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.

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.

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.

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.

Effects of ply-orientation on microstructure and properties of super-aligned carbon nanotube reinforced copper laminar composites

The super-aligned carbon nanotube(SACNT)films reinforced copper(Cu)laminar composites with different orientationsof CNT ply were fabricated by electrodeposition.The results show that the tensile strength and yield strength of cross-ply compositewith5.0%(volume fraction)of SACNT reach maximum of336.3MPa and246.0MPa respectively,increased by74.0%and124.5%compared with pure Cu prepared with the same method.Moreover,the electrical conductivities of all the prepared composites areover75%IACS.The result of TEM analysis shows that the size of Cu grain and the thickness of twin lamellae can be reduced byadding SACNT,and the refining effect in cross-ply composites is more significant than that in unidirectional ply composites.Theenhanced strength of the Cu/SACNT composites comes from not only the reinforcing effect of SACNT films but also the additionalstrengthening of the Cu grain refinement caused by CNT orientation.

Stress and buckling analysis of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets

In this paper,the stresses and buckling behaviors of a thick-walled mi-cro sandwich panel with a flexible foam core and carbon nanotube reinforced composite(CNTRC)face sheets are considered based on the high-order shear deformation theory(HSDT)and the modified couple stress theory(MCST).The governing equations of equi-librium are obtained based on the total potential energy principle.The effects of various parameters such as the aspect ratio,elastic foundation,temperature changes,and volume fraction of the canbon nanotubes(CNTs)on the critical buckling loads,normal stress,shear stress,and deflection of the thick-walled micro cylindrical sandwich panel consider-ing different distributions of CNTs are examined.The results are compared and validated with other studies,and showing an excellent compatibility.CNTs have become very use-ful and common candidates in sandwich structures,and they have been extensively used in many applications including nanotechnology,aerospace,and micro-structures.This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae.

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.

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.

Nonlocal thermal buckling and postbuckling of functionally graded graphene nanoplatelet reinforced piezoelectric micro-plate

This paper analyzes the nonlocal thermal buckling and postbuckling behaviors of a multi-layered graphene nanoplatelet(GPL)reinforced piezoelectric micro-plate.The GPLs are supposed to disperse as a gradient pattern in the composite micro-plate along its thickness.The effective material properties are calculated by the Halpin-Tsai parallel model and mixture rule for the functionally graded GPL reinforced piezoelectric(FG-GRP)micro-plate.Governing equations for the nonlocal thermal buckling and postbuckling behaviors of the FG-GRP micro-plate are obtained by the first-order shear deformation theory,the von Kármán nonlinear theory,and the minimum potential energy principle.The differential quadrature(DQ)method and iterative method are introduced to numerically analyze the effects of the external electric voltage,the distribution pattern and characteristic of GPLs,and the nonlocal parameter on the critical buckling behaviors and postbuckling equilibrium path of the FG-GRP micro-plate in thermal environment.

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.

Effects of Carbon Nanotubes by Electrophoretic Deposition on Interlaminar Properties of Two Dimensional Carbon/carbon Composites

Carbon nanotubes（CNTs） were deposited uniformly on carbon cloth by electrophoretic deposition（EPD）. Thereafter, CNT-doped clothes were stacked and densified by pyrocarbon via chemical vapor infiltration to fabricate two-dimensional（2 D） carbon/carbon（C/C） composites. Effects of EPD CNTs on interlaminar shear performance and mode Ⅱ interlaminar fracture toughness（GⅡc） of 2 D C/C composites were investigated. Results showed that EPD CNTs were uniformly covered on carbon fibers, acting as a porous coating. Such a CNT coating can obviously enhance the interlaminar shear strength and GⅡc of 2 D C/C composites. With increaing EPD CNTs, the interlaminar shear strength and GⅡc of 2 D C/C composites increase greatly and then decrease, both of which run up to their maximum values, i e, 13.6 MPa and 436.0 J·m-2, when the content of EPD CNTs is 0.54 wt%, 2.27 and 1.45 times of the baseline. Such improvements in interlaminar performance of 2 D C/C composites are mainly beneficial from their increased cohesion of interlaminar matrix, which is caused not only by the direct reinforcing effect of EPD CNT network but also by the capacity of EPD CNTs to refine pyrocarbon matrix and induce multilayered microstructures that greatly increase the crack propagation resistance through ＂crack-blocking and-deflecting mechanisms＂.

