Na0.44MnO2 nanorods have been prepared by a hydrothermal method.The experimental parameters have been systematically investigated and optimized.The results show that Na0.44MnO2 nanorods obtained via the hydrothermal t...Na0.44MnO2 nanorods have been prepared by a hydrothermal method.The experimental parameters have been systematically investigated and optimized.The results show that Na0.44MnO2 nanorods obtained via the hydrothermal treatment at 200℃for 16 h show the best electrochemical properties,which deliver the high initial discharge capacity of 110.7 mA·h/g at 50 mA/g in potential window 2.0-4.0 V.To further improve their electrochemical properties,a ball milling process with graphene has been carried out to obtain Na0.44MnO2/graphene composite.The initial discharge capacity of Na0.44MnO2/graphene composite is 106.9 mA·h/g at a current density of 50 mA/g.After 100 cycles,the residual discharge capacity is 91.8 mA·h/g and the capacity retention rate is 85.9%,which is much higher than that of pristine Na0.44MnO2 nanorods(74.7%)at the same condition.What is more,when the current density reaches 500 and 1000 mA/g,the corresponding discharge capacities of Na0.44MnO2/graphene composite are about 89 and 78 mA·h/g,respectively,indicating outstanding rate capability.展开更多
Taking the nano-sized carbon black and aniline monomer as precursor and （NH4）2S2O6 as oxidant, the well coated C/polyaniline（C/PANI） composite materials were prepared by in situ polymerization of the aniline on th...Taking the nano-sized carbon black and aniline monomer as precursor and （NH4）2S2O6 as oxidant, the well coated C/polyaniline（C/PANI） composite materials were prepared by in situ polymerization of the aniline on the surface of well-dispersed nano-sized carbon black for supercapacitor. The micro-structure of the C/PANI composite electrode materials were analyzed by SEM. The electrochemical properties of C/ PANI and PANI composite electrode were characterized by means of the galvanostatic charge-discharge experiment, cyclic voltammetric measurement and impedance spectroscopy analysis. The results show that by adding the nano-sized carbon black in the process of chemical polymerization of the aniline, the polyaniline can be in situ polymerized and well-coated onto the carbon black particles, which may effectively improve the aggregation of particles and the electrolyte penetration. What’s more , the maximum of specific capacitance of C/PANI electrode 437.6F·g -1 can be attained. Compared with PANI electrode, C/PANI electrode shows more desired capacitance characteristics, smaller internal resistance and better cycle performance.展开更多
A motor-driven linkage system with links fabricated from 3-dimensional braided composite materials was studied. A group of coupling dynamic equations of the system, including composite materials parameters, electromag...A motor-driven linkage system with links fabricated from 3-dimensional braided composite materials was studied. A group of coupling dynamic equations of the system, including composite materials parameters, electromagnetism parameters of the motor and structural parameters of the link mechanism, were established by finite element method. Based on the air-gap field of non-uniform airspace of three-phase alternating current motor caused by the vibration eccentricity of rotor, the relation of electromechanical coupling at the actual running state was analyzed. And the motor element, which defines the transverse vibration and torsional vibration of the motor as its nodal displacement, was established. Then, based on the damping element model and the expression of energy dissipation of the 3-dimentional braided composite materials, the damping matrix of the system was established by calculating each order modal damping of the mechanism.展开更多
Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of...Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of TiB2/C composite cathode material were investigated. The results show that thermogravimetrie behavior of pitch and TiB2/C green composite cathode is similar, and appears the largest mass loss rate in the temperature range from 200 to 600 ℃. The bulk density variation of sample K5 before and after baking is the largest （11.9%）, that of sample K25 is the second, and that of sample M5 is the smallest （6.7%）. The crushing strength of sample M5 is the biggest （51.2 MPa）, that of sample K2.5 is the next, and that of sample K5 is the smallest （32.8 MPa）. But, the orders of the electrical resistivity and electrolysis expansion of samples are just opposite with the order of crushing strength. The heating rate has a great impact on the microstructure of sample. The faster the heating rate is, the bigger the pore size and porosity of sample are. Compared with the heating rate between 200 and 600℃ of samples K25 and K5, that of sample M5 is slower and suitable for baking process of TiB2/C composite cathode material.展开更多
Composite materials exhibit the impressive mechanical properties of high damping and stiffness,which cannot be attained by employing conventional single materials.Along these lines,a novel material architecture is pre...Composite materials exhibit the impressive mechanical properties of high damping and stiffness,which cannot be attained by employing conventional single materials.Along these lines,a novel material architecture is presented in this work in order to fabricate composites with enhanced mechanical characteristics.More specifically,entangled metallic wire materials were used as the active matrix,whereas polyurethane was employed as the reinforcement elements.As a result,an entangled metallic wire material-polyurethane composite with high damping and stiffness was prepared by enforcing the vacuum infiltration method.On top of that,the mechanical properties(loss factor,energy consumption,and average stiffness)of the proposed composite materials were characterized by performing dynamic tests,and its fatigue characteristics were verified by the micro-interface bonding,as well as the macro-damage factor.The impact of the density,preloading spacing,loading amplitude,and exciting frequency on the mechanical properties of the composites were also thoroughly analyzed.The extracted results indicate that the mechanical properties of the composites were significantly enhanced than those of the pure materials due to the introduction of interface friction.Moreover,the average stiffness of the composites was about 10 times the respective value of the entangled metallic wire material.Interestingly,a rise in the loading period leads to some failure between the composite interfaces,which reduces the stiffness property but enhances the damping dissipation properties.Finally,a comprehensive dynamic mechanical model of the composites was established,while it was experimentally verified.The proposed composites possess higher damping features,i.e.,stiffness characteristics,and maintain better fatigue characteristics,which can broaden the application range of the composites.In addition,we provide a theoretical and experimental framework for the research and applications in the field of metal matrix composites.展开更多
