Abstract
Influences of stress ratio on the off-axis fatigue strength of a unidirectional fiber-reinforced composite T800H/2500 have been studied. Tension-tension and tension-compression fatigue tests on plain coupon specimens with fiber orientation angles θ=0,10,15,30,45 and 90゜were performed for stress ratios R=0.5,0.1,-0.3 (θ=0゜) and R=0.5,0.1,-1.0 (0゜<θ≤90゜), respectively. Also, a fatigue damage mechanics model that considers the effect of stress ratio was formulated. Fatigue strength of the unidirectional T800H/2500 decreased as the stress ratio decreased, irrespective of off-axis angle. The S-N relationships were almost linear in the range of fatigue loading up to (10)^6 cycles, regardless of off-axis angle and stress ratio. The non-dimensional effective stress based on the classical static failure theory succeeded in a unified description of the directional characteristic of the off-axis fatigue strength for all stress ratios. The proposed fatigue damage mechanics model can predict the stress-ratio dependent off-axis fatigue behavior of the unidirectional system employed.
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