微波固化环氧树脂(E44/DDM)的热性能及膨胀性能

利用微波辐照固化环氧E44／二苯甲烷二胺(DDM)体系，考察了固化温度、固化时间以及微波功率之间的关系，分析了固化过程。利用FT-IR、DSC、热膨胀仪分别表征了体系的固化度、玻璃化转变温度(Tg)、热分解温度以及热膨胀系数(α)。结果表明，与热固化过程相比，微波能显著提高E44／DDM的固化速度，缩短凝胶化时间。且微波固化物具有较高的热分解温度和较低的线膨胀系数α。     

EMC材料参数对微电子封装器件热应力的影响

利用动态机械分析仪测定环氧模塑封(EMC)材料的粘弹性数据,并用广义麦克斯韦模型表征了EMC材料的粘弹松弛特性;利用热机械分析仪获得了EMC材料在不同温度时的尺寸变化量,并通过线性拟合得到了EMC材料的热膨胀系数。使用有限元软件MSC Marc分别模拟了基于EMC粘弹性、弹性两种不同性质时,QFN器件在-55~+125℃温度条件下热应力分布,并分析了热膨胀系数对热应力的影响。结果表明:QFN器件的最大热应力出现在粘接剂、芯片和EMC材料的连接处,有限元分析中EMC的材料性质和热膨胀系数会对热应力产生较大影响。     

HA-Ti生物功能梯度材料微观组织及热应力缓和特性

本文用粉末冶金法制备了ＨＡ－Ｔｉ系生物ＦＧＭ,并测定了ＨＡ－Ｔｉ复合体材料的弹性模量和热膨胀系数．应用经典叠层板理论和热弹性力学理论分析了ＨＡ－Ｔｉ系ＮＦＧＮ双层板和ＨＡ－Ｔｉ系ＦＧＭ的制备残余热应力和热应变．结果表明,ＨＡ－Ｔｉ系生物ＦＧＭ呈现出宏观不均匀性与微观连续性的组织特征．ＨＡ－Ｔｉ系复合体材料的弹性模量在Ｔｉ－ＨＡ８０达到谷值,并受到气孔率的影响．其热膨胀系数随着ＨＡ含量和测试温度的升高而增大．残余热应力和残余热应变强烈依赖于组成分布,ＦＧＭ由于组成梯度化减小了成分变化幅度,其最大残余拉应力只有ＨＡ／Ｔｉ直接叠合体（ＮＦＧＭ）的１／３,具有显著缓和热应力的功能.     

稳态温度场下轴对称梯度功能材料的热应力分析

本文基于热弹性理论及计算数学方法，对轴对称梯度功能材料内部各点的热应力进行了理论分析。提出了稳态温度场下，环状截面梯度功能柱体的温度分布与热应力计算公式。     

孔隙率对金属-FGM-陶瓷复合ECBF板冷却变物性瞬态热应力的影响

功能梯度材料(简称FGM)是一种材料性质非均匀变化的特殊材料。根据热传导问题的基本方程,采用变分有限元法、有限差分法,结合算例,通过数值计算,最终得到冷却边界条件下夹FGM复合板瞬态热应力的分布规律,并主要研究孔隙率变化对FGM复合板瞬态热应力的影响。结果表明:当无限长板不能伸长、只能弯曲时,孔隙率对该变物性材料板瞬态热应力的影响比较显著。     

材料属性温度相关变厚度FGM圆板自由振动DQM求解

基于一阶剪切理论和哈密顿原理,研究了功能梯度材料(FGM)变厚度圆板在热环境中的自由振动问题。假设材料性质沿厚度幂指数连续变化且材料属性与温度相关,推导了问题的运动微分方程。用微分求积法(DQM)计算了变厚度FGM圆板横向振动的无量纲频率,并与各向同性等厚度圆板的固有频率进行了比较。讨论不同均匀和非均匀温度场、材料梯度变化、厚度系数变化以及不同边界条件对FGM圆板固有频率的影响。     

换热边界下变物性梯度功能材料板稳态热应力

用非线性有限元法分析了由ZrO2和Ti-6Al-4V组成的变物性梯度功能材料无限自由长板在对流换热边界下的稳态热应力问题,检验了方法的正确性,给出了该材料板的稳态热应力场分布,并与不考虑变物性时的结果进行了比较.结果表明当M=1.0时,考虑变物性的最大拉应力比不考虑变物性减小70.5%,最大压应力减小62.5%;此外,材料组分的分布形状系数M、环境介质温度、对流换热系数和孔隙度P的变化对变物性梯度功能材料板的稳态热应力场分布均有明显的影响;在本研究相同条件下,当孔隙度系数A=3.99时,陶瓷侧拉应力最大.此结果为梯度功能材料的设计制备提供了准确的理论计算依据.     

