Orientation Of Sheets Research Articles

Highly Oriented Graphite Aerogel Fabricated by Confined Liquid-Phase Expansion for Anisotropically Thermally Conductive Epoxy Composites.

Graphene-based thermally conductive polymer composites are of great importance for the removal of the excess heat generated by electronic devices. However, due to the orientation of graphene sheets in the polymer matrix, the through-plane thermal conductivity of polymer/graphene composites remains far from satisfactory. We here demonstrate a confined liquid-phase expansion strategy to fabricate highly oriented confined expanded graphite (CEG) aerogels. After being incorporated into epoxy resin (EP), the resulting EP/CEG composites exhibit a high through-plane thermal conductivity (4.14 ± 0.21 W m-1 K-1) at a quite low filler loading of 1.75 wt % (0.91 vol %), nearly 10 times higher than that of neat EP resin and 7.5 times higher than the in-plane thermal conductivity of the composite, indicating that the CEG aerogel has a high through-plane thermal conductivity enhancement efficiency that outperforms those of many graphite/graphene-based fillers. The facile preparation method holds great industrial application potential in fabricating anisotropic thermally conductive polymer composites.

Dynamic response and failure of carbon/epoxy composite sandwich subjected to underwater impulsive loading

In this work, the dynamic response and failure modes of carbon/epoxy sandwich structures with PVC foam cores subjected to underwater impulsive loading are experimentally investigated. The 3D digital image correlation technique with high speed photography is used to capture the dynamic response of the structures. The effects of loading intensity, core density, fluid-structure interaction and ply orientation of face sheets on the deformation and damage of the clamped sandwich structures are assessed. The results showed that the compression of PVC foam can effectively reduce the deformation and damage of the sandwich structures. The maximum deflection of rear face sheets increases with PVC core density increasing. The total deflection of sandwich plates including front sheets, cores and rear sheets increases with the decreasing of core density and fluid-structure interaction parameters. Additionally, the influence of ply orientation of carbon/epoxy face sheets on the blast resistance of the sandwich structures can be ignored in the range of normalized impulse intensity (0.08-0.29) used in the tests. With the loading intensity increasing, the failure modes of the sandwich plates present permanent deflection, fiber breakage at boundary and matrix crack of carbon/epoxy at front face-sheets, core compression and debonding between cores and face sheets including front and rear sheets. The results obtained from those tests can provide valuable reference to design the lightweight protective structures.

The response of pin-clamped carbon fibre-reinforced plastics composite sandwich beams with polyvinylchloride foam core under bending impact

The dynamic response of pin-clamped composite sandwich beam in terms of face-sheet effect with polyvinylchloride foam core subjected to bending impact loading was investigated in this paper. Composite sandwich beams with three different unidirectional skin layups of [0]4, [45]4 and [90]4 and two types of face-sheet thickness of 1 ([0]4) and 2 ([0]8) mm were fabricated. An explicit code, VUMAT, is written and implemented in ABAQUS/Explicit. The micro-computerised tomography scanning was used to detect adhesive layer failure. The ply angle orientation of face sheets plays an important role in the failure mechanism of the sandwich beam under bending loads. Although it is known that the fibre angle in the direction perpendicular to the bending direction is more stiff and strength, damage tolerances under bending impact loads of beams with other fibre angles were determined. In addition, as the number of layers increased, failure mechanism and load-carrying capacity of composite face sheets changed completely for increasing bending stiffness. This research provides fundamental information about the change of the failure mechanisms as the fibre angle and thickness of the face sheet were changed and in terms of interpretation with the help of finite elements using different failure criteria.

