Fracture and Interface Properties of a Composite with Long Aligned Fibers

Results on fracture, fatigue crack growth and debonding on compact tension specimens of a specially made composite material are reported. The specimens consisted of an epoxy matrix and layers of equally spaced long aligned glass fibers. The experimental data showed that for a range of fiber spacing lambda, the composite's strength sigma(A), scaled with the fiber spacing in the form of sigma(A) root lambda = constant. In all fatigue experiments, crack arrest was observed after a few fiber layers. Analysis of the experimental results was aimed at quantifying the effects of the fibers ahead of the crack tip and the contributions of the bridging fibers to the total stress intensity factor. The debonding in the bridging zone was evaluated using a one dimensional analysis. The model was calibrated with the debonding on the first row of fibers, in a typical specimen, and consequently used to describe debonding on specimens with different fiber spacing. In spite of the assumptions adopted, the model described debonding well.