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Mechanical properties and vibration responses of nanocomposite materials: A review
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In this study, the effect of isothermal and isochronal aging is reported to investigate the precipitate evolution and recrystallization of N36 zirconium alloy after β-quenching. Two groups of samples were cut from the as-received sheet of N36 zirconium alloy and subjected to solution treatment and subsequent aging at 580, 640, and 700 °C for 40 and 600 min, respectively. Optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and electron backscattering diffraction (EBSD) were utilized to characterize the microstructure and second-phase particle (SPPs) evolution. Results show that the implemented quenching after solution treatment produces fine interlaced α-plates structure conserved inside prior β grain boundaries with 12 variant directions that follow Burger misorientation characteristics. After aging for a short time, initial α-plates conserve their shape and become softer, and SPPs spread along their boundaries. Recrystallizations are finished for specimens aged at a higher temperature or for a longer time. The recrystallized structure exhibits non-uniform grains and a random SPPs distribution. Despite the differences in morphology, some recrystallization grains retain the orientation feature from the initial α-plates. Hardness declines as temperature and time rise, and no hardness peak is seen. Roughness and wettability rise with increasing ageing temperatures.
In order to evaluate the model metallic glass alloy's mechanical properties (Fe49.7 Cr17.1 Mn1.9 Mo7.4 W1.6 B15.2 C3.8 Si2.4) prepared by spark plasma sintering (SPS) which have high velocity. We made an apparatus having three-point curve testing. The comparatively bulk sizes of sample in the current study permitted the creation samples for test with a macro scale cross-section (range of mm) consistent test dimensions, and well-controlled sample sizes. Cutting using a wire saw produced remarkably sharp notches with a radius that was 3 times smaller than in earlier studies. Our three-point bending apparatus allowed us to acquire the 231 GPa and 4.91 MPam1/2 values for notch fracture toughness and young's modulus. Additionally, the results of the Vickers indentation and flexure tests for young's modulus were reliable. Vickers indentation measurements of indentation fracture toughness produced values that were a minimum of 49.9% lower than those obtained flexure using. The method for examine micro scale mechanical properties described in this study and the accompanying scrutinizes are valid to samples with different ones or compositions that are made by further means.
This study concerns the wear behaviour of metal couples used in industry, particularly in mechanical sliding systems (numerically controlled machine tools). In general, the nature of the materials of the parts of these systems which are in contact and move relatively, are medium carbon steels, thanks to their good mechanical and tribological properties. The present work aims to study, the dry sliding wear of the contact surface of the pin (machine slide) against the contact surface of a disc (machine groove) and the damage induced on the worn track. The pin is AISI 1038 and AISI 1045 steel, the disc is AISI 1055 steel. The tribological tests were carried out on a pin-disc tribometer, in an atmospheric environment. The wear of the pins being evaluated by weighing and studied according to the hardness of the pin with the variation of the normal load applied. The discussion of the results is based on SEM observations and EDS analyzes of worn surfaces and interfacial phenomena produced by dynamic contact. The results obtained indicated the influence of the applied load and the hardness on the wear of the pin and therefore on the tribological behaviour of the worn surfaces.
The aim of this study is to evaluate the elastic properties of high-density polyethylene (HDPE) using single-walled carbon nanotubes (SWCNTs) reinforcements with experimental and Finite element method (FEM) considering two different processing techniques effect. SWCNT nanoparticles were used to strengthen the HDPE matrix at the weight fractions (wt%) of 0, 0.2, 0.4, 0.6, 0.8, and 1 and the resulting nanocomposites were processed using injection and compression moulding. From each processing method, the HDPE/SWCNTs nanocomposites tensile test specimen were prepared and tested for the elastic properties. Experimental results showed that the addition of SWCNT nanoparticles for each weight fractions and both processing methods enhanced the elastic properties of HDPE. Finally, the numerical simulations were conducted using FEM for the prediction of the elastic modulus of HDPE/SWCNT nanocomposites for both processing methods. Whereby the representative volume element (RVE) model was presented with an interfacial phase region separating the load transfer between the SWCNT and HDPE with the properties obtained from the atomic modelling results. The numerical FEM elastic modulus results were found to correlate with the experimental results.
Prediction of elastic behaviour of polymer-based nanocomposite using finite element method (FEM) has attracted the attention of many researchers in the past few years. In this study, ANSYS 19.2 software was used to predict the elastic modulus of high-density polyethylene (HDPE) reinforced with single-walled carbon nanotubes (SWCNTs) at different weight fractions. Three-dimensional (3-D) representative volume element (RVE) was created by FEM using ANSYS software to estimate the elastic modulus of HDPE based nanocomposite reinforced with SWCNTs nanoparticles at 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1 wt% weight fractions. To present the FEM model for predicting the elastic modulus of HDPE/SWCNT nanocomposite, the results from atomic modelling were extracted and used for properties of matrix and fibre interface. The interfacial region was used in the model to separate the conditions of load transfer between the HDPE matrix and SWCNT fibre. Two density fractions of HDPE/SWCNTs nanocomposite were also used in terms of two different densities for both HDPE and SWCNT to investigate their effect on the elastic modulus. The modelling results showed that the increase of weight fraction of single-walled carbon nanotubes (SWCNTs) results with the increase of relative elastic modulus of the nanocomposite. The results also showed that the elastic modulus of low-density fraction HDPE/SWCNTs nanocomposite improves more compared to one of the high-density fractions at the same SWCNTs weight fraction. Rule of the mixture was also used to predict the elastic behaviour of HDPE/SWCNT nanocomposite and the results were compared to those of the FEM model for validation.
