Hollow Cylindrical Shape Research Articles

Analysis of Mechanical Properties of Carbon Nanotube Reinforced Polymer Composites Using Continuum Mechanics Approach

Carbon Nanotubes (CNT) due to their excellent mechanical, thermal and electrical properties to the best carbon fibres, have attracted composite fraternity to explore the possibility of using them as an additional reinforcement in carbon fibre reinforced polymer composites. In this paper, the effect on elastic modulus due to CNT reinforcement on exiting two phase polymer composite is studied using both finite element analysis and rule of mixture theory. The carbon nanotubes are modelled as continuum hollow cylindrical shape elastic material and mechanical property of CNT reinforced nanocomposites have been investigated using 3D represented volume Element. The matrix materials have been epoxy and PEEK whereas carbon fibres and glass fibres have been used as primary reinforcements. The mechanical properties have been evaluated for different volume fractions of CNTs and for different configuration of matrix and fibres.

TiO2 nanotubes and its composites: Photocatalytic and other photo-driven applications

Abstract

Effect of carbon nanotube orientation on the mechanical properties of nanocomposites

Carbon nanotubes (CNTs) have been regarded as ideal reinforcements of high-performance composites with enormous applications. In this paper, nano-structure is modeled as a linearly elastic composite medium, which consists of a homogeneous matrix having hexagonal representative volume elements (RVEs) and homogeneous cylindrical nanotubes with various inclination angles. Effects of inclined carbon nanotubes on mechanical properties are investigated for nano-composites using 3-D hexagonal representative volume element (RVE) with short and straight CNTs. The CNT is modeled as a continuum hollow cylindrical shape elastic material with different angles. The effect of the inclination of the CNT and its parameters is studied. Numerical equations are used to extract the effective material properties for the hexagonal RVE under axial as well as lateral loading conditions. The computational results indicated that elastic modulus of nano-composite is remarkably dependent on the orientation of the dispersed SWNTs. It is observed that the inclination significantly reduces the effective Young’s modulus of elasticity under an axial stretch. When compared with lateral loading case, effective reinforcement is found better in axial loading case. The effective moduli are very sensitive to the inclination and this sensitivity decreases with the increase of the waviness. In the case of short CNTs, increasing trend is observed up to a specific value of waviness index. It is also found from the simulation results that geometry of RVE does not have much significance on stiffness of nano-structures. The results obtained for straight CNTs are consistent with ERM results for hexagonal RVEs, which validate the proposed model results.

Analysis of elastic properties of carbon nanotube reinforced nanocomposites with pinhole defects

Due to their unique molecular structure, carbon nanotubes exhibit outstanding properties. They are regarded as ideal reinforcements of composites. In this paper, the effects of pinhole defects on mechanical properties are investigated for wavy carbon nanotubes based nanocomposites using 3-D Representative Volume Element with long carbon nanotubes. The carbon nanotubes are modeled as continuum hollow cylindrical shape elastic material with pinholes, having some curvature in its shape. These defects are considered on the single walled carbon nanotubes. The mechanical properties like Young’s modulus of elasticity are evaluated for various values of waviness index, as well as type and number of pinhole defects. The effects of interactions between both defects as well as their influence on the nanocomposites are studied under an axial loading condition. Numerical equations are used to extract the effective material properties for the different geometries of Representative Volume Elements with non-defective carbon nanotubes. The finite element method results obtained for non-defective carbon nanotubes are consistent with analytical results for cylindrical Representative Volume Elements, which validate the proposed model. It is observed that the presence of pinhole defects as well as waviness, can significantly reduces the effective reinforcement, when compared with nanotubes without pinhole defects and this reinforcement decreases with the increase of the number of pinhole defects.

