THE MACROSCOPIC ELASTICITY OF 3D WOVEN COMPOSITES

The elastic properties of graphite/epoxy composites with three-dimensi onal interlock weave reinforcement have been measured over length scal es somewhat greater than the characteristic length of the weave patter n. Orientation averaging models similar to those developed elsewhere o ver the last twenty yeats provide estimates of elastic constants that are in fair agreement with the experimental data. However, in-plane Yo ung's moduli are consistently too high and properties related to the t hrough-thickness reinforcement show considerable scatter. Most of the discrepancies can be attributed to waviness and other geometrical irre gularities in nominally straight tow segments. Much improved agreement with in-plane properties is obtained by measuring and accounting for the out-of-plane waviness of in-plane tows. Other observed distortions of in-plane tows and irregularity in through-thickness tows are very difficult to quantify experimentally. There results a significant and apparently unavoidable uncertainty in predictions of properties that d epend strongly on the through-thickness reinforcement. Nevertheless, t he utility of orientation averaging models in applications where the i n-plane properties are paramount is clearly verified.