Some of the earliest investigations concluded that the basic mechanism of fatigue in composites differs greatly due to the different reinforcements. The variety of damage modes, the complexity ot" their interactions, and the subsequent effect on engineering properties make it difficult to interpret fatigue in order to define and predict fatigue failure and lifetime for composite materials.
This paper reports the mechanical properties of 3-D T300 carbon fabric reinforced epoxy composite with a 52% fibre volume fraction, these results being compared to those of a standard 2-D fabric laminate containing the same fibre volume fraction. The static tensile and fatigue behaviour of these two types of composites were examined. Due to the greater amount of fibre aligned in the principal-stress direction, the in-plane static tensile properties of the 2-D fabric reinforced composite are better than those of the 3-D fabric reinforced composite.
The dynamic mechanical properties of fatigue behaviour of 2-D and 3-D carbon/epoxy composites were investigated. A test programme was conducted on fatigue residual strength and residual stiffness under constant-amplitude tensile fatigue loading. The experimental results show that due to the through-thickness reinforcement, the 3-D composite has significantly better fatigue properties than the corresponding 2-D composite. Theoretical analysis was used to predict the fatigue residual modulus for both 2-D and 3-D composites. It was shown that the experimental results correlate reasonably with the theoretical predictions.