Development of estimation system for fatigue life of CFRP

从1992年至1994年三年间，对CFRP在准静态和疲劳载荷作用下的非弹性变形特性进行了阐述。特别是利用显微照相技术对疲劳过程中的基体裂纹和分层等内部疲劳损伤进行了定量评价，并成功地利用声发射技术对疲劳损伤的萌生和演化进行了实时监测。这些结果表明，利用声发射法建立CFRP疲劳寿命估算系统是可行的。主要研究结果如下：1）研究了[<plus-minus>45 &lt;$]_4碳纤维复合材料圆管试件在不同加载条件下的应力-应变关系。通过对CFRP材料疲劳损伤与力学性能的详细研究，发现CFRP材料在疲劳初期表现出类似于加工硬化的行为，在疲劳后期发生宏观失稳，主要是由于材料的分层破坏。明确了弹性模量和非弹性应变是疲劳寿命的有用度量。将基于流动法则的连续损伤模型修正为考虑内部损伤萌生和演化的非弹性本构方程。4）碳纤维复合材料疲劳过程中声发射信号的功率谱能够无损识别基体裂纹、分层和纤维断裂等内部损伤，进而估算其疲劳寿命。5）在连续损伤力学框架下建立模型，描述了碳纤维复合材料疲劳过程中复杂的非弹性变形行为。

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.