Graphene Nanoplatelets Reinforcement Research Articles

Tribological characterization of a bearing coated with UHMWPE/GNPs nanocomposite coating

ABSTRACT Polymer nanocomposite coatings with low friction and high wear resistance are being developed to protect aluminium surfaces against wear and tear during dry and boundary lubrication. In the present study, pure and graphene nanoplatelets (GNPs) reinforced ultra-high molecular weight polyethylene (UHMWPE) nanocomposite coatings are deposited on aluminium thrust bearings. Each bearing makes an ROD contact with a metallic disc counterface to simulate the contact configuration in an actual bearing. A set of tests involving pure and reinforced UHMWPE coatings under dry and liquid contact lubrication is conducted. The wear test results reveal that UHMWPE/1 wt-% GNPs performs better than the reference sample significantly. It reduces the friction and wear of aluminium both in the dry and boundary lubrication conditions at different conditions. The 1 wt-% GNPs reinforcement increases the load-bearing capacity of UHMWPE by 440% in the presence of base oil.

Effects of surface modification and graphene nanoplatelet reinforcement on adhesive joint of aluminium alloys

In this study, the combinative effects of surface treatments and the reinforcement of graphene nanoplatelets (GNPs) on the adhesive joint of aluminium alloy were investigated. Aluminium alloy plates were treated with acetone cleaning, grit blasting, chemical etching, and phosphoric acid anodisation (PAA) under various conditions. The effects of hydrothermal sealing of the anodised aluminium were also studied. Surface energies of the treated aluminium plates were determined using contact angle measurements. The samples were then bonded with epoxy or GNPs reinforced epoxy adhesives. The bonding strength of the aluminium joints was measured by single lap shear tests. The joint strength was significantly affected by both surface treatment and the reinforcement of GNPs. For grit blasted and PAA samples with hydrothermal sealing, the joint strength increased by 64% and 57% respectively due to the addition of 0.42 wt% of GNPs. Across all surface treatments, the highest average shear strength (17.6 MPa) was achieved for PAA samples with hydrothermal sealing and the addition of GNPs followed by PAA samples with no sealing and pure epoxy (17.0 MPa). Fractal surface images were analysed, and the correlation between epoxy infiltration behaviour, surface treatments and nano-reinforcement was critically discussed.

Synthesis and characterization of Cu–Ni/Gr nanocomposite coatings by electro-co-deposition method: effect of current density

Cu–Ni alloys are widely used and implemented due to their remarkable mechanical and electrochemical properties in most of the engineering applications. The reinforcement of graphene nanoplatelets (Gr) in Cu–Ni alloy can be utilized to enhance the properties of Cu–Ni alloy. In the present work, Ni as an alloying element and graphene nanoplatelets as reinforcing element were co-deposited with Cu to prepare Cu–Ni/Gr composite coatings by electro-co-deposition method. The influence of various current densities on surface morphology, composition, microstructure, crystallite size, lattice strain, microhardness, coefficient of friction and corrosion resistance of the resulting composite coatings were investigated and were presented in detail. Based on the experimental results, the coatings prepared at $$6\hbox { A dm}^{-2}$$ , exhibit a reduced grain size with enhanced mechanical properties and corrosion resistance.

Nonlinear resonance of FG multilayer beam-type nanocomposites: Effects of graphene nanoplatelet-reinforcement and geometric imperfection

In this paper, the nonlinear dynamic response of a FG multilayer beam-type nanocomposite reinforced with graphene nanoplatelet (GNP) by considering the initial geometric imperfection is investigated on the basis of nonlocal strain gradient Euler-Bernoulli beam theory. Four patterns of GNP distribution incorporating the uniform distribution (UD) and O-, X-, and A- FG pattern distributions are taken into account and the effective elastic properties of the beam-type nanocomposite are evaluated in the framework of Halpin-Tsai scheme. The first-order vibrational mode is employed to represent the initial geometric imperfection of the nonlinear FG beam-type nanocomposite. Correspondingly, the nonlinear amplitude-frequency response of the imperfect FG multilayer beam-type nanostructures subjected to the excitation resonance is analyzed with the aid of multiple scale method. Firstly, the present model is validated with a comparison of two previous works. Then, a comprehensive investigation is conducted to evaluate the effects of GNP distributed pattern, weight fraction of GNPs, geometric imperfection amplitude, boundary condition, excitation amplitude, nonlocal and strain gradient size scale parameters on the nonlinear frequency-response of FG multilayer beam-type nanostructures. The current work is beneficial for the application of GNP as reinforcement to enhance mechanical performances of nanostructures.

