The effect of braid angle on the flexural performance of structural braided thermoplastic composite beams

Abstract Thermoplastic braided composite tubular beams were manufactured using commingled hybrid yarn with braid angles 30°, 45° and 60° and tested in static three-point flexure. Two principal deformation modes were observed during the flexural loading: global flexure and localised crush. The extent of each mode occurring in the three braid angle variants was measured using a linear deflectometer as well as 3D digital image correlation. Localised crushing was found to decrease significantly with increasing braided angle, accounting for 63%, 45% and 19% of the total applied deflection for the 30°, 45° and 60° beams respectively. Further, surface strain measurements obtained from 3D DIC showed increasing the braid angle led to a global flexure-dominated deformation. In addition, the stiffness and peak load increased with increasing braid angle. The observed differences in deformation modes were due to a combination of multiple braid angle-dependent properties of braided composites such as modulus, thickness etc.