共查询到20条相似文献,搜索用时 15 毫秒
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《中国科学:物理学 力学 天文学(英文版)》2015,(3)
Thermal barrier coating(TBC)systems are widely used in industrial gas-turbine engines.However,premature failures have impaired the use of TBCs and cut down their lifetime,which requires a better understanding of their failure mechanisms.In the present study,experimental studies of isothermal cycling are firstly carried out with the observation and estimation of microstructures.According to the experimental results,a finite element model is established for the analysis of stress perpendicular to the TBC/BC interface.Detailed residual stress distributions in TBC are obtained to reflect the influence of mechanical properties,oxidation,and interfacial roughness.The calculated results show that the maximum tensile stress concentration appears at the peak of TBC and continues to increase with thermal cycles.Because of the microstructural characteristics of plasma-sprayed TBCs,cracks initialize in tensile stress concentration(TSC)regions at the peaks of TBC and propagate along the TBC/BC interface resulting in the spallation of TBC.Also,the inclusion of creep is crucial to failure prediction and is more important than the inclusion of sintering in the simulation. 相似文献
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J. Rantala J. Jaarinen P. K. Kuo 《Applied Physics A: Materials Science & Processing》1992,55(6):586-595
Computer simulations have been carried out to study the effects of the experimental parameters when the mirage method has been applied to thermal diffusivity measurements of oriented polymer films. The parameters under study are the thermal diffusivity of the fluid surrounding the sample, the modulation frequency and the radius of the heating beam, the height and the radius of the probe beam, and the sample thickness and thermal diffusivity. Proposals for the optimum parameter values to maximize the measurement sensitivity for the sample diffusivity are made and the difficulties arising from the low diffusivity of the samples are described. It is also concluded that because the thermal properties of the fluid surrounding the sample have a strong contribution to the mirage signals, the signals do not include any simple feature corresponding to the sample diffusivity. Therefore it should be determined from the entire measurement data using regression methods. 相似文献
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PTR技术测量材料的热扩散系数的线性化方法 总被引:2,自引:0,他引:2
报道了一种用光热辐射 (PTR)技术测量不透明材料热扩散系数的优化方法。从光热辐射理论出发 ,在一定条件下 ,推导出位相信号和调制频率的关系表现为线性关系 ,分析实验数据得出材料的热扩散系数。 相似文献
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C. E. Bottani G. Caglioti A. Novelli P. M. Ossi 《Applied physics. B, Lasers and optics》1979,18(1):63-66
We present a method to measure the thermal diffusivity of metals. A homogeneous small heat source is fed into a cyclindrical
sample of titanium by thermoelastic compression. This heating process is followed by a thermal relaxation controlled by the
thermal diffusivity. The resulting temperature variation is detected by a miniature temperature sensor mounted on the lateral
surface of the sample. The value so obtained for the thermal diffusivity of titanium is (6.6±0.2)·10−6 m2/s.
Gruppo Nazionale Struttura della Materia del Consiglio Nazionale delle Ricerche 相似文献
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The conventional thermal-wave resonator cavity (TWRC) technique was modified by using an optical fiber as both to transmit light beam and to produce thermal wave. This technique also known shortly as OF-TWRC was used to measure liquid thermal diffusivity in a thermally thick condition. The stability of the pyroelectric signal amplitude was good over long time duration. The thermal diffusivity values of various liquids obtained by this technique are in agreement with those of literature indicating this technique is reliable as compared to the conventional TWRC technique. 相似文献
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Sajan D. George Rajesh Komban K.G.K. Warrier P. Radhakrishnan V.P.N. Nampoori C.P.G. Vallabhan 《哲学杂志》2013,93(6):717-729
A laser-induced photoacoustic technique was employed to investigate thermal transport through nanocrystalline CePO4 samples prepared via the sol–gel route. Evaluation of thermal diffusivity was carried out using the one-dimensional model of Rosencwaig and Gersho for the reflection configuration of the photoacoustic method. Structural analyses of samples revealed that they are nanoporous in nature, possessing micron-sized grains. Analysis of results shows that thermal diffusivity value varies with sintering temperature. Results are explained in terms of the variation in porosity with sintering temperature and the effects of various scattering mechanisms on the propagation of phonons through the nanoporous ceramic matrix. Further analyses confirm that apart from porosity, grain boundary resistance and interface thermal resistance influence the effective value of thermal diffusivity of the samples under investigation. 相似文献
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H. Bougrine J.F. Geys S. Dorbolo R. Cloots J. Mucha I. Nedkov M. Ausloos 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):437-443
A home made experimental set-up allows us to measure the thermal conductivity, the thermopower and the thermal diffusivity
simultaneously in the temperature range (20-300 K). Therefore the specific heat can be deduced. The role of a radiation shield
is shown to be relevant. Tests of the system are made on a 99.9% pure Cu sample and two polycrystalline cuprate ceramics for
illustration. Without any complicated optimisation, the technique indicates much promise already due to its efficiency and
rapidity.
