多孔材料性能模型研究2:实验验证

在三维网状多孔材料"八面体结构模型"及其系列基本物理、力学性能相关数理模型和表征方式基础上,本文对传导和拉伸等若干性能指标的数理关系验证进行了综述。重点讨论了数理关系的实践性、修正系数的合理性、对计算结果的影响、对应致密体的许用应力取值和塑性指数取值等问题。按照这种数理关系,通过多孔产品孔率等基本参量即可计算其电阻率等性能指标,实验结果证明了其可行性。本方法可以优越于有限元等复杂计算。     

Electrical and mechanical fully coupled theory and experimental verification of Rosen-type piezoelectric transformers

A piezoelectric transformer is a power transfer device that converts its input and output voltage as well as current by effectively using electrical and mechanical coupling effects of piezoelectric materials. Equivalent-circuit models, which are traditionally used to analyze piezoelectric transformers, merge each mechanical resonance effect into a series of ordinary differential equations. Because of using ordinary differential equations, equivalent circuit models are insufficient to reflect the mechanical behavior of piezoelectric plates. Electromechanically, fully coupled governing equations of Rosen-type piezoelectric transformers, which are partial differential equations in nature, can be derived to address the deficiencies of the equivalent circuit models. It can be shown that the modal actuator concept can be adopted to optimize the electromechanical coupling effect of the driving section once the added spatial domain design parameters are taken into account, which are three-dimensional spatial dependencies of electromechanical properties. The maximum power transfer condition for a Rosen-type piezoelectric transformer is detailed. Experimental results, which lead us to a series of new design rules, also are presented to prove the validity and effectiveness of the theoretical predictions.     

Description of the strength of porous bodies on the basis of percolation theory

A method is proposed for estimating the strength of porous materials in destructive rupture on the basis of the percolation theory of regularly packed spheres. The results of calculation by this method are in good agreement with experimental data in the whole porosity range of the material.     

Kinetic theory of transfer in heterogeneous chemical reactors in highly dispersed porous bodies

The study makes an analytic investigation of the process of transfer of a gas in chemical reactions in porous bodies on the basis of a “dusty gas” model. In the case of a free molecular condition, an expression is derived for the number of molecules which have reacted in the porous body.     

A modified damage potential to predict crack initiation: theory and experimental verification

Mesh dependency of cavity growth model due to Rice and Tracey has been overcome by integrating it over a process zone surrounding the crack tip. This integral represents a modified damage potential. The critical value of the integral for crack initiation in SA333Gr.6 material has been determined analysing a CT specimen and comparing the computed J with the experimentally measured J-initiation value. The critical value of the integral was then used to compute J-initiation in other fracture specimens having different crack-tip constraints. The critical value was also used to predict crack initiation loads in three 8 in. straight pipes and three 8 in. elbows having different measure of through-wall circumferential flaws. The computed values have been compared with the experimentally measured values. A close agreement between the computed crack initiation loads with the experimentally measured values justified the usefulness of the present modified damage potential.     

Theory and experimental verification of a model for high gradient magnetic separation.

A mathematical model of high gradient magnetic separation (HGMS) is presented, along with data on a characterized and sized feed material. The data are fitted to the model which uses elliptical co-ordinates to approximate the ribbon-like nature of the fibers. Magnetic force terms are developed for both paramagnetic and ferromagnetic particles in the vicinity of idealized matrix fibers which can either be magnetically saturated or unsaturated. The fluid flow is simulated by superimposing a boundary layer upon the solution for potential flow thus extending the range of validity to low Reynolds Numbers. Single particle trajectories are calculated in a piecewise linear manner by considering the force balance of magnetic, hydrodynamic, gravitational and inertial forces over each increment of the trajectory. By taking orientation of the fiber with respect to the field and flow direction into account, loading can be allowed for by assuming elliptical deposits. Experimental data were generated using high grade hematite prepared in ten separate size fractions. Correlation with the model is generally fairly good except for large particles where mechanical entrapment dominates the process. Considerable discussion of the results is included by analysing the physical concepts upon which the model is based. The validity of various assumptions pertinent to HGMS modeling is tested.     

