检索结果-南通市图书馆

self-propagating high temperature synthesis of Mosi_2 matrix composites

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2006年第3期25卷 225-230页

作者： Akhtar Farid s.h. Islam Materials science and Engineering school State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China

Mosi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. Mosi2 and Mosi2 matrix composites were prepared by self-propagating high temperature synthesis （shs）. Pure Mosi2 was obtained and a compound of Mosi2 and Wsi2was synthesized in the form of predominant solid solution （Mo,W）si2. By adding aluminum of 5.5 at.% to Mo-si, the crystal structure of Mosi2 changed into a mixture of tetragonal Cllb Mosi2and hexagonal C40 Mo（si,Al）2. The （Mo,W）si2-Mo（si,Al）2-W（si,Al）2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-si. however, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. shs is an effective technology for synthesis of Mosi2 and Mosi2 matrix composites.

关键词： powder metallurgy Mosi2 matrix composites self-propagating high temperature synthesis molybdenumtungsten disilicide molybdenum aluminosilicide

Effects of Nb Alloying on Nano-Crystallization Kinetics of Fe_(55-x)Cr_(18)Mo_7B_(16)C_4Nb_x(x=0, 3) Bulk Amorphous Alloys

在线全文

学校读者我要写书评

暂无评论

Journal of Materials science & Technology 2011年第8期27卷 735-740页

作者： s. Ahmadi h.R. shahverdi s.s. saremi Faculty of Engineering Department of Materials Science Tarbiat Modares University

Crystallization kinetics of Fe55-xCrzsMo7B10C4Nbx（x= 0, 3） bulk amorphous alloys were analyzed using X-ray diffraction and differential scanning; calorimetric （DsC） tests. In practice, crystallization and growth mechanism were evaluated using DsC tests at four different heating rates （10, 20, 30, and 40 K/rain） and kinetic models. Two-step crystallization behavior was observed when Fe55Cr18MOTB16C4 and Fe52Cr18MoTB16C4Nb3 bulk amorphous alloys were annealed, where Fe36Cr12M010 phase was crystallized in the first step of crystallization. Results show that Fe36Cr12Mo10 and Fe3C phases were crystallized in the structures of the alloys after further annealing： process. Activation energy for the crystallization of Fe36Cr12Mozo phase was measured to be 543 kJ/mol in Fe52Cr18MoTB16C4Nb3 alloy and 375 kJ/mol for Fe55Cr18Mo7B16C4 alloy according to Kissinger-starink model. Moreover, a two-dimensiona nucleation rate was found in Fe52Cr18Mo7B16C4Nb3 diffusion controlled growth mechanism with decreasing alloy whereas a three-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in crystallization of Fe36Crz2Mo10 phase during annealing of Fe55Cr18MoTB16C4 alloy. TEM （transmission electron microscopy） observations reveal that crystalline Fe36Cr12M010 phase nucleated in the structures of the alloys in an average size of 10 nm with completely mottled morphology.

关键词： Avrami exponent Crystallization Kinetic models Growth mechanisms Bulk amorphous alloys

Optimal design of V-type ultrasonic motor

在线全文

学校读者我要写书评

暂无评论

Journal of Central south University 2010年第6期17卷 1247-1250页

作者： JEONG s s PARK C h PARK T G school of Mechatronics Changwon National UniversityChangwon 641773Korea

V-type ultrasonic linear motor fabricated using a simple punching technique was proposed to utilize as an actuator of small precision *** stator of the motor is composed of a thin elastic body and four ceramics attached to the upper and bottom areas of the *** ceramics have each direction of *** two harmonic voltages with a 90° phase difference are applied to the ceramics,symmetric and anti-symmetric displacements will generate at the tip to produce an elliptical motion.A finite element analysis(ATILA) was conducted to simulate the motion pattern for the contact tip of the *** develop a model that generates the maximum displacement at contact tip,the FEM program was used for various *** addition,an optimal model was chosen by considering the magnitude and shape of the displacement according to changes in *** maximum elliptical displacement is shown by W2L11 model,which has a ratio of ceramic width to length of 1:***,the displacement of the contact tip is reduced by the bucking phenomenon if the ratio is larger than 1:6.

