Bending fatigue of long carbon fiber-reinforced epoxy composites

Long carbon fibers with 3.5, 4.5, 5.0 and 5.5 GPa in average tensile stress-reinforced epoxy laminates have been studied to clarify the bending fatigue behavior and fracture mechanism of advanced carbon-fiber reinforced plastic composites. Bending fatigue tests were conducted using a Schenk-type bending fatigue machine at room temperature. The fatigue limit of the composite with the cross-ply (0°/90°) laminates was related to not only compressive stress of the 0° layers in the laminates but also to heat generation during fatigue testing. For the laminates with high resistance to interlaminar fracture or with high thermal conductivity, the fatigue limit was related to the compressive stress of the 0° layers in the laminates. For the laminate with poor resistance to interlaminar fracture, the fatigue limit significantly decreased because delaminations occurred between adjacent plies of the laminate during fatigue testing. The fatigue limit of the composites with the quasi-isotropic (0°/±45°/90°) laminates was related to the compressive stress of the 0° layers in the laminates.