amount of carbon fibers in glass fiber composite, a much better performance in fatigue can be achieved for glass-carbon hybrid composite. A simple life prediction model for the hybrid composite is proposed. Model predictions are compared with experiments results from both laminated interply and intermingled intraply hybrid composites. Results suggest that synergistic effect of the reinforcing fibers is critical in governing the fatigue behavior of intraply hybrid composite.