Mechanical Characteristics of Graphene Origami-Based Functionally Graded Composite Structures in Fluid
Creators: name: Murari, Bill
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401707
subject: Solid mechanics
classificationCode: 401702
subject: Dynamics, vibration and vibration control

description: This doctoral thesis explores the mechanical characteristics of graphene-
based functionally graded (FG) composite structures in fluid environments,
drawing from a series of studies that address the challenges and opportunities
in this field. Inspired by the remarkable properties of nanocomposites
reinforced with carbon-based nanofillers i.e., high stiffness and lightweight,
the mechanical and functional potentials of these materials when applied in
extreme conditions are delved into. In particular, the focus is on the effect of
negative Poisson’s ratio (NPR) on the mechanical characteristics of graphene-
based functionally graded structures in steady and dynamic fluids.

Incorporating NPR characteristics generally deteriorates the stiffness of
structures. To overcome this, 3D graphene origami (GOri)-enabled metallic
metamaterials with highly tuneable NPR and enhanced Young’s Modulus
using molecular dynamics methods are introduced. The results show that
nanocomposites with Miura-patterned GOri exhibit remarkable NPR and
Young’s modulus at room temperature.

Predicting the material properties of 3D graphene-reinforced
nanocomposites remains challenging. In response, an efficient
micromechanical modelling approach that combines molecular dynamics
simulation and a genetic programming (GP) algorithm is adopted. These GP-
based models accurately predict critical mechanical properties, providing
essential insights for the analysis and design of FG 3D graphene-reinforced
composite structures.

Fluid Structure Interaction (FSI) is a prevalent phenomenon in various
engineering sectors. Offshore structures that extract oil and gas, whose
supports are situated in the seabed, rely on their capability to withstand high
dynamic loading in a fluid environment i.e., tides, earthquakes, and drilling. It
has been reported that 96% of marine structure accidents were linked to the
operation stage of their life while 4% of the accidents were linked to the
installation stage. This statistic highlights the pending requirement for support structures with improved vibration resistance and stiffness to significantly reduce the risk of structural failure, particularly during operation.

The initial chapters of this thesis deal with the FSI behaviour in relation
to static fluid. The fluid is described as ideal i.e., incompressible, non-viscous,
and irrotational. This parametric study is addressed by calculating the velocity
potential function and adopting Bernoulli’s principle to determine the fluid
pressure on the surface of the structure. The latter chapters are related to
dynamic fluids and their effects on the deformation behaviours of graphene-
based functionally graded composite structures. The fluid is described as a
viscous Newtonian fluid i.e., incompressible, viscous, and two-dimensional
fluid flow. The FSI is described using a simplified model based on the Navier–
Stokes equation for fluid momentum. This methodology enables the
determination of the effect of the fluid velocity and viscosity. In addition, the
effects of vortex-induced vibration (VIV) behaviours of graphene origami-
based functionally graded structures were investigated via finite element
analysis and partial differential equation solver.

Continuing the exploration, a comprehensive analysis of the structural
behaviours of FG structures composed of 3D graphene-reinforced
nanocomposites under various loading conditions while in contact with
various fluid conditions is conducted. Material properties are controlled via 3D
graphene content, GOri folding degree, graphene and metamaterial
distribution patterns, and functionalised graphene coverage graded across the
thickness of the structure. Governing equations are derived and numerically
solved using a range of methods, offering valuable insights into the engineering
design and application of functionally graded graphene origami reinforced
composite structures for improved structural performance.

In summary, this thesis contributes to the body of knowledge by
exploring the mechanical behaviours of graphene origami-based functionally
graded composite structures immersed in various fluid conditions. It offers
insights into the effects of graphene properties, fluid properties, and geometric
properties on the mechanical behaviours of graphene origami-based
functionally graded composite structures immersed in various fluid
conditions. Furthermore, it provides a novel machine learning model that can accurately and efficiently predict the vibrational characteristics of graphene origami-based functionally graded composite beams. Lastly, it examines the
linear and nonlinear structural behaviours of FG 3D graphene origami-
reinforced nanocomposite structures, thus promoting their application in
various engineering domains.