Showing papers on "Thermography published in 1994"
TL;DR: In this paper, the edge effects for crack-like defects have been calculated using the Wiener-Hopf technique and it is found that the crack surface temperature is reduced over a distance of a thermal diffusion length by heat flow around the crack edge to the cold underside of the crack.
Abstract: Thermal edge effects for crack-like defects have been calculated using the Wiener-Hopf technique. It is found that the crack surface temperature is reduced over a distance of a thermal diffusion length by heat flow around the crack edge to the cold underside of the crack. Surface thermal images have been computed for a straight-edged and a circular crack. Comparisons are presented of image profiles computed with and without inclusion of edge effects. Edge effects lead to the prediction that transient thermographic defect images should shrink with elapsed time. Experimental data are presented, which are in agreement with this prediction and demonstrate a simple means of defect sizing.
138 citations
TL;DR: In this article, heat transfer measurements were performed on two ribbed plates, with constant heat flux surfaces, using an infrared (IR) thermography technique, and the results suggested a separation-reattachment flow distribution over the plate with a pitch ratio (p/e ) of 12 and a trapped vortex flow between ribs for a p/e of 5.
66 citations
01 Jan 1994
TL;DR: In this paper, an early detection of the contrast is presented to demonstrate how it recovers the depth of the defects with accuracy and removes partially the loss of resolution produced by the lateral heat diffusion.
Abstract: Infra-red stimulated thermography is a fast and global method. Among the recently emerging NDE methods, it is probably the less intrusive one since it really needs no contact at all with the tested structure. A new inversion, using an early detection of the contrast, is presented to demonstrate how it recovers the depth of the defects with accuracy and removes partially the loss of resolution produced by the lateral heat diffusion.
38 citations
TL;DR: In this paper, a new 1-0 procedure for defect geometry characterization (depth and lateral size) was proposed, which is less sensitive to lateral diffusion but still retains high speed.
Abstract: Pulsed stimulated infrared thermography is a .powerful technique for the detection of thermally resistive defects in materials. Time-resolved analysis of the surface temperature field can then be used for the identification of· the defect characteristics (mainly its depth, its lateral size and its thermal resistance). Several such inversion procedures were proposed in the past. They are based either on a 1-0 or on a 2-to-30 modelling of thermal transfer in the inspected material. In this paper we describe a new 1-0 procedure for the defect geometry characterization (depth and lateral size). Compared to previous 1-0 methods, it is less sensitive to lateral diffusion. It however retains their high speed.
35 citations
TL;DR: It is concluded that microwave thermography can measure inflammatory activity in the knee joints of patients with inflammatory arthritis and can respond to clinical change brought about by major treatment intervention.
Abstract: Microwave thermography is the technique of measuring natural thermal radiation from body tissues of clinical interest. It is safe, requires no control of environmental conditions and exposes the patient to no ionising radiation. In this study, we found that microwave thermography of the knee joints showed weak correlation with some global parameters of disease activity. Bed rest alone for three days had no significant effect on microwave thermographic index (MTI). Intra-articular steroid injection, however, was associated with a marked fall in MTI both in the injected knee and the contra-lateral knee. We conclude that microwave thermography can measure inflammatory activity in the knee joints of patients with inflammatory arthritis and can respond to clinical change brought about by major treatment intervention.
34 citations
TL;DR: In this article, an early detection of the contrast is presented to demonstrate how it recovers the depth of the defects with accuracy and partially removes the effects produced by the lateral heat diffusion, which leads to a high accuracy as regards the identified in-depth position of the defect, and to a better identified defect shape.
