Unraveling the effect of uniaxial strain on thermoelectric properties of Mg2Si:A density functional theory study

In this work, the effect of uniaxial strain on electronic and thermoelectric properties of magnesium silicide using density functional theory（DFT） and Boltzmann transport equations has been studied. We have found that the value of band gap increases with tensile strain and decreases with compressive strain. The variations of electrical conductivity,Seebeck coefficient, electronic thermal conductivity, and power factor with temperatures have been calculated. The Seebeck coefficient and power factor are observed to be modified strongly with strain. The value of power factor is found to be higher in comparison with the unstrained structure at 2% tensile strain. We have also calculated phonon dispersion, phonon density of states, specific heat at constant volume, and lattice thermal conductivity of material under uniaxial strain. The phonon properties and lattice thermal conductivity of Mg2Si under uniaxial strain have been explored first time in this report.

Equivalent circuit model including magnetic and thermo sources for the thermo–magneto–electric coupling effect in magnetoelectric laminates

The nonlinear thermo–magneto–mechanical magnetostrictive constitutive and the linear thermo–mechanical-electric piezoelectric constitutive are adopted in this paper. The bias magnetic field and ambient temperature are equivalent to a magnetic source and a thermo source, respectively. An equivalent circuit, which contains a magnetic source and a thermo source at the input, for the thermo–magneto–electric coupling effect in magnetoelectric（ME） laminates, is established. The theoretical models of the output voltage and static ME coefficient for ME laminates can be derived from this equivalent circuit model. The predicted static ME coefficient versus temperature curves are in excellent agreement with the experimental data available both qualitatively and quantitatively. It confirms the validity of the proposed model. Then the models are adopted to predict variations in the output voltages and ME coefficients in the laminates under different ambient temperatures, bias magnetic fields, and the volume ratios of magnetostrictive phases. This shows that the output voltage increases with both increasing temperature and increasing volume ratio of magnetostrictive phases; the ME coefficient decreases with increasing temperature; the ME coefficient shows an initial sharp increase and then decreases slowly with the increase in the bias magnetic field, and there is an optimum volume ratio of magnetostrictive phases that maximize the ME coefficient.This paper can not only provide a new idea for the study of the thermo–magneto–electric coupling characteristics of ME laminates, but also provide a theoretical basis for the design and application of ME laminates, operating under different sensors.

THERMO-PIEZOELECTRIC EFFECTS ON THE POSTBUCKLING OF AXIALLY-LOADED HYBRID LAMINATED CYLINDRICAL PANELS

A compressive postbuckling analysis is presented for a laminated cylinderical panel with piezoelectric actuators subjected to the combined action of mechanical, electrical and thermal loads. The temperature field considered is assumed to be a uniform distribution over the panel surface and through the panel thickness and the electric field is assumed to be the transverse component E_Z only. The material properties are assumed to be independent of the temperature and the electric field. The governing equations are based on the classical shell theory with von Krmn-Donnell-type of kinematic nonlinearity. The nonlinear prebuckling deformations and initial geometric imperfections of the panel are both taken into account. A boundary layer theory of shell buckling,which includes the effects of nonlinear prebuckling deformations, large deflections in the postbuckling range,and initial geometric imperfections of the shell,is extended to the case of hybrid laminated cylindrical panels of finite length. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the compressive postbuckling behavior of perfect and imperfect, cross-ply laminated cylindrical thin panels with fully covered or embedded piezoelectric actuators under different sets of thermal and electrical loading conditions.The effects played by temperature rise,applied voltage,stacking sequence,the character of in-plane boundary conditions,as well as initial geometric imperfections are studied.

Finite elastic torsional instability of incompressible thermo-hyperelastic cylinder

Torsional instability of an incompressible thermo-hyperelastic cylindrical rod, subjected to axial stretching and large torsions, is examined within the framework of finite elasticity. When the cylinder is stretched and twisted by a sufficiently large degree, a knot may form suddenly at one point. This inherent elastic instability is analyzed with the minimum potential energy principle and the critical values of torsion are obtained. The distribution of stresses as well as the tensile force and the torque are studied. Effect of tem- perature change is specifically discussed.

