Geometrical and mechanical analysis of 3D-printed auxetic structures

• Main Author: Lee, Basil Xiang
• Other Authors: Zhou Kun
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/71717
• Institution: Nanyang Technological University

Additive Manufacturing (AM) otherwise known as 3D printing has gained much recognition and attention in recent years because of the value added products offered by this technology. Selective Laser Sintering (SLS) is regarded as an utmost established manufacturing process amongst the various 3D printing processes available. A high powered laser sinters powdered material, forming a solidified structure. By utilizing this advanced technology, complexed design structures that were once unable to be manufactured by conventional means are now possible. Energy absorbing materials with unique structures have allowed a wider array of applications such as shock absorption, energy dispersion as well as impact, personnel and infrastructure protection. Recently, a group of auxetic structures which exhibit excellent energy absorption capabilities were designed. These auxetic structures behave differently from convention because of their negative Poisson’s ratio. SLS allows the fabrication of these auxetic structures of complex geometries. In this project, three different groups of auxetic structural designs are studied. The first group is a set of newly designed cubic cellular structures, the second group is a series of spherical cellular structures, and the third group is a series of spherical shell structures adapted from Babaee and Bertoldi [1]. These designs are first designed on a numerical modelling platform and thereafter fabricated through the SLS process. The two designs in focus are auxetic cellular structures with 6 Holes (6H) and 12 Holes (12H) of Body Centred Cubic (BCC) crystal lattice structure. Powdered materials used are the Polyamide 12 (PA12) and the PA12 with Carbon Nanotube (CNT) nanofillers (PA12-CNT) due to their superior mechanical properties compared to their amorphous polymer counterparts. The fabricated samples are analysed and studied via two testing methods. The samples are first put through a Micro Computed Tomography (MicroCT) scan which is a non-destructive analysis of the sample, allowing us to obtain micro scale information such as thickness distribution and material porosity. Following that, the same samples undergo compression testing, providing us stress-strain behaviour of the structures relating to energy absorption capacity. These data allow us to understand the energy absorption efficiency of the 6H and 12H BCC cellular structures, as well as the effectiveness of PA12 and PA12-CNT as SLS materials.