Abstract: Stimulated Infrared Thermography (TIS) is a fast and global method for NonDestructive Evaluation (NDE). Among the recently emerging NDE methods, it is probably the less intrusive one since it really needs no contact at all with the tested structure. A new inversion technique, using an early detection of the contrast, is presented to demonstrate how it recovers the depth of the defects with accuracy and partially removes the effects produced by the lateral heat diffusion. l . INTRODUCTION The main ONERAfL3C contribution in the Non Destructive field lies in the techniques of the Stimulated Infrared Thermography (TIS) which consist in a pulse uniform illumination of the surface of the studied specimen, followed by the analysis of its InfraRed (IR) emission as a function of time /I/. Section 2 of this paper is devoted to the recent improvements brought by our group to this analysis and which allows to strongly decrease the effects of the lateral heat diffusion (3-D effects). As a consequence, the method leads to a high accuracy as regards the identified in-depth position of the defects, and to a better identified defect shape (see section 3). The advantages of this new inversion will be assessed, by performing it on artificial and natural impact defects present in composite materials. 2. TIS EARLY DETECTION 2.1. Industrial set up The set-up used in the experiments described in this paper, corresponds to the front surface configuration, i.e. illumination and detection on the same surface. The pulsed sources available in our system can be either flashes (pulse duration 4 ms) or continuous IR lamps (48 kW), the pulse being achieved, in that case, by the opening/closing of mechanical shutters electromechanically driven (the smallest pulse duration obtained with this system is 200 ms). An AGEMA 880LW records the surface temperature as a function of time during periods of times up .to 10 mn after the pulse illumination. For instance, when placed at 1.2 m from the sample surface, the system allows to obtain a field of view of 20 cm and a spatial resolution of 2 mm with the objective of 12' used for these experiments. 2..2. Inversion using the early detection The detection and the characterization of the resistive subsurface defects is achieved by seeking local emergence of thermal contrast after the pulse illumination, i.e. an increase of the local temperature above the defect with respect to the temperature in a sound region, (figure la). Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1994712 C7-48 JOURNAL DE PHYSIQUE IV Generally, the depth and the resistance of the defect are deduced from the value and the time of the maximum contrast /l/. This search is made pixel by pixel and finally leads to two synthetic images, respectively for the local depths and resistances of the subsurface defects. An alternative consists in the detection of the time corresponding to half the development of the contrast 121. The deeper the defects are, the longer these characteristic times are, with an important lateral heat diffusion as a consequence. Under these conditions, the inversion provides an underestimation of both the depths and the thermal resistances of the detected defects. a) Schematic explanations of the two detections b) Definition of the detection threshold, dT being the noise
33 citations
TL;DR: The use of the Microwave Thermography System in Forensic Medicine for the estimation of the post-mortem interval and a new device which is applied to this field for the first time is described and its mode of operation is discussed.
33 citations
Journal Article•
TL;DR: Demonstration of characteristic thermal temporomandibular joint changes suggests that electronic thermography may have potential for assessing internal derangement of the temporomanderbular joint, however, more extensive studies are needed before thermographic procedures can be accepted clinically.
Abstract: This study assessed the ability of electronic thermography to identify internal derangement of the temporomandibular joint. The study population consisted of 30 patients with internal derangement verified by temporomandibular joint arthrotomography. Electronic thermography was conducted using an Agema 870 thermographic unit. Thermal assessments included: (1) pattern recognition; (2) pattern symmetry; (3) absolute temperature measurements; (4) delta T measurements; and (5) mean temperature measurements and differences within five designated anatomic zones. Results indicated: (1) low levels of thermal symmetry in patients with internal derangement of the temporomandibular joint, and (2) absolute temperature measurements and mean temperature zone measurements showing large delta T values (0.4 degrees C to 0.8 degrees C). Demonstration of characteristic thermal temporomandibular joint changes suggests that electronic thermography may have potential for assessing internal derangement of the temporomandibular joint. However, more extensive studies are needed before thermographic procedures can be accepted clinically.
29 citations
TL;DR: In this article, a method for solving the direct problem of acoustical thermography in the one-dimensional case is proposed for theoretical calculations of the acoustobrightness temperature Ta on an object's surface from the distribution of the thermodynamic temperature and the absorption coefficients within the surface.
28 citations
TL;DR: In this article, a novel type of combustion control system is described for municipal waste incinerators using infrared thermography to obtain information about the temperature distribution in the furnace interior, which can be used for fine tuning of the total underfire air (UFA) flow.
28 citations
TL;DR: In this paper, the authors presented the analysis of the thermal gradients on the substrate of an integrated-circuit chip (telephone line interface chip) using thermographic imaging techniques.
Abstract: This paper presents the analysis of the thermal gradients on the substrate of an integrated-circuit chip (telephone line interface chip) using thermographic imaging techniques. After taking the chip thermal image using a thermal camera and doing temperature calibration, an isothermal contour map of the chip region is drawn by digital image-processing techniques proposed in this paper. By overlaying the layout mask on the isothermal contour map of the chip region, each region of the chip is easily identified. This information is of great assistance to the designer while laying out the components on the chip. >
TL;DR: In this article, the orientation fields of carbon fibres can be probed both along the surface and in depth at low modulation frequencies and in short time, which is applicable for remote analysis and prediction of material properties.
