Weight Fraction Of Nanofillers Research Articles

Free vibration analysis of functionally graded graphene platelet-reinforced metal foam doubly curved panel

In this research, free vibration characteristics of functionally graded metal foam doubly curved panels reinforced with graphene platelets and with porosities have been surveyed. Halpin Tsai's approach is utilized for extracting the effective Young modulus of porous metal foam nanocomposite and also the effective density of nanocomposite porous doubly curved shell panel is estimated by using an extended rule of mixture. The FSDT hypothesis is utilized for determining the displacement field and the Finite element and Hamilton principle are utilized for deriving the mass and stiffness matrices of the structure. Finally, the influences of several variables such as porosity distribution, porosity coefficient, GPL dispersion pattern, the weight fraction of Nanofillers, and span angles on the free vibrations characteristics of doubly curved shell panels with FG porosities and reinforced by graphene platelet have been reported in detail.

Natural Frequency Characteristics of Stiffened FG Multilayer Graphene-Reinforced Composite Plate with Circular Cutout Resting on Elastic Foundation

In this research, natural frequency response of functionally-graded multilayer graphene-reinforced composite plate with circular cutout reinforced by orthogonal stiffeners is investigated for the first time. The structure is surrounded by Winkler-type elastic support. The plate is composed of polymethyl methacrylate (PMMA) as matrix material and reinforced by graphene platelets (GPLs). The material of the orthogonal stiffeners is the same as that for the matrix. Rule of mixtures and Halpin–Tsai approach are applied to estimate the effective material properties of the composite plate. Third-order shear deformation plate theory and finite element procedure is employed to obtain the element matrices of the structure. Natural frequencies and mode shapes of the stiffened plate are reported for different variables such as nanofillers dispersion patterns, width and height of the stiffeners, aspect ratio of plate, plate thickness ratio, weight fraction of nanofillers, number of stiffeners, boundary conditions, elastic foundation stiffness parameter and size of circular cutout. The obtained results denote that with the addition of a set of stiffeners, fundamental frequency enhanced up to 32.3% with just about 10% increase of mass.

Understanding the negative permittivity behavior of polyvinyl alcohol based metamaterials under radio frequency

Functional metamaterials that exhibit negative dielectric permittivity through percolative network formation have attracted immense attention due to their significant potential for a wide range of applications in electronic devices. Negative permittivity has taken off as a research topic recent years in percolative composites. The polymer nanocomposites (PVA/H-Pa-G) were prepared using the α-Fe2O3 modified GNP and HCl doped polyaniline (Pani) based nanofillers (H-Pa-G). The as prepared samples were characterized in order to analyze their dielectric response for understanding the negative permittivity behavior. Below the percolation threshold for the polymer nanocomposite with 0.10%, 0.25% H-Pa-G nanofiller weight fraction, an increase in σac conductivity is observed with increase in frequency. The dielectric study confirmed the negative permittivity behavior for the polymer nanocomposite (0.50%, 1.00% and 2.00%) above the percolation threshold. This can be mainly attributed to the presence of the conductive network of H-Pa-G nanofiller in the PVA matrix. On the contrary, the positive permittivity is due to the insulative nature of PVA matrix. The empirical data of real permittivity was fitted using the Drude model that corresponded well with the experimental data with the fp = 1.31 GHz which is further certified by the equivalent circuit model fitting. This proposed work strongly suggest the implication of the as prepared polymer nanocomposite for the negative permittivity materials based applications.

Combination of titanium dioxide and polyhedral oligomeric silsesquioxane nanofillers to boost mechanical and rheological properties of polyolefins: Recycling possibility

Recycling of polyolefins has become a on-demand route to avoid its environmental threats. Nevertheless, drop of properties after re-extrusion necessitates use of reinforcing agents to compensate for poor mechanical properties. The incorporation of nanoparticles into plastics can boost their mechanical and rheological properties due to the hard nanocrystalline phases. This study aims to promote and identify a polyolefin-based nanocomposite by combination of TiO2 and polyhedral oligomeric silsesquioxane (POSS) at concentration of 1, 3, and 6 wt% in a twin-screw extruder. The nanocomposites were characterized for mechanical and rheological properties. Overall, the results showed that the mechanical properties were improved by adding particles up to 6 wt% loadings. The magnitude of this effect was dependent on the nanofiller weight fraction and particle size. Well-dispersion and, as a result, enhancing the viscosity, modulus, and hardness in the sample containing 3 wt% TiO2 and 3 wt%. POSS was due to the presence of hydroxyl functional groups on its surface. Glass transition temperature and crystallinity of the samples did not show a significant change due to the neutral role of nanoparticle nucleation in the matrix.

