General Assessment of Fatigue Reliability of Composite Material Structures

本课题是针对复合材料结构疲劳可靠性的综合评估而完成的。主要研究结果如下：1.研制了基于伺服脉冲加载系统的复合材料结构疲劳损伤测试系统，该系统采用双柱加载框架，在循环环境舱内安装变载荷比重复加载夹具，并可与声发射测试分析仪器连接，对复合材料结构的疲劳损伤进行系统评估.对船用玻璃、芳纶和玻璃/芳纶混杂纤维增强复合材料层合板进行了系统的三点弯曲疲劳试验。获得了标准疲劳设计数据，并通过S-N图和刚度折减曲线表征了损伤疲劳机理.采用声-超声法和声发射法对疲劳损伤效应进行了评价。结果表明，通过超声波在整个厚度范围内传播衰减的明显变化以及声发射参数（如击数和振幅），可以成功地表征疲劳损伤.对含有孔洞、分层等人工缺陷的CFRP层合板的声发射特性进行了研究。通过单调和循环三点弯曲加载，研究了缺陷对CFRP层合板强度的影响。从声发射次数、声发射振幅和声发射次数三个方面建立了声发射参数与缺陷之间的相关性.在盐水中对标准缺陷试件和FRP节点结构进行系统的疲劳试验，目前还没有获得足够的数据。载荷比对复合材料结构耐久性的影响也尚未明确。包括这些特性的一般疲劳设计数据将在不久的将来提出。

The three-years research program has been completed aiming at general assessment of fatigue reliability of composite material structures. The main results are summarized as follows :1. A testing system was developed based on a servopulser with two-column loading frames installed with repeated loading fixture under variable load ratio in circulation environment chamber which can optionally be connected with AE measuring and analyzing instruments in order to make a systematic assessment of fatigue damage of composite material structures.2. A systematic three-point flexural fatigue test was carried out on glass, aramid and glass/aramid hybrid FRP laminates for marine use in air and in water. The standard fatigue design data was obtained and the damage fatigue mechanism was characterized in terms of S-N diagrams and stiffness reduction curves.3. The acousto-ultrasonic method and the AE method were applied to evaluate the effects of progressive fatigue damage. It was shown that the fatigue damage was successfully characterized in terms of apparent change in attenuation of through-thickness ultrasonic wave propagation and some AE parameters such as hits and amplitudes.4. An attempt was made to characterize the AE properties of CFRP laminates containing several types of artificial defects such as void and delamination. The effect of defects on strength of CFRP laminates was examined by means of monotonous and cyclic three-point flexural loading. Some correlations between AE parameters and defects were established in terms of AE hits, amplitude and AE hits during load hold.5. The enough data has not yet been obtained on systematic fatigue tests on standarddefect specimens and FRP joint structures in salt water. The effect of load ratio on durability of composite material structures has also not yet been clarified. The general fatigue design data including these characterizations will be presented in the near future.