Effect of waviness on the mechanical properties of carbon nanotube based composites

Carbon nanotubes have been regarded as ideal reinforcements of high performance composites with enormous applications. In this paper, effects of wavy carbon nanotubes on mechanical properties such as elasticity and strength aspects are investigated for nanocomposites using a 3-D representative volume element with long and short wavy carbon nanotubes. The carbon nanotube is modeled as a continuum hollow cylindrical shape elastic material with some curvature in its shape. The effect of the waviness of the carbon nanotubes and its parameters are studied. Numerical equations are used to extort the effective material properties for the different geometries of representative volume elements, under axial loading for straight carbon nanotubes. It is observed that waviness significantly reduces the effective reinforcement of the nanocomposites. The effective moduli are very sensitive to the waviness and this sensitivity decreases with the increase of the waviness. In the case of short carbon nanotubes, increasing trend is observed up to a specific value of waviness index. Tensile strength analysis shows a decreasing trend of the strength against the increasing the values of waviness indices. Geometry of the RVE is also found to be affecting the strength of the carbon nanotube reinforced composites. Simulation is applied on the straight carbon nanotubes with the hexagonal representative volume element, and the results are found to be consistent with the rule of mixtures results, which validate the proposed model.

Effect of Pinhole Defects on the Elasticity of Carbon Nanotube Based Nanocomposites

Carbon nanotubes (CNTs) have been regarded as an ideal reinforcements of high-performance composites with enormous applications. In this paper, the effects of pinhole defect are investigated for carbon nanotube based nanocomposites using a 3D representative volume element (RVE) with long CNTs. The CNT is modeled as a continuum hollow cylindrical shape elastic material with pinholes in it. These defects are considered on the single wall (CNTs). The mechanical properties such as Young’s modulus of elasticity are evaluated for various pinhole locations and number of defects. The influence of the pinhole defects on the nanocomposite is studied under an axial load condition. Numerical equations are used to extract the effective material properties for the different geometries of RVEs with nondefective CNTs. The field-emission microscopy (FEM) results obtained for nondefective CNTs are consistent with the analytical results for cylindrical RVEs, which validate the proposed model. It is observed that the presence of pinhole defects significantly reduces the effective reinforcement when compared with nondefective nanotubes, and this reinforcement decreases with the increase in the number of pinhole defects. It is also found from the simulation results that the geometry of RVE does not have much significance on the stiffness of nanocomposites.

Phosphate removal by hydrothermally modified fumed silica and pulverized oyster shell

A calcined and hydrothermally annealed material for phosphate removal was prepared in a hollow cylindrical shape from fumed silica generated by a ferroalloy factory, and pulverized oyster shell. Phosphorus removal from wastewater by this material calcined at a range of temperatures (700–900 °C) and hydrothermally annealed at temperatures from 130 to 180 °C, for 8–16 h, was investigated and the most suitable physicochemical conditions were determined. XRD, SEM, EDS, and XRF techniques were used to characterize the microstructures and compositions of the materials produced, and UV–Vis spectrophotometry using the ammonium phosphomolybdate blue method was used to determine the phosphate concentration in the wastewater. The results indicate that calcium carbonate in oyster shell reacted with SiO 2 in fumed silica and formed hydrated calcium silicate after hydrothermal treatment, and the hydrated calcium silicate reacted with phosphate ions in wastewaters to form hydroxyapatite precipitate. The optimal conditions for material production were calcination at 800 °C, and hydrothermal annealing at 150 °C for 12 h. Materials made under these conditions showed 74% or 92% phosphate removal after 2 or 4 h, respectively.

Column-type multi-component force transducers and their evaluation for dynamic measurement

We describe the dynamic evaluation of multi-component force–moment transducers. Two of these transducers, which can measure three force components, Fx, Fy and Fz, and three moment components, Mx, My and Mz, were developed. One has a solid cylindrical sensing element and the other has a hollow cylindrical shape. They were calibrated statically with a force–moment calibration machine in the Physikalisch-Technische Bundesanstalt (PTB), Germany. We evaluated the dynamic characteristics of the force–moment transducers by using a shaker system and a multi-channel dynamic analyser system. The frequency range of the normal force component Fz is very wide up to 1 kHz, the test frequency in this study. However, the frequency ranges for the transverse force components and moment components are restricted to about 200 Hz and 130 Hz respectively. The column-type force–moment transducer has a high stiffness and so its frequency range is wider than that of a binocular-type force–moment transducer.