Received 9 November 1998 and Received in final form 12 July 1999 相似文献
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T. Wang X. Wang J. Guo Z. Luo K. Cen 《Applied Physics A: Materials Science & Processing》2007,87(4):599-605
In this work, a transient photon-electro-thermal (TPET) technique based on step laser heating and electrical thermal sensing
is developed to characterize the thermophysical properties of one-dimensional micro/nanoscale conductive and nonconductive
wires. In this method, the to-be-measured thin wire/tube is suspended over two electrodes and is irradiated with a step cw
laser beam. The laser beam induces a transient temperature rise in the wire/tube, which will lead to a transient change of
its electrical resistance. A dc current is applied to the sample, and the resulting transient voltage variation over the wire
is measured and used to extract the thermophysical properties of the sample. A 25.4-μm thick Pt wire is used as the reference
sample to verify this technique. Sound agreement is obtained between the measured thermal diffusivity and the reference value.
Applying the TPET technique, one can measure the thermal diffusivity of conductive single-wall carbon nanotube (SWCNT) bundles
and nonconductive cloth fibers. For nonconductive wires, a thin (∼ nm) metallic film is coated on the outside of the wire
for electrical thermal sensing. The measured thermal diffusivity for the SWCNT bundle is 2.53×10-5 m2/s, much less than the thermal diffusivity of graphite in the layer direction. For microscale cloth fibers, our experiment
shows its thermal diffusivity is at the level of 10-7 m2/s.
PACS 78.20.Nv; 42.62.-b; 65.80+n; 66.30.Xj 相似文献
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Laser-induced thermal lens study of the role of morphology and hydroxyl group in the evolution of thermal diffusivity of copper oxide 下载免费PDF全文
The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity using the single beam thermal lens (TL) technique. For this purpose, the decomposition of Cu(OH)2 into CuO is studied in a time range up to 120 h, by subjecting the sample to morphological, structural, and spectroscopic characterizations. The time evolution of thermal diffusivity can be divided into three regions for demonstrating the dynamics of the reaction. When the reaction is complete, the thermal diffusivity is also found to be saturated. In addition to the morphological modifications, from rods to flakes, the variations in the amount of hydroxyl group are attributed to be responsible for the enhancement of base fluid's thermal diffusivity by 165%. Thus the study unveils the role of hydroxyl groups in the thermal behavior of CuO. 相似文献
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Effect of Young's modulus evolution on residual stress measurement of thermal barrier coatings by X-ray diffraction 总被引:1,自引:0,他引:1
Subjected to thermal cycling, the apparent Young's modulus of air plasma-sprayed (APS) 8 wt.% Y2O3-stabilized ZrO2 (8YSZ) thermal barrier coatings (TBCs) was measured by nanoindentation. Owing to the effects of sintering and porous microstructure, the apparent Young's modulus follows a Weibull distribution and changes from 50 to 93 GPa with an increase of thermal cycling. The evolution of residual stresses in the top coating of an 8YSZ TBC system was determined by X-ray diffraction (XRD). The residual stresses derived from the XRD data are well consistent with that obtained by the Vickers indention. It is shown that the evolution of Young's modulus plays an important role in improving the measurement precision of residual stresses in TBCs by XRD. 相似文献
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S. I. Yun Ki-Dong Oh Kwon-Sang Ryu Chang-Geon Kim H. L. Park H. J. Seo Chae Kum 《Applied physics. B, Lasers and optics》1986,40(2):95-98
