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. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

The aim of the present work is the thermal non-destructive characterisation of layers at the surface of metals.The sample is sinusoidally heated by means of an argon ion laser and a focal plane array infrared camera (CEDIP IRC 320-4 LW) is used to measure the temperature variations at the surface of the layer.A numerical lock-in procedure allows the detection of very weak temperature variations at the surface of the sample, down to a few mK when working from the acquisition of hundreds of images, yielding amplitude and absolute phase maps for modulation frequencies ranging from 0.1 Hz to 1000 Hz.An inverse procedure uses the Gauss-Newton parameter estimation method, in order to identify the thermal conductivity and the optical absorption coefficient of the layer.Confidence intervals on the parameters can also be estimated by the inverse procedure.More particular attention is devoted to the study of the sensitivity coefficients, as functions of the frequency range and of the radial range along the profiles, in order to optimise the identification procedure.

Mechanical stresses, applied or residual, are identified by means of photothermal infrared thermography. Stresses are detected via their influence on thermophysical properties and more particularly on the thermal conductivity tensor. Because this influence remains weak, a sufficiently accurate identification procedure is needed as well as a significant enhancement of the signal-to-noise ratio, by means of a focal plane array camera.

The quantitative validation of the non destructive testing method begins by comparing the experimental results with a unidimensional multilayer analytical thermal model. Then, the development of an inverse procedure, using the Gauss-Newton parameter estimation method, allows the identification of the thermal resistance or the equivalent air layer thickness at the metal-metal interface. Confidence intervals on these parameters are estimated by this inverse procedure. A unidimensional numerical thermal model by finite differences as well as a tridimensional numerical model by finite elements have been tested. Finally, thermal resistance estimations are presented.

We have performed pulsed photothermal radiometric measurements of thermal diffusivity of silica-gel on thin- layer chromatography plates at two different IR wavelength regions ane obtained values in the region of D equals 0.2 mm2/s. We then proceeded to depth profiling of TLC plates with photoacoustic measurements with modulated excitation using IR and visible excitation.

We present some elements in order to improve the non-detructive procedure for the measurement of the local heat coefficients between a flat plate and an air flow.We use the pulsed photothermal radiometry method which consists of analysing the transient temperature on the front face of a wall after a sudden deposit of luminous energy by a lump.The infrared camera measures the temperature evolutions at different abscissa from the leading edge of the plate, in order to deduce the local heat coefficients for the same experiment.The results of three identifications, based on a one-dimensional model at any abscissa with constant heat transfer coefficients, are compared.

Very small temperature Variations are quantified by a statistical treatment of standard infrared equipment images. This procedure determines the signal amplitude value, comparing the noise and the noisy signal dispersions characterized by their variances. This robust and simple method has the advantage of needing no link to the reference signal and of treating any kind of signal shape. It is applied here to thermoelastic analysis of applied and residual stresses. (C) Elsevier, Paris.

The resolution of stress analysis by means of infrared thermography is limited by the optical performance of the IR imaging equipment and by heat diffusion within the sample. The optical low­ pass filtering is characterised by 1 D and 2D transfer functions, while the 2D heat diffusion is modelled by a Bessel function. Iterative procedures are used for the restoration of both the optically smoothed contrasts and the thermally attenuated spatial gradients. The technique has been tested in some academic experiments, and then applied to stress maps of actual industrial parts. Thermoelastic stress analysis by means of radiometry is realised by measuring with an infrared radiometer the very small temperature variations of a sample under mechanical loading, then by calculating a stress map, using an adequate model of the thermoelastic coupling. The essential improvement of the signal to noise ratio can be realised as well by a lock-in detection [1, 2] as by a statistical treatment [3]. A high spatial resolution is desirable, but the quantitative evaluation of steep gradients is quite difficult, since they are attenuated by both the heat diffusion and the imaging process. So, the observed stress maps are smoothed relatively to the actual ones. Restoring the original stress maps needs to use some inverse techniques, based on the direct models of optical imaging and thermal effects. Image formation operates as a low-pass filtering, which is characterised by a 2D response, usually known as the Point Spread Function (PSF), specific of each optical

An infrared thermography equipment is used to measure the temperature rise at the surface of a steel bar, simultaneously submitted to the irradiation of a modulated laser beam and to a static uniaxial mechanical stress. The camera measures the radial temperature profiles across the laser beam, in order to point out the influence of stresses on the local thermal properties. Since this influence remains rather weak, a careful identification of the properties is to be undertaken.

