Hardness of steel and thermal contact resistance

Experiments on steel samples are reported for a new type of hardness tester based on the measurement of thermal contact resistance. These experiments have been carried out using a machine-mounted probe and a newer hand-held double-probe. It is shown that, by using the double-probe, errors due to the sample not having reached ambient temperature can be avoided. Although, ideally, the thermal conductivity of the sample should be much greater than that of the probe tip, it is found that it is simple to apply a correction to the apparent hardness number if this condition is not met. The standard deviation in the Vickers hardness number H, that is yielded by the hand-held probe ranges from 10% to 14% as H changes from 150 to 850 kg mm^–2, but the observations with the machine-mounted probe indicate that a much higher accuracy than this is possible.     

On the thermal contact resistance under vacuum

The author analyzes the heat exchange under vacuum between two bodies whose adjoining surfaces are in contact at discrete spots uniformly spaced along parallel and equidistant zones. The theoretical values of the thermal contact resistance are compared with experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 5, pp. 951–957, November, 1969.     

Generalized relations for determining thermal contact resistance

By analyzing numerous experimental data dimensionless relations for calculating thermal contact resistance (TCR) over a broad range of thermal contact conditions are obtained.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 1, pp. 97–100, July, 1977.     

Shape sensitivity analysis of composites in contact using the boundary element method

This paper presents the application of the boundary element method to the shape sensitivity analysis of two-dimensional composite structures in contact. A directly differentiated form of boundary integral equation with respect to geometric design variables is used to calculate shape design sensitivities for anisotropic materials with frictionless contact. The selected design variables are the coordinates of the boundary points either in the contact or non-contact area. Three example problems with anisotropic material properties are presented to validate the applications of this formulation.     

Techniques for thermal sensitivity analysis

Techniques for computing the sensitivity of temperatures to changes in design variables needed for designing thermal protection systems are considered. It is shown that the choice of the most efficient technique depends on the ratio of number of temperature constraints to the number of design variabies, as well as on the thermal analysis method employed. The analysis is specialized to the case of a structure modelled by finite elements, and an example of an insulation panel is used demonstrate the techniques.     

Improvement of thermal contact resistance by carbon nanotubes and nanofibers

Interfacial thermal resistance results of various nanotube and nanofiber coatings, prepared by chemical vapor deposition (CVD) methods, are reported at relatively low clamping pressures. The five types of samples examined include multi-walled and single-walled nanotubes growth by CVD, multi-walled nanotubes grown by plasma enhanced CVD (PECVD) and carbon nanofibers of differing aspect ratio grown by PECVD. Of the samples examined, only high aspect ratio nanofibers and thermally grown multi-walled nanotubes show an improvement in thermal contact resistance. The improvement is approximately a 60% lower thermal resistance than a bare Si-Cu interface and is comparable to that attained by commercially available thermal interface materials.     

Shape design sensitivity analysis and optimization of two-dimensional periodic thermal problems using BEM

 A general procedure to perform shape design sensitivity analysis for two-dimensional periodic thermal diffusion problems is developed using boundary integral equation formulation. The material derivative concept to describe shape variation is used. The temperature is decomposed into a steady state component and a perturbation component. The adjoint variable method is used by utilizing integral identities for each component. The primal and adjoint systems are solved by boundary element method. The sensitivity results compared with those by finite difference show good accuracy. The shape optimal design problem of a plunger model for the panel of a television bulb, which operates periodically, is solved as an example. Different objectives and amounts of heat flux allowed are studied. Corresponding optimum shapes of the cooling boundary of the plunger are obtained and discussed. Received 15 August 2001 / Accepted 28 February 2002     

调制光热法低温接触界面层热阻研究

选择航天器和低温工程中常用金属材料铜、不锈钢,用激光光热法原理,研究低温接触界面层热阻.实验得到了铜在常温下的调制频率与相位差间的实验数据,通过对实验数据的线性拟合得到了铜的热扩散系数,以及铜-不锈钢在300K和20 K低温下的接触界面层热阻.实验表明调制光热法能够测量具有微结构特征的接触界面层热阻,且具有非接触测量的特点.     

Influences of temperature and contact pressure on thermal contact resistance at interfaces at cryogenic temperatures

The microscopic heat transfer between solid and solid at cryogenic temperatures exists in many application fields. This paper employed the Laser Photothermal Method (LPM) which is a transient and non-contact method to measure the Thermal Contact Resistance (TCR) between solid and solid in the temperature range of 70–290 K and the pressure range of 0.2–0.7 MPa. This paper analyzed the effects of the temperature and the contact pressure on the TCR at interfaces. The relationship between the TCR and the temperature at certain contact pressure was established, and the explanation about this phenomenon was given. Following, the TCR of SS 304–AlN, SS 304–Cu and SS 304–SS 304 were compared at different temperatures and contact pressures.     

