In-plane shear response of unidirectional fiber reinforced and fabric reinforced carbon/epoxy composites

The nonlinear in-plane shear properties of unidirectional fiber reinforced composites and fabric reinforced composites were compared by ±45° tension tests based on ASTM standard D3518. A set of epoxy matrix materials reinforced by unidirectional carbon tapes as well as satin and twill carbon woven fabrics were prepared. The experimental results revealed that fabric reinforced composite showed more ductile-like response in the pre-yield phase and better load bearing ability in the post-yield phase compared to the unidirectional fiber reinforced composite. There was no obvious damage on the surfaces of fabric reinforced composites prior to failure, whereas for unidirectional laminates obvious cracks and delaminations initiated from the free edges on the surface and propagated along the fibers. Finally, analysis of the Poisson's ratio fluctuations of the unidirectional composites separated the two contributors to the structural nonlinearity, the continuous micro changes and macro damage in laminae.