Understanding the dynamic response of composite material cartridges during the firing process is of great significance for improving their reliability and safety.A theoretical model describing the dynamic response of ...Understanding the dynamic response of composite material cartridges during the firing process is of great significance for improving their reliability and safety.A theoretical model describing the dynamic response of composite material cartridges is established based on the thick-walled cylinder theory and rate-dependent constitutive model of composite materials.The correctness of the theoretical model is validated through finite element simulations of cartridge deformation.The influence of chamber pressure and cartridge wall thickness on the cartridge's deformation process and stress distribution is analyzed.The results indicate that the primary deformation of composite material cartridges inside the chamber is elastic deformation.Compared to metal cartridges,composite material cartridges require higher pressure for touching-chamber and are more prone to developing gaps after unloading to ensure smooth extraction.During the deformation process,the touching-chamber behavior of the cartridge can improve the stress distribution.Under the same chamber pressure,the touching-chamber behavior can reduce the circumferential stress by approximately 30%.The inner wall surface of the cartridge is a critical area that requires attention.The touching-chamber behavior can be facilitated by appropriately reducing the cartridge wall thickness while ensuring overall strength.This study can provide guidance for the optimization design of composite material cartridges.展开更多
Cs_(x)WO_(3)/TiO_(2) composites with full-spectrum catalytic activity were prepared by solvothermal reaction.The composites were characterized using X-ray diffraction(XRD)analysis,scanning electron microscopy(SEM),tra...Cs_(x)WO_(3)/TiO_(2) composites with full-spectrum catalytic activity were prepared by solvothermal reaction.The composites were characterized using X-ray diffraction(XRD)analysis,scanning electron microscopy(SEM),transmission electron microscopy(TEM),specific surface area testing,X-ray photoelectron spectroscopy(XPS),and UV-Vis diffuse reflectance spectra(UV-Vis DRS).Cs_(x)WO_(3) and TiO_(2) were uniformly bonded together in the compos-ites.The heterojunction structure was formed.The band gap was reduced from 2.75 to 2.65 eV.The photocatalytic property of Cs_(x)WO_(3)/TiO_(2)was demonstrated by the degradation rates of 20 mg·L^(-1) methylene blue dye,which were 99.7%,91.4%,and 70.7%under irradiation from a 300 W high-pressure mercury lamp,a 500 W xenon lamp,and a 400 W infrared lamp,respectively.After five cycles of photocatalytic degradation,the composite photocatalyst still showed a degradation efficiency of 87.6%.This indicates that Cs_(x)WO_(3)/TiO_(2) has good photocatalytic degradability and cyclic stability.The photocatalytic mechanism of Cs_(x)WO_(3)/TiO_(2)was investigated.The trapping experiments of the active species showed that the main active substances were the empty hole(h+)and hydroxyl radical(·OH).展开更多
The Al 2O 3 particles reinforced aluminum matrix composite (Al 2O 3p/Al) are more and more widely used for their excellent physical and chemical properties. However, their poor machinability leads to severe tool wear ...The Al 2O 3 particles reinforced aluminum matrix composite (Al 2O 3p/Al) are more and more widely used for their excellent physical and chemical properties. However, their poor machinability leads to severe tool wear and bad machined surface. In this paper laser assisted machining is adopted in machining Al 2O 3p/Al composite and good result was obtained. The result of experiment shows in machining Al 2O 3p/Al composites the cutting force is reduced in 30%～50%, the tool wear is reduced in 20%～30% and machined surface quality is improved in laser assisted machining as compared with conventional cutting. The physical model of the cutting process is set up and explains the reason why the cutting forced are reduced. The state of the particles is the main influence of the change. When the material of cutting zone is heating by laser, the aluminum matrix becomes softer and easier in plastic deformation, which leads to the reduction of the pushing force from the tool to the machined surface. The soften aluminum matrix is more easy to be squeezed out from the machined surface, and it leads the concentration of the Al 2O 3 particles in the surface layer of machined surface. The softening effect of laser heating on aluminum matrix reduces the pushing forces of the Al 2O 3 particles on the clearance face of cutting tool, which is just the reason for the severe cutting tool wear in conventional machining of Al 2O 3p/Al composite. Because the Al 2O 3 particles were pushed in during the cutting process, the particles increased in the surface layer. Because of the difference in thermal conductivity and thermal expansion between the Al-matrix and Al 2O 3 particle, residual stress is changed in the matrix after machining due to the extrusion of the tool, deformation of the matrix and displacement of the Al 2O 3 particle in the matrix. Temperature gradient comes into the cutting zone and the work-piece surface layer, it will lead to the increase of thermal stress and misfit dislocation in the matrix. The residual stress is compressive in the laser assisted hot cutting surface, the compressive stress is nearly triple times than that in the conventional cutting surface. Some analysis on the mechanism of laser heat assisted machining of Al 2O 3p/Al composite is given in the paper too.展开更多
The electrical resistivity of TiB2/C cathode composite coating at different temperatures was measured with the electrical conductivity test device; the effects of TiB2 content and kinds of carbonaceous fillers as well...The electrical resistivity of TiB2/C cathode composite coating at different temperatures was measured with the electrical conductivity test device; the effects of TiB2 content and kinds of carbonaceous fillers as well as their mean particle size on their electrical resistivities were investigated. The results show that electrical resistivity of the coating decreases with the increase of TiB2 content and the decrease of its mean particle size. When the mass fraction of TiB2 increases from 30% to 60%, the electrical resistivity of the coating at room temperature decreases from 31.2μΩ·m to 23.8μΩ·m. The electrical resistivity of the coating at 960℃ lowers from 76.1μΩ· m to 38.4μΩ·m with the decrease of TiB2 mean particle size from 12μm to 1μm. The kinds of carbonaceous fillers have great influence on the electrical resistivity of TiB2/C composite coating at 960℃, when the graphite, petroleum coke and anthracite are used as fillers, the electrical resistivities of the coating are 20.3μΩ·m, 53.7μΩ·m and 87.2μΩ·m, respectively. For the coating with petroleum coke filler, its electrical resistivity decreases with the increase of the mean particle size of petroleum coke filler. The electrical resistivity at 960℃ decreases from 56.2μΩ·m to 48.2μΩ·m with the mean particle size of petroleum coke increasing from 44μm to 1200μm. However, too big carbonaceous particle size has adverse influence on the abrasion resistance of coating. Its proper mean particle size is 420μm.展开更多