The modified CUF-EFG method for the dynamic analysis of GPLs-CNTs-reinforced FG multilayer thick cylindrical shells under shock loadings: A modified meshless implementation

The main scope of this paper is to develop the Carrera unified formulation in cylindrical coordinates for two-dimensional meshless modelling of graphene platelet and carbon nanotube reinforced functionally graded multilayer thick cylindrical shells with the same accuracy of three-dimensional modelling. The cylindrical shell is composed of several homogeneous layers with uniform distribution of both GPL and CNT contents in each layer. The effective macroscopic mechanical properties of each GPLs and CNTs reinforced layer are estimated using the modified Halpin-Tsai (H-T) micromechanical model and rule of mixture. The volume fraction of nanofillers gradually changes layer to layer by nonlinear continuous function which leads to functionally graded (FG) distribution of nanofillers. Five grading patterns of layer distribution along the thickness direction of cylindrical shell are considered to investigate the effect of layer arrangement on dynamic behavior of cylindrical shells. The FG multilayer hybrid nanocomposite cylindrical shell is assumed to be under mechanical shock loading. The numerical method for dynamic analysis of multilayer cylindrical shell is based on element free Galerkin (EFG) method with radial basis shape functions in the framework of displacement-based Carrera unified formulation (CUF). The present EFG-CUF method is compared with analytical method for isotropic homogeneous shells and results available in the literature for FG multilayer cylindrical shells. Considering the results related to various expansion orders, proved accuracy and efficiency of proposed method for dynamic analysis of thin to thick FG multilayer cylindrical shells at high expansion orders ‘n > 2’. After verifying the analytical method, the effects of several key factors such as layer distribution patterns, volume fraction index, number of layers, nanofiller weight fraction, aspect ratios of cylinder, and damping ratio on static, free vibration, time history and wave propagation of cylinder are studied in detail.

The Influence of GPL Reinforcements on the Post-Buckling Behavior of FG Porous Rings Subjected to an External Pressure

The work focuses on the post- buckling behavior of functionally graded graphene platelet (FG-GPL)-reinforced porous thick rings with open-cell internal cavities under a uniform external pressure. The generalized rule of mixture and the modified Halpin–Tsai model are here used to evaluate the effective mechanical properties of the ring. Three types of porosity patterns are assumed together with five different GPL distributions as reinforcement across the ring thickness. The theoretical formulation relies on a 2D-plane stress linear elasticity theory and Green strain field in conjunction a virtual work principle to derive the nonlinear governing equations of the post-buckling problem. Unlike the simple ring models, 2D elasticity considers the thickness stretching. The finite element model combined with an iterative Newton–Raphson algorithm is used to obtain the post-buckling path of the ring up to the collapse. A systematic investigation evaluates the effect of the weight fraction of nanofillers, the coefficient of porosity, porosity distribution, and the GPLs distribution on the deep post-buckling path of the ring. Based on the results, it is found that the buckling value and post-buckling strength increase considerably (by approximately 80%) by increasing the weight fraction of the nanofiller of about 1%.

Torsional buckling response of FG porous thick truncated conical shell panels reinforced by GPLs supporting on Winkler elastic foundation

In the present research, torsional buckling response of thick truncated conical shell panels supporting on Winkler-type elastic medium has been surveyed. The shell is constructed from a porous metal material reinforced by graphene platelets (GPLs) in which the porosity and volume weight fraction of nanofillers are graded along the thickness of shell. Three functions for porosity distribution and five patterns of GPLs are examined. To estimate the Young modulus of the shell, Tsai-Halpin micromechanical model, and for its mass density, extended rule of mixture is employed. Linear theory of 3D elasticity in conjunction with the virtual work principle and numerical graded finite element method (FEM) are applied to derive the state of equilibrium in pre-buckling mode. Torsional buckling forces are derived by applying nonlinear Green strains and by deriving geometric stiffness matrix of the system. The effect of various parameters such as coefficient of porosity, various distributions of porosity and different nanofiller patterns, weight fraction of graphene nanofillers, semi vertex angle of cone, span angle, stiffness of elastic medium and various boundary conditions on torsional buckling loads of functionally graded (FG) porous truncated conical panel reinforced by GPLs have been presented. The main purpose of this research is obtaining the best distribution of porosity and GPLs pattern and investigating the influence of adding nano particles on the torsional buckling forces of the shell. Results denote that employing GPL-X pattern in conjunction with porosity distribution 1 provides the maximum value of buckling loads. Besides by adding the nano particles, the amount of buckling loads will increase 100%.

