材料高温力学性能理论表征方法研究进展

随着科学技术的迅猛发展,材料在高温领域的应用越来越广泛。然而高温下材料的力学性能和常温相比有很大差异,材料的高温力学性能研究和表征已成为当前的研究热点。论文文对材料在高温下力学行为理论表征方法研究的最新进展进行了总结和回顾。着重介绍了近年来高温陶瓷材料的断裂强度、金属材料的屈服强度、弹性模量与本构关系的温度相关性理论表征方法的研究进展。最后,总结已有研究工作的特点和不足之处,对材料高温力学性能理论表征方法的后续研究进行了展望,就进一步研究提供建议。     

Theory of the Local Self-Similar Regime of the Laminar Free-Convection Boundary Layer in the Neighborhood of a Vertical Wall

Asymptotic criteria of transition to the local self-similar regime are obtained for laminar natural convection in the neighborhood of a vertical wall in a stably temperature-stratified medium with arbitrary variation of the wall temperature. The real boundaries of the local self-similar regime are investigated for a power law of variation of the temperature along the vertical wall.     

Atmospheric temperature dependence of the aerosol backscattering coefficient

In extracting vertical profiles of aerosol backscattering coefficient from lidar signals, the effects of atmospheric temperature are usually ignored. In this study, these effects are analyzed using a rotational Raman–Mie lidar system, which is capable of simultaneously measuring atmospheric temperature and vertical profiles of aerosols. A method is presented to correct the aerosol backscattering coefficient using atmospheric temperature profiles, obtained from Raman scattering signals. The differences in the extracted aerosol backscattering coefficient with and without considering temperature effects are further discussed. The backscattering coefficients for scattering off clouds are shown to be more sensitive to temperature than that of aerosols and atmosphere molecules; the aerosol backscattering coefficient is more sensitive to temperature in summer due to higher atmospheric temperatures.     

Example of an exact solution of the stationary problem of two-layer flows with evaporation at the interface

Stationary two-layer liquid and gas flows with fluid evaporation at the interface are studied. On the solid impermeable boundaries of the channel, no-slip conditions are satisfied and a linear temperature distribution along the longitudinal coordinate and a condition for the vapor concentration at the upper boundary are specified. On the thermocapillary interface, remaining undeformed, the following conditions are specified: kinematic and dynamic conditions, a condition for thermal flows with mass transfer, continuity conditions for the velocity, temperature, and mass balance, and a relation for the saturated vapor concentration. An exact solution of the stationary problem for a given gas flow rate is obtained. Examples of velocity profiles are given for stationary flows of the ethanol-nitrogen system under normal and reduced gravity are given. The effect of longitudinal temperature gradients specified at the boundaries of the channel on the flow pattern is investigated.     

A Green's function approach to the deflection of a FGM plate under transient thermal loading

Summary  Green's function approach is adopted for analyzing the deflection and the transient temperature distribution of a plate made of functionally graded materials (FGMs). The governing equations for the deflection and the transient temperature are formulated into eigenvalue problems by using the eigenfunction expansion theory. Green's functions for solving the deflection and the transient temperature are obtained by using the Galerkin method and the laminate theory, respectively. The eigenfunctions of Green's function for the deflection are approximated in terms of a series of admissible functions that satisfy the homogeneous boundary conditions of the plate. The eigenfunctions of Green's function for the temperature are determined from the continuity conditions of the temperature and the heat flux at interfaces. Received 9 October 2000; accepted for publication 3 April 2001     

Influence of spatial modulation of the temperature field on the stability of two-dimensional steady flow in a horizontal layer of fluid

A study is made of the stability of the steady periodic regime that arises in a horizontal layer of fluid in the presence of spatial modulation of of the temperature on the solid bottom boundary. The upper free boundary of the layer is in contact with the atmosphere. The fundamental resonance values of the wave number of the modulation are found; there are five of them. If the temperature of the lower boundary of the layer is constant, and the temperature gradient is not too large, the fluid is in equilibrium. When the temperature gradient passes through the critical value, the equilibrium ceases to be stable, and steady convection develops in the fluid [1]. In the presence of spatial modulation of the temperature on the lower boundary of the layer the fluid cannot be in equilibrium, and a spatially periodic steady regime is established in it. The aim of the present paper is to find the critical values of the temperature gradient at which this fundamental steady regime becomes unstable and a secondary steady regime develops in the fluid. An analogous problem for the case when both boundaries of the layer are free surfaces and without allowance for the influence of the atmosphere has been solved by Vozovoi and Nepomnyashchii [2].     

