Synergistic effect of cyclic mechanical loading and moisture absorption on the bending fatigue performance of carbon/epoxy composites

This study investigates the effects of hygrothermal condition on the static bending strength, the bending fatigue and the residual bending strength of carbon/epoxy composite laminates. Displacement-controlled three-point bending fatigue tests were conducted on carbon/epoxy composite laminates of immersion for 0, 7 and 14 days, respectively. After 40000 cycles the fatigue test was stopped and the residual properties were measured on the tested specimens. The effects of hygrothermal condition and fatigue on the micrographs of the specimens have been studied by the metallurgical microscope and scanning electron microscope. Experimental results reveal that moisture absorption can accelerate damage propagation of the composite; the accumulation of irreversible structural damage under the cyclic loading leads to a change in the macroscopic mechanical properties of the composites; the bending strength and the residual strength retention decreased with increased immersion time; hygrothermal aging lowered the threshold level for the onset of fatigue.