Abstract: Fibre reinforced materials are inspected with thermal waves. We show how orientation fields of carbon fibres can be probed both along the surface and in depth at low modulation frequencies and in short time. This technique is applicable for remote analysis and prediction of material properties.
TL;DR: In this paper, lockin thermography combines the advantages of both conventional thermal wave methods and thermography using a commercial IR-camera, which allows for shorter imaging time and depth profiling.
Abstract: byWU D. The technique of lockin thermography combines the advantages of both conventional thermal wave methods and thermography using a commercial IR-camera. It allows for shorter imaging time and depth profiling. Inhomogenenous illumination and optical surface structures can be suppressed in phase images. Several examples show applicability of lockin thermography to detect and locate hidden flaws in layered material.
TL;DR: In this article, a simple method of defect sizing is proposed based on accounting for defect shrinkage, which leads to an experimentally verified prediction that transient thermographic defect images shrink systematically with elapsed time.
Abstract: Thermal edge-effects for crack-like defects have been calculated using the Wiener-Hopf technique. These lead to an experimentally verified prediction that transient thermographic defect images shrink systematically with elapsed time. A simple method of defect sizing is proposed based on accounting for defect shrinkage. Finite difference modeling is used to investigate the dependence of image shrinkage on defect size and depth.
TL;DR: In this paper, a cylinder of low-thermal conductivity material, covered by polyethylene layers, is applied on the skin, which allows partial transmission of the infrared radiation through it, and the transient and steady-state temperature increase can be obtained from measurements of radiation transmitted through the thermal insulation that was applied to the skin.
Abstract: The temperature increase of thermally insulated skin provides useful information about its blood flow and the blood temperature. The measurement of skin temperature by a contact thermometer, such as a thermistor, is not accurate, because it depends on the pressure exerted on the skin by the thermometer. In order to have reproducible measurement of the skin temperature, noncontact temperature measurement is preferable. Suitable insulation is achieved by using a cylinder of lowthermal-conductivity material, covered by polyethylene layers, which is applied on the skin. The polyethylene layers permit partial transmission of the infrared radiation through it. Preliminary results show that both the transient and the steady-state temperature increase can be obtained from measurements of radiation transmitted through the thermal insulation that was applied to the skin, and that the steady-state temperature increase is more closely related to tissue blood flow than the uncovered-skin temperature is.
TL;DR: The technique of thermal wave thermography combines advantages of both conventional thermal wave measurement and thermography using a commercial IR camera as mentioned in this paper, which allows for shorter imaging time and depth profiling.
Abstract: The technique of thermal wave thermography combines advantages of both conventional thermal wave measurement and thermography using a commercial IR camera. This technique allows for shorter imaging time and depth profiling. Non-uniformity of heating area and optical surface structures can be suppressed in phase images. Several examples show the potential applications of thermal wave thermography in the field of non-destructive testing.
31 Dec 1994
TL;DR: In this paper, a low-thermal-mass, porous, fiberglass screen was used as a radiation target sheet whose surface temperatures were detected by the infrared camera, and it was shown that those temperatures are within 1.6 C of the air temperatures.
Abstract: An important problem in the design of ventilation systems is the evaluation of occupant comfort. Local velocity and temperature distributions are two major elements that affect human comfort. Air temperature measurements across a large field require either many measuring devices or translating a single device across the field of interest, both of which are expensive and/or time consuming. This study introduces a unique technique for rapid measurements of room air temperature distribution at any cross section of interest and shows that infrared thermography can be used with good accuracy for air temperature measurements as well as airflow pattern visualization. This technique utilizes a low-thermal-mass, porous, fiberglass screen in conjunction with an infrared camera. The screen is used as a radiation target sheet whose surface temperatures are detected by the infrared camera, and it is shown that those temperatures are within 1.6 C of the air temperatures.
TL;DR: In this paper, a semi-analytical method using Green's functions was used to calculate the temperature field on and near the bead in laser welding and results were compared with the measurements obtained on one hand with an infrared thermography device and on the other hand with thermocouples located near the welding seam.