The effect of shrinkage on the cooking of meat

In this paper the cooking of meat is modeled as a process of time-dependent conduction through a constant-property medium that shrinks as its temperature increases. The overall shrinkage is the integrated result of shrinking that is distributed volumetrically through the piece of meat and depends on the temperature history at every point. The meat temperature history and associated shrinkage are determined numerically. The geometric configuration is the one-dimensional conducting slab with convective heating on both sides. Means for calculating the required cooking time are reported in the form of dimensionless charts for the temperature in the midplane of the meat slab. A numerical example shows that the cooking time calculated by accounting for meat shrinkage is appreciably shorter than the time estimate based on the classical Heisler chart for conduction in a constant-volume slab.     

高温封隔器胶筒与套管接触压力的实验研究

本文利用所研制的高温封隔器测试装置,应用高温电阻应变测试技术与有限元相结合的方法,研究了油井高温封隔器胶筒与石油套管内壁接触压力大小和分布规律,为优化高温封隔器的设计,提供有价值的数据。     

An analysis of the effect of the solid layer for the modified chemical vapor deposition process

The heat transfer problem relative to the modified chemical vapor deposition process has been analyzed and the effects of solid layer thickness, torch speed and tube rotation are studied. The quasi-steady three-dimensional energy equations have been solved for the temperature fields in the gas and the solid layer with a Gaussian heat flux boundary condition on the outer surface. Of particular interest is the effect of the solid layer thickness and the torch speed on inner surface temperature, gas temperature and thermophoretic velocity. The large change of the axial temperature distribution of the surface occurs for different solid layer thicknesses or torch speeds. The presence of the solid layer and tube rotation reduce the effects of nonuniform torch heating in the circumferential direction and the resulting surface temperatures are very uniform in this direction.     

整体道床无缝轨道纵向温度力分布规律研究

以整体道床上的新型轨道为基础，提出了一种用于计算此类轨道纵向温度力分布的新模型——轨道爬行。以此为计算依据，给出了计算温度力分布的公式和方法，指出了其一般性和在设计此类轨道时应注意的事项，同时建立了其与传统的分析模型之间的关系。     

Digital particle image velocimetry/thermometry and application to the wake of a heated circular cylinder

 Digital particle image velocimetry/thermometry (DPIV/T) is a technique whereby the velocity and temperature fields are obtained using thermochromic liquid crystal (TLC) seeding particles in water. In this paper, the uncertainty levels associated with temperature and velocity measurements using DPIV/T are studied. The study shows that large uncertainties are encountered when the temperature is measured from individual TLC particles. Therefore, an averaging procedure is presented which can reduce the temperature uncertainties. The uncertainty is reduced by computing the average temperature of the particles within the common specified sampling window used for standard DPIV. Using this procedure, the velocity and temperature distributions of an unsteady wake behind a heated circular cylinder are measured experimentally at Re=610. The instantaneous DPIV/T measurements are shown to be useful for computing statistical flow quantities, such as mean and velocity-temperature correlations. Received: 3 January 2000/Accepted: 26 June 2000     

Thermophoresis of nanoparticles hotter/colder than the surrounding dilute gases

Aerosol particles suspended in a diluted gas with non-uniform temperature distribution are expected to experience a thermophoretic force. In theoretical treatment of thermophoresis, it is usually assumed that the particle temperature is equal to the surrounding gas temperature. However, this might not always be the case. In some particular applications, the particle temperature can significantly differ from the gas temperature. In the present paper, we theoretically investigate the effect of the particle temperature on the thermophoresis of nanoparticles in the free molecule regime. Theoretical formulas for the thermophoretic force and thermophoretic velocity are obtained based on the gas kinetic theory. As examples, a spherical Ag nanoparticle suspended in a dilute He gas is considered, and the Rudyak–Krasnolutski potential is employed to model the gas–particle interaction. It is found that the influence of the particle temperature on the thermophoresis of nanoparticles can be significant. With increasing particle size, the error due to the equal gas–particle temperature assumption can be neglected.     

Stability of the Nonstationary Swept Attachment-Line Boundary Layer with Time Variation of the Surface Temperature and Gas Suction Velocity

The possibility of controlling the stability of a nonstationary boundary layer on the attachment line of a high-aspect-ratio swept wing by means of periodic variations of the surface temperature or the gas suction velocity at sub- or supersonic free-stream velocities is considered. The characteristic time scale of the variations of the surface temperature or the gas suction velocity on the attachment line is assumed to be equal to the characteristic aerodynamic time. On this assumption the stability characteristics of quasisteady attachment-line boundary layer flows are studied, the minimum values of the critical Reynolds numbers Re^* of loss of stability are determined as functions of the temperature and the suction velocity, and examples of the periodic dependence of the surface temperature and the suction velocity for which, in the case of nonstationary flow, the time-average values of Re^* exceed the analogous values for the steady-state boundary layer are constructed.     