TiB2/C cathode composites with various contents of TiB2 were prepared and their characterizations were observed and compared. The expansion of samples due to sodium and bath penetration was tested with a modified labo...TiB2/C cathode composites with various contents of TiB2 were prepared and their characterizations were observed and compared. The expansion of samples due to sodium and bath penetration was tested with a modified laboratory Rapoport apparatus and the appearances of the cut sections of specimens after electrolysis were studied. The results show that the mass of TiB2/C cathode composites with mass fraction of TiB2 less than 70% appreciably increases, but that of the composites with mass fraction of TiB2 more than 70% decreases slightly after being baked. The resistance to sodium and bath penetration of TiB2/C cathode composites increases with the increase of TiB2 content, especially in the composites with high TiB2 content. TiB2/C cathode composites have high resistance to the penetration of sodium and bath as well as good wettability by molten aluminum, and keep integrality and have little change of appearance after electrolysis, which indicates that TiB2/C cathode composites can be used as inert wettable cathode for aluminum electrolysis.展开更多
Based on the elastic theory of cylindrical shells and the theory of composite laminates,a prediction model for the residual prestress of the simplified round composite barrel for railgun is established.Only the fibre ...Based on the elastic theory of cylindrical shells and the theory of composite laminates,a prediction model for the residual prestress of the simplified round composite barrel for railgun is established.Only the fibre pretension is considered in this model.A three dimensional numerical simulation for the residual prestress in the railgun barrel is carried out,by combining the temperature differential method with the element birth and death technology.The results obtained by the two methods are compared.It reveals that the distribution trends of residual prestress are consistent.And the difference for residual prestress in the filament wound composite housing of barrel is relatively small.The same finite element method is used to analysis the residual prestress in the non-simplified composite barrels for railgun,which are under different control modes of winding tension.The results mean that the residual prestress in barrel will increase while the taper coefficient for winding is decreasing.Therefore,the sealing performance in bore is improved,but the strength of the filament wound composite housing drops.In addition,the axial and circumferential residual prestress in the filament wound composite housing with constant torque winding are close to the ones in iso-stress design for barrel.展开更多
Fused deposition modeling(FDM) is one of the latest rapid prototyping techniques in which parts can be manufactured at a fast pace and are manufactured with a high accuracy. This research work is carried out to study ...Fused deposition modeling(FDM) is one of the latest rapid prototyping techniques in which parts can be manufactured at a fast pace and are manufactured with a high accuracy. This research work is carried out to study the friction and wear behavior of parts made of newly developed Nylon6-Fe composite material by FDM. This work also involves the comparison of the friction and wear characteristics of the Nylon6-Fe composite with the existing acrylonitrile butadiene styrene(ABS) filament of the FDM machine. This Is carried out on the pin on disk setup by varying the load(5, 10, 15 and 20 N) and speed(200 and 300 r/min). It is concluded that the newly developed composite is highly wear resistant and can be used in industrial applications where wear resistance is of paramount importance. Morphology of the surface in contact with the Nylon6-Fe composite and ABS is also carried out.展开更多
Copper azide(CA), as a primary explosive with high energy density, has not been practically used so far because of its high electrostatic sensitivity. The Cu2O@HKUST-1 core-shell structure hybrid material was synthesi...Copper azide(CA), as a primary explosive with high energy density, has not been practically used so far because of its high electrostatic sensitivity. The Cu2O@HKUST-1 core-shell structure hybrid material was synthesized by the “bottle around ship” methodology in this research by regulating the dissolution rate of Cu2O and the generation rate of metal-organic framework(MOF) materials. Cu2O@HKUST-1 was carbonized to form a Cu O@porous carbon(CuO@PC) composite material. CuO@PC was synthesized into a copper azide(CA) @PC composite energetic material through a gas-solid phase in-situ azidation reaction.CA is encapsulated in PC framework, which acts as a nanoscale Faraday cage, and its excellent electrical conductivity prevents electrostatic charges from accumulating on the energetic material’s surface. The CA@PC composite energetic material has a CA content of 89.6%, and its electrostatic safety is nearly 30times that of pure CA(1.47 mJ compared to 0.05 mJ). CA@PC delivers an outstanding balance of safety and energy density compared to similar materials.展开更多
Based on the fatigue prediction model of exponential function and Whitney-Nuismer(WN) criterion of static strength for the composite material laminate with a circular hole, the stress correct factor ( β ) was put for...Based on the fatigue prediction model of exponential function and Whitney-Nuismer(WN) criterion of static strength for the composite material laminate with a circular hole, the stress correct factor ( β ) was put forward and a new fatigue prediction model for composite material laminate was set up. T300/KH304, which is recently studied and is a high capability composite material, was used as the raw material. In order to gain the factor β , the fatigue experiments of the laminates with holes in different diameters and the same ratio of width to diameter were conducted. The fatigue analysis and tests of the laminates with a hole 5 mm in diameter are carried out at different stress levels, and the results meet the engineering requirement. The simple, prompt and practical method is provided for the prediction of S-N curve of composite laminate with a circular hole.展开更多
Co3O4/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electro...Co3O4/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis （TG/DTA）, X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co3O4/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mA-h/g as the calcination temperature increases from 300 to 500 ℃, and the Co304/graphite composites synthesized at 400 ℃ show the best cycling stability without capacity loss in the initial 20 cycles. peaks, corresponding to the lithium intercalaction/deintercalation for The CV profile of the composite presents two couples of redox graphite and Co3O4, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.展开更多
Reducing the self-noise and radiated noise of torpedo is an effective way to enhance its detection and concealment capabilities.After discussing the basic principle on noise and vibration control and main noise source...Reducing the self-noise and radiated noise of torpedo is an effective way to enhance its detection and concealment capabilities.After discussing the basic principle on noise and vibration control and main noise sources in torpedo,the application of damping treatment for noise and vibration absorption was proposed in this paper.Compared composite materials(damping and metal materials)used as segment joint,their different contributions to the damping performance of base structure were investigated.The results show that the damping material can be used as segment joint effectively in vibration control.Taking cantilever beam as an example,four different damping treatments were compared in natural frequency and damping loss factor,the results show the influences of different damping layer layouts on the structure damping performance,and offer a reference for the torpedo shell design.展开更多
