Graphene-reinforced Nanocomposite Research Articles

Influence of flexoelectric effect on the bending rigidity of a Timoshenko graphene-reinforced nanorod

Abstract The focus of this work is to study the influence of flexoelectric phenomenon on the electromechanical response of graphene-reinforced nanocomposite (GNC) nanorods. An analytical model has been derived by utilizing the Timoshenko beam theory and the principle of variational work by incorporating flexoelectric effects. The GNC nanorod is subjected to a concentrated load acting downward for clamped-free and simply supported support types. The GNC is reinforced with a defective graphene sheet as it is known to show enhanced polarization. The elastic properties of defective graphene sheets have been evaluated using molecular dynamic simulations. The outcome of our model shows that the flexoelectric effect must be considered for accurate modeling of nanostructures. Irrespective of the support type, flexoelectric effect improves the stiffness of the nanorod. We also observed that the stiffness of the nanorod is significantly influenced by the support type. This work presents an opportunity for the development of high-performance graphene-based nanoactuators/sensors.

Bending and Buckling of FG-GRNC Laminated Plates via Quasi-3D Nonlocal Strain Gradient Theory

To improve the structural stiffness, strength and reduce the weight of nanoplate structure, functionally graded (FG) graphene-reinforced nanocomposite (GRNC) laminated plates are exploited in this paper. The bending and buckling behaviors of FG-GRNC laminated nanoplates are investigated by using novel quasi-3D hyperbolic higher order shear deformation plate theory in conjunction with modified continuum nonlocal strain gradient theory, which considered both length and material scale parameters. The modified model of Halpin–Tsai is employed to calculate the effective Young’s modulus of the GRNC plate along the thickness direction, and Poisson’s ratio and mass density are computed by using the rule of mixture. An analytical approach of the Galerkin method is developed to solve governing equilibrium equations of the GRNC nanoplate and obtain closed-form solutions for bending deflection, stress distributions and critical buckling loads. A detailed parametric analysis is carried out to highlight influences of length scale parameter (nonlocal), material scale parameter (gradient), distribution pattern, the GPL weight fraction, thickness stretching, geometry and size of GPLs, geometry of the plate and the total number of layers on the stresses, deformation and critical buckling loads. Some details are studied exclusively for the first time, such as stresses and nonlocality effect.

Mode I Fracture Toughness of Graphene Reinforced Nanocomposite Film on Al Substrate.

Nanocomposites were prepared by adding graphene nanoplatelets (GNP) into epoxy with a variety of loadings. The thickness of GNPs used in this study was in a range of 1 nm to 10 nm. Nanocomposite film was deposited on the aluminum (Al) substrate via a spinning coating process. Tensile tests were carried out to determine the elastic modulus, ultimate strength and fracture strain of the nanocomposites. Theoretical prediction of the fracture toughness of the film/substrate composite structure with an interfacial crack under mode I loading was derived utilizing linear elastic fracture mechanics theory. Four-point bending tests were performed to evaluate the mode I fracture toughness. It was observed that the performance of the nanocomposite, such as elastic modulus, ultimate strength, and fracture toughness, were significantly enhanced by the incorporation of GNPs and increased with the increase in GNP concentration. The elastic modulus and mode I fracture toughness of the epoxy reinforced with 1 wt.% of GNPs were increased by 42.2% and 32.6%, respectively, in comparison with pure epoxy. Dispersion of GNPs in the epoxy matrix was examined by scanning electron microscope (SEM). It can be seen that GNPs were uniformly dispersed in the epoxy matrix, resulting in the considerable improvements of the ultimate strength and fracture toughness of the nanocomposite.

On the free vibration and bending analysis of functionally graded nanocomposite spherical shells reinforced with graphene nanoplatelets: Three-dimensional elasticity solutions

This paper presents analytical investigations on the free vibration and static bending of functionally graded graphene-reinforced nanocomposite (FG-GPLRC) spherical shells. The GPL nanofillers are dispersed into polymer matrix uniformly and un-uniformly in the thickness direction with a piece-wise type, and UD, FG-O, FG-X, FG-V and FG-A types of GPL distribution patterns are taken into account. The effective material properties of graphene-reinforced nanocomposites are estimated by using the modified Halpin-Tsai multi-scaled model and the rule of mixtures. Governing differential equations for free vibration and bending of the FG-GPLRC spherical shells are derived based on the three-dimensional elasticity theory with the aid of the state space method, and the layer-wise model is employed to obtain the analytical solutions. The validity of the present method is first examined, followed by the illustrative parametric studies to further scrutinize the free vibration and static bending behaviors of the FG-GPLRC spherical shells with the various reinforcement schemes, including the distribution pattern, the weight fraction, and geometric parameter of GPLs in details.