平板式SOFC结构热应力的有限元分析

采用有限元数值计算方法, 对平板式固体氧化物燃料电池(SOFC)的结构建立了三维有限元分析模型, 模拟计算了平板式SOFC单电池在均匀温度场中由于各层部件之间的热膨胀系数差异而产生的热应力, 并对模拟结果进行了分析和讨论, 为优化平板式SOFC的材料选择和结构设计提供了依据. 计算结果表明: 在阳极(或阴极)与电解质界面处出现热应力的最大值; 界面热应力的大小及分布与电极材料的热膨胀系数和温度载荷密切相关.     

复合材料粘弹性本构关系与热应力松弛规律研究Ⅰ:理论分析

基于均匀化理论研究了复合材料粘弹性分析的多尺度方法, 以及复合材料等效热应力松弛规律。引入了等效粘弹性热应力系数张量和等效时变热膨胀系数的概念, 建立了含温度变化的复合材料热粘弹性本构关系, 并给出了基于均匀化理论的复合材料粘弹性松弛模量、等效热应力松弛系数和等效时变热膨胀系数的预测方法。对特殊复合材料的粘弹性性质进行了分析, 结果表明: (1) 复合材料的粘弹性本构关系具有与常规材料的本构关系类似的形式, 但一般复合材料的热应力松弛规律与常规材料不同, 其热膨胀不能瞬时完成, 而具有明显的时变性质;(2) 空心材料的热膨胀具有瞬时性质, 其等效时变热膨胀系数与基体材料的热膨胀系数相同, 其热应力松弛规律与基体材料的松弛规律相同;(3) 当各组分材料的松弛模量的各分量可分解成不同的系数与相同的时间函数的乘积时, 复合材料的等效时变热膨胀系数与时间无关, 其松弛规律与常规材料的松弛规律完全相同。     

圆板状SiC/C功能梯度材料残余热应力特征有限元分析

功能梯度材料残余热应力的大小及分布对其性能有效发挥及长期稳定使用有着较大的负面影响,为了尽可能充分发挥材料性能,增加材料的使用寿命,需尽可能减小残余应力以及使其合理分布.本文采用ANSYS有限元分析软件对不同叠层工艺参数的等离子体第一壁候选材料--SiC/C功能梯度材料(FGM)的残余热应力进行了数值模拟,获得了使热应力有效缓和的较适宜的工艺参数,对实际研发制备目标材料也可提供一些理论参照.相关结果表明,适量增加梯度叠层数及中间梯度层厚度可逐步有效缓和残余热应力,同时,针对本文今后应用的仍以炭材料为主体的炭基陶瓷保护层复合SiC/C FGM而言,纯SiC层厚度应取较小值,而叠层成分分布指数应取0.8～1.0为宜.     

热舒适参数选取中存在的问题分析

为了实现热舒适研究的国内外接轨、修正地区性设计规范以及促进建筑节能的可持续发展,本文针对PMV、TSV、TCV对人体热舒适性的评价结果存在差异、所得热舒适参数也不尽一致的现象,分析了产生这些现象的原因,给出了相应的建议,并提出了综合考虑国内外标准规定、现场实测及问卷调查结果来确定热舒适参数的思路。结合研究实例,利用这一方法得到了合理的室内热舒适参数。     

Experimental Investigation on the Reliability of Thermal Wave Interferometry in the Thermophysical Characterization of Plasma Sprayed Coatings

The main focus of this work is to compare thermal diffusivity and effusivity data resulting from thermal wave interferometry (TWI) experiments on tungsten coatings of different thicknesses with those obtained using reference techniques, namely, the laser flash method and scanning electron microscopy (SEM). The deviations between TWI and the latter techniques are discussed in terms of lack of data in the low frequency range. The investigation shows that the lack of data at low frequencies does not affect diffusivity measurements, while it has a strong effect on effusivity measurements for thermally thick coatings. The conclusions of this experimental study are in good agreement with theoretical predictions resulting from a sensitivity analysis reported in a previous study.     

