Jean-Francois Henry

Estimation of residual stresses induced by shot-peening. Measurement of the thermal dissipation with an infrared camera

Abstract The plasticization induced by the shot-peening treatment is an exothermic transformation. One can imagine to link the induced residual stress level to the thermal behaviour of the sample during the treatment or, at least, to propose some means of process monitoring control via temperature measurements. Steel samples were submitted to shot-peening under various conditions, both with a compressed air machine and a turbine machine. The temperature of the sample rear face was measured by IR thermography during the treatment. The thermal behaviour of the samples during the treatment have been compared to Almen intensity measurements and to residual stress measurements by the hole-drilling method. We conclude to the feasibility of process monitoring by temperature measurements. More academic experiments are being set up in order to derive quantitative relations between the thermal dissipation and the stress level.

Development and performance evaluation of a hemp–starch composite

This article describes the results of a research project carried out at the University of Reims Champagne-Ardenne. The aim of this article is to develop a new insulating material produced by bonding hemp shives with wheat starch as a binder and to characterize its physical properties such as sorption isotherm, water vapour permeability, thermal conductivity, heat capacity and porosity. The equations of coupled heat and moisture transfer within the panels are introduced. These governing equations are applied on the room level in order to assess the hygrothermal behaviour of the panels and its impact on energy consumption and indoor comfort. Simulations are performed for Nancy (France) winter conditions with the simulation environment Simulation Problem Analysis and Research Kernel (SPARK) suited for complex problems.

Non-contact photopyroelectric method applied to thermal and optical characterization of textiles. Four-flux modeling of a scattering sample

Abstract The radiative transfer equation is solving considering the textile material equivalent to an absorbing and scattering slab and using a four-flux approach. Three macroscopic values of radiative parameters are accessible from a spectrophotometer used with an integrating sphere: the directional transmittance and the hemispherical reflectance and transmittance. The four-flux model for scattering with a linearly anisotropic phase function was used to identify the absorption and scattering parameters and the geometrical factor of the textile sample. For the nine investigated cotton samples, we showed that these parameters are related to the yarn, to structure and to water content. Then, the previously developed theoretical model for the photopyroelectric method in a noncontact configuration was modified for the case of a scattering sample using the same four-flux approach. The method was used for water content measurement and thermal parameters characterization of textile materials. Full description of the correlation analysis and inversion procedure and a synthesis of the results concerning the thermal parameters are given in a second article [Duvaut et al., Rev. Sci. Instrum. 73 (2002) 1299–1303].

Investigation of thermal resistive probe behaviour used in Scanning Thermal Microscope by infrared imaging system

A new approach to estimate heat fluxes lost by the thermal-resistive probe of SThM has been used. This approach is based on an experimental set-up with infrared thermography measurement system coupled with an infrared transparent material. The measurements allow us to obtain experimental temperature profiles along the probe but also, experimental temperature profiles of samples in contact with the thermal probe. A modeling combined with these experimental results allows to estimate heat fluxes participating in the thermal balance of the probe and to define the operating temperature range to use the SThM with a higher sensitivity.

Assessment of modulated hot wire method for thermophysical characterization of fluid and solid matrices charged with (nano)particle inclusions

Recently we reported on simultaneous thermal conductivity k and thermal diffusivity a measurement of liquids and in particular of nanofluids in a configuration using an ac excited hot wire combined with lock-in detection of the third harmonic (3ω method) [1]. The conductive wire is used as both heater and sensor. The requirements for the asymptotic validity of the line heat source model are fulfilled at low modulation frequencies below a few Hz. The study of the relative sensitivity of signal amplitude and phase to changes in k and a indicates that there is an optimum frequency range for accurate and stable results. We extend by up to two decades the feasible frequency range for 3ω measurements by considering various more elaborate models for the heat transfer between the wire and the fluid. Finally we show that the same ac hot wire method can be applied to soft solid, composite materials. We measured the k enhancement of a poly(ethylene vinyl acetate) EVA polymer matrix charged with various fractions of graphite.