Vibration of piezoelectric elements surrounded by fluid media

In this paper we analyse vibrational characteristics of piezoceramic shells surrounded by acoustic media. Main results are presented for radially polarized piezoceramic PZT5 elements of hollow cylindrical shapes. The coupling in the radial direction between the solid and the acoustic media is accounted for indirectly, via impedance boundary conditions. The model based on such impedance boundary condition approximations offers a robust simplified alternative to a full scale fluid–solid interaction modelling. By using this model, we analyse numerically the influence of the boundary conditions imposed in the axial direction for long, medium, and short (disk-like) piezoceramic elements.

Modelling of high quality pasta drying: mathematical model and validation

The pasta drying process was studied using an engineering approach. The phenomena of mass and heat exchange between pasta samples and air was modelled according to the classic transport approach applied to a hollow cylindrical shape pasta. Data from the literature and from measurements were used to fix the material parameter values of both the air and dough phases. Theoretical correlations were used to obtain a good estimate of mass and heat exchange coefficients between dough samples and air. The proposed model was set by choosing the mass transfer coefficient as the unique optimisation parameter, determined by best fitting of the experimental water content data obtained under given conditions in a static dryer. The model was then validated at different temperature and air humidity drying profiles and a good agreement with the experimental results was found. Finally the model was applied to different process conditions and the drying time was calculated from the simulations.

Numerical analysis of dynamic characteristics of coupled piezoelectric systems in acoustic media

In this paper, the full dynamic model describing vibrations of piezoceramic solids of hollow cylindrical shapes and accounting for the coupling of the solids to surrounding fluid/gas media has been analysed numerically. The major attention has been given to the case of radial preliminary polarisation of piezoceramics where a strong coupling between electric and mechanical fields is an essential feature of the dynamics. An efficient numerical discretisation scheme based on the integro-interpolation approach has been proposed and representative examples of computational experiments are given.

An absolute method for determination of thermal conductivities of thermal insulators by microcalorimetry

Microcalorimetry was developed to determine thermal conductivities (λ) of thermal insulators with hollow cylindrical shapes. A special device of specimen with resistance threads wrapped on its surface and electric heater placed in its hole was designed to meet the needs of determining λ without using standard substances to calibrate the instrument. A formula for calculating the value of λ was derived. By heating in the hole and on the surface of the specimen respectively, the values of λ can be obtained conveniently by this technique. The method was tested with teflon, plexiglass, quartz glass and polyethylene. The experimental values of λ for the four substances agree well with the literatures ones. Error analysis was also made on the experimental data. It was found that the main factors affecting values of λ are: (1) The errors of determining the values of heat cumulated in specimen and materials in the space around it and (2) the errors of determining the values of inner and outer radii of cylindrical specimen.

Development of Bolt-Clamped Langevin-Type Transducer with High Mechanical Quality Factor for Excitation of Large Torsional Vibration

We have identified a crucial point for realization of a high mechanical quality factor (Q) of a bolt-clamped Langevin-type transducer used to excite large torsional vibrations of a cylindrical system. A sufficient margin of the static bearing stress over the vibratory shearing one at the interface between the components has been found necessary for a high Q as a result of some numerical simulations and experiments for two models of the transducers. A hollow cylindrical shape of the transducer is seen to have a great advantage in this respect.

