Crack Propagation in Composites With Long Aligned Fibers

Results on strength, toughness and fatigue crack growth on a specially made composite material are reported. The compact tension composite specimen consisted of an epoxy matrix and layers of long aligned glass fibers that were equally spaced. The experimental data on crack initiation strength showed that for a range of fiber spacing λ, the composite’s strength σA, scaled with a fiber spacing in the form of σAλ=κ. The effective toughness of the composite specimens increased with a decrease in fiber spacing. Fatigue crack propagation experiments were performed on specimens with the same fiber spacing and under different applied loads. Within the resolution of the observations, no fiber fracture was seen in the bridging zone. In all fatigue experiments, crack arrest was observed after a few fiber layers. Analysis of the experimental results on strength and crack growth was aimed at understanding and quantifying the effects of the fibers ahead of the crack tip on the stress and strain fields and the contributions of the bridging fibers to the total stress intensity factor Kt. The results of the numerical analysis agreed well with the toughness values obtained from the experiments. The total stress intensity factor was found to decrease with crack length.