STRENGTHENING AND REPAIRING OF RC DEEP BEAMS USING CFRP AND GFRP

There are many reasons to upgrade an existing structure such as building code changes, accidents, design errors or building use changes. Few years ago the construction industry began using fibre reinforced polymer (FRP) for structural reinforcement, typically in combination with other building materials such as wood, steel and concrete. FRP show multiple attractive properties, such as low weight to strength ratio, non-corrosiveness high fatigue strength, and case of application. This study investigated different techniques to improve the performance of RC deep beams under two concentrated vertical loads using advanced composite materials (CFRP and GFRP sheets). The primary aim of this research was to study the behaviour of deep beams strengthened and repaired in shear using carbon and glass fibres.Thirteen RC deep beam specimens were simply supported with span lengths L=1500 mm and cross sections 140 x 450 mm. The tested beams were subjected to the effects of two concentrated loads with spacing of 560, 360 and 160 mm and were divided into five groups. The test results show that the deep beams strengthened by CFRP sheets & GFRP sheets provided improvement in ultimate loads. The maximum increase in ultimate loads reached 106% & 81% respectively and the decrease in deflection for beams was attributed to the type, configurations and orientation of the FRP sheets. An analytical model was done based on code equations to predict the deformational behaviour of RC deep beams shear-strengthened with FRP composites , and obtain the failure loads by using three codes equations and compare the results with the experimental results. The proposed analytical model gave good compliance with the experimental results.

Optimum Configuration of CFRP Composites for Strengthening of Reinforced Concrete Beams Considering the Contact Constraint

In this paper, finite element analysis (FEA) was conducted using ABAQUS to simulate and evaluate the response of reinforced concrete beams strengthened with different configurations of CFRP composites. The investigated parameters include: the number of layers of CFRP sheets, compressive strength of concrete, and orientation of CFRP sheets. The beams were 1500 mm long with cross-section dimensions of 100 x 200 mm, loaded as simply supported beams under three-point loading configuration. Concrete damaged plasticity model was chosen and the models were calibrated and validated properly. The nature of the contact between the CFRP composites and concrete was carefully evaluated in order to arrive at the optimum contact definition. The results showed that the performance of the beam was noticeably improved using up to three CFRP layers; any number of CFRP layers above three were ineffective. This indicates that it is important to optimize the number of sheets in a CFRP composite based on the beam dimensions and reinforcement to minimize the cost and avoid adversely affecting the ductility of the strengthened beam. Regarding the influence of compressive strength, the enhancement in the performance of the CFRP strengthened beams was pronounced when increasing the strength, however it was not significant. The use of U-shaped layout of CFRP composites was the most effective configuration. Finally, the use of shell to solid coupling contact constraint shows the least error while allowing relative movement between beam surface and CFRP composites.

Influence of oxyfluorinated graphite on fluorinated ethylene–propylene composites as bipolar plates

Numerous studies have reported that good adhesion and fluorination of carbon materials in a fluoropolymer matrix enhance their electrical and mechanical properties. However, a composite reinforced with oxyfluorinated graphite has not been reported for improving mechanical properties. This paper discusses the fabrication of conductive fluorinated ethylene–propylene (FEP)/oxyfluorinated graphite (f-graphite) composite bipolar plates (BPs) via compression molding. To investigate the effects of fluorinating graphite, graphite with a large particle size of 500 μm was mixed with FEP powder with a small particle size of 8 μm through ball milling. The FEP/graphite composites exhibited high anisotropic electrical conductivity with the in-plane conductivity much higher than the through-plane conductivity because of the planar orientation of the graphite sheets. Therefore, the mechanical properties of the composites such as flexural strength tended to deteriorate with increasing graphite content. In particular, the FEP/f-graphite composites exhibited excellent flexural strength of 12 MPa, much higher than that of FEP/graphite composites at 9 MPa with a graphite content of 80 wt%. The interfacial interaction between FEP and f-graphite led to improved physical compatibilization, which contributed to enhance the mechanical properties of these composites. Our results are a step toward developing BPs for use in high-temperature fuel cells and heat-sink components. Graphic abstract

Highly electrically and thermally conductive silicon carbide-graphene composites with yttria and scandia additives