Flexoelectric effect on electric potential in piezoelectric graphene-based composite nanowire: Analytical and numerical modelling

In this work, an analytical model was developed to study the distribution of electric potential in a graphene reinforced nanocomposite (GRNC) nanowire. The electromechanical responses such as electric potential and deflection of cylindrical GRNC cantilevered nanowire were investigated. Moreover, the conservative fully coupled finite element (FE) models were developed to validate the analytical predictions. Analytical solution shows that the piezoelectric potential in the GRNC nanowire depends on the transverse force, but it is not a function of the force acting along its axial direction. The electric potential in the tensile and compressive sections of nanowire is antisymmetric along its cross-section, making it as a “parallel plate capacitor” for nanopiezotronics applications such as nanogenerator and piezoelectric field effect transistor due to potential drop across the nanowire which assists as the gate voltage. The predictions of potential distributions across the GRNC nanowire considering piezoelectricity show better agreement with FE predictions. Outcomes of the current work reveal that the flexoelectric effect on the electromechanical behavior of GRNC nanowire is noteworthy and cannot be ignored.

Damped dynamic behavior of an advanced piezoelectric sandwich plate

In this paper, damped dynamic deflections of an advanced piezoelectric sandwich plate (APSP) subjected to thermo-electro-mechanical loads have been studied using a meshless method. In the considered APSP, two active piezoelectric layers are attached on to the faces of a passive advanced structure consisting of two thin graphene reinforced nanocomposite (GRNC) layers and a thick porous polymeric core. In GRNC layers, graphene content is assumed to be varied according to functional distribution profiles. Using modified Halpin-Tsai’ equations, temperature dependent material properties of nanocomposite layers have been determined. Reddy’s third order theory of plates (called TSDT) is utilized to obtain the coupled governing equations, and MLS shape functions are adopted in the meshless solution. The influences of graphene content, porosity, temperature, electro-mechanical loading and structural damping on dynamic deflection behavior have been investigated. The results reveal that adding graphene volume fraction from 3% to 7% significantly affects the damping ratio, settling time and dynamic response of APSPs. However, further addition of graphene content has little effect on those responses. Moreover, embedding more pores in the core layer remarkably changes the damped dynamic behavior of APSPs due to a significant reduction in structural weight and a slight decrease in structural stiffness.

Nonlinear dynamic responses of FG graphene-reinforced nanocomposite plates in thermal environment

Nonlinear dynamic responses of functionally graded graphene-reinforced nanocomposite (FG-GRC) plates in thermal environment are studied in the present work. A modified Halpin-Tsai micromechanics model is applied to evaluate the equivalent material properties of the nanocomposite. Based on von Kármán nonlinear strains displacement relationship and the first-order shear deformation plate theory (FSDT), the nonlinear governing equations are derived by Hamilton principle. Galerkin and Runge-Kutta numerical method are employed to obtain the dynamic responses of the FG-GRC plate. Results show the GPLs distribution and temperature have remarkable effects on dynamic responses of a FG-GRC plate.

Evaluation of effective properties for smart graphene reinforced nanocomposite materials

In this study, analytical and numerical models were developed to investigate the effective properties of graphene reinforced nanocomposite (GRNC) subjected to electromechanical loading. In this analytical mechanics of material (MOM) model was developed to predict effective properties of the composite while numerical finite element (FE) model developed with the help of a representative volume element (RVE). Also, the longitudinal and transverse modulus of GRNC is determined using the Halpin-Tsai equations. Both models are showing a good agreement for loading applied along the fiber direction when compared to transverse loading. The present study highlights on developing efficient NEMS application.

