Compressive damage in 3-axis orthogonal fabric composites

This work is aimed at two goals: examining compression-induced damage in 3- axis orthogonal composites, and assessing the influence of surface loops on the damage behavior. Two types of 3-axis fabrics were made; one incorporat ed unidirectional carbon/epoxy rods along the axial direction, and the othe r employed carbon yarns in all the axes. After resin impregnation, one half of the specimens were ground to remove surface loops. Compressive tests we re conducted by using an end-supported, end-loaded fixture designed for thi ck specimens. The damage configurations can be categorized into microscopic and miniscopic levels. The microscopic damage focuses on kinking of fibers and shear failure of fiber/matrix interface, whereas the miniscopic damage focuses on kinking of axial bundles and shear failure of transverse bundle s. In many ways the miniscopic damage is a scale-up of the microscopic dama ge, although their underlying mechanisms of damage evolution are different. The loop-retained and loop-removed specimens manifest the role of loops in resisting compression. The usefulness of loops was found to lie in retaini ng the structural integrity after damage has developed. Theoretical predict ions of the critical stress for the onset of fiber microbuckling have been examined and compared with the experimentally obtained results. Some keys f or improving the compression behavior of the 3-axis composites are discusse d. (C) 2000 Elsevier Science Ltd. All rights reserved.