Effect of thermal pre/post-buckling regimes on vibration and instability of graphene-reinforced composite beams

The aim of this research is to analyze the natural frequencies and instability of laminated nanocomposite beams in thermally pre/post-buckled configurations. The thick beam consists of ten composite layers, each reinforced with graphene platelets (GPLs). It is also assumed that the beam is in contact with a generalized linear/nonlinear elastic medium. Different patterns are used to simulate selected distribution profiles of material properties through the beam thickness. Reddy’s third-order shear deformation theory within the framework of the von-Kármán assumption is implemented to derive the kinematic relation. Hamilton’s principle is used to derive the equations of motion for the uniformly heated graphene-reinforced composite beam. In the absence of an external pressure load, the Duffing-type equation is obtained and solved for the nonlinear vibration problem of the beam. The analytical solutions for the vibration and stability problems of the thermally buckled beam are obtained using the perturbation-based method. This study presents new insights into the vibration and stability problems of laminated nanocomposite beams. The influence of important parameters of the nanocomposite beam such as the weight fraction of nanofillers, the distribution pattern of GPLs, slenderness ratio, temperature variation and foundation components on the nonlinear behavior of the beam is numerically presented and discussed.

Vibration Suppression Performance of FRP Spherical-Cylindrical Shells with Porous Graphene Platelet Coating in a Thermal Environment

In this study, the vibration suppression effect of a fiber reinforced polymer (FRP) spherical–cylindrical shell coated with the porous graphene platelet (PGP) in a thermal environment is investigated. The dynamic equilibrium equation is derived by combining the first-order shear deformation theory and the Rayleigh–Ritz approach, together with the virtual spring technology and the multi-segment partition technique. After the free and forced vibration responses of this FRP combined shell with PGP coating are solved. The model is validated by the convergence analysis and comparison of the present results and literature or finite element results for different shell structures with and without coating under various boundary conditions. Using the present model, the parametric study is conducted to explore the effects of porosity distribution type, dispersion pattern of volume fraction porosity, nanofiller weight fraction, and thickness ratio of PGP coating on the transient response. This study provides a useful model and some suggestions for better improving the vibration suppression capability of coated shell structures in a thermal environment.

Influence of fumed silica nanofiller and stacking sequence on interlaminar fracture behaviour of bidirectional jute-kevlar hybrid nanocomposite

The present study aims to examine the influence of nanofiller content and stacking sequence on the interlaminar fracture properties of Jute-Kevlar hybrid nanocomposite. Mode I and Mode II interlaminar fracture properties are characterized by double cantilever beam (DCB) and end notch flexure (ENF) test samples. Bidirectional jute (J) and kevlar (K) fabrics are used as reinforcement. Nanoscaled fumed silica is used as filler reinforcement. Thirteen different types of composites are prepared with varying stacking sequences (i.e., Jute-Jute-Jute-Jute [JJJJ], Jute-Kevlar-Kevlar-Jute [JKKJ], Kevlar-Jute-Jute-Kevlar [KJJK], and Kevlar-Kevlar-Kevlar-Kevlar [KKKK]) and four nanofiller weight fraction (i.e., 0%, 1.5%, 3%, and 4.5%). It is noticed that interlaminar fiber bridging and interlaminar friction are the key factors influencing Mode I and Mode II fracture toughness, respectively. The presence of nanofiller plays a significant role in enhancing the key factors influencing the fracture toughness of the composites. A noticeable improvement in Mode II fracture toughness is found. The composite stacking sequence JKKJ with 3% fumed silica (JKKJ-3) possess maximum Mode II fracture toughness (951 J/m2), which is 37% more than kevlar fiber-reinforced composite (694 J/m2) (KKKK-0). The evidence of matrix tearing as a result of fiber pull-out, toughened matrix region, and nanofiller wrapping over the fiber are noticed from the optical microscope image of the fractured surface.

