Microstructure studies of air-plasma-spray-deposited CoNiCrAlY coatings before and after thermal cyclic loading for high-temperature application

In the present study, bond-coats for thermal barrier coatings were deposited via air plasma spraying（APS） techniques onto Inconel 800 and Hastelloy C-276 alloy substrates. Scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, X-ray diffraction（XRD）, and atomic force microscopy（AFM） were used to investigate the phases and microstructure of the as-sprayed, APS-deposited Co Ni Cr Al Y bond-coatings. The aim of this work was to study the suitability of the bond-coat materials for high temperature applications. Confirmation of nanoscale grains of the γ/γ′-phase was obtained by TEM, high-resolution TEM, and AFM. We concluded that these changes result from the plastic deformation of the bond-coat during the deposition, resulting in Co Ni Cr Al Y bond-coatings with excellent thermal cyclic resistance suitable for use in high-temperature applications. Cyclic oxidative stability was observed to also depend on the underlying metallic alloy substrate.

Response Surface Modeling of Fuel Rich and Fuel Lean Catalytic Combustion of the Stabilized Confined Turbulent Gaseous Diffusion Flames

The Response Surface Methodology (RSM) has been applied to explore the thermal structure of the experimentally studied catalytic combustion of stabilized confined turbulent gaseous diffusion flames. The Pt/γAl2O3 and Pd/γAl2O3 disc burners were situated in the combustion domain and the experiments were performed under both fuel-rich and fuel-lean conditions at a modified equivalence (fuel/air) ratio (ø) of 0.75 and 0.25 respectively. The thermal structure of these catalytic flames developed over the Pt and Pd disc burners were inspected via measuring the mean temperature profiles in the radial direction at different discrete axial locations along the flames. The RSM considers the effect of the two operating parameters explicitly (r), the radial distance from the center line of the flame, and (x), axial distance along the flame over the disc, on the measured temperature of the flames and finds the predicted maximum temperature and the corresponding process variables. Also the RSM has been employed to elucidate such effects in the three and two dimensions and displays the location of the predicted maximum temperature.

Response Surface Methodology and Artificial Neural Network Methods Comparative Assessment for Fuel Rich and Fuel Lean Catalytic Combustion

Modeling, predictive and generalization capabilities of response surface methodology (RSM) and artificial neural network (ANN) have been performed to assess the thermal structure of the experimentally studied catalytic combustion of stabilized confined turbulent gaseous diffusion flames. The Pt/γAl2O3 and Pd/γAl2O3 disc burners were located in the combustion domain and the experiments were accomplished under both fuel-rich and fuel-lean conditions at a modified equivalence (fuel/air) ratio (ø) of 0.75 and 0.25, respectively. The thermal structure of these catalytic flames developed over the Pt and Pd disc burners was scrutinized via measuring the mean temperature profiles in the radial direction at different discrete axial locations along with the flames. The RSM and ANN methods investigated the effect of the two operating parameters namely (r), the radial distance from the center line of the flame, and (x), axial distance along with the flame over the disc, on the measured temperature of the flames and predicted the corresponding temperatures beside predicting the maximum temperature and the corresponding input process variables. A three-layered Feed Forward Neural Network was developed in conjugation with the hyperbolic tangent sigmoid (tansig) transfer function and an optimized topology of 2:10:1 (input neurons:hidden neurons:output neurons). Also the ANN method has been exploited to illustrate the effects of coded R and X input variables on the response in the three and two dimensions and to locate the predicted maximum temperature. The results indicated the superiority of ANN in the prediction capability as the ranges of & F_Ratio are 0.9181 - 0.9809 & 634.5 - 3528.8 for RSM method compared to 0.9857 - 0.9951 & 7636.4 - 24,028.4 for ANN method beside lower values for error analysis terms.

