Interface Mechanics Study on Mechanisms of Fatigue Crack Initiation and Propagation in Fiber Reinforced Composite Materials

对单向碳纤维/环氧复合材料层合板的双悬臂梁试件在恒应力条件下进行了分层疲劳裂纹扩展试验，对于树脂固化温度为180ﾟC的复合材料，层间裂纹在空气中的扩展与裂纹扩展几乎是恒定的，加载频率对裂纹扩展没有影响。当试验温度由低变高时，层间裂纹扩展速率不变。另一方面，从较高温度到较低温度变化后，层间裂纹扩展速率急剧下降。加载频率对层内裂纹扩展的影响不明显，但随裂纹扩展而减小，温度越高，加载频率越高。层间疲劳裂纹的扩展速率总是高于层内疲劳裂纹的扩展速率。在水中，层间裂纹和层内裂纹的扩展速率随着裂纹的扩展而减小，它们是…测试温度越高，加载频率越低，e越高。对于树脂固化温度为130ﾟC的复合材料，层间裂纹在空气中的扩展速率与试验温度无关，而同相热疲劳试验的扩展速率与等温疲劳试验的扩展速率基本相同。在水中，温度越高，扩展速率越低，同相热疲劳扩展速率与等温疲劳扩展速率基本相同，此时温度等于热疲劳试验中的最高温度，还研究了纤维取向对层间疲劳裂纹扩展行为的影响。对于20 mm宽的试件，纤维取向角越小，生长速度越快。对于宽度为10 mm或5 mm的试件，单向层板的生长速率最高。对于10 mm宽的样品，当角度大于30ﾟ时，没有观察到纤维取向对生长速率的影响。对于5 mm宽的试件，纤维角越大，生长速度越快。在单向试件中，较宽的试件的扩展速率较高，而在裂纹面纤维取向为90ﾟ的试件中，较大的试件的扩展速率较低。对于其他纤维取向，这种关系取决于取向。较少

The delamination fatigue crack growth tests were conducted on double cantilever beam (DCB) specimens of unidirectional CF/epoxy laminates under constant DELTAK conditions.For the composites whose resin was cured at 180ﾟC,the interlaminar crack growth in air was almost constant with crack growth, and the effect of loading frequency was not observed. When the test temperature was changed from lower to higher temperature, the interlaminar crack growth rate was unaltered. On the other hand, the interlaminar crack growth rate drastically decreased after the variation from higher to lower test temperature. The effect of loading frequency was not observed also for the intralaminar crack growth, but it decreased with crack growth, and it was higher for higher temperature. The growth rate of an interlaminar fatigue crack was always higher than that of an intralaminar fatigue crack. In water, the growth rate of interlaminar cracks and intralaminar cracks decreased with crack growth, and they wer … More e higher for higher test temperature and lower loading frequency. The growth rate was lower for prior-immersion specimen than for non-immersion specimen.For the composites whose resin was cured at 130ﾟC,the interlaminar crack growth rate in air was independent of test temperature, and the growth rate for in-phase thermal fatigue tests was almost identical to that for isothermal fatigue tests. In water, the growth rate was lower for higher temperature, and the growth rate in in-phase thermal fatigue was almost the same values for the isothermal fatigue tests, where the temperature was equal to the highest temperature in the thermal fatigue tests.The effect of fiber orientation on the interlaminar fatigue crack growth behavior was also examined for this material. For the specimens of 20 mm wide, the growth rate was higher for lower angle of the fiber orientation. For the specimens of 10 mm or 5 mm wide, the growth rate for the unidirectional laminates was highest. For the specimens of 10 mm wide, the effect of the fiber orientation on the growth rate was not observed for the angles higher than 30ﾟ. For the specimens of 5 mm wide, the growth rate was higher for higher fiber angles. In the unidirectional specimens, the growth rate was higher for wider specimens, but the growth rate was lower for wider specimens in the specimens whose fiber orientation on the crack face was 90ﾟ. For other fiber orientation, the relation depended on the orientation. Less