In this study, a graphene nanoplatelets (GnPs)/acetone solution containing a small amount of resin/hardener was prepared as the spraying solution for modifying dry fabrics which are well compatible with the vacuum-assisted resin transfer infusion (VARI) process, and the GnPs-reinforced fiber laminated composites with GnPs uniformly distributed in the interlaminar regions were successfully fabricated. The results showed that the GnPs are well immobilized on the surface of carbon fibers after spray coating, and the mechanical properties and thermal conductivity of the carbon fiber/epoxy composites were effectively improved. The incorporation of 0.3 wt% GnPs produced the largest flexural strength and interlaminar shear strength, and the reinforcing mechanisms as well as failure modes of the composites were proposed. It was also noticed that the through-plane thermal conductivity of the composites consistently increases with increasing GnPs content due to the formation of effective conductive pathways between the interplies. The study suggested that the developed up-scalable spraying technique is an effective approach to deposit GnPs on dry carbon fabrics which are compatible with the economical VARI process for producing GnPs/fiber/epoxy multiscale composites with enhanced properties.
Based on Reddy’s third-order shear deformation plate theory, the nonlinear dynamic response and vibration of imperfect functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates on elastic foundations subjected to dynamic loads and temperature are presented. The plates are reinforced by single-walled carbon nanotubes which vary according to the linear functions of the plate thickness. The plate’s effective material properties are assumed to depend on temperature and estimated through the rule of mixture. By applying the Airy stress function, Galerkin method and fourth-order Runge–Kutta method, nonlinear dynamic response and natural frequency for imperfect FG-CNTRC plates are determined. In numerical results, the influences of geometrical parameters, elastic foundations, initial imperfection, dynamic loads, temperature increment, and nanotube volume fraction on the nonlinear vibration of FG-CNTRC plates are investigated. The obtained results are validated by comparing with those of other authors.
The pozzolanic effect of nanosilica (NS) particles when combined with Multi Walled Carbon Nanotubes (MWCNT) was studied in Ca(OH)2 pastes and Portland cement mortars. Experimental design techniques were used to plan the experiments and identify the effect of the nanoparticles on the properties of the cementing matrices by means of Analysis of Variance (ANOVA). Samples were prepared with different combinations of NS and MWCNT. Ca(OH)2 pastes were used to study the effect the nanoparticles had on the Calcium-Silicate-Hydrate (C-S-H) production. Portland cement mortars were used to study the effect of the nanoparticles on the compressive and flexural strength of the cementing matrices. We found that only NS had a significant effect on the C-S-H formation for up to 21 days of hydration, and that MWCNT did not present a positive effect on the mechanical strength of mortars due to the effects of reagglomeration.
A protocol has been developed for the production of epoxy-based composites containing high-volume fractions of aligned carbon nanotubes. The nanotubes were fabricated as continuous fibres or aligned mats directly from the CVD reactor, in which they were synthesized. The block composites with highly aligned and tightly packed nanotube assemblies were prepared via epoxy resin infiltration, and their volume fraction, distribution, and internal porosity being analysed prior to mechanical testing. The samples were tested in both axial tension and three-point bending. The results show that the strength and stiffness enhancements were close to pro rata with the volume fraction of the carbon nanotubes added. The failure modes were distinctly different from those characteristic of the conventional aligned carbon fibre composites. The fracture surface showed considerable evidence of pull-out of bundles of (~50) nanotubes, but the pull-out appeared to involve the resin matrix which drew out along with the bundles. Subsidiary cracks were bridged by nanotube bundles giving structures reminiscent of crazes in glassy polymers, what constitutes the distinct toughness mechanism and higher resistance to the transverse cracks propagation.
This article deals with the vibration analysis of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) shell structures. The material properties of an FG-CNTRC shell are graded smoothly through the thickness direction of the shell according to uniform distribution and some other functionally graded (FG) distributions (such as FG-X, FG-V, FG-O and FG-Λ) of the volume fraction of the carbon nanotube (CNT), and the effective material properties are estimated by employing the extended rule of mixture. An eight-noded shell element considering transverse shear effect according to Mindlin’s hypothesis has been employed for the finite element modelling and analysis of the composite shell structures. The formulation of the shell midsurface in an arbitrary curvilinear coordinate system based on the tensorial notation is also presented. The Rayleigh damping model has been implemented in order to study the effects of carbon nanotubes (CNTs) on the damping capacity of such shell structures. Different types of shell panels have been analyzed in order to study the impulse and frequency responses. The influences of CNT volume fraction, CNT distribution, geometry of the shell and material distributions on the dynamic behavior of FG-CNTRC shell structures have also been presented and discussed. Various types of FG-CNTRC shell structures (such as spherical, ellipsoidal, doubly curved and cylindrical) have been analyzed and discussed in order to compare studies in terms of settling time, first resonant frequency and absolute amplitude corresponding to first resonant frequency based on the impulse and frequency responses, and the effects of CNTs on vibration responses of such shell structures are also presented. The results show that the CNT distribution and volume fraction of CNT have a significant effect on vibration and damping characteristics of the structure.
