具有多孔基体复合相变储能材料研究

本文提出了研制一种具有多孔基体的复合相变储能材料，通过实验分析了该储能材料的融解温度、融解热、热稳定性及微相结构等性能。该储能材料是由两种有机相变材料组成，通过物理吸附的方法将其复合在多孔基体材料中。在热分析中，用示差扫描量热仪(DSC)来测定储能材料的融点、融解热，用热重分析仪(TGA)测定其热稳定性，并用扫描电镜(SEM)观测了该储能材料的微相结构。测试结果表明该储能材料具有较高的相变潜热和较好的热稳定性，可被应用于储能和热能回收系统中。     

VIP绝热性能及其影响参数分析

真空绝热板（VIP）具有10倍于传统绝热材料的优异绝热性能。对VIP有效导热系数进行了分析，表明影响VIP绝热性能主要是固体导热和辐射传热，而气体导热和对流换热可忽略不计。影响VIP整体绝热性能的因素主要有温度、气体压力、含湿率、芯材密度及芯材颗粒度等参数。     

航天器用十一种热控材料热物理性质及其与显微组织和工艺因素关系的研究

应用自行研制的激光脉冲法热导仪、小平板稳态法热导仪、铜卡计和冰卡计法比热仪, 对航天器用的十一种热控材料的导热系数、导温系数和比热及其与材料显微组织和工艺因素的关系进行了实验研究. 结果表明, 在室温至1800℃温区内, 绝热材料和防热材料的导热系数均随温度升高而增大, 多孔绝热材料的有效导热系数是由多种导热因子相互作用的结果, 并存在对应于最小导热系数的最佳密度. 所得数据为热控材料的优选提供了科学判据, 亦为航天器的热控系统热设计提供了参数.     

Thermal stresses and fracture of thin plates during cutting and welding operations

In many technological processes involving cutting or welding of thin plates there is local thermal heating or cooling at the tip of the cut by a thermal source. In this paper we analytically investigate the stress distribution induced by the point thermal source moving with a constant velocity across an infinite elastic plate. Stress intensity factor for the cut formed by the moving thermal source is calculated. It is shown that for welding the value of the stress intensity factor due to thermal stresses induced by the thermal source is equal to zero. For cutting in the case of positive values of the power of thermal source the stress intensity factors will be negative. This means that the thermal field induced by the point thermal heat source will tend to close the cut in the vicinity of the tip. The opposite situation occurs when the cut tip is cooled by the thermal source. As an example, the theory under development is shown when applied to some strength issues of thermal beam cutting of brittle materials.     

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.     

ZrO2-Ni功能梯度材料的热冲击与热疲劳行为

通过抗热震参数分析和热循环试验研究了ZrO2-Ni功能梯度材料（FGM）的热冲击与热疲劳行为及其影响因素。结果表明,ZrO2-Ni FGM热热震参数呈梯度分布,ZrO2侧抗热冲击断裂能力强而富Ni区热疲劳抗力高。其热震破坏符合热疲劳损伤机理,裂纹的准静态扩展为其控制因素。热疲劳裂纹在梯度层内以微孔聚集、连接方式萌生和扩展,而在梯度层间无横向贯穿裂纹,克服了传统陶瓷／金属结合体的界面热应力剥离问题。     

导热高分子材料在包装印刷领域的研究进展

目的综述导热高分子材料在包装印刷领域的应用及研究现状,拓展导热高分子材料的应用领域。方法首先介绍2类导热高分子材料的制备方法,即本征型和填充型导热高分子材料;其次全面综述用于包装印刷领域的导热膜/纸、导热胶黏剂和导热油墨;最后总结常用的各类导热机理模型。结果与本征型导热高分子相比,填充型导热高分子具有加工简单、成本低廉、应用面广等优点,是目前研究最多的导热高分子材料。导热膜/纸、导热胶黏剂和导热油墨具有广泛的研究基础,市场需求旺盛。导热预测模型虽能够有效预测复合材料的热导率,但会受到填料含量和粒子形貌的影响。结论导热高分子材料在包装印刷领域拥有巨大的应用需求,开展导热高分子的研究具有重要的现实和理论意义。     

基于分形理论的碳泡沫有效导热系数研究

以煤焦油基中间相沥青为原料，在一定的温度和压力条件下升温发泡，然后再经碳化、石墨化便可以制得一种高导热系数的多孔材料——碳泡沫。应用分形理论讨论了这种新型多孔材料的导热特性，推导出了碳泡沫的面积分形维数，并在此基础上建立了石墨化碳泡沫材料的导热模型，采用热阻法导出了石墨化碳泡沫材料的等效导热系数的关系式，计算出了碳泡沫的有效导热系数，计算结果与碳泡沫样品的实测值基本一致，这种方法为更好地利用其优良的导热性能提供了理论基础。     