To improve the conductivity of Y2O3-stabilized ZrO2 （YSZ） based oxygen-ion conductor, Zr0.85Y0.15O1.925-La9.33Si6O26 （YSZ-LSO） composite ceramics with the mass fraction of La9.33Si6O26 （LSO） of 15% were prepared...To improve the conductivity of Y2O3-stabilized ZrO2 （YSZ） based oxygen-ion conductor, Zr0.85Y0.15O1.925-La9.33Si6O26 （YSZ-LSO） composite ceramics with the mass fraction of La9.33Si6O26 （LSO） of 15% were prepared by using a modified coprecipitation method. The phases, microstructures and conductivities of the YSZ, LSO and YSZ-LSO were investigated by X-ray diffraction, electron microscopy and complex impedance, respectively. The results show that the as-calcined powder of YSZ-LSO composite has the grain size less than 10 nm, and the as-sintered composite ceramics are composed of YSZ and LSO phases. The conductivity can be enhanced obviously by composite method. At 700 ℃, the conductivity of the composite ceramic is 0.125 S/cm, which is one order in magnitude higher than that of the YSZ ceramic and two orders in magnitude higher than that of LSO ceramic. By analyzing the impedance spectra and modulus spectra, the interfacial effect on the conductivity improvement was proposed.展开更多
In this paper,the design,manufacture and testing of an origami protective shield with a supporting frame structure are presented.It consists of an origami shield surface and a deployable supporting frame structure tha...In this paper,the design,manufacture and testing of an origami protective shield with a supporting frame structure are presented.It consists of an origami shield surface and a deployable supporting frame structure that needs to be portable and sufficiently stiff.First,for the design of the shield surface,a threestage origami crease pattern is developed to reduce the shield size in the folded state.The shield surface consists of several stiff modular panels and layered with flexible fabric.The modular panels are made of a multi-layer composite where a ceramic layer is made of small pieces to improve durability as those small pieces enable restriction of crack propagation.Then,the supporting frame structure is designed as a chain-of-bars structure in order to fold into a highly compact state as a bundle of bars and deploy in sequence.Thus,a feature-driven topology structural optimization method preserving component sequence is developed where the inter-dependence of sub-structures is taken into account.A bar with semi-circular ends is used as a basic design feature.The positions of the bar’s end points are treated as design variables and the width of the bars is kept constant.Then,a constraint on the total length of the chain of bars is introduced.Finally,the modular panels made of multi-layer composite and the full-scale prototype of the origami shield are fabricated and tested to verify the bullet-proof performance.展开更多
Military missions in hostile environments are often costly and unpredictable,with squadrons sometimes facing isolation and resource scarcity.In such scenarios,critical components in vehicles,drones,and energy generato...Military missions in hostile environments are often costly and unpredictable,with squadrons sometimes facing isolation and resource scarcity.In such scenarios,critical components in vehicles,drones,and energy generators may require structural reinforcement or repair due to damage.This paper proposes a portable,on-site production method for molds under challenging conditions,where material supply is limited.The method utilizes large format additive manufacturing(LFAM)with recycled composite materials,sourced from end-of-life components and waste,as feedstock.The study investigates the microstructural effects of recycling through shredding techniques,using microscopic imaging.Three potential defense-sector applications are explored,specifically in the aerospace,automotive,and energy industries.Additionally,the influence of key printing parameters,particularly nonparallel plane deposition at a 45-degree angle,on the mechanical behavior of ABS reinforced with 20%glass fiber(GF)is examined.The results demonstrate the feasibility of this manufacturing approach,highlighting reductions in waste material and production times compared to traditional methods.Shorter layer times were found to reduce thermal gradients between layers,thereby improving layer adhesion.While 45-degree deposition enhanced Young's modulus,it slightly reduced interlayer adhesion quality.Furthermore,recycling-induced fiber length reduction led to material degradation,aligning with findings from previous studies.Challenges encountered during implementation included weak part adherence to the print bed and local excess material deposition.Overall,the proposed methodology offers a cost-effective alternative to traditional CNC machining for mold production,demonstrating its potential for on-demand manufacturing in resource-constrained environments.展开更多
In pursuit of more efficient and stable electrochemical energy storage materials,composite materials consisting of metal oxides and graphene oxide have garnered significant attention due to their unique structures and...In pursuit of more efficient and stable electrochemical energy storage materials,composite materials consisting of metal oxides and graphene oxide have garnered significant attention due to their unique structures and exceptional properties.Graphene oxide(GO),a two-dimensional material with an extremely high specific surface area and excellent conductivity,offers new possibilities for enhancing the electrochemical performance of metal oxides.In this work,we synthesized met-al-organic framework(MOF)and GO composites by regulating the amount of GO,and successfully prepared composites of metal oxides supported by nitrogen-doped carbon frameworks and GO through a simple one-step calcination process.Based on the electrochemical tests,the optimal amount of GO was determined.This research will provide new insights into and directions for designing and synthesizing metal oxide and graphene oxide composite materials with an ideal electro-chemical performance.展开更多
基金Project(51672234)supported by the National Natural Science Foundation of ChinaProject(1337304)supported by the Program for Innovative Research Cultivation Team in University,Ministry of Education,China
文摘Na0.44MnO2 nanorods have been prepared by a hydrothermal method.The experimental parameters have been systematically investigated and optimized.The results show that Na0.44MnO2 nanorods obtained via the hydrothermal treatment at 200℃for 16 h show the best electrochemical properties,which deliver the high initial discharge capacity of 110.7 mA·h/g at 50 mA/g in potential window 2.0-4.0 V.To further improve their electrochemical properties,a ball milling process with graphene has been carried out to obtain Na0.44MnO2/graphene composite.The initial discharge capacity of Na0.44MnO2/graphene composite is 106.9 mA·h/g at a current density of 50 mA/g.After 100 cycles,the residual discharge capacity is 91.8 mA·h/g and the capacity retention rate is 85.9%,which is much higher than that of pristine Na0.44MnO2 nanorods(74.7%)at the same condition.What is more,when the current density reaches 500 and 1000 mA/g,the corresponding discharge capacities of Na0.44MnO2/graphene composite are about 89 and 78 mA·h/g,respectively,indicating outstanding rate capability.