Comparative Appraisal of Response Surface Methodology and Artificial Neural Network Method for Stabilized Turbulent Confined Jet Diffusion Flames Using Bluff-Body Burners

The present study was conducted to present the comparative modeling, predictive and generalization abilities of response surface methodology (RSM) and artificial neural network (ANN) for the thermal structure of stabilized confined jet diffusion flames in the presence of different geometries of bluff-body burners. Two stabilizer disc burners tapered at 30° and 60° and another frustum cone of 60°/30° inclination angle were employed all having the same diameter of 80 (mm) acting as flame holders. The measured radial mean temperature profiles of the developed stabilized flames at different normalized axial distances (x/dj) were considered as the model example of the physical process. The RSM and ANN methods analyze the effect of the two operating parameters namely (r), the radial distance from the center line of the flame, and (x/dj) on the measured temperature of the flames, to find the predicted maximum temperature and the corresponding process variables. A three-layered Feed Forward Neural Network in conjugation with the hyperbolic tangent sigmoid (tansig) as transfer function and the optimized topology of 2:10:1 (input neurons: hidden neurons: output neurons) was developed. Also the ANN method has been employed to illustrate such effects in the three and two dimensions and shows the location of the predicted maximum temperature. The results indicated the superiority of ANN in the prediction capability as the ranges of R2 and F Ratio are 0.868 - 0.947 and 231.7 - 864.1 for RSM method compared to 0.964 - 0.987 and 2878.8 7580.7 for ANN method beside lower values for error analysis terms.

考虑弹头滚转姿态变化影响的防热层厚度优化

基于气动热/结构温度响应耦合计算方法,研究了弹头固定攻角再入条件下锥身典型子午面结构温度响应特性,以及滚转姿态变化时刻对各子午面结构温度响应的影响,建立了考虑弹头滚转姿态变化影响的防热层厚度优化方法,并基于该方法开展了弹头防热层厚度优化。最后,研究了滚转姿态变化次数对优化效果的影响。结果表明:在再入弹道前段进行滚转姿态变化可使外壁面气动加热量更为合理,有效降低弹体锥身壳体内壁面温升。当迎、背风面壳体内壁面最大温升约束为25 K时,与无滚转姿态变化状态下相比,滚转姿态变化设计可使防热层厚度减小0.725 mm,减小幅度为5.4%。通过与滚转姿态变化时刻的联合设计可有效降低锥身防热层厚度。与单次滚转姿态变化时相比,两次滚转姿态变化时防热层厚度减小量仅增大1.9%,增加滚转姿态变化次数对优化效果影响较小。

空间折展结构热响应研究现状与展望

中国航天正面向世界科技前沿和国家重大战略需求飞速前进,航天事业已成为我国整体发展战略的重要组成部分。近年来,随着航天核心技术的逐渐提升和突破,高精度、大尺度和轻量化的新型空间折展结构逐渐得到广泛应用,然而,其柔性大、刚度小,尤其是受空间极端环境显著影响等问题也备受关注。例如,空间折展结构中的典型应用——空间可展开天线,该新型结构作为航天和国防领域传递与获取信息的核心装备,在轨服役期间受空间热交变环境影响,其形面精度和网面稳定性问题凸显,甚至干扰航天器及其附件在轨工作姿态,从而导致航天器失效。为满足应用需求,文中归纳总结了伸展臂、太阳翼及可展开天线等空间折展结构的热致变形和热致振动等热响应研究进展。基于研究现状,从热-结构耦合情况、非线性因素、新型结构组合、结构连接及热控措施优化等方面展望空间折展结构热响应研究发展趋势,为我国空间折展结构的优化设计和防护方案提供理论依据及应用参考。

Effect of film types on thermal response,cellular structure,forming defects and mechanical properties of combined in-mold decoration and microcellular injection molding parts

Different types of polymer films were used in the combined in-mold decoration and microcellular injection molding(IMD/MIM)process.The multiphase fluid-solid coupled heat transfer model was established to study the thermal response at the melt filling stage in the IMD/MIM process.It was found that the temperature distributed asymmetrically along the thickness direction due to the changed heat transfer coefficient of the melt on the film side.When polyethylene terephthalate(PET)films were applied,the temperature of the melt-film interface increased faster and to be higher at the end of melt filling stage in comparison with the application of polycarbonate(PC)and thermoplastic polyurethane(TPU)films.And the effects of film types on the cellular structure,forming defects and mechanical properties of IMD/MIM parts were also studied experimentally.The results showed that the film types had no obvious effect on the cells size in the transition layer and the mechanical properties of the parts.Under certain film thickness,the offset distance of core layer was the largest with PET film used,while the offset distance was the smallest with TPU film used.And similar results were found for the warpage of the parts.However,an exactly opposite change occurred for the thickness of film-side transition layer and the bubble marks on the surface of the parts.

