Mechanical and geometrical analysis of 3d-printed auxetic structures

Abstract

Material development has come to a point where the advancement of metals has hit a plateau while that of polymers has seemingly just begun. This is largely due to the improvements made towards Additive Manufacturing (AM) technology which has granted the capability of fabricating complex polymers and their composites with relative ease. Exploiting this, it is made possible to implant favourable and functional properties from an additive into a polymer matrix. A proven example is the polymer nanocomposite consisting of Polyamide 12 (PA12) and minute quantities of Carbon Nanotubes (CNT). Auxetics is another area that is seeing recent development. Rather than relying purely on materials, auxetics utilises the macrostructure of components and the principle of mechanical instability for energy absorption. This field is largely driven by the broad array of applications body protection, shock resistance and energy return. Auxetic designs range from foam structures to lattices comprising of identical repeating units. Auxetics are generally geometrically complex, which makes AM a suitable means of manufacture. This project will see the fabrication of several auxetic lattices, made of PA12-CNT polymer nanocomposite, using an AM method known as Selective Laser Sintering. These auxetic lattices will comprise of the same family of repeating units but vary slightly in terms of lattice configuration and porosity. Compression tests will be conducted, allowing force-displacement and stress-strain relationships of the fabricated samples to be determined. Results will give insight on the effects of auxetic lattice design variations on auxetic behaviour and energy absorption properties. Furthermore, this project can possibly help to identify limitations and challenges faced in using SLS to produce auxetic lattices, and how they may be overcome.