Abstract: The temperature field in every point of an homogeneous plate submitted to a moving heat source is obtained with a semi analytical method using Green's functions. This method is used to calculate the temperature field on and near the bead in laser welding and results are compared with the measurements obtained on one hand with an infrared thermography device and on the other hand with thermocouples located near the welding seam. The study was made with different plate thickness. The simulated and measured temperatures with infrared thermography on the welding bead concur at some distance behind the laser beam. The temperatures depend on the welding parameters and thus on the depth of the welded seam. It is therefore possible to control power and focus conditions in laser welding by infrared surface temperature measurement
22 Jul 1994
TL;DR: In this article, the authors use DBIR image ratios to enhance surface temperature contrast, remove surface emissivity noise and increase signal-to-clutter ratios to detect defects from corrosion damage in metal airframes, heat damage in composite structures and structural damage in concrete bridge decks.
Abstract: Precise dual-band infrared (DBIR) thermal imaging provides a useful diagnostic tool for wide-area detection of defects from corrosion damage in metal airframes, heat damage in composite structures and structural damage in concrete bridge decks. We use DBIR image ratios to enhance surface temperature contrast, remove surface emissivity noise and increase signal-to-clutter ratios. We clarify interpretation of hidden defect sites by distinguishing temperature differences at defect sites from emissivity differences at clutter sites. This reduces the probability of false calls associated with misinterpreted image data. For airframe inspections, we map flash-heated defects in metal structures. The surface temperature rise above ambient at corrosion-thinned sites correlates with the percentage of material loss from corrosion thinning. For flash-heated composite structures, we measure the temperature-time history which relates to the depth and extent of heat damage. In preparation for bridge deck inspections, we map the natural day and night temperature variations at known concrete slab delamination sites which heat and coot at different rates than their surroundings. The above-ambient daytime and below-ambient nightime delamination site temperature differences correlate with the volume of replaced concrete at the delamination sites.
TL;DR: A corrected thermal imaging method for a wind-roughened water surface that can be applied even if the imaging system is placed at low altitudes, as well as on an airborne platform, is proposed.
Abstract: A corrected thermal imaging method for a wind-roughened water surface is proposed. This method can be applied even if the imaging system is placed at low altitudes, say on a ship or on land, as well as on an airborne platform. Such a technique is desirable from the following points of view: the surveillance of bioresources (fish), environmental assessments of a seaside industrial zone (hot waste water), and temporal complement and spatial interpolation of satellite observations of thermal images. The method is based on the analysis of optical characteristics of a model of a wind-roughened water surface, namely, the Gaussian–Joint North Sea Wave Project (JONSWAP) model, where the surface displacement obeys Gaussian distribution while its spectrum is specified by the JONSWAP wave spectral model. We present the basic temperature-correction formula and the algorithm for correction. The correction takes into account thermal emission of the water’s surface, radiation of the sky reflected on the water’s surface, and both absorption and emission by the atmosphere along the light path. This formula can be used for temperature correction of an infrared image of sky and random water surface. The experimental results that we obtained are encouraging.
TL;DR: Temperature measurements were taken after shots were fired by .22, .25, .32, .38-special-caliber, and 9-mm Luger pistols and revolvers with the assistance of infrared thermography.
Abstract: This study examines the temperatures at the point that bullets impact human skin. With the assistance of infrared thermography, measurements were taken after shots were fired by .22-, .25-, .32-, .38-special-caliber, and 9-mm Luger pistols and revolvers. The highest temperature readings at the entry point were recorded with the .22 caliber and the lowest with the .32 caliber. The measurement of projectile temperatures in flight resulted in readings of 147 degrees-152 degrees C for the 9-mm Luger. Language: en
01 Jan 1994
TL;DR: In this paper, different approaches to performing the thermal characterization of defects in solids are discussed including phenomenological treatment of experimental data, use of classical heat transfer solutions and minimization of functionals.
Abstract: Approaches to performing the thermal characterization of defects in solids are discussed including phenomenological treatment of experimental data, use of classical heat transfer solutions and minimization of functionals. Simple analytical expressions proposed by various authors in order to estimate defect size, depth and thickness are verified by using well defined reference temperature data.
21 Mar 1994
TL;DR: In this article, the authors used an infrared camera and heat lamps to detect unbonds in four-sheet superplastic formed/diffusion bonded (SPF/DB) panels.
