接触热阻及热湿耦合作用对火灾下钢管混凝土柱温度场影响的研究

为更好地分析火灾下钢管混凝土柱截面的温度场,建立了高温下核心混凝土的一维传热传质模型及钢管混凝土柱的传热模型,利用多物理场耦合分析软件COMSOL对核心混凝土的温度场进行了分析,而后研究了接触热阻对钢管混凝土柱截面温度场的影响。分析结果表明:考虑接触热阻和水蒸气等因素的影响后所计算的温度场能够更为真实地反映火灾下钢管混凝土柱截面温度发展的实际情况;与热传导计算模型相比,该文所述的混凝土传热传质数学模型能够更好地描述火灾下混凝土的温度场问题;不考虑接触热阻时计算的柱截面温度高于考虑接触热阻时的计算结果,且越靠近核心混凝土表面计算结果误差越大。     

内置高温热管C/C复合材料热防护结构热力耦合机制

采用内置高温热管的热防护结构是一种新型高效的热防护方式。建立了内置高温热管的C/C 复合材料热防护结构模型, 并通过罚函数的方法引入C/C 复合材料与高温热管间装配关系, 推导了一种顺序耦合的热力耦合有限元格式, 在此基础上对热防护结构进行了热力耦合计算分析, 最后对影响结构温度场与应力场的若干参数进行了参数影响分析。计算结果表明, 在典型飞行状态下, 采用内置高温热管的C/C 复合材料热防护结构能确保结构驻点温度在材料许用温度范围内; 同时, 采用预留装配间隙的方法可有效降低结构界面的接触应力。该方法也可进一步用于研究由接触热阻引起的热力耦合问题。      

直接冷却中氮化铝与无氧铜低温真空接触热导的实验研究

以5W／20K小型G-M制冷机为冷源,对低温下氮化铝（AlN）与无氧铜（OFHC）界面的接触热导进行了实验研究和分析。在45～140K内,氮化铝／无氧铜界面接触热导随温度的升高而增大,同时亦随接触压力的增加而增大。实验中同时得到了氮化铝在低温下的热导率,随温度的升高,氮化铝热导率值逐渐增大。就氮化铝低温热导率及氮化铝／无氧铜接触界面热阻随温度变化规律进行了微结构机理分析。     

高导热金属基复合材料的热物理性能

分别采用无压浸渗、气压浸渗、内氧化技术制备了高导热Al/SiC、Al/C、Cu/Al2O3复合材料.研究了增强相和界面对这三种复合材料的热导率和热膨胀系数的影响,并对这些性能进行了理论分析和数值模拟.当颗粒尺寸与界面层厚度之比固定时,颗粒尺寸对Al/SiC复合材料热导率影响很小,但界面热导率对其影响很大;Al/SiC复合材料的CTE随温度的升高而增加,随SiO2层厚度的增加而减小;碳纤维中混杂3%SiC颗粒有利于改善纤维的分布,降低Al/C复合材料的缺陷,并提高其热导率;压力加工增加了Cu/Al2O3的致密度,也提高了其热导率;可用Schapery和Kerner模型计算复合材料的热膨胀系数,用Hasselman-Johnson模型计算热导率.     

界面接触效应对不同尺度半导体制冷器性能的影响

本文建立了半导体制冷器的实际模型,讨论了界面接触效应对不同尺度半导体制冷器性能的影响,并对比分析了接触热阻、接触电阻、冷端温度等对制冷效率和单位面积制冷量的影响。研究发现:接触热阻对半导体制冷器性能的影响比接触电阻大,且界面接触效应对薄膜型半导体制冷器件性能的影响不可忽视。在设计高效率半导体制冷器时,应尽量优化其界面接触效应,并减少接触热阻。     

氮化硼/聚合物导热复合材料界面热阻调控研究进展

随着5G时代的发展，电子器件领域的热管理问题日发严峻。氮化硼（BN）是一类高热导率（TC）、高绝缘的导热填料，广泛应用于热管理领域，包括六方氮化硼（h-BN）、氮化硼纳米片（BNNS）和氮化硼纳米管（BNNT）。然而，BN表面呈化学惰性，其与基体或其他填料间亲和力低、声子谱失配等，导致了填料与基体/填料间存在明显的界面热阻，限制了复合材料TC的提升，难以满足使用要求。因此，如何调控界面热阻、设计BN/聚合物导热复合材料的热传导界面，并提高复合材料的导热能力是当前亟待解决的难题。研究者分别从理论模拟与实验验证两个角度对热流在界面传导的差异及其原因进行探索。在理论研究中，将分子动力学（MD）模拟及有限元模拟（FEA）等方法结合有效介质模型及其优化模型、Foygel模型等能够对界面热阻（ITR）进行深入的理论模拟与分析；其中，影响界面热阻的关键参数包括BN含量、尺寸及晶体状态、BN的分布形貌等。在实验设计中，为了改善填料与基体间界面热阻，首先对BN表面共价键改性或表面包覆，随后结合聚合物种类设计相应的官能团来改善BN与聚合物的界面作用力；其中BN表面的共价键改性对BN本身晶体结构有一定的破坏...     