Crystal Structure,Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile

A natural rutle sample was measured by in situ high-temperature X-ray diffraction(XRD)patterns,as well as Raman and Fourier transform infrared(FTIR).Crystal structure is refined on the sample with 1.4 mol.%Fe and 510±120 ppmw.H2 O.The unit-cell and Ti O6 octahedral volumes are expanded by 0.7%–0.8%for Fe3+incorporation,as compared with the reported Ti-pure samples.The volumetric thermal expansion coefficient(α,K-1)could be approximated as a linear function of T(K):4.95(3)×10-9×T+21.54(5)×10-6,with the averaged valueα0=30.48(5)×10-6 K-1,in the temperature range of 300–1500 K.The internal Ti-O stretching(A1 g and B2 g)and O-Ti-O bending(Eg)modes show‘red shift',whereas the multi-phonon process exhibits‘blue shift'at elevated temperature.The rotational mode(B1 g)for Ti O6 octahedra is nearly insensitive to temperature variations.The OH-stretching bands at 3279 and 3297 cm-1 are measured by high-temperature spectroscopy experiments.Both the IR-active and Raman-active OH-stretching modes shift to lower frequencies at higher temperature,with the signal intensities decreasing.And after quenching,we expect about 43%dehydration around 873 K,and 85%dehydration at 1273 K for this hydrous sample.

Thermal stability of bimodal grain structure in a cobalt-based superalloy subjected to high-temperature exposure

The present work investigates the thermal stability and mechanical properties of a Co-20 Cr-15 W-10 Ni(wt%) alloy with a bimodal grain(BG) structure.The BG structure consisting of fine grains(FGs) and coarse grains(CGs) is thermally stable under high-temperature exposure treatments of 760℃ for 100 h and 870℃ for 100-1000 h.The size of both FGs and CGs remains no significant changes after thermal exposure treatments.The microstructural stability is associated with the slow kinetics of grain growth and the pinning of carbides.The thermal stability enables to maintain the BG structures,leading to the same mechanical properties as the sample without thermal exposure treatment.In particular,the BG alloy samples after thermal exposure treatment exhibit superior mechanical properties of both high strength and high ductility compared to the unimodal grain(UG) structured ones.The BG structure of the alloy samples after thermal exposure is capable of avoiding severe loss of ductility and retaining high strength.More specifically,the ductility of the BG alloy samples after thermal exposure treatments of 870℃ for 500-1000 h is ten times higher(44.6% vs.3.5% and 52.6% vs.5.0%) than that of the UG ones.The finding in the present work may give new insights into high-temperature applications of the Co-20 Cr-15 W-10 Ni alloy and other metallic materials with a BG structure.

基于振动测量的热防护结构脱粘损伤检测方法

针对典型飞行器热防护结构脱粘损伤现场快速无损检测的需求,提出了一种基于敲击测量频响函数的脱粘损伤识别方法。首先,利用有限元方法建立了含脱粘损伤的热防护结构有限元模型并进行了振动特性分析,分析了脱粘损伤引起的结构局部刚度下降规律以及频响函数对脱粘损伤的敏感性;其次,确定了脱粘损伤识别的特征频率范围,给出了一个脱粘损伤指标;最后,采用力锤与激光多普勒测振仪对含脱粘的热防护结构进行了测量。实验结果表明,当脱粘面积达到60%时,脱粘损伤指标比健康件增加了1倍以上,当脱粘面积达到80%时,脱粘损伤指标为健康件的5倍以上,验证了所提出的方法能够有效识别出热防护结构的脱粘损伤。

基于电磁-流热双向耦合的变压器绕组温升计算及结构参数优化

变压器温升是影响其运行状态和使用寿命的关键因素。为了更准确地得到油浸式变压器绕组区域的温度场分布,采用有限元法对绕组的电磁-流热耦合过程进行了数值研究。根据电磁场及流体-温度场分布的特点,建立了变压器及绕组区域的计算模型。基于异构网格节点数据映射方法,将电磁场分析得到的绕组非平均损耗作为热源边界条件加载到流体-温度场计算网格中,并根据每次迭代时的温度对该热源进行修正,实现电磁-流热的双向耦合。在此基础上,建立热点温度与绕组结构参数之间的响应面,开展了对绕组热点温度及导体材料用量最小化的多目标优化研究。采用非支配排序遗传算法(non-dominated sorting genetic algorithm,NSGA-Ⅱ)获得了Pareto最优解,并对Pareto前沿面上的4种优化方案进行了分析。结果表明,优化后的绕组热点温度及导体用量明显降低。该文研究为变压器结构的优化设计提供了一种可行方法。

