Electro-mechanical behaviors of graphene platelets (GPLs) reinforced polymer nanocomposite structures
Creators: name: WANG, Yu
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401702
subject: Dynamics, vibration and vibration control
classificationCode: 401707
subject: Solid mechanics

description: The discovery and successful mass production of graphene and graphene derivatives, i.e. graphene platelet (GPL) and graphene oxide (GO), etc., have initiated tremendous research interests on graphene reinforced polymer composites (GRPCs) and their structures. This is due to graphene and graphene derivatives’ significant reinforcing effects on the mechanical and physical properties of the polymer matrices, demonstrating the great potential as multifunctional and high-performance material candidates for various engineering applications, such as actuator supercapacitor, electrode and flexible electronics. Considerable work has been found on the analysis of structural performances of GRPC structures. However, most of these works only involve the mechanical properties of GRPCs. Relatively less work has been identified on considering the effects of physical properties GRPC, i.e. dielectric permittivity, on the structural behaviors of GRPC, despite of its essential in developing smart structures with
capability of active tuning. To fill existing research gap, the present research will investigate the buckling behaviors of graphene platelets reinforced composite (GPLRC) cylindrical shells with/without a cutout together with the structural behaviors of GPLRC structures, i.e. beams and plates under electrical loading by numerical method.

Firstly, the compressional and torsional buckling behaviors of functionally graded graphene platelets reinforced composite (FG-GPLRC) cylindrical shell with/without a cutout is investigated by finite element analysis (FEA) using commercial software Abaqus. GPLs are selected as reinforcements while epoxy is selected as matrix. Modified Halpin-Tsai model is adopted to predict Young’s modulus of GPLRC while the mass density and Poisson’s ratio are obtained by rule of mixture. The functionally graded (FG) distribution patterns and the average weight fraction have remarkable influences on cylindrical shell’s stiffness, which will be analyzed systematically. The reinforcing effects of GPLs are dependent on the geometry, including length-to-width ratio and length-to-thickness ratio, which are also included in the discussion. Cutout is sometimes unavoidable in engineering applications to accommodate functionally components, i.e. switches. This chapter also studies the influences of existing cutout on the torsional buckling and compressional buckling of the cylindrical shell. The effects of size, geometry, position and orientation of cutout on the compressional and torsional buckling behaviors are systematically studied.

In the next part, the structural behaviors, i.e. bending, free vibration, forced vibration and buckling, of GPLRC beam subjected to electrical loading are analyzed using numerical method. Young’s modulus and dielectric permittivity of GPLRC are predicted using effective medium theory (EMT) in the chapter while the mass density and Poisson’s ratio are simply obtained by rule of mixture. Timoshenko beam theory is adopted to describe the displacement of the beam and von Kármán nonlinear relationship is employed to derive strain field in the beam. The governing equations are established using variation method, i.e. Hamilton’s principle and principle of virtual work. Differential quadrature method (DQM) is adopted to discretize the governing equations. Parametric studies are implemented to study different factors on structural behaviors of the beam, including the geometry of the beam, the weight fraction of GPLs, the geometry of the GPLs as well as the attributes of applied electrical loading, including
the voltage of direct current (DC) component and the frequency of alternate current (AC) component.

In what follows, functionally graded distribution patterns are incorporated in GPLRC structures. The structural behaviors, including bending, free vibration and buckling of FG-GPLRC plate under electrical loading are studies. Similar to previous chapter, the elastic property and dielectric property are estimated by EMT while the mass density and Poisson’s ratio are obtained by rule of mixture. Mindlin–Reissner plate theory is adopted to describe the displacement of the plate while the strain field of the plate is obtained by von Kármán nonlinear relationship. The governing equations are formulated by variation method, including Hamilton’s principle and principle of virtual work, and discretized by DQM. After that, the
influences of different factors, including the average volume fraction of GPLs, the functionally graded distributions patterns, the slope factor of functionally graded patterns, the diameter-tothickness ratio of GPL together with the attributes of electrical loading (including the voltage
of DC component and the frequency of AC component) on structural behaviors of FG-GPLRC plate are studied.

In summary, the thesis offers a systematic investigation on the compressional and torsional buckling of FG-GPLRC cylindrical shell with/without a cutout as well as the structural behaviors of GPLRC structures subjected to both mechanical and electrical loadings. The work is envisaged to provide guidelines to develop GPL-based smart composites and structures.