基金Project(2005CB623703) supported by the National Basic Research Program of China project(5JJ30103) supported bythe Natural Science Foundation of Hunan Province
文摘Taking the nano-sized carbon black and aniline monomer as precursor and （NH4）2S2O6 as oxidant, the well coated C/polyaniline（C/PANI） composite materials were prepared by in situ polymerization of the aniline on the surface of well-dispersed nano-sized carbon black for supercapacitor. The micro-structure of the C/PANI composite electrode materials were analyzed by SEM. The electrochemical properties of C/ PANI and PANI composite electrode were characterized by means of the galvanostatic charge-discharge experiment, cyclic voltammetric measurement and impedance spectroscopy analysis. The results show that by adding the nano-sized carbon black in the process of chemical polymerization of the aniline, the polyaniline can be in situ polymerized and well-coated onto the carbon black particles, which may effectively improve the aggregation of particles and the electrolyte penetration. What’s more , the maximum of specific capacitance of C/PANI electrode 437.6F·g -1 can be attained. Compared with PANI electrode, C/PANI electrode shows more desired capacitance characteristics, smaller internal resistance and better cycle performance.
基金Project(50175031) supported by the National Natural Science Foundation of China
文摘A motor-driven linkage system with links fabricated from 3-dimensional braided composite materials was studied. A group of coupling dynamic equations of the system, including composite materials parameters, electromagnetism parameters of the motor and structural parameters of the link mechanism, were established by finite element method. Based on the air-gap field of non-uniform airspace of three-phase alternating current motor caused by the vibration eccentricity of rotor, the relation of electromechanical coupling at the actual running state was analyzed. And the motor element, which defines the transverse vibration and torsional vibration of the motor as its nodal displacement, was established. Then, based on the damping element model and the expression of energy dissipation of the 3-dimentional braided composite materials, the damping matrix of the system was established by calculating each order modal damping of the mechanism.
基金Project (2005CB623703) supported by the Major State Basic Research and Development Program of ChinaProject (2008AA030502) supported by the National High-Tech Research and Development Program of China
文摘Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of TiB2/C composite cathode material were investigated. The results show that thermogravimetrie behavior of pitch and TiB2/C green composite cathode is similar, and appears the largest mass loss rate in the temperature range from 200 to 600 ℃. The bulk density variation of sample K5 before and after baking is the largest （11.9%）, that of sample K25 is the second, and that of sample M5 is the smallest （6.7%）. The crushing strength of sample M5 is the biggest （51.2 MPa）, that of sample K2.5 is the next, and that of sample K5 is the smallest （32.8 MPa）. But, the orders of the electrical resistivity and electrolysis expansion of samples are just opposite with the order of crushing strength. The heating rate has a great impact on the microstructure of sample. The faster the heating rate is, the bigger the pore size and porosity of sample are. Compared with the heating rate between 200 and 600℃ of samples K25 and K5, that of sample M5 is slower and suitable for baking process of TiB2/C composite cathode material.
基金National Natural Science Foundation of China(Grant No.52175162,51805086 and 51975123)Natural Science Foundation of Fujian Province(Grant No.2019J01210)Health education joint project of Fujian Province(Grant No.2019-WJ-01)。
文摘Composite materials exhibit the impressive mechanical properties of high damping and stiffness,which cannot be attained by employing conventional single materials.Along these lines,a novel material architecture is presented in this work in order to fabricate composites with enhanced mechanical characteristics.More specifically,entangled metallic wire materials were used as the active matrix,whereas polyurethane was employed as the reinforcement elements.As a result,an entangled metallic wire material-polyurethane composite with high damping and stiffness was prepared by enforcing the vacuum infiltration method.On top of that,the mechanical properties(loss factor,energy consumption,and average stiffness)of the proposed composite materials were characterized by performing dynamic tests,and its fatigue characteristics were verified by the micro-interface bonding,as well as the macro-damage factor.The impact of the density,preloading spacing,loading amplitude,and exciting frequency on the mechanical properties of the composites were also thoroughly analyzed.The extracted results indicate that the mechanical properties of the composites were significantly enhanced than those of the pure materials due to the introduction of interface friction.Moreover,the average stiffness of the composites was about 10 times the respective value of the entangled metallic wire material.Interestingly,a rise in the loading period leads to some failure between the composite interfaces,which reduces the stiffness property but enhances the damping dissipation properties.Finally,a comprehensive dynamic mechanical model of the composites was established,while it was experimentally verified.The proposed composites possess higher damping features,i.e.,stiffness characteristics,and maintain better fatigue characteristics,which can broaden the application range of the composites.In addition,we provide a theoretical and experimental framework for the research and applications in the field of metal matrix composites.