关键词： ultrasonic motor piezo-actuator finite element method optimal design elliptical motion

Electrical features of radio-frequency atmospheric pressure helium discharge with and without dielectric electrodes

在线全文

学校读者我要写书评

暂无评论

Plasma science and Technology 2019年第2期21卷 60-67页

作者： h AshRAF s Z A shAh h I A QAZI M A KhAN s hUssAIN M A BADAR s NIAZ M shAFIQ Department of Physics University of Sargodha Department of Physics Quaid-i-Azam University

A comparative study of radio-frequency atmospheric pressure glow discharge(rf APGD)generated in helium with and without dielectric electrodes to investigate the effect of electrodes insulation on electrical features of APGD is presented. In the α mode, both the rf APGDs remain volumetric, stable and uniform. In the γ mode, the APGD without dielectric electrodes shrinks into a constricted plasma column whereas APGD with dielectric electrodes remains stable and retains the same volume without plasma constriction even at higher densities of discharge current. A comparison of electrical features of both rf APGDs in normal and abnormal glow discharge regimes is presented. In both APGDs with and without dielectric electrodes,impedance measurements have been performed and compared with equivalent circuit *** measured impedance data is found to be in good agreement with simulated data.

关键词： radiofrequency atmospheric pressure glow discharge dielectric electrodes plasma stability control

Thermal vibration of functionally graded porous nanocomposite beams reinforced by graphene platelets

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2020年第8期41卷 1209-1226页

作者： M.h.YAs s.RAhIMI Department of Mechanical Engineering Razi UniversityKermanshah 67346-67149Iran

The thermal vibration of functionally graded(FG)porous nanocomposite beams reinforced by graphene platelets(GPLs)is *** beams are exposed to the thermal gradient with a multilayer *** temperature varies linearly across the thickness *** different types of dispersion patterns of GPLs as well as porosity distributions are *** material properties vary along the thickness *** using the mechanical parameters of closed-cell cellular solid,the variation of Poisson’s ratio and the relation between the porosity coefficient and the mass density under the Gaussian random field(GRF)model are *** using the halpin-Tsai micromechanics model,the elastic modulus of the nanocomposite is *** equations of motion based on the Timoshenko beam theory are obtained by using hamilton’s *** equations are discretized and solved by using the generalized differential quadrature method(GDQM)to obtain the fundamental *** effects of the weight fraction,the dispersion model,the geometry,and the size of GPLs,as well as the porosity distribution,the porosity coefficient,the boundary condition,the metal matrix,the slenderness ratio,and the thermal gradient are presented.

关键词： thermal vibration functionally graded(FG) porous material graphene platelet(GPL) Timoshenko beam

Flexural-wave-generation using a phononic crystal with a piezoelectric defect

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2023年第8期44卷 1241-1262页

作者： s.h.JO D.LEE Department of Mechanical Roboticsand Energy EngineeringDongguk UniversitySeoul 04620Republic of Korea Department of Mechanical Engineering Seoul National UniversitySeoul 08826Republic of Korea

This paper proposes a method to amplify the performance of a flexural-wave-generation system by utilizing the energy-localization characteristics of a phononic crystal(PnC)with a piezoelectric defect and an analytical approach that accelerates the predictions of such wave-generation *** proposed analytical model is based on the Euler-Bernoulli beam *** proposed analytical approach,inspired by the transfer matrix and s-parameter methods,is used to perform band-structure and time-harmonic analyses.A comparison of the results of the proposed approach with those of the finite element method validates the high predictive capability and time efficiency of the proposed model.A case study is explored;the results demonstrate an almost ten-fold amplification of the velocity amplitudes of flexural waves leaving at a defect-band frequency,compared with a system without the ***,design guidelines for piezoelectric-defect-introduced PnCs are provided by analyzing the changes in wave-generation performance that arise depending on the defect location.

关键词： phononic crystal(PnC) defect wave-generation fexural wave analytical model

Effect of different geometrical non-uniformities on nonlinear vibration of porous functionally graded skew plates: A finite element study

在线全文

学校读者我要写书评

暂无评论

Defence Technology（防务技术） 2022年第6期18卷 918-936页

作者： h.s.Naveen Kumar subhaschandra Kattimani Department of Mechanical Engineering National Institute of Technology KarnatakaSurathkal575025India