Recovery Stress and Storage Modulus of Microwave-Induced Graphene-Reinforced Thermoresponsive Shape Memory Polyurethane Nanocomposites

A special class of smart material was developed using shape memory polyurethane (SMPU) elastomer and graphene nanoplatelets (GNPs) via melt-blending process using micro-compounder. The shape recovery of the developed composites was studied under microwave irradiation. The nanocomposites were developed having 0.2, 0.4, 0.6, and 0.8 phr GNPs in the SMPU matrix. The effects of GNP reinforcement on morphology, shape memory effects, and viscoelastic properties of the composites were investigated. The recovery stress of virgin SMPU increased with reinforcement and maximized on the incorporation of 0.6 phr GNPs. The deformation-induced shape memory creation process influenced significantly the recovery stress of composites as compared to virgin SMPU. The recovery stresses of SMPU at 50, 75, and 100% strain were 1.5, 1.7, and 1.9 MPa, whereas the values of GNP-SMPU composites were 3.2, 3.4, and 4.1 MPa corresponding to 0.6 phr GNP reinforcement. The value of storage modulus above the glass transition temperature of SMPU increased from 9.2 to 15.1 MPa on the addition of 0.6 phr GNPs. The peak of the damping factor, tan δ shifted toward higher temperatures with the increased GNP content. The morphological study confirms the uniform dispersion of GNPs in the SMPU matrix. The microwave-induced heating of 0.8 phr GNP composite shows 80% shape recovery in 60 s, which is faster than convectional heating.

Investigation of crystallinity, mechanical properties, fracture toughness and cell proliferation in plasma sprayed graphene nano platelets reinforced hydroxyapatite coating

Graphene nanoplatelets (GNPs) (0, 1 wt% and 2 wt%) reinforced hydroxyapatite (HA), denoted by HA, HA-1G and HA-2G respectively, coatings were fabricated on titanium substrate (Ti-6Al-4V) through atmospheric plasma spraying. The major parameters such as porosity, crystallinity, mechanical properties, toughness and cell proliferation were manipulated by varying plasma power from 15 kW to 35 kW and content of GNPs. For the coating synthesized at all plasma power, GNPs were found to be retained by Raman spectroscopy. GNPs reinforcement has led to an improvement in the crystallinity of the composite coatings as compared to HA coatings. On the contrary to it, increase in plasma power from 15 kW to 35 kW resulted in decrease in crystallinity for all three individual coating. Further, Increment in plasma power from 15 kW to 35 kW delivered a significant enhancement in hardness, elastic modulus and fracture toughness up to 81%, 149% and 282% respectively for HA-1 wt% GNPs coating, while it improved to 20%, 50% and 173% respectively on the addition of 2 wt% GNPs in HA coating fabricated at 35 kW. Enhancement in hardness, elastic modulus and fracture toughness was due to three simultaneous reasons: (1) Reduction in porosity (2) Uniform dispersion of GNPs and (3) Toughening mechanism offered by GNPs. Further, the addition of GNPs showed a remarkable improvement in the rate of cell proliferation in the HA coating. A detailed discussion over the reasons behind every results have been made profoundly.

Characterization of thick carbon/basalt hybrid fiber polyester composites with graphene nanoplatelets

Abstract The effect of the hybridization of basalt and carbon fabrics on physical and mechanical properties of the thick carbon and basalt hybrid woven composites manufactured by compression molding was investigated in this study. Monotype (all carbon and all basalt) and their hybrid woven fabric layer combinations were used to reinforce polyester resin. However, the effect of the Graphene Nanoplatelets (GNPs) reinforcement was also examined in polyester matrix by adding different volume fractions between 0.1 and 2 wt.-%. Afterward, the optimized GNPs at the ratio of 0.1 wt.-% was used in one of the hybrid composite combinations (10C10BGNP) in order to improve fiber matrix adhesion. The specimens were subjected to three different tests including tensile, flexural and impact tests as well as morphological characterization by SEM and XRD. Results showed that tensile strengths of thick carbon/basalt hybrid composites are higher than the tensile strengths of thick monotype carbon and basalt composites. The best tensile properties were achieved in 14C6BP hybrid composites while the highest flexural performance of 501 MPa and the highest impact energy of 14.32 J was achieved in 10C10BP hybrid composites with the addition of GNPs. Moreover, the ratio of the basalt fiber content increased the impact energy of hybrid composites to a level comparable to that of all basalt fiber composites.