基金supported by the National Defense National Defense Pre-Research Foundation of China(Grant no.301030102)。
文摘Understanding the dynamic response of composite material cartridges during the firing process is of great significance for improving their reliability and safety.A theoretical model describing the dynamic response of composite material cartridges is established based on the thick-walled cylinder theory and rate-dependent constitutive model of composite materials.The correctness of the theoretical model is validated through finite element simulations of cartridge deformation.The influence of chamber pressure and cartridge wall thickness on the cartridge's deformation process and stress distribution is analyzed.The results indicate that the primary deformation of composite material cartridges inside the chamber is elastic deformation.Compared to metal cartridges,composite material cartridges require higher pressure for touching-chamber and are more prone to developing gaps after unloading to ensure smooth extraction.During the deformation process,the touching-chamber behavior of the cartridge can improve the stress distribution.Under the same chamber pressure,the touching-chamber behavior can reduce the circumferential stress by approximately 30%.The inner wall surface of the cartridge is a critical area that requires attention.The touching-chamber behavior can be facilitated by appropriately reducing the cartridge wall thickness while ensuring overall strength.This study can provide guidance for the optimization design of composite material cartridges.
文摘Cs_(x)WO_(3)/TiO_(2) composites with full-spectrum catalytic activity were prepared by solvothermal reaction.The composites were characterized using X-ray diffraction(XRD)analysis,scanning electron microscopy(SEM),transmission electron microscopy(TEM),specific surface area testing,X-ray photoelectron spectroscopy(XPS),and UV-Vis diffuse reflectance spectra(UV-Vis DRS).Cs_(x)WO_(3) and TiO_(2) were uniformly bonded together in the compos-ites.The heterojunction structure was formed.The band gap was reduced from 2.75 to 2.65 eV.The photocatalytic property of Cs_(x)WO_(3)/TiO_(2)was demonstrated by the degradation rates of 20 mg·L^(-1) methylene blue dye,which were 99.7%,91.4%,and 70.7%under irradiation from a 300 W high-pressure mercury lamp,a 500 W xenon lamp,and a 400 W infrared lamp,respectively.After five cycles of photocatalytic degradation,the composite photocatalyst still showed a degradation efficiency of 87.6%.This indicates that Cs_(x)WO_(3)/TiO_(2) has good photocatalytic degradability and cyclic stability.The photocatalytic mechanism of Cs_(x)WO_(3)/TiO_(2)was investigated.The trapping experiments of the active species showed that the main active substances were the empty hole(h+)and hydroxyl radical(·OH).
文摘The Al 2O 3 particles reinforced aluminum matrix composite (Al 2O 3p/Al) are more and more widely used for their excellent physical and chemical properties. However, their poor machinability leads to severe tool wear and bad machined surface. In this paper laser assisted machining is adopted in machining Al 2O 3p/Al composite and good result was obtained. The result of experiment shows in machining Al 2O 3p/Al composites the cutting force is reduced in 30%～50%, the tool wear is reduced in 20%～30% and machined surface quality is improved in laser assisted machining as compared with conventional cutting. The physical model of the cutting process is set up and explains the reason why the cutting forced are reduced. The state of the particles is the main influence of the change. When the material of cutting zone is heating by laser, the aluminum matrix becomes softer and easier in plastic deformation, which leads to the reduction of the pushing force from the tool to the machined surface. The soften aluminum matrix is more easy to be squeezed out from the machined surface, and it leads the concentration of the Al 2O 3 particles in the surface layer of machined surface. The softening effect of laser heating on aluminum matrix reduces the pushing forces of the Al 2O 3 particles on the clearance face of cutting tool, which is just the reason for the severe cutting tool wear in conventional machining of Al 2O 3p/Al composite. Because the Al 2O 3 particles were pushed in during the cutting process, the particles increased in the surface layer. Because of the difference in thermal conductivity and thermal expansion between the Al-matrix and Al 2O 3 particle, residual stress is changed in the matrix after machining due to the extrusion of the tool, deformation of the matrix and displacement of the Al 2O 3 particle in the matrix. Temperature gradient comes into the cutting zone and the work-piece surface layer, it will lead to the increase of thermal stress and misfit dislocation in the matrix. The residual stress is compressive in the laser assisted hot cutting surface, the compressive stress is nearly triple times than that in the conventional cutting surface. Some analysis on the mechanism of laser heat assisted machining of Al 2O 3p/Al composite is given in the paper too.
基金Project(2005CB623703) supported by the State Key Fundamental Research and Development Programof China project(5JJ30103) supported by the Natural Science Foundation of Hunan Province
文摘The electrical resistivity of TiB2/C cathode composite coating at different temperatures was measured with the electrical conductivity test device; the effects of TiB2 content and kinds of carbonaceous fillers as well as their mean particle size on their electrical resistivities were investigated. The results show that electrical resistivity of the coating decreases with the increase of TiB2 content and the decrease of its mean particle size. When the mass fraction of TiB2 increases from 30% to 60%, the electrical resistivity of the coating at room temperature decreases from 31.2μΩ·m to 23.8μΩ·m. The electrical resistivity of the coating at 960℃ lowers from 76.1μΩ· m to 38.4μΩ·m with the decrease of TiB2 mean particle size from 12μm to 1μm. The kinds of carbonaceous fillers have great influence on the electrical resistivity of TiB2/C composite coating at 960℃, when the graphite, petroleum coke and anthracite are used as fillers, the electrical resistivities of the coating are 20.3μΩ·m, 53.7μΩ·m and 87.2μΩ·m, respectively. For the coating with petroleum coke filler, its electrical resistivity decreases with the increase of the mean particle size of petroleum coke filler. The electrical resistivity at 960℃ decreases from 56.2μΩ·m to 48.2μΩ·m with the mean particle size of petroleum coke increasing from 44μm to 1200μm. However, too big carbonaceous particle size has adverse influence on the abrasion resistance of coating. Its proper mean particle size is 420μm.
