Date of Award

Spring 2019

Project Type

Dissertation

Program or Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Yaning Li

Second Advisor

Brad L Kinsey

Third Advisor

Yannis P Korkolis

Abstract

Emerging in the last decade, mechanical metamaterials have many engineering advantages due to unusual mechanical properties. Auxetic (with negative Poisson’s ratio) mechanical metamaterials, as an important family of these materials, have broad engineering applications including the design of new materials with increased indentation resistance, shear resistance, energy absorption capability and variable permeability.

Chiral auxetic mechanical metamaterial is a sub-family of the auxetic material, which is with a geometry that is non-superposable on its mirror image. Compared to symmetric auxetic materials, such as re-entrant honeycombs or periodic porous materials, which have random handedness after instability, chiral materials have deterministic handedness and therefore are expected to have more robust auxetic effects under manufacturing errors with both small and large deformations.

Moreover, due to the chirality, the deformation mechanisms of this sub-family of auxetic materials are quite interesting: for 2D cases, there will be shear-compression/tension coupling effects; and for 3D cases, there will be twist-compression/tension coupling effects.

In this dissertation, through innovative 2D and 3D designs, a new family of auxetic chiral mechanical metamaterials were systematically developed. Besides auxetic effects, several new deformation mechanisms were designed and thoroughly investigated, such as a sequential cell opening mechanism, a rotation-induced chiral pattern transformation triggered either by mechanical instability or shape memory effects, and shear/twist-compression/tension coupling effects. To prove the concept, multi-material 3D printing was extensively used to fabricate hybrid designs for both uniaxial and bi-axial compression/tension experiments. A novel bi-axial compression apparatus was designed and fabricated via 3D printing to perform bi-axial compression on a uniaxial material testing machine.

To better understand the mechanical behaviours of these materials and predict the mechanical properties of the designs, both sophisticated structural models and advanced continuum models such as monoclinic material model and micropolar elasticity are used for mechanical modelling.

In summary, through the innovative designs, the database of existing chiral auxetic metamaterials is significantly expanded which expedites the discovery of new mechanical properties and behaviours. Also, the extended database enables the development of advanced constitutive models either within classic continuum theory or beyond.

Download

Share

COinS