Session: 01-03 Polymers: Systems Engineering and Design

Paper Number: 93965

93965 - Additive Manufacturing of Star Structured Auxetic Lattice Samples With Overhanging Links 

A key capability of Additive Manufacturing (AM) is the ability to produce highly complex components such as lattice structures. A prominent space for this is auxetic lattice structures. Auxetic lattices contract laterally in response to compression which increases specific energy absorption, indentation resistance and shear resistance and are beginning to open avenues for novel strain response design. Applications are most prominent in medical and sports engineering due to the high monetary value of performance. Stents, implants, and impact absorbing linings in sporting equipment are among the most investigated applications.

Auxetic lattice unit cells were designed using a novel structure to minimise stress concentration and produce a wide elastic range while achieving near isotropy in the auxetic response. They were developed using an approach intended to be applied to allow localised optimisation of stress responses with low computational cost. This was achieved through an enumeration of the fundamental unit cell using polynomial centre line and link thicknesses functions, which allowed a strict constraint of link thickness and path to be used to account for the limitations of printer resolution. The unit cell had the flexibility to optimise the curved links and to be easily adapted to different forms for exploration of comparative properties in stiffness, isotropic range, auxetic response and degree of anisotropy.

The designed star cells, however, require an overhang that is not conducive to most forms of AM. Methods of making the lattice structures suitable for AM are subsequently investigated. Structures were manufactured for mechanical testing using thermoplastic polyurethane filament combined with polyvinyl acetate support at cubic cell scales between 2cm and 4cm, and the removal of support and quality of the resulting parts were compared. It was found that the limiting geometric feature of the cell prints were the link thickness and the clearance of the closest contact distances formed by the re-entrant mechanism, and that when assembled it was impractical to adjust the cells should print errors arise. To address this, layered assembly of lattices was explored and found to be a viable method to manufacture the 3D auxetic lattices. Layers were determined to ease the production process and establish achievability of the structures. Layered manufacturing is found to be a practical approach which allowed investigation of cells and give greater access for removal of support. Feet were added to make the layers stackable and give a surface for adhesives to be applied to. Superglue proved to be a suitable adhesive for the produced samples. The scale at which overhanging lattices are possible is outlined and new ways to make novel lattice structures which facilitate a wider array of metamaterial behaviours were subsequently introduced.

Presenting Author: Benedict A. Rogers The University of Bath

Presenting Author Biography: Benedict Rogers is currently in his first year of a PhD at the University of Bath, UK. He is part of the ART_AI CDT in the Department of Computer Science and has a Masters degree from the same University in the Department of Mechanical Engineering and currently works across both departments. His primary interests are geometric optimisation, continuum mechanics, metamaterials and additive manufacturing.

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