The present study proposes to investigate the properties of graphene based nano patch antenna considering the semi-infinite, geometries of the graphene attaining zigzag and armchair structures. The antenna designs are simulated on HFSS software and the performance is analyzed in terahertz band based on the different electronic properties. Depending on the edge shapes of structure obtained after cutting the infinite graphene sheet, arrangements formed are named as the zigzag and armchair. As these configurations exhibit different electronic properties, it is suggested that the respective graphene antenna will also lead to varying radiations properties. It is evident from the various results in terms of return loss, gain, radiation efficiency and bandwidth that the graphene antenna based on zigzag arrangement realizes better characteristic as compared to armchair arrangement.
In this article, an analytical approach was developed for rectangular nanoplatelet reinforced composites. This approach could be used for estimating mechanical properties such as elastic modulus subjected to applied axial and thermal loads. Two sets of displacement were required for calculating the mechanical properties; thus, two sets of matrix/platelet displacement solutions, the far-field solution and the transient solution were precisely derived and superposed to achieve simplified analytical expressions for the matrix/platelet stress field components and the platelet axial stress field components in the entire composite system, including the platelet end region, by adding the imaginary platelet. The present research were compared and verified with the results of Mori-Tanaka and Halpin-Tsai and also, experimental results. The results were in good agreement with both experimental data and other published theoretical predictions. The present model was found to be very accurate and relatively simple in predicting Young's modulus of nanocomposites and was capable of correctly predicting effects of nanoplatelet aspect ratio, nanoplatelet weight and volume fraction.
Flexible fiber-shaped energy storage devices have been studied and developed intensively over the past few years to meet the demands of modern electronics in terms of flexibility, weavability and being lightweight. In this review, fiber electrodes and flexible fiber energy storage devices containing solid-state supercapacitors (SCs) and lithium-ion batteries (LIBs) are carefully summarized with particular emphasis on their electrode fabrication, structure design and flexibility. In addition, emerging wire-shaped integrated energy systems, combined energy storage and solar cells, as well as other electronic devices to realize self-charging and self-powered integrated systems are specifically highlighted.
Carbon fiber reinforced plastics/polymers (CFRPs) offer excellent mechanical properties that lead to enhanced functional performance and, in turn, wide applications in numerous industrial fields. Post machining of CFRPs is an essential procedure that assures that the manufactured components meet their dimensional tolerances, surface quality and other functional requirements, which is currently considered an extremely difficult process due to the highly nonlinear, inhomogeneous, and abrasive nature of CFRPs. In this paper, a comprehensive literature review on machining of CFRPs is given with a focus on five main issues including conventional and unconventional hybrid processes for CFRP machining, cutting theories and thermal/mechanical response studies, numerical simulations, tool performance and tooling techniques, and economic impacts of CFRP machining. Given the similarities in the experimental and theoretical studies related to the machining of glass fiber reinforced polymers (GFRPs) and other FRPs parallel insights are drawn to CFRP machining to offer additional understanding of on-going and promising attempts in CFRP machining.
Composites based on epoxy resin and differently aligned multi-walled carbon nanotube (MWCNT) sheets have been developed using hot-melt prepreg processing. Aligned MWCNT sheets were produced from MWCNT arrays using the drawing and winding technique. Wavy MWCNTs in the sheets have limited reinforcement efficiency in the composites. Therefore, mechanical stretching of the MWCNT sheets and their prepregs was conducted for this study. Mechanical stretching of the MWCNT sheets and hot stretching of the MWCNT/epoxy prepregs markedly improved the mechanical properties of the composites. The improved mechanical properties of stretched composites derived from the increased MWCNT volume fraction and the reduced MWCNT waviness caused by stretching. With a 3% stretch ratio, the MWCNT/epoxy composites achieved their best mechanical properties in this study. Although hot stretching of the prepregs increased the tensile strength and modulus of the composites considerably, its efficiency was lower than that of stretching the MWCNT sheets.
The discovery of ‘fullerenes’ added a new dimension to the knowledge of carbon science1; and the subsequent discovery of ‘carbon nanotubes’ (CNTs, the elongated fullerene) added a new dimension to the knowledge of technology2;. Today, ‘nanotechnology’ is a hot topic attracting scientists, industrialists, journalists, governments, and even the general public. Nanotechnology is the creation of functional materials, devices, and systems through control of matter on the nanometer scale and the exploitation of novel phenomena and properties of matter (physical, chemical, biological, electrical, etc.) at that length scale. CNTs are supposed to be a key component of nanotechnology. Almost every week a new potential application of CNTs is identified, stimulating scientists to peep into this tiny tube with ever increasing curiosity.
A concerted survey is presented of the existing theories for predicting the strength and modulus of particulate-filled polymeric composites. The macroscopic behaviour of particulate composites is affected by the size, shape, and the distribution of the inclusions. The interfacial adhesion between the matrix and inclusion is also important. The limitation of theoretical models in describing these parameters and expressing the experimental data on the macroscopic behaviour is demonstrated.
A brief historical review of carbon nanotube research is presented and some basic definitions relevant to the structure and
properties of carbon nanotubes are provided.
Carbon nanotubes are unique nanostructures that can be considered conceptually as a prototype one-dimensional (1D) quantum
wire. The fundamental building block of carbon nanotubes is the very long all-carbon cylindrical Single Wall Carbon Nanotube
(SWNT), one atom in wall thickness and tens of atoms around the circumference (typical diameter ~1.4nm). Initially, carbon
nanotubes aroused great interest in the research community because of their exotic electronic properties, and this interest
continues as other remarkable properties are discovered and promises for practical applications develop.