First principle investigation of the electronic and thermoelectric properties of Mg2C

In this paper, electronic and thermoelectric properties of Mg_2C are investigated by using first principle pseudo potential method based on density functional theory and Boltzmann transport equations. We calculate the lattice parameters,bulk modulus, band gap and thermoelectric properties（Seebeck coefficient, electrical conductivity, and thermal conductivity） of this material at different temperatures and compare them with available experimental and other theoretical data. The calculations show that Mg_2C is indirect band semiconductor with a band gap of 0.75 eV. The negative value of Seebeck coefficient shows that the conduction is due to electrons. The electrical conductivity decreases with temperature and Power factor（PF） increases with temperature. The thermoelectric properties of Mg_2C have been calculated in a temperature range of 100 K–1200 K.

SHAPE MEMORY EFFECT OF PU IONOMERS WITH IONIC GROUPS ON HARD-SEGMENTS

SMPU （shape memory polyurethane） non-ionomers and ionomers, synthesized with poly（c-caprolactone） （PCL）, 4, 4＇-diphenylmethane diisocyanate （MDI）, 1,4-butanediol （BDO）, dimethylolpropionic acid （DMPA） were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content.

不同储层渗透率下稠油油藏火驱开发特征

储层渗透率直接影响火驱过程中的驱替压差、油墙的形成与聚集速度,明确渗透率对稠油火驱开发的影响规律十分必要。采用自主开发的燃烧管装置和多孔介质热效应监测装置,开展了火驱实验,分析不同渗透率下辽河稠油油藏火驱特征。结果表明:储层渗透率为650×10^(-3)μm^(2)时,火驱过程中各热电偶峰值温度达到550℃,燃烧前缘推进中温度没有下降,说明该渗透率下燃烧过程放热效率高,能够解除燃烧初期的油墙封堵;热效应监测装置能够高效快速地监测由于原油氧化燃烧反应所导致的温度变化,储层渗透率为480×10^(-3)μm^(2)时庙5区稠油燃烧峰值温度比储层渗透率为300×10^(-3)μm^(2)时高107℃,说明渗透率的提高增强了燃烧初期的放热,从而缓解了油墙的封堵效应。研究结果对不同渗透率稠油油藏火驱开发具有理论指导意义。

Coupled thermal-optic effects and electrical modulation mechanism of birefringence crystal with Gaussian laser incidence

We study the Gaussian laser transmission in lithium niobate crystal（LiNbO3） by using the finite element method to solve the electromagnetic field＇s frequency domain equation and energy equation. The heat generated is identified by calculating the transmission loss of the electromagnetic wave in the birefringence crystal, and the calculated value of the heat generated is substituted into the energy equation. The electromagnetic wave＇s energy losses induced by its multiple refractions and reflections along with the resulting physical property changes of the lithium niobate crystal are considered.Influences of ambient temperature and heat transfer coefficient on refraction and walk-off angles of O-ray and E-ray in the cases of different incident powers and crystal thicknesses are analyzed. The E-ray electrical modulation instances, in which the polarized light waveform is adjusted to the rated condition via an applied electrical field in the cases of different ambient temperatures and heat transfer coefficients, are provided to conclude that there is a correlation between ambient temperature and applied electrical field intensity and a correlation between surface heat transfer coefficient and applied electrical field intensity. The applicable electrical modulation ranges without crystal breakdown are proposed. The study shows that the electrical field-adjustable heat transfer coefficient range becomes narrow as the incident power decreases and wide as the crystal thickness increases. In addition, it is pointed out that controlling the ambient temperature is easier than controlling the heat transfer coefficient. The results of the present study can be used as a quantitative theoretical basis for removing the adverse effects induced by thermal deposition due to linear laser absorption in the crystal, such as depolarization or wave front distortion, and indicate the feasibility of adjusting the refractive index in the window area by changing the heat transfer boundary conditions in a wide-spectrum laser.