Dense silicon carbide/graphene nanoplatelets (GNPs) and silicon carbide/graphene oxide (GO) composites with 1 vol.% equimolar Y2O3–Sc2O3 sintering additives were sintered at 2000 °C in nitrogen atmosphere by rapid hot-pressing technique. The sintered composites were further annealed in gas pressure sintering (GPS) furnace at 1800 °C for 6 h in overpressure of nitrogen (3 MPa). The effects of types and amount of graphene, orientation of graphene sheets, as well as the influence of annealing on microstructure and functional properties of prepared composites were investigated. SiC-graphene composite materials exhibit anisotropic electrical as well as thermal conductivity due to the alignment of graphene platelets as a consequence of applied high uniaxial pressure (50 MPa) during sintering. The electrical conductivity of annealed sample with 10 wt.% of GNPs oriented parallel to the measuring direction increased significantly up to 118 S·cm−1. Similarly, the thermal conductivity of composites was very sensitive to the orientation of GNPs. In direction perpendicular to the GNPs the thermal conductivity decreased with increasing amount of graphene from 180 W·m−1 K−1 to 70 W·m−1 K−1, mainly due to the scattering of phonons on the graphene – SiC interface. In parallel direction to GNPs the thermal conductivity varied from 130 W·m−1 K−1 up to 238 W·m−1 K−1 for composites with 1 wt.% of GO and 5 wt.% of GNPs after annealing. In this case both the microstructure and composition of SiC matrix and the good thermal conductivity of GNPs improved the thermal conductivity of composites.

Assembling reduced graphene oxide hydrogel with controlled porous structures using cationic and anionic surfactants

The roles of cationic and anionic surfactants in assembling reduced graphene oxide hydrogels (RGOHs) and controlling their porous structures are studied in this work. The mechanisms of the surfactant effects were studied by x-ray diffraction, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and electrochemical methods. The morphology and structure of graphene oxide and RGOH were examined by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The experimental results showed that surfactants could modify the structure of as-prepared RGOH but did not change the chemical or physical properties of the reduced graphene oxide (RGO) sheets. The modification was achieved by changing the orientation of graphene oxide sheets in aqueous solutions. It was also found that RGOH could not be prepared in the presence of high dosages of cationic surfactant because the RGO sheets were stacked piecewise with just one orientation and could not be cross-linked at any angle. The presence of an anionic surfactant did not affect the formation of RGOH but only enlarged the pores in its cross-linking structure. In addition, RGOHs prepared with anionic surfactants were found to have a higher specific capacitance compared to RGOHs prepared with cationic surfactants.

Assessment of dynamic properties of hybrid ribbon reinforced multifunctional composite sandwich plates: Numerical and experimental investigation

Abstract This study investigates numerically and experimentally the effect of longitudinal ribbon reinforcement in conventional honeycomb structure on the various dynamic characteristics of a hybrid composite sandwich plate. Longitudinal strips are considered to be embedded along the transverse directions at various locations of a honeycomb core material without and with carbon nanotubes (CNT) reinforcement in a composite sandwich plate. The governing differential equations of motion of the various hybrid honeycomb composite sandwich plate configurations with strips inserted in conventional honeycomb structures as core layer having top and bottom face composite layers are derived using higher order shear deformation theory (HSDT) and solved numerically using a four noded rectangular finite element. Further, experimental investigations are performed by fabricating the various strips embedded hybrid honeycomb core material with and without CNT reinforcement to evaluate the shear and loss moduli using the alternative dynamic approach. The efficacy of the developed finite element formulation is demonstrated by comparing the experimental and numerical results obtained in terms of natural frequencies and loss factors for the various prototypes of honeycomb composite sandwich plates. Also, the effect of variation in CNT content and thickness of longitudinal ribbon reinforcement in conventional honeycomb core material and ply orientation of the face sheets on the various dynamic properties of hybrid composite structures are studied under various end conditions. This study proposes that the ribbon reinforcement location and the addition of CNTs in honeycomb core materials strongly influence the stiffness, damping and transverse vibration displacements of the ribbon reinforced hybrid composite sandwich plates.

