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.     

正交各向异性材料结构热变形和热应力分析的无网格法计算模型及应用正交各向异性材料结构热变形和热应力分析的无网格法计算模型及应用

利用无网格伽辽金法（Element-free Galerkin,EFG）建立了正交各向异性材料结构热变形和热应力分析的计算模型,并推导了正交各向异性材料结构热弹性问题的EFG法离散控制方程。选择复合材料冷却栅管算例验证了计算模型和程序的正确性,利用该计算模型分析了具有不同材料方向角及热导率因子、热膨胀系数因子和主次泊松比因子的汽轮机叶轮,得到了其热变形总位移和Mises应力,讨论了材料方向角和上述正交各向异性材料因子对其热变形总位移和Mises应力的影响规律,给出了这些参数的合理取值范围,并选取一组参数与各向同性材料结构进行了热变形和热应力对比分析。结果表明,基于EFG法的热变形总位移和Mises应力的计算精度比有限元法高,材料方向角同时影响热变形总位移和Mises应力的大小和方向,而正交各向异性材料因子只影响热变形总位移和Mises应力的大小,不影响其方向。在复合材料结构设计过程中,合理选取材料方向角和正交各向异性材料因子可有效减小结构热变形和热应力。      

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。     

Preliminary study on theory and experiment of photo-mechanics manufacturing and detecting technologies based on laser thermal stress

Mechanical effects of laser thermal stress is a new manufacturing technology, which is made use of thermal stress by high power laser acted on the surface of metal material to generate stress field. The technologies such as formation by laser thermal stress, measurement by laser scratch, measurement by XRD and so on are formed based on mechanics effects of laser thermal stress. The mechanisms of formation by laser thermal stress, measurement by laser scratch and measurement by XRD are analyzed. The theory of photo-mechanics manufacturing based on laser thermal stress is originally put forward whose experiment is primitively researched, and the manufacturing theory by mechanics effects of laser thermal stress is established.     

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 Conductivity,Thermal Diffusivity,and Heat Capacity of Gaseous Argon and Nitrogen

Low-pressure thermal conductivity and thermal diffusivity measurements are reported for argon and nitrogen in the temperature range from 295 to 350 K at pressures from 0.34 to 6.9 MPa using an absolute transient hot-wire instrument. Thermal conductivity measurements were also made with the same instrument in its steady-state mode of operation. The measurements are estimated to have an uncertainty of 1% for the transient thermal conductivity, 3% for the steady-state thermal conductivity, and 4% for thermal diffusivity. The values of isobaric specific heat, derived from the measured thermal conductivity and thermal diffusivity, are considered accurate to 5% although this is dependent upon the uncertainty of the equation of state utilized.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom     

Evolution of microstructures and thermal properties with heat treatment for absorbing, emitting and scattering fibrous medium

The microstructure changes of a fibrous insulation for thermal protection system were examined before and after thermal exposures at different temperatures between 1000 °C and 1400 °C. The consequent thermal properties, i.e., thermal conductivity, extinction coefficient, albedo of scattering, and linear coefficient of phase function at different stages were measured by using a developed experimental device and data processing method. The effects of microstructure changes on the thermal properties degradation were discussed. It was found that the devitrification of mullite and the microstructure changes induced by heat treatment had a significant influence upon the thermal properties, and higher temperature treatment yielded a strong increase in thermal conductivity of fibrous insulation. The results also indicated that the relative contribution of conductive and radiative heat transfer would be re-regulated after high temperature thermal annealing.     

Temperature and Thermal Balance Monitoring and Control in Dialysis

Temperature and thermal balance have been studied in an effort to explain better tolerance of ultrafiltration during isolated ultrafiltration and other convective techniques as compared to conventional hemodialysis. The large number of published studies has led to the conclusion that negative thermal balance of the extracorporeal circuit ameliorates hemodynamic stability by increased vasoreactivity and increased peripheral resistance. On the other hand, measurement of dialysis efficiency (urea removal) did not unequivocally confirm the theoretically predicted decrease in efficiency of "cool" dialysis. Another suggested application of temperature and thermal balance for assessing bioincompatibility is currently hampered by the ability of existing technology to evaluate thermal parameters of the extracorporeal circuit only. Publications on impact of negative thermal balance of the extracorporeal circuit on ultrafiltration‐induced changes in blood volume give contradictory results. Further studies are needed for elucidation of the impact of thermal balance on overall biological response to dialysis.     

Thermal properties of Pure and Doped TGS,DTGS, TGFB and DTGFB single crystals

The thermal properties of pure and doped single crystals of TGS type materials were determined over the temperature range 20 to 90°C. Measurements of the thermal conductivity were made along the principal crystallographic axes and were found to be independent of temperature. Impurity incorporation generally decreased the thermal conductivity with Zn doping exhibiting the largest effect. The thermal diffusivity of these materials was calculated from measurements of thermal conductivity, specific heat and density.     

