Energy absorbing behaviour of additively manufactured auxetic composite lattices

Abstract

Cellular lattices, for example honeycombs, are commonly integrated within a variety of engineering applications as they combine excellent energy absorbing capabilities with high specific strength and stiffness. However, this performance is generally limited to one loading orientation with mechanical properties in the other two directions significantly reduced.
The main aim of this thesis is to assess the in-plane energy absorbing capabilities of auxetic cellular lattices and compare them to a conventional lattice. Because of their counterintuitive behaviour, auxetic structures have the potential to enhance the multi-directional performance of cellular lattices given the advantageous mechanical properties they possess. Under an applied load, an auxetic material behaves differently than how a conventional material would act because of the negative Poisson’s ratio.
Three auxetic cellular lattices were selected, these include: the re-entrant, double arrowhead and anti-tetra-chiral topologies, which were compared to a conventional, non-auxetic hexagonal lattice. Through the development of a novel cellular design tool, the geometry of each lattice and how this influences relative volume was studied.
Samples were additively manufactured using a short fibre composite 3D printing material and then experimentally tested under uni-axial tensile and compression testing, 3-point bending and low velocity impact. The results chapters focus on the testing and comparison of the cellular lattices under the previously mentioned testing methods. Lattices with identical outer volumes were analysed to assess the influence of unit cell topology on the compressive, bending and tensile performance.
Finally, three hybrid auxetic lattices which combine alternate layers of hexagonal (non-auxetic) and re-entrant, double arrowhead or anti-tetra-chiral (auxetic) unit cells have been proposed and a preliminary computational study has been undertaken. A computational simulation was experimentally validated and revealed that the hexagonal-double arrowhead hybrid is capable of providing an increase in specific energy absorption over the conventional hexagonal lattice when both were loaded axially.

Thesis is embargoed until 31 December 2024.

Date of Award	Dec 2022
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Zafer Kazancı (Supervisor) & Brian Falzon (Supervisor)