The multicatalytic proteinase complex (proteasome): structure and conformational changes associated with changes in proteolytic activity

The multicatalytic proteinase complex or proteasome is a high-molecular-mass multisubunit proteinase which is found in the nucleus and cytoplasm of eukaryotic cells. Electron microscopy of negatively stained rat liver proteinase preparations suggests that the particle has a hollow cylindrical shape (approximate width 11 nm and height 17 nm using methylamine tungstate as the negative stain) with a pseudo-helical arrangement of subunits rather than the directly stacked arrangement suggested previously. The side-on view has a 2-fold rotational symmetry, while end-on there appears to be six or seven subunits around the ring. This model is very different from that proposed by others for the proteinase from rat liver but resembles the structure of the simpler archaebacterial proteasome. The possibility of conformational changes associated with the addition of effectors of proteolytic activity has been investigated by sedimentation velocity analysis and dynamic light-scattering measurements. The results provide the first direct evidence for conformational changes associated with the observed positive co-operativity in one component of the peptidylglutamylpeptide hydrolase activity as well as with the stimulation of peptidylglutamylpeptide hydrolase activities by MnCl2. In the latter case, there appears to be a correlation between changes in the shape of the molecule and the effect on activity. KCl and low concentrations of SDS may also act by inducing conformational changes within the complex. Sedimentation-velocity measurements also provide evidence for the formation of intermediates during dissociation of the complex by urea, guanidinium chloride or sodium thiocyanate. Dissociation of the complex either by these agents or by treatment at low pH leads to inactivation of its proteolytic components. The results suggest that activation and inhibition of the various proteolytic activities may be mediated by measurable changes in size and shape of the molecules.

Various microtubular patterns in dorsal root ganglia (DRG) in pyridoxine neurotoxicity

The term “microtubule” (MT) has been ascribed to a complex group of subcellular structures deploying at least two common characteristics: a hollow cylindrical shape and a diameter of less than 30 nm. Some authors, however, regard MT as composed of tubulin with well known roles in the organization of the cytoskeleton and different cellular functions such as secretion, mitosis, and motion. In alteration of the neuronal cytoskeletal organization in neurotoxicity, their tubulin composition has usually been unquestioned. Recently observed unusual MT aggregation patterns in pyridoxine neurotoxicity definitely raised questions as to the composition of some of the groups of microtubules which fulfill the general definition. At least three different patterns of MT aggregations were seen in neuronal cytons of DRG of dogs treated with high doses of pyridoxine.The large MT aggregates made up of numerous superimposed sheets of MT in parallel arrays and having different orientation in close proximity to ribosomes and membranes of rough endoplasmic reticulum (RER) have already been reported.

A gas-solid reaction model for flash wood pyrolysis

A theoretical modelling study of wood flash pyrolysis has been carried out using the single pellet technique. The model considers the transient behaviour of a single wood particle undergoing a fast thermal decomposition reaction. Mass transfer, pressure gradients in the pellet, heat transfer via convection, conduction and radiation, and structural changes occurring in the particle are accounted for. The wood particle is assumed to consist of fibres of hollow cylindrical shape. The pyrolysis reaction occurs at an interface within each fibre, which moves with time. The kinetic mechanism for the reaction assumes the wood to decompose according to two parallel reactions yielding tar and and (gas + char). Tar is then assumed to decompose further by secondary homogeneous cracking reactions to yield gas. The results of the modelling work compare favourably with experimental data of conversion and temperature over a wide range of operating temperatures.

Formation of astrophysical jets by a contracting magnetic accretion disk

In the present paper, we discuss an MHD model for the formation of astrophysical jets, in which the directed flows are ejected along the rotation axis of an accretion disk formed from a cloud having a large scale magnetic field parallel to the angular momentum axis of the disk. The acceleration of jets is due to the j × B force in the relaxing magnetic twist which is produced by the rotation of the disk. The characteristic features of the jets, predicted by our mechanism and hopefully to be proven by observations, are the helical velocity and the hollow cylindrical shape of the jet, with a diameter of roughly the size of the region from which the accretion disk collected its mass. Justification for the assumption of the perpendicular orientation of the disk, or the parallelism of the jets, to the external magnetic field may be provided by the fact that the component of rotation whose axis is perpendicular to the field may have been damped in the earlier phase of the cloud contraction.