General Assessment of Fatigue Reliability of Composite Material Structures

完成了为期三年的复合材料结构疲劳可靠性综合评估研究计划。主要研究成果如下：1.研制了一套基于两柱加载机架的伺服脉冲仪，在循环环境舱中安装了变载荷比重复加载夹具，并可选择与声发射测量分析仪器连接，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/芳纶混杂玻璃钢层合板在空气和水中进行了系统的三点弯曲疲劳试验。获得了标准的疲劳设计数据，并用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，穿透厚度的超声波传播衰减和声发射参数如击数、幅值等参数的明显变化，成功地表征了疲劳损伤。对含有孔洞和分层等人工缺陷的碳纤维复合材料层合板的声发射性能进行了研究。通过单调和循环三点弯曲加载试验，研究了缺陷对CFRP层合板强度的影响。根据载荷保持过程中的声发射击数、幅度和声发射击数，建立了声发射参数与缺陷之间的关系。对于标准缺陷试件和FRP节点结构在盐水中的系统疲劳试验，目前还没有足够的数据。荷载比对复合材料结构耐久性的影响也尚不清楚。包括这些特性在内的一般疲劳设计数据将在不久的将来公布。

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.