Nonlinear stability of advanced sandwich cylindrical shells comprising porous functionally graded material and carbon nanotube reinforced composite layers under elevated temperature

The nonlinear stability of sandwich cylindrical shells comprising porous functionally graded material(FGM) and carbon nanotube reinforced composite(CNTRC)layers subjected to uniform temperature rise is investigated. Two sandwich models corresponding to CNTRC and FGM face sheets are proposed. Carbon nanotubes(CNTs) in the CNTRC layer are embedded into a matrix according to functionally graded distributions. The effects of porosity in the FGM and the temperature dependence of properties of all constituent materials are considered. The effective properties of the porous FGM and CNTRC are determined by using the modified and extended versions of a linear mixture rule, respectively. The basic equations governing the stability problem of thin sandwich cylindrical shells are established within the framework of the Donnell shell theory including the von K’arm’an-Donnell nonlinearity. These equations are solved by using the multi-term analytical solutions and the Galerkin method for simply supported shells.The critical buckling temperatures and postbuckling paths are determined through an iteration procedure. The study reveals that the sandwich shell model with a CNTRC core layer and relatively thin porous FGM face sheets can have the best capacity of thermal load carrying. In addition, unlike the cases of mechanical loads, porosities have beneficial effects on the nonlinear stability of sandwich shells under the thermal load. It is suggested that an appropriate combination of advantages of FGM and CNTRC can result in optimal efficiency for advanced sandwich structures.

Evaluation for cell affinity of the composite material containing carbon nanotubes

The composite material of poly-(L-lactide) (PLLA) and carbon nanotubes (CNTs) were prepared. Itssurface morphologies and property were worked out by us-ing atomic force microscopy (AFM) and contact angle meas-urement. Moreover, the prime cytocompatibility was used to investigate the biocompatibility of the composite materialcontaining CNTs and the effects of CNTs on one aspect of cell function, cell affinity. The results obtained indicate that thecomposite material of PLLA and CNTs possesses good bio-compatibility for both the 3T3 fibroblasts and Oct-1 os-teoblast-like cells. The addition of CNTs will greatly affectcell affinity of the material, which may be disadvantage for the cell adhesion.

Bulk Composite Nanomaterial with Multiwall Carbon Nanotubes

The properties of the composite nanomaterials (CNM) based on bovine serum albumin (BSA) and multi-walled carbon nanotubes (MWCNT), both functionalized and non-functionalized, were investigated. In order to obtain the solid-state bulk CNM from the ultradispersed aqueous solutions of 25 wt.% BSA and (0.0015 - 0.04) wt.% MWCNT, the methods of nanotechnology and laser technology were used. It is revealed that the CNM density is 10% - 20% higher than that of water and the hardness is higher than that of BSA by a factor of 3 - 6 times. An increase in hardness Hv (by Vickers) of CNM correlated with an increase in the concentration of MWCNT, and Hyreached ~300 MPa for the case of the non-functionalized MWCNT, while for the case of the functionalized MWCNT, i.e. MWCNTf, Hy was 25% lower.

Functional porous carbon-based composite electrode materials for lithium secondary batteries

The synthetic routes of porous carbons and the applications of the functional porous carbon-based composite electrode materials for lithium secondary batteries are reviewed. The synthetic methods have made great breakthroughs to control the pore size and volume, wall thickness, surface area, and connectivity of porous carbons, which result in the development of functional porous carbon-based composite electrode materials. The effects of porous carbons on the electrochemical properties are further discussed. The porous carbons as ideal matrixes to incorporate active materials make a great improvement on the electrochemical properties because of high surface area and pore volume, excellent electronic conductivity, and strong adsorption capacity. Large numbers of the composite electrode materials have been used for the devices of electrochemical energy conversion and storage, such as lithium-ion batteries （LIBs）, Li-S batteries, and Li-O2 batteries. It is believed that functional porous carbon-based composite electrode materials will continuously contribute to the field of lithium secondary batteries.