Introduction Fruits and vegetables used in various processed products, as well as in fresh market sales, are expected to comply with the certain quality standards. However. quality is everything but a single parameter state and, therefore, a variety of subjective and objective measurements are usually performed. In particular, the firmness and maturity are considered important attributes to the quality of fruits and vegetable crops. Presently. these parameters are usually determined either destructively (by a pressure tester) or by means of ultrasound; a development of alternative methods has been strongly encouraged in the recent years.

Thermoelastic stress analysis is a full-field stress measurement technique complementary to local techniques like strain gages. Generally, the heat transfer inside the material is neglected with respect to the frequency of the cyclical loading. An adiabaticity criterion is established to assert this simplification as a function of the thermal diffusion length and the spatial stress gradients. Under nonadiabatic conditions, heat diffusion attenuates the spatial temperature gradients, which leads to an underestimation of stress concentrations. Analytical and numerical considerations allow for the quantification of the spatial resolution. Finally, several inverse techniques can restore the thermally attenuated contrasts.

In dynamic fatigue testing experiments, the thermoelastic effect links the local stress level and the local temperature variation in a material. Though quite minute, this effect can be readily measured by standard infrared thermography. Since neglecting the heat conduction is not relevant in the case of good conductors at high excitation frequencies, an adiabaticity criterion is established. An inverse technique to restore the thermally attenuated contrasts is proposed, using the finite element method for the direct heat conduction modelling. This technique has successfully be applied to an academical test sample. Measurements performed on some automotive parts under cyclic loading are presented. Besides, the influence of highly emissive coatings will be shortly discussed.

A statistical method of signal processing allows for the quantification of small periodic temperature changes, using a standard IR camera and short image sequences without the necessity of any synchronization device. The attenuation of the signal in a high emissivity coating such as a black paint has been quantified by means of a 1D thermal model. This same model is used to analyze the heat conduction effects on thermoelastic stress measurements. By analogy with the resolution power of optical systems, a “thermal spatial resolution power” is calculated. The spatial resolution appears to be limited by the heat conduction at low frequencies and by the performance of the radiometer at high frequencies.

Results of several experiments aimed at testing authenticity and at inspecting quality of foodstuffs are presented. Adulteration of red paprika spice by red lead, the effect of thermal treatment on stability of ultrafiltrated milk protein concentrate, thermal properties of carbohydrate gels, measurement of infrared absorption coefficients for hexanoic acid vapors and the nondestructive inspection of fruit firmness are the topics discussed.

L'analyse thermoelastique des contraintes mecaniques par radiometrie consiste tout d'abord en la mesure des tres faibles variations de temperature d'un objet sous excitation mecanique avec un radiometre infrarouge a balayage. Ensuite, une carte de contraintes est calculee a partir des variations de temperature en faisant appel a un modele adapte du couplage thermoelastique. Une methode statistique de traitement des donnees a ete developpee pour ameliorer la resolution thermique des equipements de thermographie infrarouge standard, afin d'atteindre une resolution suffisante en termes de mesure de contraintes. Cette methode a ete testee sur un echantillon d'interet purement academique et les cartes de contraintes obtenues ont ete comparees aux resultats fournis par la modelisation par elements finis. Des mesures ont ete effectuees sur quelques pieces d'automobile, notamment sur une bielle et une roue en acier. Une etude theorique a ete menee, d'abord dans le cas d'une geometrie uni-dimensionnelle et ensuite pour une geometrie 2 d, ce qui nous permet de quantifier l'influence des revetements emissifs et de la diffusion thermique dans l'echantillon. Nous proposons quelques techniques inverses pour restaurer les contrastes thermiques attenues. Une de ces techniques a ete testee a l'aide de la methode des elements finis