文摘TiB2/C cathode composites with various contents of TiB2 were prepared and their characterizations were observed and compared. The expansion of samples due to sodium and bath penetration was tested with a modified laboratory Rapoport apparatus and the appearances of the cut sections of specimens after electrolysis were studied. The results show that the mass of TiB2/C cathode composites with mass fraction of TiB2 less than 70% appreciably increases, but that of the composites with mass fraction of TiB2 more than 70% decreases slightly after being baked. The resistance to sodium and bath penetration of TiB2/C cathode composites increases with the increase of TiB2 content, especially in the composites with high TiB2 content. TiB2/C cathode composites have high resistance to the penetration of sodium and bath as well as good wettability by molten aluminum, and keep integrality and have little change of appearance after electrolysis, which indicates that TiB2/C cathode composites can be used as inert wettable cathode for aluminum electrolysis.
文摘Based on the elastic theory of cylindrical shells and the theory of composite laminates,a prediction model for the residual prestress of the simplified round composite barrel for railgun is established.Only the fibre pretension is considered in this model.A three dimensional numerical simulation for the residual prestress in the railgun barrel is carried out,by combining the temperature differential method with the element birth and death technology.The results obtained by the two methods are compared.It reveals that the distribution trends of residual prestress are consistent.And the difference for residual prestress in the filament wound composite housing of barrel is relatively small.The same finite element method is used to analysis the residual prestress in the non-simplified composite barrels for railgun,which are under different control modes of winding tension.The results mean that the residual prestress in barrel will increase while the taper coefficient for winding is decreasing.Therefore,the sealing performance in bore is improved,but the strength of the filament wound composite housing drops.In addition,the axial and circumferential residual prestress in the filament wound composite housing with constant torque winding are close to the ones in iso-stress design for barrel.
基金PTU Jalandhar,Manufacturing Research Lab GNDEC,Ludhiana and DST GOI for financial support
文摘Fused deposition modeling(FDM) is one of the latest rapid prototyping techniques in which parts can be manufactured at a fast pace and are manufactured with a high accuracy. This research work is carried out to study the friction and wear behavior of parts made of newly developed Nylon6-Fe composite material by FDM. This work also involves the comparison of the friction and wear characteristics of the Nylon6-Fe composite with the existing acrylonitrile butadiene styrene(ABS) filament of the FDM machine. This Is carried out on the pin on disk setup by varying the load(5, 10, 15 and 20 N) and speed(200 and 300 r/min). It is concluded that the newly developed composite is highly wear resistant and can be used in industrial applications where wear resistance is of paramount importance. Morphology of the surface in contact with the Nylon6-Fe composite and ABS is also carried out.
基金the financial support by Postgraduate Research & Practice Innovation Program from Jiangsu Science and Technology Department under Grant number KYCX19_0320。
文摘Copper azide(CA), as a primary explosive with high energy density, has not been practically used so far because of its high electrostatic sensitivity. The Cu2O@HKUST-1 core-shell structure hybrid material was synthesized by the “bottle around ship” methodology in this research by regulating the dissolution rate of Cu2O and the generation rate of metal-organic framework(MOF) materials. Cu2O@HKUST-1 was carbonized to form a Cu O@porous carbon(CuO@PC) composite material. CuO@PC was synthesized into a copper azide(CA) @PC composite energetic material through a gas-solid phase in-situ azidation reaction.CA is encapsulated in PC framework, which acts as a nanoscale Faraday cage, and its excellent electrical conductivity prevents electrostatic charges from accumulating on the energetic material’s surface. The CA@PC composite energetic material has a CA content of 89.6%, and its electrostatic safety is nearly 30times that of pure CA(1.47 mJ compared to 0.05 mJ). CA@PC delivers an outstanding balance of safety and energy density compared to similar materials.
文摘Based on the fatigue prediction model of exponential function and Whitney-Nuismer(WN) criterion of static strength for the composite material laminate with a circular hole, the stress correct factor ( β ) was put forward and a new fatigue prediction model for composite material laminate was set up. T300/KH304, which is recently studied and is a high capability composite material, was used as the raw material. In order to gain the factor β , the fatigue experiments of the laminates with holes in different diameters and the same ratio of width to diameter were conducted. The fatigue analysis and tests of the laminates with a hole 5 mm in diameter are carried out at different stress levels, and the results meet the engineering requirement. The simple, prompt and practical method is provided for the prediction of S-N curve of composite laminate with a circular hole.
基金Project(2007CB613607) supported by the National Basic Research Program of China Projects(2009FJ1002, 2009CK3062) supported by the Science and Technology Program of Hunan Province, China
文摘Co3O4/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis （TG/DTA）, X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co3O4/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mA-h/g as the calcination temperature increases from 300 to 500 ℃, and the Co304/graphite composites synthesized at 400 ℃ show the best cycling stability without capacity loss in the initial 20 cycles. peaks, corresponding to the lithium intercalaction/deintercalation for The CV profile of the composite presents two couples of redox graphite and Co3O4, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.
