Basic Study on Remaining Strength Evaluation of Advanced Composite Materials Damaged by Severe Earthquake Loading

对两种单向碳纤维/环氧复合材料制成的双悬臂梁（DCB）试件进行了恒定DELTAK疲劳裂纹扩展试验。研究了加载频率、试验温度和环境对层间分层疲劳裂纹扩展的影响。在空气中没有观察到循环频率的影响。试验温度的影响与材料和环境有关。纤维与裂纹扩展方向夹角越大，层间疲劳裂纹扩展速率越低。速率还取决于试样宽度。超载后疲劳裂纹扩展速率加快，而金属材料的疲劳裂纹扩展速率通常减慢。光纤桥接的裂纹尖端屏蔽可能会因过载而减弱（或最小化）。除了上述连续纤维增强塑料外，还对工程产品中广泛使用的短玻璃纤维增强塑料（GFRP）进行了应力松弛试验，以评估界面剪应力。基于粘弹性模型和应力松弛试验，分析了表面处理、应变速率、混合压力对拉伸和疲劳性能的影响。

Constant DELTAK fatigue crack propagation tests were conducted with double cantilever baam (DCB) specimens made of two kinds of unidirectional CF/epoxy laminates. The effects of loading frequency, test temperature, and environment on the interlaminar delamination fatigue crack growth were investigated. The effect of cyclic frequency was not observed in air. The effect of test temperature was found to depend on material and environment. The interlaminar fatigue crack propagation rate was lower for higher angle between fiber and crack propagation direction. The rate also depended on specimen width.Fatigue crack propagation rate accelerated after overloading while it usually decelerates in metallic materials. Crack tip shielding by fiber bridging may diminish (or minimize) by overloading.In addition to the continuous fiber reinforced plastic mentioned above, stress relaxtion tests of short glass fiber reinforced plastics (GFRP), which is widely employed in engineering products, were conducted to evaluate interfacial shear stress. Based on the visco-elastic model and stress relaxation tests, the effects of surface treatment, strain rate, mixing pressure on tensile and fatigue properties were analyzed.