Confinement effects on the orientation of graphene in multilayer polymer nanocomposites during lamination: A molecular dynamics simulation

As a stacking form of ultrathin polymer films, multilayer nanostructures are of great interest in various applications. Coarse-grained molecular dynamics simulations were carried out to understand the confinement effects on the orientation of graphene sheets in multilayer polymer films during lamination. The influences of position, strain rate, expansion type, and arrangement pattern on the orientation of graphene sheets in the near-boundary and internal layers were considered. It was found that the confinement effects induce the graphene sheets to gradually orient parallel to the plane of the layer during lamination. Such effects are more obvious in the near-boundary layer than in the internal layer. With the same strain, a smaller strain rate gives rise to more obvious effects on the in-plane orientation of graphene sheets in both the near-boundary and internal layers. Biaxial expansion also makes the graphene sheets orient more parallel to the plane of the layer. This work is helpful for better understanding the lamination process and the designing of multilayer nanocomposites.

Construction of Dual Orientation Crystalline Structure in Poly(vinyl alcohol)/Graphene Oxide Nano-Composite Hydrogels and Reinforcing Mechanism

Oriented poly(vinyl alcohol) (PVA)/graphene oxide (GO) nanocomposite hydrogels with different draw ratios were prepared by stretching during a freezing/thawing process. The PVA/GO samples with a draw ratio of 200% had significantly enhanced mechanical properties by formation of a microfibrillar structure, while the tensile strength and compressive modulus respectively reached as high as 11.60 and 4.05 MPa, outperforming the unoriented samples with an increase of 167% and 540%, respectively. During the freezing/thawing process under stress, the orientation factor, crystallinity, and cross-linking density (υe) of PVA/GO samples increased steadily, while the regularly arranged fibrillar bundle structure increasingly formed, and the size of the porous structure decreased. Besides that, additional PVA crystals formed with decreasing long period (L), crystalline region (Lc), and lamellae size (Llateral). Due to the synergic orientation of GO sheets and nucleation effect, the oriented PVA/GO samples showed an or...

Core‐Shell Nanoparticle Probe Scintillation Proximity Assays for Biological Samples

To achieve the overall goal of sensitive and selective radioisotope detection in aqueous samples, we have developed a novel polystyrene‐core silica‐shell nanoparticle scintillator platform (nanoSPA). nanoSPA enabled separation‐free quantification of radiolabeled analytes in complex samples as demonstrated by scintillation proximity assays via protein‐tag, biotin, and antibody binding as well as by other methods such as chemical crosslinking and adsorption.β‐particle emitting radionuclides such as 3H, 33P, and 35S are useful molecular labels due to their small size but are challenging to detect and quantify with spatial and temporal resolution in biological samples due to their low energies (Emax ≤ 300 keV) and short penetration depths (≤ 0.6 mm). Activity measurements for these β‐emitters are usually made in milliliter volumes of liquid scintillation cocktail (LSC), a mixture of energy‐absorbing organic solvents, surfactants, and scintillant fluorophores, which is incompatible with living cells and dynamic biological measurements. Alternatively, solid polymer or inorganic crystals can be used, but the orientation of polymer sheets, the large size of polymer particles (> 2μm) and the high density of inorganic scintillators can result in inaccurate counting. nanoSPA avoids the toxicity of LSC as well as many of the limitations of polymer and inorganic crystal scintillators. The polystyrene acts as an absorber for energy from emitted β‐particles and is loaded with scintillant fluorophores to which the energy is transferred, leading to photon emission at visible wavelengths. The silica shell serves as a hydrophilic shield for the polystyrene core and facilitates functionalization with specific binding molecules for scintillation proximity assays. In this way, the short penetration depths of low‐energy β‐particles are used advantageously, as radiolabeled analytes that are not close enough to the nanoparticle surface (primarily bound to the surface during an assay) are less likely to be detected, resulting in low background signal. Selectivity was determined to be up to 30 times greater for bound 3H‐analytes over unbound 3H analytes when the labeled species was covalently bound to nanoSPA, 18 times greater for antibody functionalized nanoSPA, 8 times greater for biotin functionalized nanoSPA, and 4 times greater for ssDNA functionalized nanoSPA. We have also measured and monitored peptide phosphorylation with kinase and 33P ɣ ‐ ATP. nanoSPA not only facilitates measurement of radiolabeled analytes in bulk aqueous solutions, but due to the small diameter and the protection of the hydrophobic polymer core by the silica shell, nanoSPA particles could potentially be used as cellular or intracellular imaging probes.Support or Funding InformationThis work was supported in part by the National Science Foundation under grant number 1807343, the National Institutes of Health via the National Institute of Biomedical Imaging and Bioengineering under grant number R21EB019133 and the National Institute of General Medical Sciences under grant number 1R01GM116946.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Alternative stacking sequences in hexagonal boron nitride

