Damage accumulation in a woven fabric composite.

Damage development in transparent woven glass fibre reinforced epoxy laminates manufactured from two different commercial cloths has been investigated under quasi-static and cyclic loading. Of the two different cloths, one was woven using untwisted fibre bundles, the second cloth was woven using a fibre bundle which was formed by twisting three smaller bundles together. All laminates were fabricated using a wet lay-up process to impregnate two layers of cloth prior to curing. Uniaxial quasi-static tension and tension-tension fatigue tests were carried out on coupons from both sets of laminates. Observations of the damage caused by the different loading modes were made in two ways, In-situ observations of coupons held within the testing machine allowed the damage to be monitored during testing. Observations of metallographically polished edge- sections containing damage allowed the through-thickness characteristics of the damage to be observed. The major damage morphology observed m both laminates under both types of loading was matrix cracking. The crack morphology observed in laminates reinforced with the cloth woven using untwisted fibre bundles was similar to the cracks observed in cross-ply laminates. This similarity allowed the damage to be quantified by a line density measurement analogous to that used for cross-ply laminates. The damage observed in the laminates reinforced with the cloth woven using twisted fibre bundles was more complicated. This complex damage required quantification by measurements from both the plan view and the edge-section. Shear-lag analysis was used to model the stiffness reduction of the laminates due to cracking damage. Equivalent laminates based on a cross-ply lay-up were derived. The reduced stiffness of the region of the laminate affected by the cracking was calculated using shear-lag and the stiffness of this region was then combined with the stiffness of the rest of the laminate to give the reduced stiffness of the laminate as a whole. The test data and the model predictions showed good agreement for both laminates