On the behaviour of flattened tubular Bi-axial and Tri-axial braided composites in tension

Abstract

The effect of braid angle and number of axial tow insertions on the behavior of flattened tubular braided composites (carbon fibre/epoxy resin) has been investigated. Two type of braids i.e. bi-axial and tri-axial (i.e. 6 and 12 inserted axial tows), for three braid angles (35°, 45° and 55°), have been studied. The stress–strain curve for the bi-axial braided composites is pseudo-ductile in nature, with a smooth transition into a plateau region at low strains, accompanied by necking of the composite. By contrast, the tri-axial braided composites show an initially high peak stress, related to the deformation and fracture of the axial tows, and subsequent plateau-like behaviour accompanied by neck formation, the extent of which appears to be determined by the strain-to-failure of the composite. For the bi-axial braids, an increase in braid angle produced decreased strength, axial modulus and specific energy absorption, but an increase in strain to failure. Inserted axial tows produced increased strengths and Young's moduli, but a decrease in specific energy absorption (except for 55°) and strain to failure. In all cases, the braided composites outperformed the specific energy absorption of aluminium.