Forced vibration analysis of nano-composite rotating pressurized microbeam reinforced by CNTs based on MCST with temperature-variable material properties

In this study, free and forced vibration analysis of nano-composite rotating pressurized microbeam reinforced by carbon nanotubes （CNTs） under magnetic field based on modify couple stress theory （MCST） with temperature-variable material propertiesis presented. Also, the boundary conditions at two ends of nano-composite rotating pressurized microbeam reinforced by CNTs are considered as simply supported. The governing equations are obtained based on the Hamilton＇s principle and then computed these equations by using Navier＇s solution. The magnetic field is inserted in the thickness direction of the nano-composite microbeam. The effects of various parameters such as angular velocity, temperature changes, and pressure between of the inside and outside, the magnetic field, material length scale parameter, and volume fraction of nanocomposite microbeam on the natural frequency and response systemare studied. The results show that with increasing volume fraction of nano-composite microbeam, thickness, material length scale parameter, and magnetic fields, the natural frequency increases. The results of this research can be used for optimization of micro-structures and manufacturing sensors, displacement fluid, and drug delivery.

CIPs@Mn_(0.8)Zn_(0.2)Fe_(2)O_(4)-CNTs复合材料低频吸波性能研究

随着5G无线通信与低频雷达侦察技术的飞速发展,低频电磁波辐射已成为当代的严重问题。目前,中高频段吸波材料的研究已趋于成熟,而设计低频段吸波材料仍面临巨大的挑战,亟待研究者们解决。基于四分之一波长相消机制,本研究设计了0.5~3 GHz低频段复合吸波材料。采用简单的一步水热法,诱导铁氧体在羰基铁粉与碳纳米管表面生长,制备出CIPs@Mn_(0.8)Zn_(0.2)Fe_(2)O_(4)-CNTs三元复合材料,对比研究了碳纳米管含量对材料吸收峰频率的影响。实验结果表明,引入碳纳米管,一方面为材料带来了界面极化、偶极极化等额外的损耗机制,增加了材料的衰减系数;另一方面基于四分之一波长相消机制,高介电与高磁导率的耦合,使材料在低频段获得良好的阻抗匹配。最终,在4 mm厚度下,样品分别在2.11与1.75 GHz处,获得了–40.8与–32.1 dB的反射损耗,–10 dB带宽分别为1.70~2.70 GHz和1.40~2.20 GHz。该复合材料制备工艺简单,低频吸收性能良好,具有很大的应用潜力,为开发更有效的低频吸波材料提供了新的思路和方法。

Electroless plating Ni-P matrix composite coating reinforced by carbon nanotubes

Ni-P matrix composite coating reinforced by carbon nanotubes (CNTs) was deposit ed by electroless plating. The most important factors that influence the content of carbon nanotubes in deposits,such as agitation,surfactant and carbon nanot ubes concentration in the plating bath were investigated. The surface morphology,structure and properties of the Ni-P-CNTs coating were examined. It is found that the maximum content of carbon nanotubes in the deposits is independent of carbon nanotubes concentration in the plating bath when it is up to 5 mg/L. The test results show that the carbon nanotubes co-deposited do not change the str ucture of the Ni-P matrix of the composite coating,but greatly increase the ha rdness and wear resistance and decrease the friction coefficient of the Ni-P-C NTs composite coating with increasing content of carbon nanotubes in deposits.

Nonlinear in-plane thermal buckling of rotationally restrained functionally graded carbon nanotube reinforced composite shallow arches under uniform radial loading

The nonlinear in-plane instability of functionally graded carbon nanotube reinforced composite(FG-CNTRC)shallow circular arches with rotational constraints subject to a uniform radial load in a thermal environment is investigated.Assuming arches with thickness-graded material properties,four different distribution patterns of carbon nanotubes(CNTs)are considered.The classical arch theory and Donnell’s shallow shell theory assumptions are used to evaluate the arch displacement field,and the analytical solutions of buckling equilibrium equations and buckling loads are obtained by using the principle of virtual work.The critical geometric parameters are introduced to determine the criteria for buckling mode switching.Parametric studies are carried out to demonstrate the effects of temperature variations,material parameters,geometric parameters,and elastic constraints on the stability of the arch.It is found that increasing the volume fraction of CNTs and distributing CNTs away from the neutral axis significantly enhance the bending stiffness of the arch.In addition,the pretension and initial displacement caused by the temperature field have significant effects on the buckling behavior.