Buckling analysis of embedded graphene oxide powder-reinforced nanocomposite shells

In this study, the buckling analysis of a Graphene oxide powder reinforced (GOPR) nanocomposite shell is investigated. The effective material properties of the nanocomposite are estimated through Halpin-Tsai micromechanical scheme. Three distribution types of GOPs are considered, namely uniform, X and O. Also, a first-order shear deformation shell theory is incorporated with the principle of virtual work to derive the governing differential equations of the problem. The governing equations are solved via Galerkin’s method, which is a powerful analytical method for static and dynamic problems. Comparison study is performed to verify the present formulation with those of previous data. New results for the buckling load of GOPR nanocomposite shells are presented regarding for different values of circumferential wave number. Besides, the influences of weight fraction of nanofillers, length and radius to thickness ratios and elastic foundation on the critical buckling loads of GOP-reinforced nanocomposite shells are explored.

Analysis of the effect of manufacturing imperfections in the elastic properties of platelet nanocomposites

We have developed and validated a conceptually simple model capable of predicting the macroscale elastic properties of a platelet nanocomposite. The model allows for studying the individual and combined effect of the parameters with influence on those properties, namely nanofiller weight fraction, misalignment, dispersion quality, size distribution and nanofiller-matrix interfacial characteristics. The model shows a very good correlation with experimental results. The interfacial characteristics under different strain states are evaluated at the nanoscale by means of a cohesive model which considers out-of-plane strains and angular distortions, so that the full, strain-dependent elastic tensor can be calculated, allowing for homogenization and subsequent study of the effect of filler orientation, dispersion quality and size distribution on the elastic properties at the macroscale. The use of a low complexity nanoscale model allows us to conceptually and quantitatively explain the causes underlying the divergences between the expected and experimental macroscale material stiffness experimentally found by different researchers.

Evolution of structural, electrical, and mechanical response of 3D robust network and conducting mechanically modified glass fabric-polyester composites with devisable 1D VGCNF

3D robust network unsaturated polyester-glass fabric composites modified with varying amount VGCNF are prepared through combined hand lay-up techniques followed by a filtering membrane vacuum-assisted method. The electro-thermal-mechanical behaviors of the nanocomposites are studied. Critical nanofiller weight fraction is observed at which thermal and mechanical properties showed maximum enhancement. On the other hand, no such critical nanofiller weight fraction for maximum enhancement of electrical properties. However, minimum nanofiller weight fraction is required to form critical percolation threshold at which insulating changes to conductive. The addition of nanofiller results in crystallization, graphitization and structural distortion of the composite. The enhancement in tensile and flexural strengths of 56.17% and 53.26% are obtained respectively at the critical weight fraction of 2 wt% VGCNF. Similarly, enhancement in electrical conductivity of 9 order magnitude was obtained for UP/GF nanocomposite with 3 wt% VGCNF. The microscopy studies showed the random and uniform dispersion of nanofiller in the matrix along with mechanical interlocking between matrix and reinforcement which is solely by the new methodology adopted for the preparation of nanocomposite.

Non-isothermal crystallization of ethylene-vinyl acetate copolymer containing a high weight fraction of graphene nanosheets and carbon nanotubes

The effect of the different geometrical dimensionality of two dimensional graphene nanosheets (2D GNSs) and one dimensional carbon nanotubes (1D CNTs) on the non-isothermal crystallization of an ethylene-vinyl acetate (EVA) copolymer at high loading (5 wt%) was studied. Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process. Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents, with a noticeably increased onset crystallization temperature of EVA. A high weight fraction of nano-fillers slowed the overall crystallization rate of composites. At the same crystallization temperature, the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion. Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nanofillers and polymer chains, as well as spatial restriction.

In-situ synchrotron x-ray scattering study on isothermal crystallization of ethylene-vinyl acetate copolymers containing a high weight fraction of carbon nanotubes and graphene nanosheets

The effect of two dimensional graphene nanosheets (2D GNSs) and one dimensional carbon nanotubes (1D CNTs) on the isothermal crystallization of an ethylene–vinyl acetate (EVA) copolymer at a high loading (5 wt.%) was studied by in-situ synchrotron wide-angle X-ray diffraction. The morphology observations indicated a homogeneous dispersion of GNSs and CNTs in EVA which formed a constrained environment (3D network or 2D layered structure) for ethylene–vinyl acetate EVA crystallization, respectively. The results of wide-angle X-ray diffraction showed a high weight fraction of nano-fillers slowed the crystallization rate of composites. The crystallization behavior of EVA was confined by 2D planar GNSs more seriously than 1D tubular CNTs owing to a more completed and closed layered GNS network.

