Recent Progress in Wrapped Tow Reinforced (WrapToR) Composite Truss Structures
Creators: name:  BENJAMIN KING SUTTON WOODS 
Publisher: name: Proceedings of the Aerospace Europe Conference - EUCASS - CEAS - 2023
Year: 2023
Subjects: COMPOSITES
TRUSS STRUCTURES
AEROSPACE STRUCTURES

description: The Wrapped Tow Reinforced (WrapToR) truss manufacturing process allows for low cost, scalable manufacturing of high structural efficiency composite truss structures. The technology, originally developed in 2009, has since been under development at the University of Bristol, where significant progress has been made in the manufacturing of WrapToR trusses, numerical tools for predicting and improving structural performance, and WrapToR based Hierarchical Space Frames (WrapToR-HSFs). The concept has also been expanded into other structural forms with new capabilities. The very high levels of structural performance achieved motivate wider uptake, and key focus areas for future work are identified. 1. The structural advantages of composite truss structures Before exploring the WrapT oR technology, it is useful to first consider the history of trusses in general and composite trusses in particular, and to discuss their advantages and disadvantages, alongside new technologies which have been developed to address some of these shortcomings. 1.1. The history of truss structures Truss structures have been known in various forms since antiquity, and while their exact origin is unknown, they are at least as old as the early Bronze age -based on archaeological evidence of wooden truss roof supports in central Germany [l]. Trusses then progressively permeated architecture throughout the world as efficient solutions for supporting long spans. There was a very rapid rise in the popularity of this approach during the construction of the first railroad networks across the United States and Europe, with wooden truss bridges being particularly well suited to the rapid expansion of the US network, as locally sourced timber could be made into reasonably easy to manipulate members and assembled via simple methods, as opposed to the slow to build and more craftsman dependent stone piers and arches of traditional bridge building. When iron and then steel became available, an explosion of progress erupted across the globe, with many new truss designs being trialled and iterated before a slow convergence towards simple and efficient designs such as the Warren, Pratt, and Howe trusses. The usage of trusses and space frames (the fully three-dimensional, volume filling version of truss structures) also expanded outside of bridges and buildings to include towers, aircraft wing and fuselage structures, automobile chassis, cranes, and even roller coasters, amongst many others, and they remain very common structural solutions in our modern society. Trusses became so common because of their very high levels of structural efficiency. This is achieved through three primary exploitations of structural scaling laws. Firstly, using small amounts of material placed far apart gives trusses very large second moments of area for a low mass, which then gives the structure high stiffness and strength. In effect, this approach gives the small members very large moment arms over which to resolve the global bending moments carried by the structure, lowering the forces required to do so. Secondly, by grouping this small amount of material into localised discrete members (as opposed to spreading it thinly into continuous walls), the local second moments of area are increased in a highly non-linear fashion, which allows for a number of stability-driven failure modes (e.g. buckling, crippling, etc.) to be avoided. Finally, and most famously, the arrangement of these straight members into triangular patterns leads to the resolving of applied forces and moments as predominantly axial forces in the members, allowing them to act as stretch-dominated as opposed to bending-dominated structures, which are inherently more efficient. Beautifully, these three tricks can be used recursively, which is to say they have the same positive benefits if Copyright 2023 by Benjamin Woods. Posted online by the EU CASS association with permission.