Development of estimation system for fatigue life of CFRP

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Inelastie deformation fehavior of CFRP under quasi-statie and fatigue loading has been elucidated for three years from 1992 to 1994. Specially, internal fatigue damages of matrix crack and delamination in the fatigue process were quantitatinely estimated by means of micrography, and furthermore on-time monitoring of fatigue damage initiation and evolution by AE method was carried out successfully. From these results, it makes clean that a estimation system for fatigue life of CFRP is possibly developed with AE method. Results obtained in the research are as follows ;1)Stress-strain relationships of [<plus-minus>45ﾟ]_4 CFRP tubular specimen were elucidated under various loading conditions. It was recognized that matrix showed similar behavior as work-hardening at the early stage of fatigue and that macroscopical buckling occured at the last stage of fatigue by delamination.2)From detail investigation between fatigue damage and mechanical properties of CFRP,it made clean that elastic modulus and inelastic strain were useful measures for the fatigue life.3)The continuum damage model based on the flow rule was modified to a inelastie constitutine equation in considering initiation and evolution of internal damage. And then, the modified model was applied to experimental results successfully.4)Power spectrum of AE signal in fatigue process of CFRP was able to nondestructively identify the internal damages such as matrix crack, delamination and fiber breakage, and furthermore it could estimate the fatigue life.5)Complex inelastic deformation behavior of CFRP in fatigue process was described by modeling in frame of the continuum damage mechanics.