| Research Abstract |
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
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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
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