In this study, a combined analytical and finite element‐based micromechanical modeling is performed to characterize the elastic properties of carbon nanotube (CNT) reinforced polymer nanocomposites and validated with experimental work. First, coordinates of armchair and zigzag type CNTs are generated using MATLAB based on the geometric structure of the CNTs and imported to the computational software ANSYS to model and characterize the elastic properties of the individual single‐walled CNT (SWCNT) and multi‐walled CNT by applying various loading and boundary conditions. The present developed finite element method (FEM) model of CNTs is validated with the available literature in terms of elastic properties. Subsequently, the equivalent elastic properties of CNT reinforced epoxy nanocomposites are determined through representative volume element (RVE) model by finite element simulations and Mori‐Tanaka homogenization techniques by replacing CNTs with equivalent fibers as microinclusions. The equivalent elastic properties of nanocomposite obtained by the FEM and analytical model are compared and validated with the experimental results. Further, the detailed parametric study is performed to investigate the influence of tube chirality, volume fraction, and orientation of CNT in terms of the elastic properties of the nanocomposite. It was observed that the armchair type CNT reinforced nanocomposites are stiffer than the zigzag type SWCNT reinforced nanocomposites in terms of elastic moduli. Further, it was noticed that the tube chirality and the number of walls of CNTs have significantly influenced the elastic behavior of nanocomposites. It can be concluded that the presented combined model provides an efficient methodology and comprehensive understanding to analyze the elastic behavior of CNTs and CNT reinforced nanocomposites. So, the presented combined numerical and experimental study could serve as a guideline in micromechanical modeling and characterization of elastic behavior of CNT‐reinforced polymer nanocomposites. In this study, a combined analytical and finite element based micromechanical modeling is performed to characterize the elastic properties of carbon nanotube reinforced polymer nanocomposites and validated with experimental work. The equivalent elastic properties of nanocomposite obtained by the finite element method and analytical model are compared and validated with the experimental results obtained.
Piezoelectric vibration energy harvesters have attracted much attention due to its potential to replace currently popular batteries and to provide an sustainable power sources. Many researchers have proposed ways to increase the performance of piezoelectric energy harvesters like bandwidth, working frequency and output performance. Here in this contribution, we propose the method of using elastic extensions to tune the performance of a piezoelectric energy harvester. Mathematical model of the proposed device is derived and analyzed. Numerical simulations are done to investigate the influences of the derived parameters, like length ratio λl, bending stiffness ratio λB, and line density ratio λm. Results show that the elastic extension does change the motion of the proposed device and help tune the performance of piezoelectric energy harvesters.
This article aims to provide a general overview of what has been achieved recently in the scientific community on the manufacturing monitoring and structural health monitoring of polymer-matrix composites (PMC) using in-situ piezoelectric sensors. Some industrial applications with the underlying issues and potential solutions will finally be discussed in the concluding section.
Keywords: Polymer-matrix composites (PMCs); In-situ piezoelectric sensors; Process monitoring; Structural health monitoring; Non-destructive testing; Smart materials.
This work deals with functionally graded piezoelectric energy harvesting from vibrations of functionally graded beam under travelling multi oscillators. To this propose, a functionally graded piezoelectric harvester is stuck under the beam span. The material properties of the beam and piezoelectric patch are assumed to be graded through the thickness direction according to a functionally graded pattern. The generalized Hamilton's principle and Euler Bernoulli beam theory are adopted for derivation of governing equations of electro-mechanical materials. The system of equations for is derived by using. This principle leads to the two sets of second order differential equations as the governing equations of motion for both beam and oscillator. These governing equations are coupled by the contact forces between the oscillator and beam. Finally, the finite element formulations of the problem are presented. A comprehensive parameter study is done to find the effects of material distribution, mass ratio, velocity, damping ratio, spring constant of the oscillators as well as time lags between each moving vehicles on the harvested energy. The results reveal the significant effects of the model parameters on the harvested energy from vibrations of the graded beam under travelling multi-moving oscillators.
The vibration and damping characteristics of epoxy composites reinforced by pristine and functionalized multi-walled carbon nanotubes (MWCNTs) were investigated experimentally for potential use as integral passive damping elements in structural composite applications. The MWCNTs were introduced into the acetone solvent and then mixed with epoxy resin through a sonication process and mechanical stirring. The solvent was evaporated from the mixture by means of magnetic hot plate and the hardener was added once it was cooled down to room temperature. The MWCMTs/epoxy mixture was then injected into a mold to form the nanocomposite specimens. Nanocomposite specimens were fabricated for six different MWCNT loadings (0.02, 0.041, 0.061, 0.123, 0.25 and 0.37 wt%). Microstructural analysis, tensile and bending tests were carried out to examine the effect of pristine multi-walled carbon nanotubes (p-MWCNTs) and functionalized multi-walled carbon nanotubes (f-MWCNTs). The frequency response functions (FRFs), coherence and phase diagrams of nanocomposites were measured using a forced vibration technique. A periodic up-chirp signal was generated by a shaker to excite the cantilever nanocomposite specimen at the base. The damped natural frequencies and damping ratios were obtained for different loadings of MWCNTs. The experimental results indicated that the damped natural frequencies of p-MWCNTs/epoxy and f-MWCNTs/epoxy composites increased by adding MWCNTs up to 0.12 wt.%, and decreased at higher MWCNTs content. Addition of p-MWCNTs were improved the damping ratio of nanocomposites. While the damping ratios from f-MWCNTs at loadings of 0.02–0.06 wt.% were higher than those from p-MWCNTs, they did not increase at higher CNTs contents for the first mode of vibration.