Plates, Beams and Shells Reinforced by CNTs or GPLs: A Review on Their Structural Behavior and Computational Methods

Since the initial observation of carbon nanotubes(CNTs)and graphene platelets(GPLs)in the 1990 and 2000s,the demand for high-performance structural applications and multifunctional materials has driven significant interest in composite structures reinforced with GPLs and CNTs.Incorporating these nanofillers into matrix materials markedly enhances the mechanical properties of the structures.To further improve efficiency and functionality,func-tionally graded(FG)distributions of CNTs and GPLs have been proposed.This study presents an extensive review of computational approaches developed to predict the global behavior of composite structural components enhanced with CNT and GPL nanofillers.The analysis focuses on key structural elements,such as plate-type configurations,cylindrical and curved shells,and beams,emphasizing the computational techniques utilized to simulate their mechanical behavior.The utilization of three-dimensional elasticity theories and equivalent single-layer(ESL)frameworks,which are widely employed in the modeling and analysis of these composites,is comprehensively discussed.Additionally,the paper examines various mechanical performance aspects,including static,buckling,post-buckling,vibrational,and dynamic responses for the mentioned structures.The unique features of hybrid nanocomposites,combining CNTs and GPLs,are also analyzed.Furthermore,the study delves into the fabrication and processing techniques of these materials,with a particular focus on strategies to mitigate nanofiller agglomeration.The review extends to cover thermal and electrical properties,durability under environmental exposure,fatigue resistance,and vibration-damping characteristics.In conclusion,the paper underscores the necessity for ongoing advancements in computational modeling to facilitate improved design,analysis,and optimization of nanocomposite structures.Future research opportunities in this rapidly advancing domain are also outlined.

Tailoring Anti-Impact Properties of Ultra-High Performance Concrete by Incorporating Functionalized Carbon Nanotubes

Replacing micro-reinforcing fibers with carbon nanotubes(CNTs)is beneficial for improving the impact properties of ultra-high performance concrete(UHPC);however,the weak wettability and dispersibility of CNTs and the weakly bonded interface between CNTs and UHPC limit their effectiveness as composites.Therefore,this study aims to enhance the reinforcement effect of CNTs on the impact properties of UHPC via functionalization.Unlike ordinary CNTs,functionalized CNTs with carboxyl or hydroxyl groups can break the Si-O-Ca-O-Si coordination bond in the C-S-H gel and form a new network in the UHPC matrix,effectively inhibiting the dislocation slip inside UHPC matrix.Furthermore,functionalized CNTs,particularly carboxyl-fu nctionalized CNTs,co ntrol the crystallization process and microscopic morphology of the hydration products,significantly decreasing and even eliminating the width of the aggregate-matrix interface transition zone of the UHPC.Moreover,the functionalized CNTs further decrease the attraction of the negatively charged silicate tetrahedron to Ca2+in the C-S-H gel,while modifying the pore structure(particularly the nanoscale pore structure)of UHPC,leading to the expansion of the intermediate CS-H layer.The changes in the microstructures of UHPC brought about by the functionalized CNTs significantly enhance its dynamic compressive strength,peak strain,impact toughness,and impact dissipation energy at strain rates of 200-800 s^(-1).Impact performance of UHPC containing a small amount of carboxyl-functionalized CNTs(especially the short ones)is generally better than that of UHPC containing hydroxyl-functionalized and ordinary CNTs;it is even superior to that of UHPC with a high steel fiber content.

