Numerical homogenization and experimental study of the influence of graphite content and voids on the coefficients of thermal expansion of 2017 Aluminium matrix composites

International audienceThis paper investigated the use of Graphite in aluminum matrix in order to improve the durability for thermal management systems. Thus, the effective coefficient of thermal expansion (CTE), of aluminum matrix composites (AMC) with random spatial distributions of Graphite particles were studied with numerical samples. Using the finite element analysis, 3D thermo-elastic problems were solved with the application of different boundary conditions on a representative volume element (RVE) containing different volume fraction of spherical Graphite particles. A quasi-linear decrease of the CTE of the composites was observed as the Graphite volume fraction increases. The comparison of the numerical results of the CTE with theoretical ones showed a good agreement with the Schapery upper bound model. Due to the incompatibility of the CTE between matrix and particles, the addition of Graphite was prominent on the thermal stress of the composites. A sensitive effect of voids showed on thermo-elastic property. The obtained experimental results of CTE confirmed the trend depicted in the simulation results when the voids were incorporated. © 2020 Elsevier Lt

Effective Emissivity Measurements of Powders and Their Mixtures

International audienceIn this paper, an experimental measurement technique of the effective emissivity of powders is presented for a given spectral field, using the reflectance hemisphere method. This technique consists of heating a powder filled into a Teflon (r) cell, through a thin copper layer. The apparent temperature of the powder surface is then measured by an infrared camera, either directly or through an orifice arranged into the hemisphere. The effective emissivity is identified by comparing the flux emitted by the powder surface and that emitted by a specular hemisphere taken as a reference blackbody, for the same temperature and the same spectral wavelength field. The results are presented for a metallic and an insulating powder, and validated with literature values. The effective emissivities of powder mixtures are also presented in this paper

Use of a pseudo-random heating excitation to investigate the thermal properties of thermally fragile materials

International audienceIn this numerical study, a photothermal method with random excitation is implemented in order to measure the thermal diffusivity of thermally fragile materials. The principle of this technique is based on rebuilding the sample impulse response through input-output cross-correlatoin. A D-optimality criterion is used to determine the optimal duration of the experiment. The thermophysical properties are identified through the rebuilt impulse response using an iterative method which minimizes the gap between simulated measurements and theoretical temperature calculated using the thermal quadripoles method. The obtained results show a good agreement with literature values

High Temperatures ^ High Pressures, 2003/2004, volume 35/36, pages 281 ^ 288 DOI:10.1068/htjr120

Parameter estimation of orthotropic solids with uncertainty in the sensor position: use of Levenberg ^ Marquardt and conjugate gradient method

Thermal characterization of poorly conducting solids by the flash method

International audienceEstimation of the thermal diffusivity of a poorly conducting solid placed between two metallic layers by the flash method is described. The method consists of applying a brief heat pulse to the front face of the three-layer composite and measuring the temperature rise versus time of the rear face. The thermal contact resistance between the layers and the heat transfer coefficient are obtained simultaneously with the thermal diffusivity of the poorly conducting solid. These parameters are identified by minimisation of the least-squares function comparing the measured and the calculated temperatures. Three models are developed using the thermal quadrupole method. An optimal design of the experiment is also presented and the choice of thermal model for parameter estimation is discussed. The experimental results are in good agreement with the theoretical analysis

High Temperatures ^ High Pressures, 2003/2007, volume 35/36, pages 633 ^ 647 DOI:10.1068/htjr140 Thermal characterization of poorly conducting solids by the flash method

Abstract. Estimation of the thermal diffusivity of a poorly conducting solid placed between two metallic layers by the flash method is described. The method consists of applying a brief heat pulse to the front face of the three-layer composite and measuring the temperature rise versus time of the rear face. The thermal contact resistance between the layers and the heat transfer coefficient are obtained simultaneously with the thermal diffusivity of the poorly conducting solid. These parameters are identified by minimisation of the least-squares function comparing the measured and the calculated temperatures. Three models are developed using the thermal quadrupole method. An optimal design of the experiment is also presented and the choice of thermal model for parameter estimation is discussed. The experimental results are in good agreement with the theoretical analysis. Nomenclature ai thermal diffusivity (m 2 s �1) Greek symbols Cp heat capacity (J kg �1 K �1) r density (kg m �3) ei layer thickness (m) y1 Laplace temperature on the front h heat transfer coefficient (W m �2 K �1) face of the first layer (K s