低温真空下Cu-Cu界面间接触热阻的实验研究

简单介绍了低温真空下固体界面间的接触热阻现象,搭建了一个能较精确测量圆柱型及薄片型材料间接触热阻的实验台。在真空环境下,测量了低温真空下Ｃｕ－Ｃｕ界面间的接触热阻。实验数据表明,接触热阻与压力、温度有关一定的依赖关系。最后,根据修正Ｇ－Ｗ模型,对实验结果进行了理论理论分析与比较,表明实验结果是正确的。     

低温真空下Cu—Cu界面间接触热阻的实验研究

简单介绍了低温真空下固体界面间的接触热阻现象,搭建了一个能较精确测量圆柱型及薄片型材料间接触热阻的实验台。在真空环境下,测量了低温真空下Ｃｕ－Ｃｕ界面间的接触热阻。实验数据表明,接触热阻与压力、温度有关一定的依赖关系。最后,根据修正Ｇ－Ｗ模型,对实验结果进行了理论理论分析与比较,表明实验结果是正确的。     

双热流法测定低温真空下固体界面的接触热阻

本文介绍了低温真空下固体界面间的接触热阻机理,重点介绍一种采用双热流计法既能精确测量圆柱型又能测量薄片型试样间接触热阻的装置,该装置还能同时测量材料的热导率。同时,文中给出一些材料在低温真空下的接触热阻值。     

Cu-FeS复合材料导热性能的计算研究

为了研究质量分数为15%FeS的Cu-FeS自润滑材料内部结构与导热性能的关联, 采用分子动力学的方法, 在考虑界面热阻的情况下构建原子模型, 对增强相和复合材料导热性能进行模拟研究。结果表明: FeS在600K、 900K时会发生有利于热传导的结构变化, 系统界面热阻随着FeS尺寸的增大而减小, 颗粒大于100nm时, 界面热阻趋于一定值。通过计算所得导热率与实验数值较接近, 误差的引起是由于计算没有考虑温度升高对界面结合的破坏、 界面的不完整性、 基体内部缺陷、 弥散相的大小等因素。验证了HasselmanJohnson方法对于预测该复合材料的合理性。      

A general and efficient computational procedure for modelling the Kapitza thermal resistance based on XFEM

The thermal resistance of an interface between two materials, conceptualized by Kapitza, is an important physical phenomenon encountered in many situations of practical interest. The numerical treatment of this phenomenon has up to now run into difficulties due to the temperature discontinuity. In this work, a general and efficient computational procedure for modelling the Kapitza thermal resistance is proposed, which is based on the extended finite element method (XFEM) in tandem with a level-set method. The steady thermal conduction in a two-phase material with the Kapitza thermal resistance at the interface is first formulated in a variational way and then numerically treated with the proposed computational procedure. Different three-dimensional numerical examples with known analytical solutions show the high accuracy and robustness of the proposed computational procedure in capturing the temperature jump across an interface.     

Bounds on the effective thermal conductivity of composites with imperfect interface

A new model is developed to bound the effective thermal conductivity of composites with thermal contact resistance between spherical inclusions and matrix. To construct the trial temperature and heat flux fields which satisfy the necessary interface conditions, the transition layer for each spherical inclusion is introduced. For the upper bound, the trial temperature field needs to satisfy the thermal contact resistance conditions between spherical inclusions and transition layers and the continuous interface conditions between transition layers and remnant matrix. For the lower bound, the trial heat flux field needs to satisfy the continuous interface conditions between different regions. It should be pointed out that the continuous interface conditions mentioned above are absolutely necessary for the application of variational principles, and the thermal contact resistance conditions between spherical inclusions and transition layers are suggested by the author. According to the principles of minimum potential energy and minimum complementary energy, the bounds of the effective thermal conductivity of composites with imperfect interfaces are rigorously derived. The effects of the size and distribution of spherical inclusions on the bounds of the effective thermal conductivity of composites are analyzed. It should be shown that the present method is simple and does not need to calculate the complex integrals of multi-point correlation functions. Meanwhile, the present method provides an entirely different way to bound the effective thermal conductivity of composites with imperfect interface, which can be developed to obtain a series of bounds by taking different trial temperature and heat flux fields. In addition, the present upper and lower bounds are finite when the thermal conductivity of spherical inclusions tends to ∞ and 0, respectively.     

Crack propagation modeling on the interfaces of thermal barrier coating system with different thickness of the oxide layer and different interface morphologies

A finite element model (FEM) is developed to simulate the crack development in a typical plasma sprayed thermal barrier coatings system in consequence of the stresses induced by thermal cycling, the growth of the oxide layer and different interface morphologies. The thermo-mechanical model is designed to takes into account a non-homogenous temperature distribution and the effects of the residual stress generated during coating process.     