Effect of motion of the medium on the photophoresis of hot hydrosol particles

The photophoretic motion of a solid spherical particle in a viscous fluid is described theoretically in the Stokes approximation for small Péclet and Reynolds numbers and large temperature differences near the particle. In solving the hydrodynamic equations, an exponential-power law is used for the temperature dependence of the viscosity. The heat transfer equations are solved using the method of matched asymptotic expansions. The possibility of the experimental observation of photophoresis in liquids is discussed.     

温度对冲击相变波传播的影响

冲击加载下,相界面的传播是一热力耦合过程。相变波阵面不仅是力学和物质间断面,也是温度界面。为考虑温度对相变波传播的影响,本文首先建立了相界面上的热传导方程和热力耦合的相变本构方程,然后采用一维特征线理论和有限差分数值计算相结合的方法,分析了温度界面和相变波的基本相互作用规律,进而给出了连续温度梯度下和绝热冲击下相变波传播规律。结果表明,温度对相变波传播的作用主要体现在两个方面,一方面是作为温度界面将与各类间断面相互作用,另一方面冲击相变波阵面后区域热力学状态变化影响卸载波结构。其原因在于相变方式（可逆、不可逆）和相变阈值应力具有强烈的温度相关性。     

An experiment on the breakup of impinging droplets on a hot surface

Breakup characteristics of liquid droplets impinging on a hot surface are investigated experimentally with the wall temperatures in the Leidenfrost temperature range of 220–330°C for n-decane fuel. Factors influencing droplet breakup are wall temperature, impinging velocity, droplet diameter and impinging angle. The 50% breakup probability shows that the impinging velocity decreases linearly with the droplet diameter increase and there exists an optimum impinging angle near 80° having the minimum value in the impinging velocity for given wall temperature and droplet size. Near the wall temperature of 250°C corresponding to the Leidenfrost temperature, a peculiar nonlinear behavior in the breakup probability is observed.This work was supported by the Turbo and Power Machinery Research Center, Seoul National University.     

On the decay process of turbulence at large Reynolds and Peclet numbers

When fluctuating temperature field is considered to be super imposed on a general field of eddy turbulence, the early period decay phenomena in regard to velocity, temperature and velocity-temperature are guided by three dynamical equations that are obtained here in a straightforward manner. The equations so obtained are simplified for the case of homogeneous turbulence and subsequently for the case of homogeneous and isotropic turbulence.     

A stochastic model for the high-temperature plasticity of metals

High temperature plasticity of metals at temperatures larger than fifty percent of melting temperature is, at least for stress ranges of technical interest, explained by thermally activated dislocation movements, where the structure of the material, i.e. distribution and strength of the internal barriers, which act against these movements, are of strong influence on these processes.The characterization of this structure by transition probabilities of a discrete Markov-chain results in a stochastic model which is able to represent essential and typical features which are characteristics for high temperature plasticity, such as stationary creep, dependence of the internal structure on stress, and temperature or transition times to stationary creep after changes of these loads, in an at least qualitatively satisfactory manner, and which allows for an examination of the effects of assumptions about the deformation mechanisms on the microscale.The model is derived from the well known assumption that the energy of the flow units obeys a Boltzmann-distribution and that the external stress increases the probability for the passing of the internal barriers in the direction of its action. In contrast to older models of this kind, strain hardening and recovery are included, by assuming that the distribution of the flow-units over the height of the barriers is changed by their movement, which results in hardening, and by a recovery-process which depends on the microstresses and temperature.     

Numerical simulation of the galvanizing process during GA to GI transition

This paper presents the application of a three‐dimensional finite element solution algorithm for the prediction of the velocity, temperature and species concentration fields in an industrial continuous galvanizing bath. Simulations were carried out using a parallel CFD software developed at IMI‐NRC. The turbulent flow, heat and mass transfer has been solved using a high Reynolds number k–ε model. Simulations were carried out for the case when the density of the molten metal depends only on the temperature and also for the case when both temperature and Al concentration affect the density. When considering the buoyancy effect of the Al concentration, differences are especially apparent during the melting of ingots with high Al content. Otherwise, thermal effects are dominant. The continuous monitoring of the temperature and the Al and Fe content in an industrial bath was used to validate the flow, temperature and compositional variations. A period of three hours, corresponding to three different ingot additions, was simulated successfully, resulting in a good agreement of the temperature and compositional variations. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.