Graphene Nanoribbon Composites

It is well established that pristine multiwalled carbon nanotubes offer poor structural reinforcement in epoxy-based composites. There are several reasons for this which include reduced interfacial contact area since the outermost nanotube shields the internal tubes from the matrix, poor wetting and interfacial adhesion with the heavily cross-linked epoxy chains, and intertube slip within the concentric nanotube cylinders leading to a sword-in-sheath type failure. Here we demonstrate that unzipping such multiwalled carbon nanotubes into graphene nanoribbons results in a significant improvement in load transfer effectiveness. For example, at ∼0.3% weight fraction of nanofillers, the Young's modulus of the epoxy composite with graphene nanoribbons shows ∼30% increase compared to its multiwalled carbon nanotube counterpart. Similarly the ultimate tensile strength for graphene nanoribbons at ∼0.3% weight fraction showed ∼22% improvement compared to multiwalled carbon nanotubes at the same weight fraction of nanofillers in the composite. These results demonstrate that unzipping multiwalled carbon nanotubes into graphene nanoribbons can enable their utilization as high-performance additives for mechanical properties enhancement in composites that rival the properties of singlewalled carbon nanotube composites yet at an order of magnitude lower cost.

Fracture and Fatigue in Graphene Nanocomposites

Graphene, a single-atom-thick sheet of sp-bonded carbon atoms, has generatedmuch interest due to its high specific area and novel mechanical, electrical, and thermal properties. Recent advances in the production of bulk quantities of exfoliated graphene sheets from graphite have enabled the fabrication of graphene–polymer composites. Such composites show tremendous potential for mechanical-property enhancement due to their combination of high specific surface area, strong nanofiller–matrix adhesion and the outstanding mechanical properties of the sp carbon bonding network in graphene. Graphene fillers have been successfully dispersed in poly(styrene), poly(acrylonitrile) and poly(methyl methacrylate) matrices and the responses of their Young’s modulus, ultimate tensile strength, andglass-transition temperaturehave been characterized. However, to the best of our knowledge there is no report on the fracture toughness and fatigue properties of graphene–polymer composites. Fracture toughness describes the ability of a material containing a crack to resist fracture and it is a critically important material property for design applications. Fatigue involves dynamic propagation of cracks under cyclic loading and it is one of the primary causes of catastrophic failure in structural materials. Consequently, the material’s resistance to fracture and fatigue crack propagation are of paramount importance to prevent failure. Herein we report the fracture toughness, fracture energy, and fatigue properties of an epoxy polymer reinforced with various weight fractions of functionalized graphene sheets. Remarkably, only 0.125% weight of functionalized graphene sheets was observed to increase the fracture toughness of the pristine (unfilled) epoxy by 65% and the fracture energy by 115%.Toachievecomparableenhancement,carbonnanotube (CNT) and nanoparticle epoxy composites require one to two orders of magnitude larger weight fraction of nanofillers. Under fatigue conditions, incorporation of 0.125% weight of functionalized graphene sheets drastically reduced the rate of crack propagation in the epoxy 25-fold. Fractography analysis

Enhanced Mechanical Properties of Nanocomposites at Low Graphene Content

In this study, the mechanical properties of epoxy nanocomposites with graphene platelets, single-walled carbon nanotubes, and multi-walled carbon nanotube additives were compared at a nanofiller weight fraction of 0.1 +/- 0.002%. The mechanical properties measured were the Young's modulus, ultimate tensile strength, fracture toughness, fracture energy, and the material's resistance to fatigue crack propagation. The results indicate that graphene platelets significantly out-perform carbon nanotube additives. The Young's modulus of the graphene nanocomposite was approximately 31% greater than the pristine epoxy as compared to approximately 3% increase for single-walled carbon nanotubes. The tensile strength of the baseline epoxy was enhanced by approximately 40% with graphene platelets compared to approximately 14% improvement for multi-walled carbon nanotubes. The mode I fracture toughness of the nanocomposite with graphene platelets showed approximately 53% increase over the epoxy compared to approximately 20% improvement for multi-walled carbon nanotubes. The fatigue resistance results also showed significantly different trends. While the fatigue suppression response of nanotube/epoxy composites degrades dramatically as the stress intensity factor amplitude is increased, the reverse effect is seen for graphene-based nanocomposites. The superiority of graphene platelets over carbon nanotubes in terms of mechanical properties enhancement may be related to their high specific surface area, enhanced nanofiller-matrix adhesion/interlocking arising from their wrinkled (rough) surface, as well as the two-dimensional (planar) geometry of graphene platelets.