Multi-walled carbon nanotubes (MWCNTs) have wide application prospects but also exhibit notable biotoxicity that is tightly associated with macrophages. Macrophages simultaneously act as initiators and defenders in MWCNT-induced organ lesions, and targeting macrophages with MWCNTs may be a potential immunotherapy and oncotherapy approach. This review focuses on the impacts of MWCNTs on macrophages and further discusses the influence of MWCNT characteristics on their bioactivity. Based on existing studies, MWCNTs stimulate macrophage migration, induce secretion of various cytokines and activate inflammatory pathways in macrophages, especially NLRP3-mediated IL-1β production. This inflammatory state, together with the oxidative stress and cell membrane lesions induced by MWCNTs, contributes to decreased phagocytic ability and cell viability, which finally results in cell apoptosis and necrosis. A series of intracellular and systemic components, such as toll-like receptor, high-mobility group box 1, Rho-associated kinases, scavenger receptor and complement components, may be involved in the above-mentioned cell-MWCNT interactions. The characteristics of MWCNTs can influence their bioactivity in macrophages both mechanically and chemically. The size (length and/or diameter), functionalization, purification and even the experimental method can affect the influence of MWCNTs on macrophages, and a better understanding of these MWCNT characteristics may benefit utilization of this nanomaterial in associated nanomedical applications.
Floating catalyst chemical vapor deposition (FCCVD) can produce buckypaper, a kind of CNT film, at large-scale with low cost. However, individual CNTs in the buckypaper are mostly randomly oriented, which significantly limits their electrical and mechanical properties. Here we report an innovative approach, water-assisted shear stretching (WASS), which can significantly improve CNT alignments and consequently enhance the electrical and mechanical properties. In addition, we define a unique “alignment factor” to quantify the alignment degree, and to estimate the effect of alignment on the mechanical and electrical properties of CNT assemblies. The high mechanical strength and excellent electrical conductivity of the WASS-processed buckypaper enhance their potential for applications in new electronic technologies and high-strength lightweight aerospace structures.
This research presents an investigation into the free vibration of a sandwich plate with a transversely flexible polymeric core and two carbon nanotubes reinforced nanocomposite face sheets based on high-order sandwich plate theory. The material properties are considered to be temperature- and moisture-dependent. The mathematical model of the face sheets is developed based on the classical plate theory and modified strain gradient theory. Also, Eshelby–Mori–Tanaka approach is used to estimate the material properties of the face sheets and consider the agglomeration effect of carbon nanotubes. The governing equations of motion which included the size effect as well as hygrothermal effect are derived based on Hamilton’s principle and solved by means of Navier’s solution method. The influence of various parameters such as agglomeration effect and the volume fraction of carbon nanotubes, material length scale parameters, aspect and side ratios, temperature changes, and humidity condition is presented. In addition, orthotropic Pasternak foundation is taken into account to study the influence of orthotropic angle on the vibrational behavior of the sandwich plate, and also a comparison of a symmetric sandwich plate and two types of asymmetric ones is carried out for different values of normal and shear Pasternak foundation modulus. Employing carbon nanotubes reinforced nanocomposite face sheets, orthotropic Pasternak foundation and size-dependent theory leads to an increase in the stiffness of the sandwich structure and considering the temperature and humidity changes and agglomeration effect of carbon nanotubes in the face sheets helps to achieve the results with higher accuracy which can be used in modern engineering applications.
We find thermal stresses developed in Ceramic Matrix Composite (CMC) cylindrical shells reinforced with aggregated Carbon Nanotubes (CNTs) with heat flux prescribed on the inner surface and temperature on the outer surface. Null surface tractions are prescribed on these two surfaces and the cylinder edges are clamped. The material properties are homogenized by using a two-parameter Eshelby-Mori-Tanaka (EMT) approach. Material properties of the ceramic are assumed to depend upon the temperature, and the smooth variation of the CNT volume fraction through the shell thickness is assumed to be described either by a sigmoidal function or profile-O or profile-X often used in the literature. The one-way coupled thermo-mechanical problem is analyzed by first numerically solving the nonlinear heat equation with the Generalized Differential Quadrature Method (GDQM), and then the linear mechanical problem by using Reddy's Third-order Shear Deformation Theory (TSDT) and the GDQM. For the same thermal boundary conditions and the volume fraction of CNTs, the maximum hoop, the in-plane shear and the transverse normal stresses developed in the cylinder are highest for the profile-X of CNTs. The aggregation factor noticeably influences the maximum transverse normal and the maximum hoop stresses developed in the cylinder.