Buckling and Frequency Responses of a Graphene Nanoplatelet Reinforced Composite Microdisk

This is the first research on the vibration and buckling analysis of a graphene nanoplatelet composite (GPLRC) microdisk in the framework of a numerical based generalized differential quadrature method (GDQM). The stresses and strains are obtained using the higher-order shear deformable theory (HOSDT). Rule of the mixture is employed to obtain varying mass density, thermal expansion, and Poisson’s ratio, while the module of elasticity is computed by modified Halpin–Tsai model. Governing equations and boundary conditions of the GPLRC microdisk are obtained by implementing Extended Hamilton’s principle. The results show that outer to inner ratios of the radius ([Formula: see text], ratios of length scale and nonlocal to thickness [Formula: see text] and [Formula: see text], and GPL weight fraction [Formula: see text] have a significant influence on the frequency and buckling characteristics of the GPLRC microdisk. Another necessary consequence is that by increasing the value of the [Formula: see text], the distribution of the displacement field extends from radial to tangent direction, especially in the lower mode numbers, this phenomenon appears much more remarkable. A useful suggestion of this research is that, for designing the GPLRC microdisk at the low value of the [Formula: see text], more attention should be paid to the [Formula: see text] and [Formula: see text], simultaneously.

In situ synthesis of high content graphene nanoplatelets reinforced Cu matrix composites with enhanced thermal conductivity and tensile strength

The difficulty of dispersing high content of graphene nanoplatelets (GNPs) in the metal matrix limits the strengthening efficiency of GNPs reinforcement. Herein, high content GNPs were synthesized on the surface of Cu powders using chemical vapor deposition with solid carbon source incorporating impregnation-reduction route, which made GNPs uniformly dispersed and improved the interfacial bonding between GNPs and Cu matrix. Then, the composites were densified by vacuum hot pressed sintering followed by multi-step hot rolling process, during which the orientation distribution of GNPs was achieved. After a rolling reduction of 70%, the composite materials containing 12 vol% GNPs were increased by 44% in yield strength (256 MPa) compared with that of pure Cu (178 MPa). Furthermore, the in-plane thermal conductivity was increased by 17% (441 W/mK) when the GNPs content is 15 vol%. This work sheds light on designing structural and functional integrated Cu matrix composites.

Role of the Hybrid Addition of Carbon Nanotubes and Graphene Nanoplatelets on the Corrosion Behavior of Plasma‐Sprayed Aluminum Oxide Nanocomposite Coating

The effect of synergistic reinforcement of two types of carbon nanofillers, carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), on the corrosion behavior of plasma‐sprayed alumina (Al2O3) nanocomposite coating in 3.5 wt% NaCl solution is studied. Incorporation of 1 wt% CNT and 0.5 wt% GNP into the Al2O3 matrix reduces the corrosion current density of the matrix from 2.78 to 0.21 μA cm−2, which drastically leads to a 13 times reduction in the corrosion rate of the Al2O3 matrix as compared with pure Al2O3 coating. The plausible reasons to this improvement are characterized by the filling of gaps, crevices, and microholes in the Al2O3 matrix by CNTs and GNPs and hydrophobic nature as well as chemical inertness of these reinforcements to the aggressive environment. Further, the corrosion products are analyzed by X‐ray diffraction and Raman spectroscopy for a much deeper insight into the mechanism of corrosion protection by these carbonaceous reinforcements. For the first time, the effect of CNT and GNP reinforcement on the corrosion behavior of plasma‐sprayed coatings is investigated.