石墨化参数对四向炭/炭复合材料残余应力的影响

依据四向编织炭/炭复合材料的结构特点,建立了能反映其编织方式和空间构型的单元体胞模型.在单胞几何模型和介观计算力学基础上,采用有限元方法研究了在不同石墨化温度、降温梯度和界面刚度情况下四向编织炭/炭复合材料的残余热应力分布.研究表明:低温石墨化复合材料的残余热应力比高温石墨化时小.界面刚强度低时石墨化过程中残余热应力比界面刚强度高时小.冷却速率越快,残余热应力越大.     

Ultimate Bearing Capacity Analysis and Sizing Optimization of a Cracked Reactor Pressure Vessel in the Coupled Thermo-Mechanical Field

Pressurized thermal shock (PTS) can subject a crack surface to a very high tensile stress. Also the material toughness is obviously decreased in the cooling process, so it is necessary to study the influence of PTS on the ultimate bearing capacity of a reactor pressure vessel with defects. A 3-D finite element model is established for the beltline region around an inner crack. The FEM is used to reveal the transient temperature field and stress field, and the XFEM is adopted to simulate the ductile crack propagation. To ensure that the strength requirement is satisfied, the ultimate internal pressures of vessels with different crack sizes and different wall thicknesses are obtained. The result shows that the ultimate bearing capacity of the base wall with shallow surface cracks at high temperature is mainly controlled by tensile strength, while it is also affected by the fracture toughness of the material under the severe PTS. The stress in the early stage of the PTS is mainly the thermal stress, and later is the thermo-mechanical coupling stress. The impact of the crack depth on the bearing capacity of the structure is much greater than that of the crack length.     

Finite element study of the fibre–matrix interface behaviour of [10°/90°] laminated composites under tensile loading

A three-dimensional unit cell has been developed and modelled using the finite element method to investigate the interface failure behaviour of SiCf/Si3N4 composites under tensile loading at room and elevated temperatures. The model idealizes the composite as a regular rectangular array of fibres in 0° and 90° orientations embedded in the matrix. It introduces three-dimensional contact elements between the fibre and the matrix to simulate the interface conditions between the two phases. Slippage between 0° and 90° layers is also considered by introducing another set of contact elements at the layer separation planes. Two interface conditions, namely, infinitely strong and weakly bonded, are considered to establish the correlation with the experimental data. To simulate the weak interface, the fibre and the matrix are assumed to slide over one another with shear stress through the Coulomb mechanism. The same assumption has been adopted for the layer separation planes. A finite element model utilizing these concepts has been developed. Stress–strain behaviour and the local stress distributions at various ambient temperatures within the unit cell, are presented. The investigation has also been extended to include the effects of residual stresses in the finite element model. It is shown that the model yields results that correlated reasonably well with the experimental data. © 1998 Kluwer Academic Publishers     

NUMERICAL MODELLING OF TWIN-ROLL CASTING BY THE COUPLED FLUID FLOW AND HEAT TRANSFER MODEL

The twin-roll process is modelled by a coupled fluid flow and phase change model by means of a versatile finite element method. Here, a simple numerical scheme is proposed to solve the problem of determining the interface shape under the thermal equilibrium condition. The procedure is based on a finite element method using a transform technique. The simple numerical method provides an efficient and accurate way to find the interface position and shape with arbitrary boundary geometry. This method can easily be implemented on the existing finite element program, and provides a simple and efficient tool to simulate the solidification as well as the fluid flow problem of the twin-roll casting process. © 1997 by John Wiley & Sons, Ltd.     

Quantitative evaluation of the adhesion of metallic coatings using cylindrical substrate

This paper introduces an effective interfacial fracture toughness test based on interface fracture mechanics theory. This testing method uses a circumferentially notched tensile (CNT) specimen, which is ideally suited for determining the interfacial fracture resistance of coatings. Unlike other interfacial fracture tests, this test is simple to prepare, requires minimum test setup and is easy to model. An interfacial pre-crack was generated between a nickel coating and mild steel cylindrical substrate to evaluate adhesion strength. In situ acoustic and SEM analyses were used to determine the crack initiation or the critical load of failure. The critical energy release rate, critical stress intensity factors and phase angle were determined using the J integral which was determined by applying the critical load to the finite element model. A detailed finite element analysis was carried out to study the effect of different interface pre-crack positions and mode mixity on energy release rate for different notch angles and elastic modulus ratios. The cracking resistance of the interface was characterised by the notch angle of CNT specimens. The analysis showed an increase in interfacial fracture toughness as phase angle increases and was significant when the phase angle was large. The combined results of computational and experimental analysis showed that any defect or stress concentration at the interface could significantly weaken the adhesion of coating.