Carbon nanotubes (CNTs) have attracted great attention due to their remarkable mechanical and electrical properties. Incorporation of CNTs can significantly improve the properties of cement-based materials, especially the electrical conductivity. However, agglomeration of CNTs is frequently encountered which can largely weaken the functionality of composites. In this work, enhanced dispersion of carbon nanotubes in cement-based materials has been achieved by using three dispersants and in combination with ultrasonic vibration. The influence of dispersants on the electrical conductivity and mechanical properties of cement paste incorporated with CNTs has been investigated. It is shown that enhanced dispersion of CNTs achieved by the use of dispersants significantly improves the electrical conductivity through the formation of electrical networks in the cement-based composite at mature stage. Air bubbles introduced by the dispersant in cement-based composites reduces its electrical conductivity significantly. Moreover, the air bubbles also lead to a large decrease of the compressive strength of CNTs reinforced cement-based composites.
High-performance lightweight composites are sizably manufactured by impregnating continuous aligned carbon nanotube sheet (buckypapers) with self-reinforcing polyphenylene (Parmax) solution and followed by hot-press. The high processing pressure flattens nanotubes, which preferably π-stack with the aromatic rings of Parmax chain, and accordingly improve the load transfer. Both tensile strength and Young's modulus of the thermoplastic composites increase with the alignment degree of nanotubes, and can reach 950MPa and 94GPa, respectively, for the composite containing 50%-stretched buckypaper. The highly aligned nanotubes also boost phonon transfer (70WmK-1) and the electric conductivity (425Scm-1) of the composite along the alignment direction. These combined outstanding properties would enable the thermoplastic composites in wide applications as multifunctional material.
A continuous development of advanced manufacturing technologies have been accredited with the aerospace industry. Year after year the demand for economic manufacturing, reduction of fuel consumption while increasing the range at the same time is pursued. This requires a high level of productivity and maximum quality. To achieve these goals, an up-to-date technological development within the industry is necessary. With new machine developments, innovative production engineering, efficient process planning and organization concept, production technology makes an essential contribution to the further development of globally active companies. The MIC2015 is presented from the Institute of Production Engineering and Machine Tools in cooperation with the Machining Innovations Network e.V. and takes place at the Hannover Centre for Production Technology (PZH, Garbsen, Germany). Renowned experts from industry and research will present the latest trends, newest know-how and research results in 37 speeches.
The scientific session is sponsored by The International Academy for Production Engineering (CIRP). All contributions to the scientific session are published in "Procedia CIRP” by Elsevier.
This research explores the history and structure of carbon nanotubes and the current technologies and methods available for synthesizing, purifying, and assembling carbon nanotubes. Furthermore, the current state of fabrication of carbon nanotubes has not reached a level where they can be commercialized. The most commonly used techniques of chemical vapor deposition (CVD), arc discharge, and laser ablation are discussed in detail with emphasis placed on three criteria: cost, rate, and flexibility. Satisfactory achievement in these three areas will result in the ability to have carbon nanotubes as a product. Assembly methods like nanopelleting and individual transplanting has helped make great strides towards reaching a state of commercialization, but several advancements need to take place with respect to carrying current processes out on a larger scale at affordable prices.
In-situ observation of tensile tests were performed to investigate the strengthening mechanisms of multi-walled carbon nanotube (MWCNT) reinforced Al matrix composites (AMCs). Carbon nanotubes (CNTs) were effectively incorporated and aligned in AMCs through a conventional powder metallurgy route. During tensile failure, the fracture process of CNTs in fabricated AMCs was clearly observed, suggesting the effective load transfer between the matrix and CNTs, and between inner walls of MWCNTs. Due to the small reinforcing effect of other factors, load transfer strengthening dominantly contributed to the observed high strengthening efficiency in CNT/Al composite, agreeing with the predicted results of the shear-lag model. This study provided evidence supporting the theory behind load transfer strengthening mechanisms of CNTs in metal matrix composites.
For all engineers and students coming to finite element analysis or to ANSYS software for the first time, this powerful hands-on guide develops a detailed and confident understanding of using ANSYS's powerful engineering analysis tools. The best way to learn complex systems is by means of hands-on experience. With an innovative and clear tutorial based approach, this powerful book provides readers with a comprehensive introduction to all of the fundamental areas of engineering analysis they are likely to require either as part of their studies or in getting up to speed fast with the use of ANSYS software in working life. Opening with an introduction to the principles of the finite element method, the book then presents an overview of ANSYS technologies before moving on to cover key applications areas in detail. Key topics covered: Introduction to the finite element method Getting started with ANSYS software stress analysis dynamics of machines fluid dynamics problems thermo mechanics contact and surface mechanics exercises, tutorials, worked examples With its detailed step-by-step explanations, extensive worked examples and sample problems, this book will develop the reader's understanding of FEA and their ability to use ANSYS's software tools to solve their own particular analysis problems, not just the ones set in the book. * Develops a detailed understanding of finite element analysis and the use of ANSYS software by example * Develops a detailed understanding of finite element analysis and the use of ANSYS software by example * Exclusively structured around the market leading ANSYS software, with detailed and clear step-by-step instruction, worked examples, and detailed, screen-by-screen illustrative problems to reinforce learning.
The objective of the present paper is to investigate the bending, buckling and vibration behaviors of carbon nanotube-reinforced composite (CNTRC) beams. The beams resting on the Pasternak elastic foundation, including a shear layer and Winkler spring, are considered. The single-walled carbon nanotubes (SWCNTs) are aligned and distributed in polymeric matrix with different patterns of reinforcement. The material properties of the CNTRC beams are estimated by using the rule of mixture. Various shear deformation theories are employed to deal with the problems. The mathematical models provided in this paper are numerically validated by comparison with some available results. New results of bending, buckling and vibration analyses of CNTRC beams based on several higher-order shear deformation theories are presented and discussed in details. Several aspects of beam types, spring constant factors, carbon nanotube volume fraction, etc., are taken into investigation.