Abstract: Experimental and analytical methods were used to study heating techniques for infrared thermography inspection of superplastic formed/diffusion bonded (SPF/DB) structural components. Various thermal loads were investigated to determine the parameters required for highest flaw detection sensitivity. Finite element analysis was used to determine optimal heating techniques. According to the analysis, short burst, high intensity heating on the inspection side of the part is required for the highest flaw detection sensitivity. The analytical results were verified using an infrared camera and heat lamps to detect unbonds in four-sheet SPF/DB panels. Good quantitative agreement between the analysis and laboratory experiments was obtained.
TL;DR: In this article, the authors measured pool flames of heptane, kerosene, and crude oil in a 2.7m square tank, storing thermal images as TV color images with 25,600 data points every 0.1 second, and analyzed statistically to obtain the distribution of mean radiance, standard deviation and coefficient of variation in the thermography image.
Abstract: Pool flames of heptane, kerosene, and crude oil in a 2.7m square tank were measured by thermography, storing thermal images as TV color images with 25,600 data points every 0.1 second. These apparent temperature images can be converted to irradiance by simple approximations. A series of data recorded continuously at 0.1 second intervals (70 images for one fuel) were analyzed statistically to obtain the distribution of mean radiance, standard deviation and coefficient of variation in the thermography image. The contours of mean radiance, standard deviation and coefficient of variation related to radiance were made, and the flame structure of pool flames are considered from a radiation point of view. The height of maximum radiance from the tank top are obtained from the contours of the mean radiance. Mean paths of formation, growth, and dissipation of vortices are obtained by the contours of the standard deviation on radiance. The stable flame regions and the lower part of plume regions are also obtained by using the contours of the coefficient of variation based on radiance. Flame structures obtained by processing thermographic data are also compared with previous work by McCaffrey who defined flame, intermittent, and plume regions by the temperature and velocity distribution along the center line of flames. By this comparison, statistical analysis using thermographic data is also useful to assess the flame structure of large pool fire flames. Finally, the radiative characteristics of the continuous flame, intermittent, and plume regions, are established.
TL;DR: In this paper, a non-destructive and noncontact technique for evaluation of the plastic region near a crack by using infrared thermography is proposed, where the temperature rise of the material surface near the crack in weldment is measured by the infrared camera.
Abstract: Plastic deformation near a crack takes an important role relating to the failure or the fracture of the structure. In the present paper, a nondestructive and noncontact technique for evaluation of the plastic region near a crack by using infrared thermography is proposed. The temperature rise of specimen surface near a crack in weldment is measured by the infrared thermography. It is assumed that the heated region by the work of plastic deformation corresponds to the plastic zone near a crack. The effect of the welding residual stress on the shape and dimensions of the heated region is examined in the present study. The temperature rise and the heated region are compared with the plastic deformation obtained by the elasto-plastic finite element analysis. In addition, the usefulness and the limitations of the application of infrared thermography to the evaluation of the plastic region are discussed.
Patent•
18 Feb 1994
TL;DR: In this article, a heat sensitive camera picks up an image of the surface of an object to be investigated; the thermal image is analyzed by computer to calculate the presence of subsurface flaws, and a three-dimensional display, representing the internal structure of the object is generated.
Abstract: A heat sensitive camera picks up an image of the surface of an object to be investigated; the thermal image is analyzed by computer to calculate the presence of subsurface flaws, and a three-dimensional display, representing the internal structure of the object is generated. The thermal image may be collected passively. The method may be used to investigate the wall thickness of a pipe wall from the exterior; in this case the computer may first calculate the thickness of the pipe wall from the thermal image to allow a three dimensional display of the interior of the pipe to be generated.
01 Jan 1994
TL;DR: In this article, a method of surface temperature measurement by infrared thermography in a lubricated contact has been developed, which needs the determination of global radiometric coefficients and leads to radiometric equations.
Abstract: A method of surface temperature measurement by infrared thermography in a lubricated contact has been developed. The capabilities of the camera are examined. The analysis, which needs the determination of global radiometric coefficients and leads to radiometric equations is presented. The calibration of emissivity and transmittivity coefficients of the involved materials is reported. The validity of the method is tested and discussed.
TL;DR: In this paper, an infrared thermal video system (TVS-5000) was used to measure the temperature distribution of a body surface and an engineering work station (EWS) for image processing of the thermal image.
Abstract: The system consists of an infrared thermal video system (TVS-5000), by which the temperature distribution of a body surface can be measured, and an engineering work station (EWS), by which image processing of the thermal image can be carried out. Various method for heating or cooling the specimen have been examined. Further more, an image processing expert system has been developed to obtain definite images of the defects