Multi-wall carbon nanotubes reinforced aluminum composites synthesized by hot press sintering and squeeze casting

Multi-wall carbon nanotubes (MWNTs) have high mechanical properties and are considered a kind of realistic reinforcement for polymers, ceramics and metals. The hot press sintering and squeeze casting were adopted to synthesize MWNTs reinforced aluminum composites. In hot press sintered MWNTs/Al composites, MWNTs agglomerates distribute along aluminum powders and have low bonding strength with aluminum. But MWNTs agglomerates distribute evenly in the squeeze cast MWNTs/Al composites. Some dispersed nanotubes bond well with aluminum matrix and few dislocations can be found in the nanotube areas, which implies little thermal residual stress in squeeze cast MWNTs/Al composites. This indicates that the strengthen mechanisms in nanometer sized MWNTs/Al composites may be different from that in micrometer sized whisker composites.

Effects of carbon nanotubes on hydrogen storage property of Mg-based nanocomposites

Mg-based hydrogen storage nanocomposites added with carbon nanotubes(CNTs) were prepared by mechanical milling under the atmosphere of hydrogen. The results show that because of their own excellent heat conductivity and good hydrogen storage ability, the carbon nanotubes improve the mass transfer and heat transfer properties of the Mg-based nanocomponents, thus enhancing the kinetic property of hydrogen absorption and desorption of the hydrogen storage nanocomposites, and raising the hydrogen storage capacity. Due to the addition of the carbon nanotubes, the milling stress in the process of preparing the Mg-based nanocomposites is reduced, the components can be closely bonded easily, and the additives can play better catalytic roles.

Large deflection response-based geometrical nonlinearity of nanocomposite structures reinforced with carbon nanotubes

This paper deals with the nonlinear large deflection analysis of functionally graded carbon nanotube-reinforced composite(FG-CNTRC)plates and panels using a finite element method.Based on the first-order shear deformation theory(FSDT),the proposed model takes into account the transverse shear deformations and incorporates the geometrical nonlinearity type.A C^0 isoparametric finite shell element is developed for the present nonlinear model with the description of large displacements and finite rotations.By adopting the extended rule of mixture,the effective material properties of FG-CNTRCs are approximated with the introduction of some efficiency parameters.Four carbon nanotube(CNT)distributions,labeled uniformly distributed(UD)-CNT,FG-VCNT,FG-O-CNT,and FG-X-CNT,are considered.The solution procedure is carried out via the Newton-Raphson incremental technique.Various numerical applications in both isotropic and CNTRC composite cases are performed to trace the potential of the present model.The effects of the CNT distributions,their volume fractions,and the geometrical characteristics on the nonlinear deflection responses of FG-CNTRC structures are highlighted via a detailed parametric study.

Vibration characteristics of piezoelectric functionally graded carbon nanotube-reinforced composite doubly-curved shells

This paper presents an analytical solution for the free vibration behavior of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) doubly curved shallow shells with integrated piezoelectric layers. Here, the linear distribution of electric potential across the thickness of the piezoelectric layer and five different types of carbon nanotube(CNT) distributions through the thickness direction are considered. Based on the four-variable shear deformation refined shell theory, governing equations are obtained by applying Hamilton's principle. Navier's solution for the shell panels with the simply supported boundary condition at all four edges is derived. Several numerical examples validate the accuracy of the presented solution. New parametric studies regarding the effects of different material properties, shell geometric parameters, and electrical boundary conditions on the free vibration responses of the hybrid panels are investigated and discussed in detail.

The effect of initial geometric imperfection on the nonlinear resonance of functionally graded carbon nanotube-reinforced composite rectangular plates

The purpose of the present study is to examine the impact of initial geometric imperfection on the nonlinear dynamical characteristics of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) rectangular plates under a harmonic excitation transverse load. The considered plate is assumed to be made of matrix and single-walled carbon nanotubes(SWCNTs). The rule of mixture is employed to calculate the effective material properties of the plate. Within the framework of the parabolic shear deformation plate theory with taking the influence of transverse shear deformation and rotary inertia into account, Hamilton’s principle is utilized to derive the geometrically nonlinear mathematical formulation including the governing equations and corresponding boundary conditions of initially imperfect FG-CNTRC plates. Afterwards, with the aid of an efficient multistep numerical solution methodology, the frequency-amplitude and forcing-amplitude curves of initially imperfect FG-CNTRC rectangular plates with various edge conditions are provided, demonstrating the influence of initial imperfection,geometrical parameters, and edge conditions. It is displayed that an increase in the initial geometric imperfection intensifies the softening-type behavior of system, while no softening behavior can be found in the frequency-amplitude curve of a perfect plate.