文摘Reducing the self-noise and radiated noise of torpedo is an effective way to enhance its detection and concealment capabilities.After discussing the basic principle on noise and vibration control and main noise sources in torpedo,the application of damping treatment for noise and vibration absorption was proposed in this paper.Compared composite materials(damping and metal materials)used as segment joint,their different contributions to the damping performance of base structure were investigated.The results show that the damping material can be used as segment joint effectively in vibration control.Taking cantilever beam as an example,four different damping treatments were compared in natural frequency and damping loss factor,the results show the influences of different damping layer layouts on the structure damping performance,and offer a reference for the torpedo shell design.
基金Project(50872155) supported by the National Natural Science Foundation of China
文摘To improve the conductivity of Y2O3-stabilized ZrO2 （YSZ） based oxygen-ion conductor, Zr0.85Y0.15O1.925-La9.33Si6O26 （YSZ-LSO） composite ceramics with the mass fraction of La9.33Si6O26 （LSO） of 15% were prepared by using a modified coprecipitation method. The phases, microstructures and conductivities of the YSZ, LSO and YSZ-LSO were investigated by X-ray diffraction, electron microscopy and complex impedance, respectively. The results show that the as-calcined powder of YSZ-LSO composite has the grain size less than 10 nm, and the as-sintered composite ceramics are composed of YSZ and LSO phases. The conductivity can be enhanced obviously by composite method. At 700 ℃, the conductivity of the composite ceramic is 0.125 S/cm, which is one order in magnitude higher than that of the YSZ ceramic and two orders in magnitude higher than that of LSO ceramic. By analyzing the impedance spectra and modulus spectra, the interfacial effect on the conductivity improvement was proposed.
基金supported by the Chinese Studentship Council(Grant No.201908060224)the National Natural Science Foundation of China (Grant Nos.11872310,11972308)。
文摘In this paper,the design,manufacture and testing of an origami protective shield with a supporting frame structure are presented.It consists of an origami shield surface and a deployable supporting frame structure that needs to be portable and sufficiently stiff.First,for the design of the shield surface,a threestage origami crease pattern is developed to reduce the shield size in the folded state.The shield surface consists of several stiff modular panels and layered with flexible fabric.The modular panels are made of a multi-layer composite where a ceramic layer is made of small pieces to improve durability as those small pieces enable restriction of crack propagation.Then,the supporting frame structure is designed as a chain-of-bars structure in order to fold into a highly compact state as a bundle of bars and deploy in sequence.Thus,a feature-driven topology structural optimization method preserving component sequence is developed where the inter-dependence of sub-structures is taken into account.A bar with semi-circular ends is used as a basic design feature.The positions of the bar’s end points are treated as design variables and the width of the bars is kept constant.Then,a constraint on the total length of the chain of bars is introduced.Finally,the modular panels made of multi-layer composite and the full-scale prototype of the origami shield are fabricated and tested to verify the bullet-proof performance.
基金Generalitat Valenciana(GVA)and Spanish Ministry of Science and Innovation(Grant Nos.TED2021-130879 B-C21,CIACIF/2021/286,PID2023-151110OB-I00,and CIPROM/2022/3)to provide funds for conducting experiments and software licensessupported by the National Research Foundation,Prime Minister's Office,Singapore under its Campus for Research Excellence and Technological Enterprise(CREATE)programme。
文摘Military missions in hostile environments are often costly and unpredictable,with squadrons sometimes facing isolation and resource scarcity.In such scenarios,critical components in vehicles,drones,and energy generators may require structural reinforcement or repair due to damage.This paper proposes a portable,on-site production method for molds under challenging conditions,where material supply is limited.The method utilizes large format additive manufacturing(LFAM)with recycled composite materials,sourced from end-of-life components and waste,as feedstock.The study investigates the microstructural effects of recycling through shredding techniques,using microscopic imaging.Three potential defense-sector applications are explored,specifically in the aerospace,automotive,and energy industries.Additionally,the influence of key printing parameters,particularly nonparallel plane deposition at a 45-degree angle,on the mechanical behavior of ABS reinforced with 20%glass fiber(GF)is examined.The results demonstrate the feasibility of this manufacturing approach,highlighting reductions in waste material and production times compared to traditional methods.Shorter layer times were found to reduce thermal gradients between layers,thereby improving layer adhesion.While 45-degree deposition enhanced Young's modulus,it slightly reduced interlayer adhesion quality.Furthermore,recycling-induced fiber length reduction led to material degradation,aligning with findings from previous studies.Challenges encountered during implementation included weak part adherence to the print bed and local excess material deposition.Overall,the proposed methodology offers a cost-effective alternative to traditional CNC machining for mold production,demonstrating its potential for on-demand manufacturing in resource-constrained environments.
基金supported by the National Natural Science Foundation of China(51971157)Shenzhen Science and Technology Program(JCYJ20210324115412035,JCYJ202103-24123202008,JCYJ20210324122803009 and ZDS-YS20210813095534001)Guangdong Foundation for Basic and Applied Basic Research Program(2021A1515110880).
文摘In pursuit of more efficient and stable electrochemical energy storage materials,composite materials consisting of metal oxides and graphene oxide have garnered significant attention due to their unique structures and exceptional properties.Graphene oxide(GO),a two-dimensional material with an extremely high specific surface area and excellent conductivity,offers new possibilities for enhancing the electrochemical performance of metal oxides.In this work,we synthesized met-al-organic framework(MOF)and GO composites by regulating the amount of GO,and successfully prepared composites of metal oxides supported by nitrogen-doped carbon frameworks and GO through a simple one-step calcination process.Based on the electrochemical tests,the optimal amount of GO was determined.This research will provide new insights into and directions for designing and synthesizing metal oxide and graphene oxide composite materials with an ideal electro-chemical performance.