The central impact of a mass on a simply supported laminated composite plate under initial stress is investigated. The contact force and the dynamic response of the plate are obtained by solving a nonlinear integral equation. The energy transferred from the mass to the plate during impact is also obtained by use of a normalized contact force. It is found that a higher initial tensile stress elevates the maximum contact force, but reduces the contact time, the deflection, and the stresses. It is also noted that a higher tensile initial stress results in less energy transfer from the striking mass to the plate.
The formation of carbon nanotube networks around the structural reinforcement in fiber composites has enabled in situ monitoring of matrix damage accumulation. Real-time monitoring of damage development under fatigue loading was studied. The electrical response of the fatigue specimens change synchronously with the applied fatigue loading and enable a quantitative measure of the damage state. The fatigue response of the nanotube network was examined and the damage accumulation validated using microscopic technique. Various damage stages in composite cross-ply laminates under fatigue loading can be clearly detected by adopting the quantitative parameter, damaged resistance change. The sensitivity of the technique to the onset and accumulation of damage may enable future life prediction methodologies.
Conventional micro-fiber-reinforced composites provide insight into critical structural features needed for obtaining maximum composite strength and stiffness: the reinforcements should be long, well aligned in a unidirectional orientation, and should have a high reinforcement volume fraction. It has long been a challenge for researchers to process CNT composites with such structural features. Here we report a method to quickly produce macroscopic CNT composites with a high volume fraction of millimeter long, well aligned CNTs. Specifically, we use the novel method, shear pressing, to process tall, vertically aligned CNT arrays into dense aligned CNT preforms, which are subsequently processed into composites. Alignment was confirmed through SEM analysis while a CNT volume fraction in the composites was calculated to be 27%, based on thermogravimetric analysis data. Tensile testing of the preforms and composites showed promising mechanical properties with tensile strengths reaching 400MPa.
An embedded carbon nanotube in a polymer matrix is replaced with an equivalent long fiber for predicting the mechanical properties of the carbon nanotube/polymer composite. A 3-D finite element model consisting of a carbon nanotube, inter-phase and surrounding polymer is built. The inter-phase region is treated using van der Waals interactions. Comparing finite element analysis results and the rule of mixture we observed that the latter overestimates the properties of investigated composite and cannot capture the difference between the micro- and nanoscale. Developed equivalent fiber consisting of carbon nanotube and inter-phase region can be appropriately used in micromechanical equations.
Carbon nanotubes (CNTs) are one of the wonders of modern science. Discovered a little over 15 years ago, they have shown the research community an outstanding set of properties. In terms of mechanical properties, they exhibit extremely high young's modulus, which, coupled with a high strain to break, leads to unsurpassed strength to break. CNTs also demonstrate superior thermal conductivity, good electrical capacity and high thermal stability. In light of these properties, CNTs are expected to be introduced into a wide variety of new materials aimed at applications for various fields, such as high-performance composites, biological and chemical sensors, magnetic recording, nanoelectronic devices and flat panel displays. One such promising application is CNT-reinforced composite materials, exhibiting the possibility of outstanding mechanical properties. In practice, however, many reports indicate that nanocomposites are weaker or only slightly stronger than the neat resins. Several factors are believed to be the primary source of this discrepancy, namely poor nanotube dispersion in resin, inadequate alignment of the nanotubes, and weak interfacial bonding between nanotubes and resins. As a result, these have become crucial investigation issues for developing high-performance nanocomposites. In this dissertation, fundamental understanding of the interfacial phenomena between carbon nanotubes and polymer matrices are studied. Both molecular dynamics (MD) simulation, an effective approach to investigate nanoscale behaviors, and experimental investigation, are utilized to achieve this goal. First, we examine the interface formation phenomena between a Single Wall Carbon Nanotube (SWNT) and the resin, prior to curing, in the case of the Epon862 resin system. The MD simulation results outline the validity of some of the current theories, such as molecular migration and reduction of molecular mobility of the resin, while they seem to indicate some other mechanisms are not present in this resin system, such as molecular wrapping around the SWNTs. Second, existing MD simulation models of nanotube pullout are analyzed and modified to examine the energy of certain material systems more correctly, and to characterize interfacial shear strength in SWNT/polymer composites. The interfacial bonding and load transfer behaviors between the different SWNTs' configurations (open end, capped end, functionalized end) and three different matrices (polystyrene, polyethylene and Epon862) were examined using the modified models. The results of the modified models effectively reveal the effects of different tube configurations and resin matrices on the interfacial strength during a simulated pullout. Finally, we use MD simulation to investigate the coefficient of thermal expansion (CTE) of individual SWNTs, SWNT ropes, as well as SWNT nanocomposites. Experiments were also carried out in order to gain further insight in the results. It is found that, while the CTE of individual nanotubes is of low negative value, the CTE of the same tubes within a rope or a nanocomposite can significantly change. We also find that SWNTs can be utilized to tailor the CTE of the Epon862 resin system, depending on the functionalization of the SWNTs prior to their introduction in the resin. Finally, a new twisting vibration mode was revealed in SWNT ropes that should prove critical in further SWNT rope studies utilizing MD simulation.
