General Assessment of Fatigue Reliability of Composite Material Structures

针对复合材料结构疲劳可靠性的一般评估，完成了为期三年的研究计划。主要研究结果总结如下：为了对复合材料结构的疲劳损伤进行系统的评估，在循环环境室中，采用两柱加载框架安装可变载荷比重复加载夹具的伺服脉冲发生器，可选配声发射测量和分析仪器。对船用玻璃、芳纶和玻璃/芳纶复合玻璃钢层压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进行性疲劳损伤效果进行了评价。结果表明，通过超声传播的衰减和命中数、振幅等声发射参数的明显变化，可以很好地表征疲劳损伤。对含孔洞和分层等几种人工缺陷的CFRP复合材料的声发射性能进行了表征。采用单调和循环三点弯曲加载的方法，研究了缺陷对CFRP层合板强度的影响。从声发射命中数、幅值和保持载荷时的声发射命中数等方面建立了声发射参数与缺陷之间的相关关系。标准缺陷试件和FRP接缝结构在盐水中的系统疲劳试验尚未获得足够的数据。载荷比对复合材料结构耐久性的影响也尚未明确。包括这些特征在内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.