Study on the thermo-optic properties of DR1/PMMA composite

This paper reports that the thermo-optic coefficient （dn/dT） as well as thermal expansion coefficients （β） of DR1/PMMA polymer film are measured for both TE （transversal electric） and TM （transversal magnetic） polarizations by using an attenuated total reflection configuration at the wavelengths of 832nm. The thermo-optic coefficients of DR1/PMMA are negative and as high as the order of 10^-4/℃. The influences of dopant concentration, poling process and photobleaching process on the thermo-optic properties of DR1/PMMA are also investigated.

Dynamic thermo-mechanical coupled simulation of statistically inhomogeneous materials by statistical second-order two-scale method

In this paper,a statistical second-order twoscale（SSOTS） method is developed to simulate the dynamic thcrmo-mechanical performances of the statistically inhomogeneous materials.For this kind of composite material,the random distribution characteristics of particles,including the shape,size,orientation,spatial location,and volume fractions,are all considered.Firstly,the repre.sentation for the microscopic configuration of the statistically inhomogeneous materials is described.Secondly,the SSOTS formulation for the dynamic thermo-mechanical coupled problem is proposed in a constructive way,including the cell problems,effective thermal and mechanical parameters,homogenized problems,and the SSOTS formulas of the temperatures,displacements,heat flux densities and stresses.And then the algorithm procedure corresponding to the SSOTS method is brought forward.The numerical results obtained by using the SSOTS algorithm are compared with those by classical methods.In addition,the thermo-mechanical coupling effect is studied by comparing the results of coupled case with those of uncoupled case.It demonstrates that the coupling effect on the temperatures,heat flux densities,displacements,and stresses is very distinct.The results show that the SSOTS method is valid to predict the dynamic thermo-mechanical coupled performances of statistically inhomogeneous materials.

Dynamic thermo-mechanical coupled response of random particulate composites:A statistical two-scale method

This paper focuses on the dynamic thermo-mechanical coupled response of random particulate composite materials. Both the inertia term and coupling term are considered in the dynamic coupled problem. The formulation of the problem by a statistical second-order two-scale （SSOTS） analysis method and the algorithm procedure based on the finite-element difference method are presented. Numerical results of coupled cases are compared with those of uncoupled cases. It shows that the coupling effects on temperature, thermal flux, displacement, and stresses are very distinct, and the micro- characteristics of particles affect the coupling effect of the random composites. Furthermore, the coupling effect causes a lag in the variations of temperature, thermal flux, displacement, and stresses.

Experimental investigation of the cyclic degradation of the one-way shape memory effect of NiTi alloys

Based on stress-and strain-controlled cyclic tension-unloading-heat-cooling tests,cyclic degradation of the one-way shape memory effect(OWSME)of NiTi shape memory alloys(SMAs)was investigated.It was seen,in thermo-mechanical coupled cyclic tests,that residual strain after each cycle accumulated,but the martensite reorientation stress and dissipation energy-per-cycle decreased as the number of cycles increased.Meanwhile,the cyclic degradation of OWSME was aggravated by increasing the stress/strain amplitude.In addition,the stress-strain response of NiTi SMAs was further investigated by performing simultaneous thermo-mechanical coupled cyclic tests with various phase-angle differences between the mechanical and thermal cyclic loadings.It can be concluded that such cyclic response depends significantly on prescribed phase-angle differences.Obtained experimental results are helpful for both the development of constitutive models and engineering applications of NiTi SMAs.

循环加卸载条件下考虑温度的煤体本构模型

随着煤炭资源深部开采趋于“常态化”,深入了解处于高地应力和高地温环境中深部煤体在扰动条件下的力学性质及其损伤演化规律,对煤矿深部开采具有重要意义。选取平煤十二矿己16-17-17200工作面的煤体为研究对象,开展了在不同温度条件下三轴循环加卸载试验,分析了温度对试件峰值强度、变形模量、泊松比等基本力学参数的影响。将不同加卸载速率相关的应力-应变问题转化为时间-应力-应变问题,同时引入分数阶导数理论和连续介质损伤理论,提出了一个考虑了热-力耦合作用的分数阶粘弹塑性本构方程,通过试验数据验证了其有效性。结果表明:煤体变形模量随着循环次数的增加呈出现线性减小的趋势,而煤体泊松比减速上升,在峰值应力处达到极值,然后降低,表明循环加卸载作用对煤体基本力学性能有劣化作用。随着温度的升高,煤体峰值强度非线性减小,损伤累积变缓,对应的应变逐渐增大,表明升温能增强煤体延性变形能力,加速煤体损伤的发展。在循环加卸载过程中,输入能密度、弹性能密度和耗散能密度在煤体破坏失稳阶段随温度升高呈现出明显的衰减现象,说明高温加剧了煤体内部的损伤,降低了煤体强度,使得破坏所需外界输入能量减少。考虑温度影响的分数阶粘弹塑性模型可以较好地描述深部煤体在循环加卸载条件下的力学行为。模型适用于热力耦合下深部煤体的复杂应力状态。