Torsional Buckling of Functionally Graded Multilayer Graphene Nanoplatelet-Reinforced Cylindrical Shells

Exact solutions for the torsional bifurcation buckling of functionally graded (FG) multilayer graphene platelet reinforced composite (GPLRC) cylindrical shells are obtained. Five types of graphene platelets (GPLs) distributions are considered, and a slope factor is introduced to adjust the distribution profile of the GPLs. Within the framework of Donnell’s shell theory and with the aid symplectic mathematics, a set of lower-order Hamiltonian canonical equations are established and solved analytically. Consequently, the critical buckling loads and corresponding buckling mode shapes of the GPLRC shells are obtained. The effects of various factors, including the geometric parameters, boundary conditions and material properties on the torsional buckling behaviors are investigated and discussed in detail.

Friction stir processing of squeeze cast A356 with surface compacted graphene nanoplatelets (GNPs) for the synthesis of metal matrix composites

Friction stir processing (FSP) was applied to graphene nanoplatelets (GNPs) physically compacted on the surface of squeeze cast A356 alloy to incorporate GNPs within the matrix and to improve its mechanical properties. Squeeze casting resulted in finer size silicon and intermetallic compounds in cast microstructure, and subsequently FSP further refined the microstructure of squeeze cast A356 alloy, and GNP reinforced A356 alloy. The finer Si particles, intermetallics and graphene dispersed in the matrix increased the yield and ultimate tensile strength of FSP squeeze cast A356 alloy compared to the results reported in prior literature for FSP A356 alloy. Eutectic Si needles have been converted to fine spherical particles during FSP and were uniformly distributed within the nugget zone. The crystallite size of GNPs which were physically adhered to the surface of squeeze cast alloy prior to FSP decreased after FSP as a result of deformation. Thus, a combination of squeeze casting, and friction stir processing and incorporation of GNPs reinforcement in the A356 matrix is a promising route to further improve its mechanical properties.

Graphene nanoplatelets: A promising corrosion inhibitor and toughening inclusion in plasma sprayed cerium oxide coating

Present article communicates the successful fabrication of plasma sprayed graphene nanoplatelets (GNPs) reinforced ceria (CeO2) composite coating. Later, various characterizations confirm the presence of survived GNPs into CeO2 matrix and its transformation to few layered graphene during plasma spraying. The reinforcement of GNPs led a significant enhancement in corrosion resistance and mechanical performance. Addition of 5 wt% GNPs in CeO2 displayed an exceptional reduction in corrosion rate about ∼15 times in 3.5 wt% NaCl solution, while superior improvement of 50% in hardness, 98% in elastic modulus and 185% in fracture toughness during indentation has been observed. The GNPs acted as promising corrosion inhibitor and prevented infiltration of electrolytic salts (NaCl) through the coating. Apart from these, entanglement of few layer GNPs with CeO2 matrix and GNP crack bridging between two crack banks enhanced the mechanical performance of the matrix. As a whole, GNPs reinforcement owed the combined improvement in corrosion resistance as well as mechanical performance, which would make it a better option for advanced technological applications.

Fabrication of bulk aluminum-graphene nanocomposite through friction stir alloying

Friction stir alloying is primarily employed for the fabrication of surface composite to improve surface properties like hardness, wear resistance, and corrosion resistance without significantly affecting the bulk properties of the alloy. The present study demonstrates the novel method for the fabrication of bulk aluminum-graphene nanoplatelets composite by using friction stir alloying. Here, the novelty is shown through the method of graphene nanoplatelets incorporation in the stir zone. For this purpose, a channel is fabricated on the cross-sectional surface of the aluminum plate and filled with graphene nanoplatelets. It is then covered by the cross-sectional surface of another aluminum plate of same dimensions and friction stir alloying is carried out. Reference material (RM) is also fabricated at the same parameters without any graphene nanoplatelet reinforcements for the performance evaluation of the nanocomposite. The microhardness of the fabricated composite increased by ∼57% as compared to the reference material. However, the tensile strength of the fabricated Al-graphene nanoplatelet composites decreased marginally as compared to reference material. The strengthening of the composite is explained systematically by various mechanisms. The results of microhardness and tensile test were corroborated with various characterization methods such as optical micrographs, scanning electron microscopy, atomic force microscope, and X-ray diffraction.