定位夹具对CNTs/6061Al复合材料超声波焊接接头质量影响研究

采用超声波焊接制备CNTs增强铝基复合材料,针对超声波焊接定位不准,接头搭接面不贴合等问题,基于定位夹具以保证焊接过程质量,在工艺参数组合焊接能量500J,焊接压力0.45MPa,焊接振幅35μm下进行焊接试验。利用扫描电镜(SEM)、能谱仪(EDS)等对接头界面组织和成分进行了研究,并对焊接接头进行了剪切力和硬度测试。结果表明:在定位夹具下焊接的接头界面发生明显塑性且CNTs在铝基体扩散较好,接头强度显著提升,剪切力平均值达到786.55N、硬度为72HV,本研究对现有的有色金属超声波焊接制造工艺提出一种新的解决思路和方案,具有一定的工程应用价值和经济效益。

Preparation of multi-walled carbon nanotube-reinforced TiNi matrix composites from elemental powders by spark plasma sintering

Carbon nanotube (CNT)-reinforced TiNi matrix composites were synthesized by spark plasma sintering (SPS) employing elemental powders.The phase structure,morphology and transformation behaviors were studied.It was found that thermoelastic martensitic transformation be-haviors could be observed from the samples sintered above 800 ℃ even with a short sintering time (5min),and the transformation tempera-tures gradually increased with increasing sintering temperature because of more Ti-rich TiNi phase formation.Although decreasing the sin-tering temperature and time to 700 ℃ and 5min could not protect defective MWCNTs from reacting with Ti,still-perfect MWCNTs re-mained in the specimens sintered at 900 ℃.This method is expected to supply a basis for preparing CNT-reinforced TiNi composites.

Thermal conductivity of carbon nanotube-silver composite

The molecular level mixing method was extended to fabricate carbon nanotube reinforced silver composite. The influence of type of carbon nanotubes（single/multiwall） reinforcement and their mode of functionalization（covalent/non-covalent） on thermal conductivity of silver composite was investigated. X-ray diffraction and electron diffraction spectroscopy（EDS） confirm the presence of silver and carbon in the composite powder. High resolution scanning electron microscopy and transmission electron microscopy ascertain embedded, anchored and homogeneously implanted carbon nanotubes in silver matrix. Effect of covalent functionalization on multiwall carbon nanotubes was monitored by Raman and Fourier transform infrared spectroscopy. These investigations confirm the addition of functional groups and structural integrity of carbon nanotubes even after covalent functionalization. Thermal conductivity of composites was measured by a laser flash technique and theoretically analyzed using an effective medium approach. The experimental results reveal that thermal conductivity decreases after incorporation of covalently functionalized multiwall nanotubes and single wall carbon nanotubes. However, non-covalently functionalized multiwall nanotube reinforcement leads to the increase in effective thermal conductivity of the composite and is in agreement with theoretical predictions derived from effective medium theory, in absence of interfacial thermal resistance.

Optimal design of functionally graded Pm PV/CNT nanocomposite cylindrical tube for purpose of torque transmission

Carbon nanotube(CNT)/polymer nanocomposites have vast application in industry because of their light mass and high strength. In this work, a cylindrical tube which is made up of functionally graded(FG) PmP V/CNT nanocomposite, is optimally designed for the purpose of torque transmission. The main confining parameters of a rotating shaft in torque transmission process are mass of the shaft, critical speed of rotation and critical buckling torque. It is required to solve a multi-objective optimization problem(MOP) to consider these three targets simultaneously in the process of design. The three-objective optimization problem for this case is defined and solved using a hybrid method of FEM and modified non-dominated sorting genetic algorithm(NSGA-II), by coupling two softwares, MATLAB and ABAQUS. Optimization process provides a set of non-dominated optimal design vectors. Then, two methods, nearest to ideal point(NIP) and technique for ordering preferences by similarity to ideal solution(TOPSIS), are employed to choose trade-off optimum design vectors. Optimum parameters that are obtained from this work are compared with the results of previous studies for similar cylindrical tubes made from composite or a hybrid of aluminum and composite that more than 20% improvement is observed in all of the objective functions.