The effect of soft-metal coatings and linings on contact thermal resistance

The article presents the results of an experimental investigation of the thermal resistance of contacts with coatings and linings of soft metals (silver, copper) at compressive stresses of up to 56 ·10⁵ N/m² over a temperature range of 250–600°C. The specimens were made of different kinds of stainless steel or of a molybdenum alloy.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 5, pp. 871–879, November, 1969.     

Pressure dependence of the thermal contact resistance for rough surfaces

The contact resistance is expressed analytically as a function of load for elastic and elastoplastic contacts by taking the rough surface as consisting of spherical projections with a normal distribution.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 19, No. 1, pp. 62–67,July, 1970.     

Determining thermal resistance of contact between finished wavy metallic surfaces

A design formula for determining the thermal resistance of a contact is obtained using functions describing the relief of real wavy surfaces.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 5, pp. 779–785, May, 1977.     

The significance of thermal contact resistance in two-layer thermal-barrier-coated turbine vanes

A study was conducted to determine whether the thermal contact resistance (TCR) between layers is important in heat transfer through two-layer plasma-sprayed thermal barrier coatings (TBCs) applied to turbine vanes. The results obtained with a TBC system of an NiCrAlY bond and an yttria-stabilized zirconia ceramic showed that the TCR between the layers was negligible. This result also verified other results obtained with a different coating system of an NiCr bond and a calcia-stabilized zirconia ceramic.     

Determining contact thermal resistance for unsteady heat transfer between touching bodies

A procedure for determining the contact heat transfer coefficient from the amount of heat received by a body during the transient state between touching bodies is proposed. The results obtained by way of experimental verification agree with data obtained under steady-state heat transfer conditions.     

Modeling the impact of a molten metal droplet on a solid surface using variable interfacial thermal contact resistance

An analytical model of the true area of contact between molten metal and a rough, solid surface has been used to calculate thermal contact resistance and to predict how it changes with surface roughness, substrate thermal properties and contact pressure. This analytical model was incorporated into a three-dimensional, time-dependent numerical model of free-surface flows and heat transfer. It was used to simulate impact, spreading and solidification of molten metal droplets on a solid surface while calculating contact resistance distributions at the liquid–solid interface. Simulations were done of the impact of 4 mm diameter molten aluminum alloy droplets and 50 μm diameter plasma sprayed nickel particles on steel plates. Predicted splat shapes were compared with photographs taken in experiments and simulated substrate temperature variation during droplet impact was compared with measurements.     

Isogeometric contact analysis using mortar method

In the present work, an isogeometric contact analysis scheme using mortar method is proposed. Because the isogeometric analysis is employed for contact analysis, the geometric exactness of the contact region is maintained without any loss of geometric data because of geometry approximation. Thus, the proposed method can overcome underlying shortcomings that result from the geometric approximation of contact surfaces in the conventional finite element (FE)‐based contact analysis. For an isogeometric contact analysis, the schemes for treating the contact conditions and detecting the real contact surfaces are essentially required. In the proposed method, the mortar method is adopted as a nonconforming contact treatment scheme because it is expected to be in good harmony with the useful characteristics of nonuniform rational B‐spline A new matching algorithm is proposed to combine the mortar method with the isogeometric analysis to guarantee consistent contact surface information with the nonuniform rational B‐spline curve. The present scheme is verified by patch test and the well‐known problems which have theoretical solutions such as interference fit and the Hertzian contact problem. It is shown that the problems with curved contact surfaces which are difficult to treat by conventional approaches can be easily dealt with. Copyright © 2011 John Wiley & Sons, Ltd.     

Boundary-only element analysis of crack contact under thermal shock

This paper presents a multi-domain boundary integral equation approach of thermally excited crack surface interference observed under thermal transient conditions. According to this model, crack surface displacements and tractions are not free but subject to constraints simulating contact and prevailing overlapping of crack surfaces. The multi-domain approach allows the two faces of a crack to be modeled in independent sub-regions of the body, avoiding singularity difficulties and making it possible to analyze crack closure problems with contact stresses over part of the cracked faces. Crack-tip singularities are modeled through quarter-point elements. In order to approach the interference configuration, the interfacial traction distribution and solve the resulting equations, an iterative numerical procedure is applied. The numerical solution of this non-linear problem yields crack surface displacements and consequently the crack surface interference. Fracture parameters are evaluated from nodal displacements of singular elements utilizing proper formulas. Various results are illustrated and discussed for edge-cracks subjected to steady-state or thermal shock conditions.