Effect of graphene nano-platelet addition on the microstructure and spark plasma sintering kinetics of zirconium diboride

In this paper, the effect of graphene nano-platelet (GNP) addition on the microstructure and sintering kinetics of ZrB2 during spark plasma sintering (SPS) is presented. SPS was carried out at 1800 °C temperature and 50 MPa pressure. GNP addition resulted in an increase in the relative density from 84% to 97%. Retention of GNPs after SPS was confirmed through Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) in conjunction with X-ray diffraction (XRD) and Raman spectroscopy. The effect of GNP reinforcement on sintering kinetics, microstructure and mechanical properties (Vickers micro hardness and indentation fracture toughness) are discussed. The ZrB2 -GNP samples showed different activation energies at different temperature ranges which are explained based on the likely processes that are involved during sintering. Final stage of sintering exhibited lower activation energy during which the GNP aided grain boundary sliding enhancing the densification. Several toughening mechanisms such as GNP fracture, GNP shearing, GNP bending and GNP pullout were observed.

Additive Manufacturing of PLA-Based Composites Using Fused Filament Fabrication: Effect of Graphene Nanoplatelet Reinforcement on Mechanical Properties, Dimensional Accuracy and Texture.

Fused filament fabrication (FFF) is a promising additive manufacturing (AM) technology due to its ability to build thermoplastics parts with advantages in the design and optimization of models with complex geometries, great design flexibility, recyclability and low material waste. This technique has been extensively used for the manufacturing of conceptual prototypes rather than functional components due to the limited mechanical properties of pure thermoplastics parts. In order to improve the mechanical performance of 3D printed parts based on polymeric materials, reinforcements including nanoparticles, short or continuous fibers and other additives have been adopted. The addition of graphene nanoplatelets (GNPs) to plastic and polymers is currently under investigation as a promising method to improve their working conditions due to the good mechanical, electrical and thermal performance exhibited by graphene. Although research shows particularly promising improvement in thermal and electrical conductivities of graphene-based nanocomposites, the aim of this study is to evaluate the effect of graphene nanoplatelet reinforcement on the mechanical properties, dimensional accuracy and surface texture of 3D printed polylactic acid (PLA) structures manufactured by a desktop 3D printer. The effect of build orientation was also analyzed. Scanning Electron Microscope (SEM) images of failure samples were evaluated to determine the effects of process parameters on failure modes. It was observed that PLA-Graphene composite samples showed, in general terms, the best performance in terms of tensile and flexural stress, particularly in the case of upright orientation (about 1.5 and 1.7 times higher than PLA and PLA 3D850 samples, respectively). In addition, PLA-Graphene composite samples showed the highest interlaminar shear strength (about 1.2 times higher than PLA and PLA 3D850 samples). However, the addition of GNPs tended to reduce the impact strength of the PLA-Graphene composite samples (PLA and PLA 3D850 samples exhibited an impact strength about 1.2–1.3 times higher than PLA-Graphene composites). Furthermore, the addition of graphene nanoplatelets did not affect, in general terms, the dimensional accuracy of the PLA-Graphene composite specimens. In addition, PLA-Graphene composite samples showed, in overall terms, the best performance in terms of surface texture, particularly when parts were printed in flat and on-edge orientations. The promising results in the present study prove the feasibility of 3D printed PLA-graphene composites for potential use in different applications such as biomedical engineering.

Elastic buckling and vibration analysis of FG polymer composite plates embedding graphene nanoplatelet reinforcements in thermal environment

The present article proposes a comprehensive buckling and vibration analysis of functionally graded (FG) polymer composite plates reinforced with graphene platelets (GPLs). The effective material properties of the FG-GPLRC plates are accurately computed by using various ad-hoc micromechanical models. Several graphene nanoplatelets distribution patterns, within the polymer matrix, are investigated. The governing differential equations (GDEs) are derived by using Hamilton’s principle combined with the method of the power series expansion of the displacement components and the Gauss theorem. They are, then, solved in an exact sense by using the Navier-type closed-form solution. Various case-studies are addressed to show the high level of accuracy of the proposed formulation. Moreover, the effect of length-to-thickness ratio, volume fraction, aspect ratio, variable kinematics as well as GPLs distribution pattern is discussed.