Covalent organic frameworks/carbon nanotubes composite with cobalt(II)pyrimidine sites for bifunctional oxygen electrocatalysis

With characteristics and advantages of functional composite materials,they are commendably adopted in numerous fields especially in oxygen electrocatalysis,which is due to the significant synergies between various components.Herein,a novel bifunctional oxygen electrocatalyst(Co-CNT@COF-Pyr)has been synthesized through in-situ growth of covalent organic frameworks(COFs)layers on the outer surface of highly conductive carbon nanotubes(CNTs)followed by coordination with Co(Ⅱ).For electrocatalytic OER,Co-CNT@COF-Pyr reveals a low overpotential(438 mV)in alkaline electrolyte(1.0 M aqueous solution of KOH)with a current density of 10 mA cm^(-2),which is comparable to most discovered COF-based catalysts.For electrocatalytic ORR,CoCNT@COF-Pyr exhibits a low H_(2)O_(2) yield range(9.0%-10.1%)and a reaction pathway close to 4e^(-)(n=3.82-3.80)in alkaline electrolyte(0.1 M aqueous solution of KOH)within the test potential range of 0.1-0.6 V vs.RHE,which is superior to most reported COF-based catalysts.Hence,this research could not only offer an innovative insight into the construction of composites,but also facilitate the practical application of renewable fuel cells,closed water cycle,and rechargeable metal-air batteries.

Application and structure of carbon nanotube and graphene-based flexible electrode materials and assembly modes of flexible lithium-ion batteries toward different functions

In recent years,the rapid development of portable/wearable electronics has created an urgent need for the development of flexible energy storage devices.Flexible lithium-ion batteries(FLIBs)have emerged as the most attractive and versatile flexible electronic storage devices available.Carbon nanotubes(CNTs)are hollow-structured tubular nanomaterials with high electrical conductivity,large specific surface area,and excellent mechanical properties.Graphene(G)is to some extent comparable to CNTs,because both have unlimited value in flexible electrodes.Herein,a systematic summary of the application of CNT and G in FLIBs electrodes is presented,including different functional applications and services at different temperatures.Furthermore,the effects of electrode structures,including powder,wire-shaped,and film-shaped structures,on electrochemical properties is highlighted.The assembly structures of the FLIBs consisting of CNT and G-based flexible electrodes to realize different functions,including bendability,stretchability,foldability,self-healing,and self-detecting,are systematically reviewed.The current challenges and development prospects of flexible CNT and G-based flexible electrodes and corresponding FLIBs are discussed.

Remarkable carbon dioxide catalytic capture (CDCC) leading to solid-form carbon material via a new CVD integrated process (CVD-IP): An alternative route for CO_2 sequestration

Through our newly-developed ＂chemical vapor deposition integrated process （ISVD-IP）＇＂ using carbon OlOXlae （t..u2） as me raw matenal and only carbon source introduced, CO2 could be catalytically activated and converted to a new solid-form product, i.e., carbon nanotubes （CO2-derived） at a quite high yield （the single-pass carbon yield in the solid-form carbon-product produced from CO2 catalytic capture and conversion was more than 30% at a single-pass carbon-base）. For comparison, when only pure carbon dioxide was introduced using the conventional CVD method without integrated process, no solid-form carbon-material product could be formed. In the addition of saturated steam at room temperature in the feed for CVD, there were much more end-opening carbon nano-tubes produced, at a slightly higher carbon yield. These inspiring works opened a remarkable and alternative new approach for carbon dioxide catalytic capture to solid-form product, comparing with that of CO2 sequestration （CCS） or CO2 mineralization （solidification）, etc. As a result, there was much less body volume and almost no greenhouse effect for this solid-form carbon-material than those of primitive carbon dioxide.