The relative orientation of successive sheets, i.e. the stacking sequence, in layered 2D materials is central to the electronic, thermal, and mechanical properties of the material. Often different stacking sequences have comparable cohesive energy, leading to alternative stable crystal structures. Here we theoretically and experimentally explore different stacking sequences in the van der Waals bonded material hexagonal boron nitride (h-BN). We examine the total energy, electronic bandgap, and dielectric response tensor for five distinct high symmetry stacking sequences for both bulk and bilayer forms of h-BN. Two sequences, the generally assumed AA′ sequence and the relatively unknown (for h-BN) AB (Bernal) sequence, are predicted to have comparably low energy. We present a scalable modified chemical vapor deposition method that produces large flakes of virtually pure AB stacked h-BN; this new material complements the generally available AA′ stacked h-BN.

Porosity distribution in laser-sintered polymeric thin sheets as revealed by X-ray micro tomography

Laser Sintering (LS) is an additive manufacturing technology that is progressively used to manufacture functional products for end-use applications. However, LS technology provides limited ability to produce thin-walled structures that feature high material quality. A key parameter determining the quality of LS polymeric parts is porosity. This article presents a new approach towards clarifying the porosity characteristics of thin-walled structures produced by LS. Therefore, thin sheets of different thickness built in different orientations within the building chamber are examined by means of X-ray micro tomography. The porosity analysis includes the overall porosity, pore number density, pore size distribution and porosity distribution along the thickness of the thin sheets. The results show that the porosity characteristics strongly depend on the thickness and the build orientation of the thin sheets. This investigation helps to estimate the quality of three dimensional hollow bodies produced by LS and moreover, contributes to a better understanding of the pore formation in LS processes.

Effect of Heat Treatment Under High Magnetic Field on Crystallographic Orientation and Magnetic Properties of Non-Oriented Electrical Steel Sheets

With the objective of improving and controlling the magnetic properties of non-oriented electrical steel sheets, the effects of an external dc magnetic field applied during heat treatment were studied. In this paper, we report on the effects of the direction of the magnetic field applied during heat treatment by comparing the magnetic properties of the samples. The heat treatment temperature was controlled to be 1123 and 1273 K. During heat treatment, the magnetic field was applied parallel to the rolling direction or rolling transverse direction of sheet samples, and the magnetic field strength was 10 T. The magnetic properties of a sample heat-treated under the magnetic field vary with the direction of the materials because of their magnetic anisotropy. The magnetic anisotropy could be reduced by controlling the magnetic characteristics by applying an external magnetic field during cooling. To conduct a crystallographic study, the evaluation of crystal orientation was carried out using electron backscatter diffraction (EBSD). Crystal orientation distribution could be analyzed by the crystal analysis of the sample heat-treated in a magnetic field using EBSD.

Effect of Surface Textures of Iron Substrate on the Crystal Orientation Relationship between Electrodeposited Zinc and Iron

To investigate the effect of iron texture on the crystal orientation relationship between iron and zinc, Zn deposition was performed galvanostatically at 1500 A/m2 at a charge density of 1.48 × 104 C/m2 onto high-purity electrolytic iron and cold rolled steel sheets in an agitated sulfate solution at 40°C. Fe with a large grain size showed an orientation relationship of {110}Fe//{0001}Zn. However, when the angle of inclination between the {110}Fe plane and the surface of electrolytic Fe was increased, the deviation in the orientation relationship {110}Fe//{0001}Zn increased. This result suggests that the orientation relationship of {110}Fe//{0001}Zn is difficult to maintain during the deposition when the inclination angle of the {110}Fe plane from the surface of electrolytic Fe increases. As a result, the epitaxial growth of Zn changes to random growth. Zn deposited on cold rolled steel sheets with a small grain size showed an orientation of {0001}, regardless of the orientation of Fe. This indicates that the orientation of the deposited Zn is more affected by the overpotential for deposition than by the orientation of steel sheets at the initial stage of deposition. Although strain was introduced into the high-purity electrolytic Fe with sandblasting, the orientation relationship of {110}Fe//{0001}Zn did not change remarkably, showing that the strain of Fe substrate has little effect on the orientation relationship between Fe and deposited Zn.

