Overbraiding of Pultruded Rods for Hierarchical Composites

Hierarchical advanced composites using pultruded rods as a component are under development. Unlike traditional ply based composites, using rods as a building block makes the composite intrinsically three dimensional, opening up a new design space. Rods, consisting of highly aligned carbon fibres in an epoxy matrix, are used to form larger structures with a second matrix. Inspired by nature, the hierarchical composites will incorporate structure at a range of different length scales intended to improve the performance of the composite under compression.

Overbraiding is considered a promising option at both the rod and structural member scales following results of earlier work which showed an improvement in compressive performance when a structural member is overwound, due to the radial compression from the overwind. This paper discusses manufacturing challenges in overbraiding small diameter (<1 mm) pultruded rods, including the achievable lay length and braid angle, using a circular maypole microbraider. A novel ‘fuzzy carbon’ overbraid concept is presented, with potential to improve shear support in the matrix region surrounding the rod.