Coupled thermal–mechanical modeling of carbon fibers reinforced polymer composites for damage detection

An analytical solution is derived to describe the correlation between the thermal resistance change and fiber damage evolution in unidirectional composites under loading conditions. A key parameter, thermal characteristic length, is obtained, which represents the sensitivity of the thermal property change to mechanical damage. A coupled thermal–mechanical model is also developed to predict the failure stress, internal fiber breakage and thermal resistance change as a function of applied strain. The results show that the number of fiber breaks is proportional to thermal resistance change during loading while the thermal resistance change increases exponentially with increasing the applied strain. The analytical solution is in good agreement with the numerical results. Finite element models are developed to verify the coupled thermal–mechanical models. The present study shows that longitudinal thermal resistance change is sensitive to damage in a predictable manner and can be used together to improve the reliability of damage assessment during loading of carbon fiber reinforced polymer.     

Thermal conductivity of inhomogeneous materials

The effective thermal conductivity is calculated from the rate of entropy production per unit volume. Thermal conductivity and the temperature field are expressed in terms of Fourier components and these are related. The rate of entropy production is then obtained in terms of the volume-averaged thermal conductivity and the Fourier components of thermal conductivity. A simple expression for the effective thermal conductivity is found. In the case of striations it leads to well-known results. The formalism is applied to solids with inhomogeneously distributed solutes. It is shown that the thermal conductivity is less than the volume-averaged thermal conductivity and that homogenization by diffusion increases the thermal conductivity. Similar results would apply to the electrical conductivity of inhomogeneous alloys.     

Strain engineering of thermal conductivity in graphene sheets and nanoribbons: a demonstration of magic flexibility

Graphene is an outstanding material with ultrahigh thermal conductivity. Its thermal transfer properties under various strains are studied by reverse nonequilibrium molecular dynamics. Based on the unique two-dimensional structure of graphene, the distinctive geometries of graphene sheets and graphene nanoribbons with large flexibility and their intriguing thermal properties are demonstrated under strains. For example, the corrugation under uniaxial compression and helical structure under light torsion, as well as tube-like structure under strong torsion, exhibit enormously different thermal conductivity. The important robustness of thermal conductivity is found in the corrugated and helical configurations of graphene nanoribbons. Nevertheless, thermal conductivity of graphene is very sensitive to tensile strain. The relationship among phonon frequency, strain and thermal conductivity are analyzed. A similar trend line of phonon frequency dependence of thermal conductivity is observed for armchair graphene nanoribbons and zigzag graphene nanoribbons. The unique thermal properties of graphene nanoribbons under strains suggest their great potentials for nanoscale thermal managements and thermoelectric applications.     

Application of the Thermal Quadrupoles Method to Semitransparent Solids

In this study, the thermal quadrupoles method is extended to semitransparent layered solids. Using this method, the surface temperature of semitransparent multilayered materials is calculated as a function of the optical and thermal properties of each layer. This result eventually leads to determination of the thermal diffusivity, thermal resistance, and/or optical absorption coefficient of layered materials using photothermal techniques. The thermal quadrupoles method is applied to determine the thermal contact resistance in glass stacks.     

基于单光束干涉仪的机床主轴热误差实时测量

主轴热误差是数控机床的主要热误差源,本提出了一种使用三路单光束干涉仪（SBI3）进行机床主轴热误码差的非接触式实时测量方法。可以快速准确地测量主轴热误差。实验结果表明,所测立式加工中心主轴热误差沿Z轴方向最大,约为50μm,测量误差约为1.0μm。     

Thermal conductivity and thermal diffusivity analyses of low-density polyethylene composites reinforced with sisal, glass and intimately mixed sisal/glass fibres

The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fibre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120–350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containing perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the presence of Fe²⁺ ions in the glass fibres. The linear variation in thermal conductivity with fibre loading is explained with the help of a model suggested by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied flux is a maximum for SRP owing to the anisotropic nature of sisal fibre. The difference is marginal for GRP on account of its isotropic nature. The position of GSRP is found to be intermediate. It can been observed that the variation of thermal diffusivity with temperature is just opposite to that of thermal conductivity. This may be due to a reduction in the mean free path of phonons. An empirical equation is derived to explain the variation in thermal conductivity and thermal diffusivity with temperature.     