We have used a modified photothermal probe beam deflection system with a back pumping configuration for the measurements of the temperature-dependent thermal diffusivity of atmospheric air. The results are consistent and reasonably well agree with the literature values. The measured thermal diffusivity values are the same for the same measuring temperature regardless of the beam offsets and the deflecting surface temperatures. For the gas with known temperature-dependent thermal diffusivity, this method can be used to deduce the temperature of a gas from the measured thermal diffusivity value. 相似文献
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Thermal mode spectroscopy (TMS) has been recently proposed for accurately measuring thermal diffusivity of solids from a temperature decay rate of a specific thermal mode selected by three-dimensional (anti)nodal information [Phys. Rev. Lett., 117, 195901 (2016)]. In this paper, we find out the following advantages of TMS by use of perturbation analyses. First, TMS is applicable to the measurement of high-thermal diffusivity with a small-size specimen. Second, it is less affected by thermally resistive films on a specimen in the sense that the resistance at the interface does not affect the first-order correction of thermal diffusivity. Third, it can perform doubly accurate measurement of the thermal diffusivity specified at a thermal equilibrium state even if the diffusivity depends on temperature in the sense that the measurement can be performed within tiny temperature difference from the given state and that the decay rate of the slowest decaying mode is not affected by the dependence. 相似文献
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在理论上分析了各向异性材料的热扩散率,给出了沿表面任意方向的热扩散率与主热扩散率的关系,从而为实验确定材料中任意方向的热扩散率提供了理论依据。 相似文献
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A. P.L. Siqueira I. A. Esquef M. G. da Silva L. C.M. Miranda H. Vargas 《The European physical journal. Special topics》2008,153(1):431-433
In this paper we describe a new, simple and fast
photothermal method for characterizing simultaneously the thermal
diffusivity and thermal effusivity. The improved PTGA essentially combines a
photoacoustic cell and a thermal wave pyroelectric cell enclosed in a single
compact gas analyzer. The photo- acoustic cell is kept filled with nitrogen
and sealed. The pyroelectric cell is also filled with nitrogen and after
some warm up time, the nitrogen is exchanged to the gas of interest. It is
shown that the analysis of the transient and saturation signals of both
photoacoustic and pyroelectric cells are capable of measuring the thermal
properties with an accuracy of 5%. The measurements were performed for
hydrocarbons as ethane and propane, which are combustible gases. Knowing
thermal diffusivity and effusivity, others important properties can be
determinate: the thermal conductivity and the volumetric thermal capacity. 相似文献
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J.L. Jiménez-Pérez R. Gutierrez Fuentes E. Ramón-Gallegos J. Tánori-Cordova 《Applied Surface Science》2008,255(3):701-702
In this work, it is reported the gold nanoparticles synthesis, their characterization, and their application to the enhancement of the thermal transport in a cellular culture medium. The Au nanoparticles (NPs), with average size of 10 nm, contained into a culture medium (DMEM (1)/F12(1)) (CM) increased considerably the heat transfer in the medium. Thermal lens spectrometry (TLS) was used to measure the thermal diffusivity of the nanofluids. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression, for transient thermal lens, to the experimental data. Our results show that the thermal diffusivity of the culture medium is highly sensitive to the Au nanoparticle concentration and size. The ability to modify the thermal properties to nanometer scale becomes very important in medical applications as in the case of cancer treatment by using photodynamic therapy (PDT). A complementary study with UV-vis and TEM techniques was performed to characterize the Au nanoparticles. 相似文献
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针对激光辐照热障涂层材料的平面应变问题,提出热障涂层热弹性分析的基本方程,对定常温度场给出级数形式解析解,并用最小余能原理和变分法分析了结构的热弹性应力场,研究了最大应力和界面应力的分布特征,并就一些物理参数的影响进行了讨论。结果表明,热障涂层的主要破坏因素为表面拉伸应力,界面应力相对较小,但在自由边界有集中现象,剥落应力大于剪切应力,是导致涂层破坏的重要原因。涂层厚度增加会改变厚度方向上的应力分布,界面应力向中心集中。 相似文献