This article presents the investigation of nonlinear vibration analysis of tapered porous functionally graded skew(TPFGs)plate considering the effects of geometrical non-uniformities to optimize the thickness in the structural *** TPFGs plate is analyzed considering linearly,bi-linearly,and exponentially varying *** plate’s effective material properties are tailor-made using a modified power-law distribution in which gradation varies along the thickness direction of the TPFGs *** the non-linear finite element formulation to develop the kinematic equation’s displacement model for the TPFGs plate is based on the first-order shear deformation theory(FsDT)in conjunction with von Karman’s *** nonlinear governing equations are established by hamilton’s *** direct iterative method is adopted to solve the nonlinear mathematical relations to obtain the nonlinear *** influence of the porosity distributions and porosity parameter indices on the nonlinear frequency responses of the TPFGs plate for different skew angles and variable thicknesses are studied for various geometrical *** influence of taper ratio,variable thickness,skewness,porosity distributions,gradation,and boundary conditions on the plate’s nonlinear vibration is *** nonlinear frequency analysis reveals that the geometrical nonuniformities and porosities significantly influence the porous functionally graded plates with varying thickness than the uniform ***,exponentially and linearly variable thicknesses can be considered for the thickness optimizations of TPFGs plates in the structural design.

关键词： Functionally graded material shear deformation theory Porosity distributions Variable thickness Geometrical skewness Nonlinear free vibration

Calculation of the infrared frequency and the damping constant (full width at half maximum) for metal organic frameworks

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2019年第6期28卷 324-331页

作者： M Kurt h Yurtseven A Kurt s Aksoy Department of Physics Canakkale 18 Mart University17100 CanakkaleTurkey Department of Physics Middle East Technical University06531 AnkaraTurkey Lapseki ICDAs CIB MTAL high school 17100 CanakkaleTurkey

The ρ(Nh2) infrared(IR) frequencies and the corresponding full width at half maximum(FWhM) values for(Ch3)2 Nh2 FeⅢ M Ⅱ(hCOO)6(DMFe M, M = Ni, Zn, Cu, Fe, and Mg) are analyzed at various temperatures by using the experimental data from the literature. For the analysis of the IR frequencies of the ρ(Nh2) mode which is associated with the structural phase transitions in those metal structures, the temperature dependence of the mode frequency is assumed as an order parameter and the IR frequencies are calculated by using the molecular field theory. Also, the temperature dependence of the IR frequencies and of the damping constant as calculated from the models of pseudospin(dynamic disorder of dimethylammonium(DMA+) cations)–phonon coupling(Ps) and of the energy fluctuation(EF), is fitted to the observed data for the wavenumber and FWhM of the ρ(Nh2) IR mode of the niccolites studied here. We find that the observed behavior of the IR frequencies and the FWhM of this mode can be described adequately by the models studied for the crystalline structures of interest. This method of calculating the frequencies(IR and Raman) and FWhM of modes which are responsible for the phase transitions can also be applied to some other metal organic frameworks.

关键词： infrared(IR) frequency full width at half maximum(FWhM) phase transitions ρ(Nh2) mode niccolites

Dynamic and buckling analysis of polymer hybrid composite beam with variable thickness

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2020年第5期41卷 785-804页

作者： s.AFshIN M.h.YAs Department of Mechanical Engineering Razi UniversityKermanshah 67149Iran

This work deals with a study of the dynamic and buckling analysis of polymer hybrid composite(PhC) beam. The beam has variable thickness and is reinforced by carbon nanotubes(CNTs) and nanoclay(NC) simultaneously. The governing equations are derived based on the first shear deformation theory(FsDT). A three-phase halpinTsai approach is used to predict the mechanical properties of the PhC. We focus our attention on the effect of the simultaneous addition of NC and CNT on the vibration and buckling analysis of the PhC beam with variable thickness. Also a comparison study is done on the sensation of three impressive parameters including CNT, NC weight fractions, and the shape factor of fillers on the mechanical properties of PhC beams,as well as fundamental frequencies of free vibrations and critical buckling load. The results show that the increase of shape factor value, NC, and CNT weight fractions leads to considerable reinforcement in mechanical properties as well as increase of the dimensionless fundamental frequency and buckling load. The variation of CNT weight fraction on elastic modulus is more sensitive rather than shear modulus but the effect of NC weight fraction on elastic and shear moduli is fairly the same. The shape factor values more than the medium level do not affect the mechanical properties.

关键词： polymer hybrid composite(PhC) halpin-Tsai carbon nanotube(CNT) nanoclay(NC) free vibration buckling load