In order to provide a method to control conformity of insulation of buildings after restoration, Protomeres project was launched under Prebat 2005 program. This work deals with the development of an experimental protocol for the diagnostic of multi-layered insulated building walls. In a previous study, a test bench was set up in order to measure front and back side temperatures of standard panels compounded of 1cm of plaster and various thicknesses of polystyrene. The panels considered have insulation thicknesses of 2, 6 and 10cm. In the present work, the panels are fixed on walls in laboratory to test real situations in constructions. The front side is painted in standardized black color and heated by two halogen lamps of 500W. A CEDIP Jade Long wave infrared camera and thermocouples are used to carry out temperature measurements during an exposure time and subsequent cooling. In a second time, a one dimensional model based on thermal quadruples and Laplace transforms was developed under Matlab environment. This model simulates a three-layered wall with a blade of air between polystyrene and concrete. Finally, a method of identification of physical parameters is implemented by performing least square minimization based on Levenberg-Marquardt method. The experimental measurements are compared to theoretical results and by minimization we obtain thermal conductivity and diffusivity as well as thickness of the two layers.
This work deals with the development of an experimental protocol for the diagnostic of multi-layered insulated building walls. First, a test bench is set up in order to measure front and back sides temperatures of standard panels. The panels considered have insulation thicknesses of 2, 6 and 10cm. The front side is heated by two halogen lamps of 500W. A CEDIP Jade Long wave infrared camera and thermocouples are used to carry out temperature measurements. In a second time, a one dimensional model based on thermal quadruples and Laplace transforms was developped under Matlab environment. Also, we developped a three dimensional model based on finite volumes using Fluent computational code. Finally, a method of identification of physical parameters is implemented by performing least square minimization based on Levenberg-Marquardt method. The experimental measurements are compared to theoretical results and by minimization we obtain thermal conductivity and diffusivity as well as thickness of the two layers.
An experimental analysis of the orthogonal cutting process is presented. Machining experiments have been performed using advanced techniques. A high-speed camera is coupled with an infrared thermal measurement aid on a dynamic test bench. This continuously reveals the deformations occurring on the flank of a chip, and the infrared camera gives information on the variation of thermal radiation (see the pictures under the abstract). The challenge consists of understanding the effect of machinability improvement treatments on metallic materials.
The study deals with the long-term reliability of a high precision
pressure sensor using bellows mainly made of electroplated Ni. Bellows are expected to stay in service for many decades. Their high cycle fatigue behavior has to be known to assess the probability of airtightness loss. A specific high cycle fatigue setup, put in a resonant machine that is displacement-controlled, has been designed. An infrared thermographic technique is used to determine the mean fatigue limit of bellows. Increases in the mean temperature of the bellows with the displacement range are monitored. Several authors empirically relate the mean fatigue limit of a flat specimen to a rapid temperature change. A similar analysis is performed in the present case by using the bellows mean temperature. Finite element computations allow us to estimate a mean fatigue stress threshold for
electroplated Ni. This result is compared with those obtained
mechanically in a Woehler diagram.
KEYWORDS: Nonuniformity corrections, Staring arrays, Sensors, Temperature metrology, Calibration, Black bodies, Thermography, Cameras, Infrared cameras, Body temperature
In the last decade, a technology of thermal imagers was developing on the basis of new infrared detectors, as well for civil and military uses. These imagers implement miniaturised infrared detectors laid out in a matrix placed in the optical focal plane of the imager. The technology of the FPA associates the detector matrix to specific electronics allowing detection and addressing on each pixel. This technology allowed a fast improvement of the performance of the thermal imager. Nevertheless, their use in thermography measurement requires some metrological care. The principal problem is both the uniformization of the pixel’s response and the temporal stability of this uniformization. The second problem consists in the compensation of the thermal drift. In this paper, we present some practical solutions developed by CEDIP infrared systems to perform non uniformity and thermal drift corrections. Performance and limits are reviewed.
The heat generated in frictional organs like brakes and clutches induces thermal distortions which may lead to localized contact areas and hot spots developments. Hot spots are high thermal gradients on the rubbing surface. They count among the most dangerous phenomena in frictional organs leading to damage, early failure and unacceptable braking performances such as brake fade or undesirable low frequency vibrations called hot judder. In this paper, an experimental study of hot spots occurrence in railway disc brakes is reported on. The aim of this study was to better classify and to explain the thermal gradients appearance on the surface of the disc. Thermograph measurements with an infrared camera have been carried out on the rubbing surface of brake discs on a full-scale test bench. The infrared system was set to take temperature readings in snap shot mode precisely synchronized with the rotation of the disc. Very short integration time allows reducing drastically haziness of thermal images. Based on thermographs, a classification of hot-spots observed in disc brakes is proposed. A detailed investigation of the most damaging thermal gradients, called macroscopic hot spots (MHS) is given. From these experimental researches, a scenario of hot spots occurrence is suggested step by step. Thanks to infrared measurements at high frequency with high resolution, observations give new highlights on the conditions of hot spots appearance. Comparison of the experimental observations with the theoretical approaches is finally discussed.
This paper aims to illustrate the advantages of Lock-In Thermography (LIT) as a non-destructive, real time and non- contact technique to analyze and to locate thermo-mechanical mechanisms in materials and structures. Due to the first and second principles of thermodynamics, there is a relationship between temperature and mechanical behavior laws. LIT is classically used to measure linear thermo-elastic effect to evaluate stresses in structures under periodic, random or transient loading. The new digital processing D-MODE presented allows extracting non-linear coupled thermo-mechanical effects (dissipated energy) cycle by cycle during a fatigue test on specimens and on real structures. This quantity much smaller than thermo-elastic source needs a high sensitive thermal imaging camera and a dedicated algorithm to separate dissipated energy from thermo-elastic source. On the other hand, it has been known for a long time that there is a correlation between plasticity in materials and the appearance of heat dissipation. More recently, it was shown there is a clear relationship between fatigue limit and occurrence of dissipated energy. We propose to improve these two methods by using LIT instead of temperature rise measurement to predict crack occurrence in real structures. At last we present some industrial applications in automotive and aircraft industries.
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