Characterization of saturated porous bodies

Measurement of the response of a saturated body to mechanical and thermal strains can be used to determine the permeability and viscoelastic properties of the body. For example, bending a saturated beam creates a pressure gradient in the pores, and as the liquid flows to equilibrate the pressure, the force required to sustain a fixed deflection decreases. Analysis of the kinetics of force relaxation yields the permeability, in addition to the elastic modulus of the body; if viscoelastic relaxation of the solid phase occurs, it can also be measured. This method permits measurement of very low permeabilities in minutes or hours, but it is useful only for structurally homogeneous materials (such as cement paste) that can be formed into slender beams. For concrete, it is more practical to find the permeability by analysis of thermal expansion kinetics. When a saturated body is heated, the liquid expands more than the solid, and the expansion of the liquid stretches the solid network like a spring; consequently, the apparent thermal expansion coefficient is high. During an isothermal hold, the solid phase squeezes the liquid out of the pores and the body contracts. Analysis of the kinetics of thermal dilatation yields the permeability of the body. Recent experiments reveal an anomalously high thermal expansion coefficient for the water confined in the small pores of cement paste.     

Moisture-retaining capacity and structure of porous bodies

The moisture-retaining capacity p(ω) of nonswelling porous bodies is explained from the point of view of the statistical geometry of the pore space, and on the basis of the resulting representation of p(ω) it is shown that it is possible to obtain the distributions of pores with respect to the radii and their derivative.     

Casting solidification analysis and experimental verification

Finite element methods are being applied to a number of manufacturing processes such as rolling, forging, etc. This paper focuses on the effort to simulate turbine blade casting using commercially available software. Comparisons between experimental and analytical results are presented for simple geometries. A novel solution to the radiation boundary condition problem is discussed.     

Characterisation of structural parameters of finely divided and porous materials by a new adsorption isotherm

An adsorption isotherm log log p = C+nlog v was developed and applied earlier. The isotherm has been used to determine the structural parameters of adsorbents. The application of the isotherm has been extended to determine separation factor of mixture of gases, surface area of adsorbed monolayer from energy consideration, categorisation of micropores etc. It is shown that equation of Lewis et al. for partial adsorption and equation of Langmuir can be deduced from isotherm equation of John. Advantages of John's isotherm are enumerated.     

Effective thermal conductivity of moistened porous bodies

This article examines a method and results of measurement of the effective thermal conductivity of porous materials impregnated with a liquid and proposes an interpretation of the physical processes of heat and mass transfer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 2, pp. 281–287, February, 1987.     

Filtration of rarefied gas through porous bodies

The filtration of a rarefied gas through porous bodies of various structures, porosities, and geometries was studied under various flow modes with the Knudsen number ranging from 10^–4to 2.5.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 5, pp. 820–828, November, 1972.     

Toward the phenomenological theory of drying

Interrelated processes of the transfer of heat, mass, and deformation of disperse systems with a prevailing role of coagulation links in the structure are considered. The determining processes occurring during their drying under ordinary conditions are singled out. The procedure for calculating large displacements and deformations on shrinkage of material during its drying has been developed. Basic rheological bodies are used in calculations. The possibility of destruction of an elastic material is considered. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 55–65, May–June, 2007.     

Connection between elastic moduli and thermal conductivities of anisotropic short fiber reinforced thermoplastics: theory and experimental verification

Cross-property connections for two phase composites derived recently by the authors are specified for short fiber reinforced thermoplastics. They are verified by comparison with experimental data on glass fiber reinforced composites available in literature. The comparison demonstrates a good agreement for the entire set of nine orthotropic constants with the exception of C₃₃. The results make it possible to estimate anisotropic elastic constants from the conductivity measurements.     