A deep feed-forward neural network for damage detection in functionally graded carbon nanotube-reinforced composite plates using modal kinetic energy

This paper proposes a new Deep Feed-forward Neural Network(DFNN)approach for damage detection in functionally graded carbon nanotube-reinforced composite(FG-CNTRC)plates.In the proposed approach,the DFNN model is developed based on a data set containing 20000 samples of damage scenarios,obtained via finite element(FE)simulation,of the FG-CNTRC plates.The elemental modal kinetic energy(MKE)values,calculated from natural frequencies and translational nodal displacements of the structures,are utilized as input of the DFNN model while the damage locations and corresponding severities are considered as output.The state-of-the art Exponential Linear Units(ELU)activation function and the Adamax algorithm are employed to train the DFNN model.Additionally,in order to enhance the performance of the DFNN model,the mini-batch and early-stopping techniques are applied to the training process.A trial-and-error procedure is implemented to determine suitable parameters of the network such as the number of hidden layers and the number of neurons in each layer.The accuracy and capability of the proposed DFNN model are illustrated through two distinct configurations of the CNT-fibers constituting the FG-CNTRC plates including uniform distribution(UD)and functionally graded-V distribution(FG-VD).Furthermore,the performance and stability of the DFNN model with the consideration of noise effects on the input data are also investigated.Obtained results indicate that the proposed DFNN model is able to give sufficiently accurate damage detection outcomes for the FG-CNTRC plates for both cases of noise-free and noise-influenced data.

A Novel Multiscale Reinforcement by In-Situ Growing Carbon Nanotubes on Graphene Oxide Grafted Carbon Fibers and Its Reinforced Carbon/Carbon Composites with Improved Tensile Properties

In-situ growing carbon nanotubes （CNTs） directly on carbon fibers （CFs） always lead to a degraded tensile strength of CFs and then a poor fiber-dominated mechanical property of carbon/carbon composites （C/ Cs）. To solve this issue, here, a novel carbon fiber-based multiscale reinforcement is reported. To synthesize it, carbon fibers （CFs） have been first grafted by graphene oxide （GO）, and then carbon nanotubes （CNTs） have been in-situ grown on GO-grafted CFs by catalytic chemical vapor deposition. Characterizations on this novel reinforcement show that GO grafting cannot only nondestructively improve the surface chemical activity of CFs but also protect CFs against the high-temperature corrosion of metal catalyst during CNT growth, which maintains their tensile properties. Tensile property tests for unidirectional C/Cs with different preforms show that this novel reinforcement can endow C/C with improved tensile properties, 32% and 87% higher than that of pure C/C and C/C only doped with in-situ grown CNTs. This work would open up a possibility to fabricate multiscale C/Cs with excellent global performance.

Static and Dynamic Analyses of Composite Beam Bonded with MFC Actuator

Investigated by this study is an MFC actuator attached to the surface of a Carbon Fiber Reinforced Polymer(CFRP)composite beam to form a beam actuator system.Analytically capturing the characteristics of such system is essential.A novel analytical methodology considering the transverse shear strain and active stiffening effect is proposed,which was newly applied to analyze the static and dynamic behaviors of the beam actuator system.The governing equations of the beam actuator system were obtained via generalized Hamilton’s principle.A distributed transfer function formulation was developed.Then,the closed form solution was derived by using the Green’s function.Frequency response,natural frequencies,and modal shapes of the beam actuator system were obtained.The solution is analytical without using any truncated series or admissible functions at any arbitrary boundary conditions.Finite Element Method(FEM)results were also obtained to compare with that of the proposed method.The predictions of the analyses were verified experimentally,which shows the correctness and effectiveness of the proposed method.