平滑铝护套电缆蛇形敷设下热机械效应的有限元分析

近些年我国对平滑铝护套电缆的关注度持续提高,但目前相关敷设方面的研究尚有不足。针对电缆敷设过程中由于导体发热引起的热机械应力可能造成的安全问题,本文建立了平滑铝护套电缆在垂直蛇形敷设下的有限元模型,计算分析了垂直蛇形敷设情况下电缆的热机械效应。结果表明:垂直蛇形敷设电缆通过产生蛇形弧的侧向滑移,使其由于热效应引起的轴向力远小于直线敷设电缆,满足电缆长期安全运行条件;随着温度的升高,垂直蛇形敷设的侧向滑移量逐渐增大且增加趋势和理论计算结果相符,轴向力先从拉伸力转变为压缩力后逐渐增大;通过适当增大垂直蛇形敷设电缆的弧幅和半蛇形节距,可降低电缆产生的轴向力。

热−力耦合作用下垃圾土体积变形特性和模型研究

城市生活垃圾填埋场因有机质降解产热导致其内部温度长期高于环境温度,引发工程运维问题。垃圾土温控三轴试验结果发现,温度变化引起的垃圾土体积应变与应力水平有关,且弹性体积应变占比较大,影响以塑性体积应变为硬化参数的弹塑性本构模型研究。在前期试验基础上,采用GDS温控应力路径三轴仪,研究了排水条件下温度对垃圾土中黏土体积变形特性和压缩特性的影响,并与相同条件下垃圾土体积变形特性进行比较,揭示了温度变化对垃圾土体积变形特性的影响机制。基于垃圾土温控三轴试验结果,推导了垃圾土热弹塑性压缩指数λT和热弹性压缩指数κT的确定方法;采用等效应力原则,假设温度变化引起的弹塑性体积应变等于某一等效应力增量引起的弹塑性体积应变,建立了垃圾土在热−力耦合作用下的体变计算模型,并对模型进行了验证分析。研究结果表明,孔隙比是影响垃圾土温度体积应变的主要因素;垃圾土的λT和κT随初始固结应力的增加而减小,比黏土高一个数量级;选取常温下相应固结应力水平的回弹指数κ和压缩指数λ比例值(κ/λ)能够较好地模拟热−力耦合作用下垃圾土的体积变形特性。

基于硅基微环谐振器的Fano共振线型产生和调谐研究进展

Fano共振的线型具有明显不对称特征,在光学通信、调制和传感等领域中极具应用潜力。首先对微环谐振器的各种线型进行了介绍,强调了Fano共振线型的独特优势,其次依据结构分类梳理了国内外基于硅基微环谐振器产生Fano共振的研究现状,然后介绍了基于热光效应的Fano共振调谐的研究进展,最后展望了硅基微环谐振器的Fano共振的发展及应用。