High-power CMUTs: design and experimental verification

Capacitive micromachined ultrasonic transducers (CMUTs) have great potential to compete with piezoelectric transducers in high-power applications. As the output pressures increase, nonlinearity of CMUT must be reconsidered and optimization is required to reduce harmonic distortions. In this paper, we describe a design approach in which uncollapsed CMUT array elements are sized so as to operate at the maximum radiation impedance and have gap heights such that the generated electrostatic force can sustain a plate displacement with full swing at the given drive amplitude. The proposed design enables high output pressures and low harmonic distortions at the output. An equivalent circuit model of the array is used that accurately simulates the uncollapsed mode of operation. The model facilities the design of CMUT parameters for high-pressure output, without the intensive need for computationally involved FEM tools. The optimized design requires a relatively thick plate compared with a conventional CMUT plate. Thus, we used a silicon wafer as the CMUT plate. The fabrication process involves an anodic bonding process for bonding the silicon plate with the glass substrate. To eliminate the bias voltage, which may cause charging problems, the CMUT array is driven with large continuous wave signals at half of the resonant frequency. The fabricated arrays are tested in an oil tank by applying a 125-V peak 5-cycle burst sinusoidal signal at 1.44 MHz. The applied voltage is increased until the plate is about to touch the bottom electrode to get the maximum peak displacement. The observed pressure is about 1.8 MPa with -28 dBc second harmonic at the surface of the array.     

Diffusional extraction of material from model porous bodies

The solution and diffusional extraction of solid materials from porous membranes is investigated theoretically and experimentally.     

Monte Carlo simulation for energy deposition of an ionisation chamber based on the equivalent electron source theory and experimental verification for the theory

The main research described in this paper includes three sections. First, research on the response of the stainless steel ball-shaped ionisation chamber by experimental methods. Secondly, calculation of the response of the chamber with the general Monte Carlo EGS4 code in order to compare with the equivalent electron source theory by calculation methods. Finally, calculation of the response of the ionisation chamber with the equivalent electron source theory. The results show that the calculated results of the equivalent electron source theory coincide very well with those of the experiments when the atomic number of the chamber wall is close to one of the gases (such as Ar and Kr), and the calculated results coincide with those of the experiments to a certain extent when the atomic number of the chamber wall is not close to one of the gases (such as He and Xe).     

Strengthening of porous alumina bodies using carboxylate-alumoxane nanoparticles

Aqueous solutions of acetate-functionalized alumina nanoparticles (A-alumoxane), with an average particle size of 28 nm, have been used as alumina precursors for the infiltration of porous -alumina bodies in order to produce composite structures with homo-interfaces between substrate and infiltrate. Alternatively, if metal doped-methoxy(ethoxyethoxy)acetic acid-functionalized alumina nanoparticles (M-doped MEEA-alumoxane; M = Ca, Er, La, Ti, and Y), with an average particle size of 67 nm, are used in combination with A-alumoxane, a hetero-interface is formed between substrate and infiltrate. Samples were characterized by SEM, BJH, hardness and bend strength measurements. The bulk hardness of the -alumina substrates increases with sintering temperature, but this increase is significantly smaller than the effect of infiltration. The composite hardness generally increases with decreased average pore size although the exceptions to this trend suggest that the identity of the infiltrate is of equal or greater importance. Overall the hetero-interfaces show higher strength than the homo-interface; the latter showing only slightly better performance than high temperature sintering. For the samples fired at 1000°C, the MgAl₂O₄/Al₂O₃ and CaAl₁₂O₁₉/Al₂O₃ combinations appear to provide the greatest enhancement, with both the LaAl₁₁O₁₈/Al₂O₃ and Y₃Al₅O₁₂/Al₂O₃ hetero-interface samples show marked increase in hardness between 1000 and 1400°C. The elastic modulus and bend strength of the -alumina substrate increases significantly for the Er₆Al₁₀O₂₄/Al₂O₃ and LaAl₁₁O₁₈/Al₂O₃ infiltrates. The identity of the hetero-interface has a significant effect on the bulk properties of the composite.