The recent progress of functionally graded CNT reinforced composites and structures

In the last decade,the functionally graded carbon nanotube reinforced composites(FG-CNTRCs)have attracted considerable interest due to their excellent mechanical properties,and the structures made of FG-CNTRCs have found broad potential applications in aerospace,civil and ocean engineering,automotive industry,and smart structures.Here we review the literature regarding the mechanical analysis of bulk CNTR nanocomposites and FG-CNTRC structures,aiming to provide a clear picture of the mechanical modeling and properties of FG-CNTRCs as well as their composite structures.The review is organized as follows:(1)a brief introduction to the functionally graded materials(FGM),CNTRCs and FG-CNTRCs;(2)a literature review of the mechanical modeling methodologies and properties of bulk CNTRCs;(3)a detailed discussion on the mechanical behaviors of FG-CNTRCs;and(4)conclusions together with a suggestion of future research trends.

Function-Integrative Textile Reinforced Concrete Shells

This paper presents the development and technological implementation of textile reinforced concrete (TRC) shells with integrated functions, such as illumination and light control. In that regard the establishment of material, structural and technological foundations along the entire value chain are of central importance: From the light-weight design idea to the demonstrator and reference object, to the technological implementation for the transfer of the research results into practice. The development of the material included the requirement-oriented composition of a high-strength fine grained concrete with an integrated textile reinforcement, such as carbon knitted fabrics. Innovations in formwork solutions provide new possibilities for concrete constructions. So, a bionic optimized shape of the pavilion was developed, realized by four connected TRC-lightweight-shells. The thin-walled TRC-shells were manufactured with a formwork made of glass-fibre reinforced polymer (GFRP). An advantage of the GFRP-formwork is the freedom of design concerning the formwork shape. Moreover, an excellent concrete quality can be achieved, while the production of the precast concrete components is simple and efficient simultaneously. After the production the new TRC-shells were installed and assembled on the campus of TU-Chemnitz. A special feature of the research pavilions are the LED light strips integrated in the shell elements, providing homogeneous illumination.

高模量高强韧碳纳米管/铝合金复合材料研究进展

碳纳米管/铝合金(CNT/Al)复合材料作为新一代航天航空和武器装备用新型轻量化结构材料的典型代表,近年来其制备技术与应用技术研究都取得了长足进展。本文首先综述CNT/Al复合材料各种制备技术与工程化瓶颈,重点介绍可工程化的叠片粉末冶金与元素合金化相结合的基元组装制备技术,分析该技术制备的大尺寸CNT/2A12Al复合材料在室温与高温下的力学性能与阻尼性能;其次阐述CNT/Al复合材料的强韧化原理,重点介绍CNT晶内化分布与晶粒异构构型这2种可实现强塑性同步提升的强韧化策略;最后展示该复合材料的变形加工以及应用技术研究进展,并展望该材料的应用前景和未来研究重点。

碳纳米管增强复合材料Timoshenko梁弯曲和屈曲行为分析

考虑碳纳米管(carbon nanotubes,CNTs)的尺度效应,研究宏观尺度下碳纳米管增强复合材料(carbon nanotubes reinforced composites,CNTRCs)梁的弯曲和屈曲行为。在EMT(Eshelby-Mori-Tanaka)方法的基础上,利用非局部理论提出了可表征CNTs尺度效应的非局部EMT本构模型。根据Timoshenko梁理论,采用哈密顿原理得到CNTRCs梁的静力学微分方程和边界条件。求解简支边界条件下CNTRCs梁的弯曲响应和极限屈曲载荷,并与文献进行对比验证所建模型和求解方法的正确性。分析了CNTs的尺度效应参数和体积分数以及复合材料梁的长细比等因素对简支CNTRCs梁弯曲响应和极限屈曲载荷的影响规律。结果表明,考虑CNTs的尺度效应会削弱结构等效刚度,且CNTs体积分数和尺度效应参数对大长细比CNTRCs梁的弯曲响应和极限屈曲载荷的影响幅度较大。