Research aimed at producing new nanocomposites with improved properties has dramatically increased in the last decade, especially on materials tailored at a nanometric level, such as fullerenes and carbon nanotubes. The use of nanoforms as reinforcement of organic polymers has opened the possibility of developing novel ultra-strong and conductive nanocomposites. Nevertheless, the challenge of manufacturing multifunctional composite materials based on nanostructures is still open, in particular in the details of the corresponding interfacial properties, which are particularly relevant in these systems. This paper reviews the main technical activities in this field, focusing on the most important parameters that influence the behavior of their interface, discussing recent advances, as well as current and future trends in research.
Composites have set the standard for high strength materials for several decades. With the discovery of nanotubes, new possibilities for reinforced composites have arisen, with potential mechanical properties superior to those of currently available materials. This paper reports the properties of epoxy matrix reinforced with fibres of carbon nanotubes (CNTs) which, in many ways, are similar to standard composites reinforced with commercial fibres. The composites were formed by the back diffusion of the uncured epoxy into an array of aligned fibres of CNTs. The fibre density and volume fraction were measured from thermogravimetric analysis (TGA). Properties in tension and compression were measured, and the level of fibre-matrix interaction analysed fractographically. The results show the significant potential for this route to CNT reinforcement. (C) 2008 Elsevier Ltd. All rights reserved.
Graphene oxide nanoribbons (GONRs) and chemically reduced graphene nanoribbons (crGNRs) were dispersed at high concentrations in chlorosulfonic acid to form anisotropic liquid crystal phases. The liquid crystal solutions were spun directly into hundreds of meters of continuous macroscopic fibers. The relationship of fiber morphology to coagulation bath conditions was studied. The effects of colloid concentration, annealing temperature, spinning air gap and pretension during annealing on the fibers' performance were also investigated. Heat treatment of the as-spun GONR fibers at 1500 °C produced thermally reduced graphene nanoribbon (trGNR) fibers with a tensile strength of 378 MPa, Young's modulus of 36.2 GPa and electrical conductivity of 285 S/cm, which considerably higher than in other reported graphene-derived fibers. This better trGNR fiber performance was due to the air-gap spinning and annealing with pretension that produced higher molecular alignment within the fibers, as determined by X-ray diffraction and scanning electron microscopy. The specific modulus of trGNR fibers is higher than the commercial general purpose carbon fibers and commonly used metals such as Al, Cu and steel. The properties of trGNR fibers can be further improved by optimizing the spinning conditions with higher draw ratio, annealing conditions with higher pretensions, and using longer flake GONRs. This technique is a new high-carbon-yield approach to make the next generation carbon fibers based on solution-based liquid crystal phase spinning.
The mechanical behavior of multiwalled carbon nanotube/epoxy composites was studied in both tension and compression. It was found that the compression modulus is higher than the tensile modulus, indicating that load transfer to the nanotubes in the composite is much higher in compression. In addition, it was found that the Raman peak position, indicating the strain in the carbon bonds under loading, shifts significantly under compression but not in tension. It is proposed that during load transfer to multiwalled nanotubes, only the outer layers are stressed in tension whereas all the layers respond in compression. © 1998 American Institute of Physics.
This work provides information on the characterization of carbon nanotube (CNT) skeletons, or Buckypapers, using contact angle and thermogravimetric analysis (TGA) measurements. The preparation of composites using these CNT skeletons and an epoxy resin by impregnation in vacuum and cure in two moulds with different release surfaces is described. Preliminary results for the mechanical performance of the produced composites using mini-tensile test specimens and their characterization by TGA, dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM) is also presented.
A connection between the stiffness of carbon nanotubes (CNT) and their mesoscopic physical behaviour is presented. Persistence
lengths of CNT and bundles are calculated and shown to be in macroscopic range (0.03–1mm for an individual tube), exceeding
by many orders of magnitude the typical diameters (around 1–3nm). Consequently, thermal fluctuations can be neglected when
scaling analysis is applied to randomly packed (as produced) CNT network, leading to an approximate equation of state for
such material. Beyond the linear elasticity, the outmost CNT are shown to gradually split from the bent bundles; this permits
access of solvent or reacting species to the CNT walls, an important mechanism promoting solubilization and chemical functionalization
of nanotubes.
Numerical simulations of the properties of dielectric nanocomposites using local field calculations are performed. Thus the dipole-dipole interactions and interactions between the dipoles and the electrodes are considered. The simulations are based on the microscopic local field method and a dynamic Monte Carlo algorithm. In the context of dielectric binary mixtures no analytic solution exists for a given microstructure. Such a problem can only be solved numerically. The approximations for such a system using macroscopic mixing rules can be misleading. We compare the results obtained by the local field method to the classical mixing rules of Maxwell-Garnett and Polder-van Santen. In the context of a polar guest phase in a non-polar host phase the impact of the nanodielectric inclusion modeled by permanent dipoles into the host matrix is investigated. For a two phase system with polar and non-polar units we simulate all interactions and investigate the ferroelectric hysteresis. The ferroelectric hysteresis is observed for the modeled P(VDF/TrFE) structure with dielectric layers on both sides. We will see that many effects which are unique for a given microstructure can not be observed by the application of a strategy of homogenization which is the case for all empirical mixing rules.