On the Optimization of Open Truss Interlaced Composite Structures Featuring Continuous Yarns

Abstract

Topology optimization (TO) is the process of maximizing the structural efficiency of parts by removing material from zones within the part envelope that do not carry significant loads. Designs produced with TO typically include free forms and intricate shapes that lend well to additive manufacturing (AM) techniques when traditional materials are used. However, conventional slicing used in AM techniques is not suited for manufacturing structural, continuous yarn polymer-matrix fibre reinforced composites (PMFRCs) as it cannot lead to carbon yarns extending along load transmission paths defined in 3D. Due to this limitation, it is not currently possible to perform true 3D TO on PMRFCs with continuous yarns as already possible with metal and polymer parts. As a result, PMFRCs may outperform metal alloys in terms of tabulated specific properties but in the current state of industrial technology, additively manufactured metal structures can outperform structures made from PMFRCs. Previous work showed that TO continuous yarn PMFRC parts can be made by interlacing dry continuous yarn in 3D. The configuration of the resulting dry yarn truss is then optimized for maximizing specific structural stiffness of the resulting 3D TO PMFRC part through iterative yarn tension adjustments. The objective of the present work is to further optimize the geometries of PMFRC trusses by means of a seven-step sequential process. The process begins with a static finite element analysis (FEA) to extract principal stress fields and proceeds through a series of algorithmic steps including stress path generation, main stress path selection, triangulated structure construction via k-neighbours triangulation, optimization of yarn alignment with the principal stress field, graph-based construction of individual yarn paths and graph-based structural thickening to properly model yarn cross-sections. Together, these steps enable the design of truss-like structures that follow mechanically optimized stress trajectories.