J043031 平織CFRP擬似等方積層板の非相似型等寿命線図に基づく変動疲労寿命の予測([J04303]高分子基複合材料の加工と評価(3))

Abstract

Effects of variable fatigue loading with alternate R-ratios on the fatigue life of a quasi-isotropic woven fabric CFRP laminate have been studied. First, constant amplitude fatigue tests are performed on plain coupon specimens of the CFRP laminate at different stress ratios in order to obtain a baseline set of fatigue data for this investigation. Then, variable R-ratio fatigue tests are carried out during which the stress ratio of fatigue loading alternates between two values keeping the level of maximum fatigue stress constant. The fatigue life of the composite under variable R-ratio loading is examined not only for different pairs of stress ratios, but also for different levels of maximum fatigue stress. By comparing the fatigue lives under constant and variable R-ratio fatigue loading conditions, the effect of alternation in R-ratio on the fatigue life of the CFRP laminate is elucidated. Experimental results demonstrate that a small change in R-ratio has a degrading effect and affects to reduce the total number of cycles to failure, while a large change in R-ratio brings about a retardation effect in damage accumulation, when the maximum fatigue stress is relatively high. The retardation effect due to variation in R-ratio disappears under fatigue loading with a low maximum fatigue stress. Finally, the anisomorphic constant fatigue diagram is applied to prediction of the fatigue life of the CFRP laminate subjected to the alternate R-ratio loading using representative cumulative fatigue damage rules.