湿热力作用下粉砂质泥岩开裂特性研究

为探究湿热力作用下粉砂质泥岩的开裂特性,开展裂隙演化试验,得到湿热力单因素及多因素耦合循环作用下粉砂质泥岩的裂隙演化规律,同时利用X射线衍射、扫描电镜研究其微观结构变化特征,分析宏观和微观试验结果关联性,揭示湿热力作用下粉砂质泥岩裂隙扩展机制.研究结果表明:粉砂质泥岩裂隙发育表现为增长-平缓趋势;在单因素循环作用中,湿度循环(浸水~烘干)最易造成粉砂质泥岩开裂,温度循环(5~60℃)次之,荷载循环(0~50 kPa)最弱;在多因素耦合循环作用中,裂隙发育程度排序为:湿热力>湿热>湿力>热力,验证了湿度循环致裂性最强的结论.湿热力耦合循环作用15次后裂隙率达0.92%,裂隙条数增至30条,平均长度延伸至60.58 mm,而平均宽度稳定在0.47 mm左右.孔隙率与裂隙率的灰关联度最大,为0.813,即微观结构变化中孔隙发育与裂隙扩展的关联程度最大.湿热力耦合循环作用中,湿度循环引起黏土矿物晶层间距变化,导致颗粒破碎、孔隙扩张形成微裂隙,温度循环使试样产生差异性热应力、水分分布,促使微裂隙发育贯通,荷载作用增加尖端应力,最终导致裂隙网络形成.

带孔形状记忆合金薄板弹热性能的实验和理论研究

NiTi形状记忆合金因其优异的弹热效应在新兴固态制冷领域具备广阔的应用前景.然而,该类合金较高的相变临界应力使得其弹热效应需要很高的机械载荷来驱动,对固态制冷器件的小型化和大规模应用带来了挑战.文章通过在NiTi形状记忆合金薄板上引入孔洞,揭示了孔洞体积分数、分布形式对薄板弹热性能的影响.结果表明,孔洞造成的应力集中效应能够在显著降低薄板相变驱动力的同时,有效增加薄板的整体制冷温度和吸热量.薄板在变形过程中的整体力-位移响应和温度演化强烈依赖于孔洞体积分数,孔洞分布形式仅仅影响薄板的局部应力-应变-温度场,而对整体的热-力响应影响较小.进一步地,基于应力对数客观率,在不可逆热力学框架下建立了形状记忆合金有限变形热-力耦合本构模型,并完成了模型的有限元移植.通过与实验结果的对比发现,提出的本构模型能够很好地预测孔洞对NiTi形状记忆合金薄板变形行为和弹热性能的影响,从而为该类合金带孔薄板的设计提供理论工具.

SiC复合包壳在辐照后LOCA工况下的热力耦合行为及其影响机制研究

碳化硅(SiC)复合包壳的热-力学性能和抗辐照性能较强,是一种优异的轻水堆事故容错燃料包壳,其结构完整性对反应堆安全运行至关重要.本文综合考虑各层材料的辐照效应,开展了SiC复合包壳在轻水反应堆稳态运行1146天后发生失水事故(Loss of Coolant Accident,LOCA)期间的热-力耦合行为数值模拟,获得了CVD-SiC单质层的第一主应力分布和演化规律,并对应力演化的影响机制开展了分析.结果表明:LOCA期间内部CVD-SiC单质层的最大拉应力先迅速增加,后缓慢增加,存在开裂的风险;包壳外压降低是内部CVD-SiC单质层最大拉应力及复合材料层损伤因子快速增加的重要原因;内压随着温度的升高而增大,是内部CVD-SiC单质层最大拉应力及复合材料层损伤因子继续增加到峰值的原因;复合包壳管在稳态运行阶段存在较大的径向温差,由于LOCA初期温差的降低引起的热应力对内部CVD-SiC单质层的最大拉应力也产生了显著的影响,有望通过提高碳化硅纤维增强复合材料的热导率来降低复合包壳管的失效风险.

基于绝缘硅的微环谐振可调谐滤波器

采用电子束光刻和感应耦合等离子刻蚀等工艺,研制了一种基于绝缘硅材料的的微环谐振可调谐滤波器.滤波器微环半径为5μm左右,波导截面尺寸为(350～500nm)×220nm不等.测试结果表明,波导宽度为450nm时器件性能最为理想,其自由频谱宽度为16.8nm,1.55μm波长附近的消光比为22.1dB.通过对微环滤波器进行热光调制,在21.4℃～60℃温度范围内实现了4.8nm波长范围的可调谐滤波特性,热光调谐效率达到0.12nm/℃.研究了基于单环和双环的多通道上下载滤波器,实验结果表明多通道滤波器的信号传输存在串扰,主要是不同信道之间的串扰,尤其在信号上载时,会在相邻信道产生较大串扰.