Realizing the Accurate Measurements of Thermal Conductivity over a Wide Range by Scanning Thermal Microscopy Combined with Quantitative Prediction of Thermal Contact Resistance

Quantitative thermal performance measurements and thermal management at the micro-/nano scale are becoming increasingly important as the size of electronic components shrinks. Scanning thermal microscopy (SThM) is an emerging method with high spatial resolution that accurately reflects changes in local thermal signals based on a thermally sensitive probe. However, because of the unclear thermal resistance at the probe-sample interface, quantitative characterization of thermal conductivity for different kinds of materials still remains limited. In this paper, the heat transfer process considering the thermal contact resistance between the probe and sample surface is analyzed using finite element simulation and thermal resistance network model. On this basis, a mathematical empirical function is developed applicable to a variety of material systems, which depicts the relationship between the thermal conductivity of the sample and the probe temperature. The proposed model is verified by measuring ten materials with a wide thermal conductivity range, and then further validated by two materials with unknown thermal conductivity. In conclusion, this work provides the prospect of achieving quantitative characterization of thermal conductivity over a wide range and further enables the mapping of local thermal conductivity to microstructures or phases of materials.     

On the determination of the thermal diffusion factor from column measurements

A new method for experimental determination of the thermal diffusion factor _T for binary gas mixtures with a thermal diffusion column (TDC) is developed, based on A. M. Rozen's equation of TDC. The experimental results for _T are obtained in a reduced form in this approximation. An experimental reference point, determined in the same TDC with a standard gas mixture, is used for the transformation of the results for _T in absolute units. The proposed method is applicable for arbitrary gas mixtures, irrespective of the mass difference of the components.     

Analysis of the Photoacoustic Detector Signal for Thermal Diffusivities of Gases

A resonant and a nonresonant photoacoustic detector were used to determine thermal diffusivities of gases. With a nonresonant detector thermal diffusivities can be determined in a wide range between 10^–3 and 10^–7 m²·s^–1, whereas experiments with the resonant detector deliver thermal diffusivities in a range that is about a factor of 100 smaller. As refrigerants—HFCs, HCFCs, and hydrocarbons—are absorbents in the infrared at a wavelength of 3.39 m, their thermal diffusivity can be determined without the addition of a trace gas, particularly at pressures below 0.01 MPa. At pressures above 0.1 MPa, the addition of ammonia as a trace gas is recommended. The absorption wavelength is then 1.531 m. A simulation model for the nonresonant photoacoustic detector is presented for the design of a detector and for an extended error analysis.     

An Investigation of the Thermophysical Properties of a Liquid in a Flow Using the Method of Pulse Heating

The theoretical principles are described of measuring the thermophysical properties of a liquid in a flow during a short pulse of heating a quick-response probe. A plane probe and a linear probe are used to measure the thermal activity, thermal conductivity, thermal diffusivity, and kinematic viscosity of some liquids at different velocities of flow.     

Identification of the thermal properties of materials using methods of the calculus of variations

A solution of the heat-conduction problem when a linear pulsed source of heat acts in the plane of contact of two semibounded bodies, obtained using methods of the variational-iterational calculus, is presented. The results of tests of a number of heat-insulating materials are given. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 34–36, July, 2007.     

基于问卷调查和现场测试的麦加轻轨站台热环境研究

为评测高温干燥沙漠气候环境中开放式站台在空调状态下的热环境,实测了站台空气温度、平均辐射温度、空气相对湿度及空气流速等热环境参数,进行了基于ASHRAE七级热感觉标尺的热舒适调查问卷.测量及调查结果表明,站台环境热中性温度为31.0℃,高于ASHARAE推荐热舒适温度;80％满意度时的可接受温度范围为[27.7℃,34.3℃],较ASHRAE推荐温度范围更宽.     

Determination of the Thermophysical Properties of Halogenated Hydrocarbons in a Heat-Conducting Calorimeter

The values of the coefficients of thermal expansion and compressibility, isobaric heat capacity and thermal diffusivity of three brominated saturated hydrocarbons of butyl bromide, hexyl bromide and heptyl bromide are measured in a heat-conducting calorimeter at a temperature of 298–363 K in the pressure range of 0.098–147 MPa. The experimental data on the isobaric heat capacity are compared to the calculation results. Generalized dependences are suggested to determine the heat capacity and thermal diffusivity.     

Influence of Thermal Properties on the Sensitivity of Thermal Wave Interferometry for the Characterization of Plasma-Sprayed Coatings

Thermal wave interferometry (TWI) is used as a means for measuring the thermal properties of plasma-sprayed coatings. The solution of the inverse problem is influenced by the magnitude of the signal-to-noise ratio and the amount of data available. This is investigated using a sensitivity analysis. The critical factors that determine the accuracy and the limitations of the technique are discussed. Numerical and experimental thermal wave tests confirm the range of applicability and the accuracy of TWI for measuring thermal properties.