Static and dynamic response of graphene nanocomposite plates with flexoelectric effect

In this work, the electromechanical behaviors of graphene reinforced nanocomposite (GRNC) plates with flexoelectric effect were studied by using Kirchhoff's plate theory, Navier's solution and extended linear piezoelectricity theory in conjunction with the mechanics of materials (MOM) and finite element models. The static and dynamic responses of simply supported flexoelectric GRNC nanoplates under different loadings such as uniformly distributed, varying distributed, inline and point loads were investigated. The developed MOM and FE models envisage that the effective piezoelectric constants of a GRNC account for the actuating capability in its transverse direction due to the applied electric field in the plane. The elastic properties of pristine and defective graphene sheets were also estimated via molecular dynamics (MD) simulations and the obtained results are found in good agreement with the existing experimental and numerical results. Our results reveal that the flexoelectric effect on the static and dynamic responses of GRNC nanoplate is substantial and cannot be neglected. The electromechanical response of GRNC plates can be engineered to attain the desired deflection characteristics and resonant frequencies for a range of nanoelectromechanical systems using different boundary conditions as well as geometrical parameters such as aspect ratio/thickness of nanoplate and volume fraction of graphene.

Graphene-Reinforced Biodegradable Resin Composites for Stereolithographic 3D Printing of Bone Structure Scaffolds

A biodegradable UV-cured resin has been fabricated via stereolithography apparatus (SLA). The formulation consists of a commercial polyurethane resin as an oligomer, trimethylolpropane trimethacrylate (TEGDMA) as a reactive diluent and phenylbis (2, 4, 6-trimethylbenzoyl)-phosphine oxide (Irgacure 819) as a photoinitiator. The tensile strength of the three-dimensional (3D) printed specimens is 68 MPa, 62% higher than that of the reference specimens (produced by direct casting). The flexural strength and modulus can reach 115 MPa and 5.8 GPa, respectively. A solvent-free method is applied to fabricate graphene-reinforced nanocomposite. Porous bone structures (a jawbone with a square architecture and a sternum with a round architecture) and gyroid scaffold of graphene-reinforced nanocomposite for bone tissue engineering have been 3D printed via SLA. The UV-crosslinkable graphene-reinforced biodegradable nanocomposite using SLA 3D printing technology can potentially remove important cost barriers for personalized biological tissue engineering as compared to the traditional mould-based multistep methods.

Vibro-acoustic analysis of functionally graded graphene-reinforced nanocomposite laminated plates under thermal-mechanical loads

This paper investigates the vibro-acoustic characteristics of functionally graded graphene-reinforced nanocomposite (FG-GRC) laminated plates under thermal-mechanical loads. It is assumed that the graphene nanoplatelets (GPLs) are distributed with random directions but homogeneous dispersion in each layer while the weight fraction of GPLs shows a layer-wise variation along the thickness direction. The material properties are assumed to be temperature-dependent and are estimated through Halpin-Tsai micromechanical model. The governing differential equations are derived based on Hamilton's principle and the third-order shear deformation plate theory (TSDT). The natural frequencies and vibration displacements of a simply supported FG-GRC plate are obtained by employing the Navier method. The acoustic radiation is calculated through Rayleigh integral method. Results show that the vibro-acoustic characteristics of FG-GRC plates are significantly influenced by the distribution pattern, weight fraction, temperature and geometric parameter of the plate. A coupling effect between temperature and the width to thickness ratio of a plate is found when analyzing the influence of temperature on vibro-acoustic characteristics of FG-GRC plates.

Polylactic acid-based polyurethane/polyamide 6,12 and graphene nanocomposite: Structure and physical property study for packaging application

ABSTRACTThis effort reports on novel polylactic acid-derived polyurethane (PU) and polyamide 6,12 (PA6,12)-based blends and graphene-reinforced nanocomposite. PU/PA6,12 (50:50) blend was opted as matrix based on molecular weight and shear stress performance. PU/PA6,12 with 5 wt% graphene (PU/PA6,12/graphene 3) showed improved T0 and Tmax of 515 and 541°C relative to neat blend. PU/PA6,12/graphene 3 also revealed significantly high tensile (53 MPa) and flexural strength (1,711 MPa). For Eschericia coli, Staphylococcus, and Pseudomonas bacterial strains, nanocomposite with higher graphene loading produced significant inhibitory effects. Novel nanocomposites displayed fine antimicrobial and barrier properties against O2 and H2O to be used as a packaging material.