Microstructural aspects of Thermal Stress Resistance of high-strength engineering ceramics. Part I: Data of thermal stress resistance of high-strength engineering ceramics

Based on the criteria for the improvement of thermal shock resistance mainly two microstructural aspects of thermal stress resistance are discussed: First, the influence of microstructure on thermal shock resistance to fracture initiation, and second, the improvement of thermal shock resistance on the basis of microstructural considerations. In this connection, data of thermal stress resistance (thermal shock and thermal cycling) of various engineering ceramic materials are presented. Using laboratory grades with well-defined microstructures the interdependence between various microstructural variables and the mechanical and thermal properties, which control the thermal shock resistance, is discussed and the relation to thermal shock resistance is outlined by the example of the two materials, dense and porous reaction-bonded Si₃N₄. Moreover, the improvement of thermal shock resistance by microstructural optimization is demonstrated. Some examples of the improvement of thermal stress resistance by developing advanced composite materials are given. The paper is divided into three parts: Part I: Data of Thermal Stress Resistance of High-Strength Engineering Ceramics Part II: Influence of Microstructure on Thermal Shock Resistance of High-Strength Engineering Ceramics Part III: Improvement of Thermal Stress Resistance of High-Strength Engineering Ceramics.     

An analytical method for thermal stresses of a functionally graded material cylindrical shell under a thermal shock

In this paper, the thermal stresses of a thin functionally graded material (FGM) cylindrical shell subjected to a thermal shock are studied. An analytical method is developed. The studied problem for an FGM cylindrical shell is reduced to a plane problem. A perturbation method is used to solve the thermal diffusion equation for FGMs with general thermal properties. Then, the transient thermal stresses are obtained. The results show that the thermal shock is much easier to result in failure than the steady thermal loading. The present method can also be used to solve the crack problem of an FGM cylindrical shell with general thermal properties.     

Thermophysical Properties of Plant Leaves and Their Influence on the Environment Temperature

It is known that the thermal properties of a material influence the temperature around it. Once heated, the rate at which a material transfers the absorbed heat into the surroundings is determined by the thermal effusivity (or thermal inertia) of the material, and it depends on the well-known thermal properties, thermal conductivity, and specific heat capacity. Since a direct measurement of these properties is rather difficult for thin biological specimens such as plant leaves, a photothermal technique is used to measure the thermal effusivity, thermal diffusivity, thermal conductivity, and specific heat capacity for a few representative species of plant leaves. Measurements have been carried out on fresh as well as dry leaves to estimate the differences in their properties. Thermal properties of plant leaves are compared with the corresponding properties of two materials abundant in the environment and discussed. The influence of thermal properties, particularly the thermal effusivity and specific heat capacity, of plant leaves on controlling the temperature of the environment around them is discussed.     

Studies on the diffraction image of a thermal lens

We calculated the intensity distribution behind a thermal lens by using a numerical quadrature of the Fresnel diffraction integral and compared it to several given approximate models for laser light detection in the center behind a thermal lens, which includes a new approximate solution of the diffraction integral with applicability to strong thermal lenses. Consideration of the aberrant nature of the thermal lens is crucial even if the thermal lens is weak. A simple approximate formula for the position of the most intense interference ring stating a linear dependence of the thermal lens strength is given. The transverse profile of a weak thermal lens is discussed. It is shown that spherical aberration modifies the central intensity even if a Gaussian profile is observed.     

霜层综合导热系数的研究

提出了霜层综合导热系数概念。认为霜层导热系数除了应考虑霜层结构复杂性还应计及蒸汽凝华潜热释放的影响。从霜层能量平衡分析出发，导出霜层综合导热系数是霜层有效导热系数和蒸汽有效导热系数之和。据此计算的霜层综合导热系数与实验数据符合较好。     

热传导对双陶瓷热障涂层隔热效果影响研究

为了更好地设计双陶瓷热障涂层结构,考察在制备和服役过程中热导率的变化对隔热效果的影响,建立了双陶瓷热障涂层半透明数学模型,采用有限元ANSYS软件模拟了稳态隔热效果.结果表明:顶层陶瓷层的热导率增大降低了隔热效果,且随顶层厚度增加隔热效果降低幅度增大;第2层陶瓷层的热导率增大降低了隔热效果,且随顶层厚度增加隔热效果降低幅度减小;陶瓷层半透明且衰减系数很小时,顶层厚度增加,隔热效果先快速后缓慢增加至不变甚至略有降低,且远低于相同条件下不透明时.顶层陶瓷层热导率变化对隔热效果影响大于第2层陶瓷层.