洛阳某高校宿舍热舒适性调查与分析

宿舍热环境直接影响着学生的睡眠质量和身心健康。通过调查得到学生的作息模式,对宿舍热环境、热舒适和热感觉进行了评价。对热舒适的影响因素进行了分析,研究结论对高校宿舍热环境的研究和改善具有重要参考作用。     

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。     

车室内热环境的计算模型与数值模拟

用计算流体力学与计算传热学的方法对车室内的非均匀热环境进行了模拟与数值计算。文中首先对车室内的热环境建立了相应的计算模型,然后进行了相应的数值计算。计算中不仅考虑了空气温度、空气流速、空气湿度、太阳辐射和车室内热辐射的影响,而且还考虑了车窗玻璃表面的几何形状、周围物体的物理特性和热特性对车室内热环境的影响。因此该模型可以用于预测车室内不均匀热环境的特性,以便为人体局部热舒适性的评价提供必要的计算数据。     

中碳合金奥氏异常分解与碳化物粒化

探讨了中碳合金钢结构钢件的热变形（锻、轧）成形与锻后调质相结合的途径,研究表明,通过控制热变形得到形变（加工硬化态）奥氏体、或未形变奥氏体过控制冷却均可使之发生异常分解,直接得到调质型组织,并达到传统调质的要求。     

The thermal diffusivity and conductivity of transformation-toughened solid solutions of alumina and chromia

The thermal diffusivity of a series of solid solutions of alumina and chromia transformation toughened with a dispersed phase of unstabilized zirconia was measured by means of the laser-flash method from room temperature to 1400° C. It was found, in general, that the thermal diffusivity could be decreased significantly by the combined effects of solid solution alloying, microcracking and by the presence of the low conductivity dispersed phase of zirconia. The decrease in thermal diffusivity by microcracking was found to be present in the solid solution with low chromia content which underwent extensive grain growth. The effectiveness of solid solution formation and microcracking on thermal diffusivity was found to be greatest at the lower and intermediate ranges of temperature. The decrease in the thermal diffusivity due to the zirconia inclusions was found to be effective over the total temperature range. A numerical example is presented for the thermal conductivity calculated from the thermal diffusivity multiplied by the volumetric heat capacity.     

Thermal Conductivity of Nitrogen-Methane Mixtures at Temperatures Between 300 and 425 K and at Pressures Up to 16 MPa

The thermal conductivities of nitrogen and three mixtures of nitrogen and methane at six nominal temperatures between 300 and 425 K have been measured as a function of pressure up to 16 MPa. The relative uncertainty of the thermal conductivity measurements at a 95% confidence level is estimated to be less then 1%. The data obtained and the results of the low-density analysis were used to test two prediction methods for the thermal conductivity of gas mixtures under pressure and for the thermal conductivity of dilute polyatomic gas mixtures. Reasonable agreement was found with expressions for predicting thermal conductivity of nonpolar mixtures in a dilute-gas limit developed by Schreiber et al. The scheme underestimates the experimental thermal conductivity with deviations not exceeding 3%. The prediction scheme for the thermal conductivity of gas mixtures under pressure suggested by Mason et al. and improved by Vesovic and Wakeham underestimates the experimental thermal conductivities throughout, likely due to its use of the Hirchsfelder–Eucken equation at the low-density limit.     

膨胀石墨/石蜡复合材料的制备及热管理性能

石蜡作为相变材料(PCM),膨胀石墨(EG)为导热增强剂,制备不同EG含量的膨胀石墨/石蜡(EG/PCM)复合材料。采用瞬态热线法测量样品的导热系数;把EG/PCM应用于锂离子电池热管理,研究不同EG含量的EG/PCM热管理性能;采用ANSYS软件分析EG/PCM的导热系数对锂离子电池热管理的影响。结果表明:EG的加入大幅度提高了PCM的导热系数,EG含量≥9%时,EG/PCM的导热系数呈各向异性;锂离子电池表面温度随EG含量增加而减小,EG(12)/PCM(88)表现出优异的热管理性能;适当地提高EG/PCM的径向导热系数,有利于提高它的热管理性能。     

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.     

热分析质谱法的发展历史沿革、现状和展望

热分析的发展已整整跨越了一个世纪。当今它已成为近代仪器分析领域中的一个重要分支学科。1963年，H.G..Langer和R.S.Gohlke首次实现热分析和质谱联用。此后。由于计算机技术的应用和发展，使热分析技术及其与质谱的联用技术，又有了许多新的发展甚至突破。热分析质谱法的应用范围十分广阔。它不仅在有机材料，无机材料，还可以在有机－无机等复合材料的研制工作中得到广泛应用。热分析质谱联用技术的应用在我们国内虽然是近十年的事情，但已经引起人们浓厚的兴趣和密切关注。可以预见热分析质谱联用技术在我国的材料热化学和热物理研究以及环保技术，航天技术，信息技术等领域中将发挥更大的作用。     

聚乳酸/石墨/多壁碳纳米管复合材料的制备及性能

通过共溶剂法制备了由石墨(GN)和多壁碳纳米管(MWCNTs)掺杂的聚乳酸(PLA)纳米复合材料,借助扫描电镜等手段,研究了MWCNTs用量对复合材料微观结构、热稳定性、导热和导热性能及介电性能的影响。结果显示,MWC-NTs和GN在PLA基体中形成了稳定的导电和导热网络结构,从而导致复合材料具有较低的导电和导热逾渗阈值,其值约为MWCNTs/GN=0.5/1。MWCNTs和GN均匀分散和协同增强效应促使复合材料热稳定性、导热和导电性能明显提高。与纯PLA相比,填料在逾渗阈值附近的复合材料的初始分解温度提高了近16℃,导热系数提高了1倍,体积电阻降低了109数量级。     

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.