Combined strengthening effect of nanocrystalline matrix and graphene nanoplatelet reinforcement on the mechanical properties of spark plasma sintered aluminum based nanocomposites

Al-0.5 wt% GNP nanocomposites with both microcrystalline and nanocrystalline matrices, were synthesized via spark plasma sintering. The strengthening effects of nanocrystalline Al matrix and GNP reinforcement have been systematically studied. Nanocrystalline Al compact (without GNPs), in comparison to microcrystalline one, exhibited 57% and 53% improvement in yield strength and ultimate tensile strength. Addition of 0.5 wt% physio-chemically functionalized GNPs in the nanocrystalline Al matrix led to further enhancement in the yield strength and ultimate tensile strength by 85% and 44%, respectively. This is attributed to the homogenous distribution of the functionalized nanometric GNPs with high elastic modulus and strength, resulting in 99% densification. The elastic moduli of the nanocomposites measured by nanoindentation matched well with the values estimated by applying micromechanics models, owing to the very good densification of the nanocomposites. Contributions from different strengthening mechanisms viz. load transfer, grain refinement, CTE mismatch and Orowan strengthening were calculated. Load transfer strengthening mechanism showed highest (73%) contribution in enhancing the strength of the nanocomposite. The mode of failure in microcrystalline Al compact was ductile and changed to mixed mode with the incorporation of GNPs. On the contrary, the Al-GNP nanocomposite with nanocrystalline matrix exhibited completely brittle mode of fracture.

Differential neural cell adhesion and neurite outgrowth on carbon nanotube and graphene reinforced polymeric scaffolds

Carbon nanomaterials, such as graphene nanoplatelets (GNPs) and multiwalled carbon nanotubes (MWCNTs) are potential candidates in a large number of biomedical applications. The present study investigates the effect of the difference in morphology of these materials on neural cell regeneration on a biodegradable scaffold. Electrical conductivities of all the hybrid scaffolds are found to be in between that of MWCNT/chitosan scaffold (highest-conductivity) and GNP/chitosan scaffold (lowest-conductivity). While, hybrid scaffolds show improvement in elastic modulus and ultimate tensile strength over MWCNT/chitosan and GNP/chitosan scaffolds. The protein adsorption isotherms of bovine serum albumin (BSA) show greater equilibrium constant (Keq) on GNP/chitosan composites as compared to MWCNT/chitosan composites, proving more potential for cell adhesion in the former. Interactions of HT-22 hippocampal neurons with MWCNT/chitosan, GNP/chitosan and various MWCNT/GNP hybrid chitosan matrices prove cytocompatibility. The neurons acquire elongated geometry on the MWCNT/chitosan scaffold, while GNP reinforcement drives the neurons to spread cellular processes radially.

Thermal conductivity of graphene nanoplatelet/cycloaliphatic epoxy composites: Multiscale modeling

Composite materials using cycloaliphatic epoxy (CE) resins are used in some structural applications that require resistance to aggressive environments. Specifically, CE-based composites are used for structural reinforcement in aluminum conductor composite core (ACCC) high-voltage power lines. However, CE resins have a relatively low thermal conductivity, which makes it difficult to dissipate localized heating due to transmission line faults. Graphene nanoplatelet (GNP) reinforcement can potentially improve the thermal conductivity of CE composites (∼0.2 W/m-K) due to its superior in-plane thermal conductivity (∼5300 W/m-K). In this study, the thermal conductivities of GNP/CE composites are investigated by multiscale modeling using molecular dynamics (MD) and micromechanics simulation techniques. Different levels of GNP dispersion and aspect ratio are studied and compared to experimental data established herein and in the literature. The thermal conductivity of GNP/CE composites increases with increased GNP content, dispersion, and aspect ratio. Additionally, covalently functionalized GNP/CE systems are simulated to determine the effect of functionalization on thermal conductivity. The transverse thermal conductivity of GNP/CF/CE hybrid composites is further investigated and validated with experimental values. This study establishes a unique multiscale modeling approach for predicting thermal conductivity of polymer nanocomposite materials (and hybrid composite materials) based on molecular structure of the nano-reinforcement/polymer interface.