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Abstract
The effect of stress ratio on tension-tension fatigue behavior and mode I delamination fatigue crack propagation behavior was investigated for Toray T300/#3601, T800/#3601 and T800/#3631 laminates. Unidirectional laminates and quasi-isotropic laminates were used for tension-tension fatigue tests. For delamination fatigue crack propagation tests, double cantilever beam specimens made of unidirectional laminates were used. For the tension fatigue tests, the slope of the relation between the normalized maximum stress and the number of cycles to failure was very small. For delamination fatigue crack growth tests, the exponent of the power function in the relation between the crack propagation rate and the stress intensity range was very large. The analysis of the equivalent stress intensity range proposed by the authors showed that the contribution of the maximum stress was large in delamination fatigue crack propagation. A similar analysis was applied to the results of the tension fatigue tests. The contribution of the maximum stress was also large in tension fatigue fracture. The degree of the contribution of the maximum stress in the tension fatigue tests was almost the same as that in the delamination fatigue crack growth tests. A comparison between the mechanism of tension-tension fatigue fracture and that of delamination fatigue crack growth was made on the basis of the fractographic observation.