Enhanced through‐plane thermal conductivity of polyamide 6 composites with vertical alignment of boron nitride achieved by fused deposition modeling

Thermally conductive composites consisting of polymer/boron nitride (BN) fabricated by conventional molding method can hardly achieve high through‐plane thermal conductivities (TPTCs) because the alignment of BN sheets would orient along the direction of melt flow. Based on the characteristics of fused deposition modeling (FDM), we design three printing methods to research on the orientation of BN sheets. In this article, enhanced TPTC samples of PA6/BN composites with vertical alignment of BN are achieved by FDM, and the maximum of TPTC of samples is 2.03 W·m−1·K−1. Suitable design can reduce the negative effects of voids produced during the deposition of filaments. It's proved that FDM is an effective method to fabricate high TPTC products using less fillers by reasonable design. POLYM. COMPOS., 40:3375–3382, 2019. © 2019 Society of Plastics Engineers

Effect of starch reduced graphene oxide on thermal and mechanical properties of phenol formaldehyde resin nanocomposites

Phenol formaldehyde (PF) resins are one of the oldest synthesized and very widely used resins. Their properties can be improved with the incorporation nano-fillers even with lower loadings. Graphene materials have attracted significant attention in recent years owing to its exceptional thermal, mechanical and electrical properties. Herein, we report a very simple and effective way to reduce graphene oxide (GO) by using highly abundant potato starch instead of conventionally used toxic and hazardous reducing agents like hydrazine. The reduced GO (RGO) is then effectively incorporated into PF resin by optimizing various processing parameters. The reinforcing effect of RGO sheets on the PF matrix was investigated by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The effect of RGO on thermal properties of the polymer nanocomposites was studied using Thermogravimetric Analysis (TGA). The mechanical properties of PF/RGO composites were studied by tensile and Izod impact tests. The fracture mechanism of the composites was investigated by Scanning Electron Microscopy. Theoretical prediction of the mechanical properties of the nanocomposites using Halpin-Tsai models gave sufficient information regarding the orientation of graphene sheets in PF matrix.

Rheo-optical Analysis of Functionalized Graphene Suspensions.

Wet processing of graphene sheets is a potentially interesting route for the economically viable creation of graphene-based composites. In the present work, flow dichroism and small-angle light scattering are used to investigate the dispersion of functionalized graphene sheets in a suspension and their response to shear flow. In line with expectations from scaling theory at rest, the functionalized graphene sheets are present as Brownian flat sheets, and there is no evidence of significant crumpling. More surprisingly, we find that the rate-dependent orientation of these molecularly thin sheets can be described by numerical predictions for hard spheroidal sheets, making quantitative predictions of the flow-induced orientation possible. Further comparison of the flow-induced orientation of thick gold decahedra with the thin graphene sheets shows that, except for effects of polydispersity, the flow-induced orientation is predicted well quantitatively. Adequate prediction of the effects of flow on the orientation of graphene sheets makes it possible to design wet processed graphene-based composite materials.

The Influence of Molecular Weight on the Orientation and Properties of Polymethyl Methacrylate Sheets

The influence of molecular weight on the process of orientation stretching and the combination of physicomechanical characteristics of specimens of polymethyl methacrylate (PMMA) is examined. Orientation stretching and increase in the molecular weight of PMMA from 0.52 to 4.6 × 106 g/mol lead to a considerable increase in strength and elastic modulus (σt by a factor of 2.6, E by a factor of 2.5). It is established that the deformation characteristics of oriented PMMA specimens increase by a factor of 10 when the molecular weight is increased from 0.52 to 4.6 × 106 g/mol, which opens up new possibilities in the processing of sheets and films of PMMA.