基于响应面法的单元发动机喷注器优化设计

针对某新研单元发动机喷注器热阻优化的问题,采用仿真计算分析研究支架结构参数对支架热阻与结构强度的影响,并基于响应面法(RSM)对喷注器支架进行结构优化设计。计算结果表明:在计算范围内,对支架隔热性能影响最大的是支架高度,其次是支架厚度,最后是支架孔直径。随着支架高度的增加,支架热阻逐渐增大,而支架热阻则随着支架厚度与孔直径的增加而降低。对支架结构等效应力影响最大的是支架孔直径,其次是支架高度,最后是支架厚度,并且随着支架孔直径的增加,支架结构等效应力逐渐增大,而支架最大等效应力随着支架高度和厚度的增加而减小。通过采用响应面法改进后的支架在结构强度满足发动机力学环境的条件下,喷注器热阻得到明显提高。

Thermal fatigue behaviors of SiC power module by Ag sinter joining under harsh thermal shock test

The excellent properties of SiC bring new challenges for the device packaging.In this study,the bonding strength,fracture behaviors and microstructural evolution of micron-porous Ag joint were elevated during thermal cycling(–50 ℃–250 ℃) in SiC/DBC(direct bonding copper) die attachment structure for different time.During harsh thermal shock test,the strength of sintered joint deceased gradually with the increase of cycling number,and the value just was half of the value of as-sintered after 1 000 cycles.Coarsening of Ag grains was observed in micron-porous joint with the structure inhomogeneity and defects increasing,which were the reasons of the strength decease.In addition,it was also found that the fracture behavior of sintered joints was changed from ductile deformation of Ag grain to brittle fracture of crack propagation after 1 000 cycles.This study will add the understanding in the mechanical properties of Ag sinter joining and its applications at high temperature.

Thermal-structural response and low-cycle fatigue damage of channel wall nozzle

To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads,the fnite volume fluid-thermal coupling calculation method and the fnite element thermal-structural coupling analysis technique are applied.In combination with the material lowcycle fatigue behavior,the modifed continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles.Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a signifcant role in the thermal-structural response by altering the material properties;the thermal-mechanical loads interaction results in serious deformation mainly in the front region of slotted liner.In particular,the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib,where the fatigue failure takes place initially;with the increase in nozzle work cycles,the residual plastic strain accumulates linearly,and the strain amplitude and increment in each work cycle are separately equal,but the fatigue damage grows up nonlinearly.As a result,a simplifed nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle.The predicted node life is obviously conservative to the Miner＇s life.In addition,several workable methods have also been proposed to improve the channel wall nozzle durability.

Nonlinear thermo-structural behavior of sandwich panels with truss cores under through-thickness gradient temperature field

A theoretical analysis is presented to predict the nonlinear thermo-structural response of metallicsandwich panels with truss cores under through-thickness gradient temperature field, which is acommon service condition for metallic thermal protection system （TPS）. The in-planetemperature distribution is assumed to be uniform, and through-thickness temperature field isdetermined by heat conduction. Two typical conditions are analyzed： nonlinear thermal bendingin fixed inside surface temperature, and thermal post-buckling in fixed temperature differencebetween two surfaces. Temperature-dependent mechanical properties are considered, andgradient shear stiffness and bending stiffness due to non-uniform temperature is included. Resultsindicate that the temperature-dependent material properties obviously affect bending resistance;however, the effect is negligible on post-buckling behavior. Influences of geometric parameters onthe thermo-structural behavior of the sandwich panel according to the present theoretical modelare discussed.

围护结构动态热响应机理及应用

动态性是围护结构传热的本质属性,动态热响应机理是其动态运行规律的体现。围护结构在夏季的动态性比在冬季表现更为典型,因此该文开展隔热建筑的围护结构动态性机理及应用研究。通过研究围护结构的动态热响应机理提出围护结构最大防热量G_(max),该指标兼顾多种工况下围护结构热性能的评价。以夏热冬冷地区的重庆为例进行模拟分析。研究发现:G_(max)<60 W/m^(2)时,提升墙体最大防热量可有效提升其动态热响应性能;G_(max)在60~90 W/m^(2)之间时,提升墙体最大防热量可较少提升其动态热响应性能;G_(max)>90 W/m^(2)时,提升墙体最大防热量反而会降低其动态热响应性能。

基于主动加热型分布式温度感测光缆的土体导热系数测量方法

主动加热型分布式温度感测技术(AH-DTS)可通过植入土体中的光缆实现不同层位土体导热系数的分布式连续测量,但AH-DTS光缆导热系数测量方法的准确性和敏感性有待进一步研究。通过室内试验,对比了碳纤维加热感测光缆(CFHC)和铜网加热感测光缆(CMHC)的热响应过程,通过数值模拟验证了光缆结构对导热系数测量结果的影响。研究结果表明:(1)CFHC和CMHC的热响应过程可通过微分法分为光缆内部传热、纤-土过渡以及土体稳定传热3个阶段,光缆结构差异导致传热速率不同,使得CFHC导热系数测量初始时刻比CMHC提前100 s;(2)光缆尺寸与比热容差异下CFHC的升温值更高,相同测温精度CFHC的导热系数测量结果较CMHC更加稳定准确;(3)增大加热功率或延长加热时间均会提高CFHC和CMHC测量土体导热系数的准确性。研究成果为该技术的进一步完善和推广提供了重要依据。

基于响应面法的分级注水泥器结构优化

分级注水泥器在实际使用过程中结构刚度不能完全达到固井需求,经常由于结构变形造成循环孔打开或关闭失败。为此,采用响应面优化方法对分级注水泥器本体和滑套的5个关键尺寸参数进行改进,以达到提高结构刚度的目的。优化结果表明:采用拉丁超立方试验设计法的计算结果拟合出滑套最大变形量与质量,本体总变形、径向变形及质量的响应曲面;根据拟合的响应面,通过多目标遗传算法预测出滑套和本体设计变量的最优参数组合,并进一步构建了相应的优化模型;通过对滑套及本体进行热流固耦合分析可得,优化后滑套最大变形量减少了47.3%,本体最大总变形量减少了32.0%,本体最大径向变形量减少了62.7%。所得结论可为分级注水泥器设计提供理论参考。

三维堆叠封装TSV互连结构热扭耦合应力分析与优化

建立了三维硅通孔(TSV)芯片垂直堆叠封装结构有限元分析模型,对模型在热扭耦合加载下进行了仿真分析;分析了TSV材料参数与结构参数对TSV互连结构热扭耦合应力的影响;采用了响应面与模拟退火算法对在热扭耦合加载下TSV互连结构参数进行优化设计。结果表明:TSV互连结构最大热扭耦合应力应变位于铜柱与微凸点接触面外侧;微凸点材料为SAC387时,TSV互连结构热扭耦合应力最大,该应力随SiO_(2)层厚度的增大而增大,随铜柱直径的增大而先增大后减小,随铜柱高度的增大而减小;最优参数水平组合为铜柱直径50μm、铜柱高度85μm、SiO_(2)层厚度3μm,优化后的最大热扭耦合应力下降了5.3%。

矿用通风服对人体热生理反应的影响试验研究

为明确矿用通风服对人体热生理的影响效果,探究不同环境温度、人体劳动强度、矿用通风服管路结构及通风量与人体热生理反应的关系,基于人工环境试验舱以及试验测量仪器,开展真人受训试验,收集记录试验数据,分析在36种不同工况下3种不同管路结构矿用通风服的人体热生理变化情况,结合双变量相关分析功能,寻求3种管路结构下不同环境温度、服装通风量、劳动强度3因素与人体热生理之间的相关性。结果表明:3种通风服衣内微空间的风量分布均匀性为横向型>混合型>竖向型。针对整体效果而言,在同一工况下,管路结构影响显著程度由高到低依次为横向型、混合型和竖向型;环境温度主要影响平均皮肤温度与心率,通风量主要影响收缩压与舒张压,劳动强度主要影响出汗量。