Proceedings Volume 2473

Thermosense XVII: An International Conference on Thermal Sensing and Imaging Diagnostic Applications

Sharon A. Semanovich
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Proceedings Volume 2473

Thermosense XVII: An International Conference on Thermal Sensing and Imaging Diagnostic Applications

Sharon A. Semanovich
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 28 March 1995
Contents: 8 Sessions, 41 Papers, 0 Presentations
Conference: SPIE's 1995 Symposium on OE/Aerospace Sensing and Dual Use Photonics 1995
Volume Number: 2473

Table of Contents

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Table of Contents

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  • Buildings and Infrastructures
  • Additional Paper
  • Buildings and Infrastructures
  • Predictive Maintenance
  • Professionalism
  • Nondestructive Testing I
  • Nondestructive Testing II
  • Research and Development
  • Products and Processes
  • Nondestructive Testing II
Buildings and Infrastructures
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State of the art of aerial thermography in Iceland: thermography of geothermal areas during the past 20 years
Sigfus Bjornsson, Kolbeinn Arnason
Aerial thermography was first applied in Iceland in the early sixties in conjunction with the suboceanic eruption of Surtsey. The same technique was subsequently applied (in the late sixties, early seventies) to some major geothermal areas in Iceland. Although it gave a global view of heat on the surface, local geologists/geophysicists were not impressed by the inroad of this space technology. According to this view, the technique lacked sensitivity, resolution, means of calibration, and gave very distorted images. Although microwave remote sensing (applied in glaciology) and processing of Landsat data (including IR) was practiced, aerial thermography lay at rest in Iceland until the mid eighties, when it was taken up again first for demonstration purposes using an instrument we rented jointly with the Geodetic Institute, but later it would be based on our own developments. Our work being application driven, due to the way this development is financed, the emphasis in the late eighties/early nineties was mainly on the near infrared range. For the last three years it has shifted however towards the far infrared range again and focused on geothermal areas, both for scientific purposes as well as for natural heat reservoirs for distance heating networks. Aerial thermography of wide area natural heat and energy distribution networks sets stringent requirements, e.g. to sensitivity and temporal, spatial as well as spectral resolutions. Efforts to meet that goal in Iceland have led to new developments based on wide aperture line scanners covering swaths in the flight direction, frame based focal plane cameras and on improved signal processing and data processing procedures. A particular emphasis has been on error corrections due to unpredictable aircraft movements.
TX model: a quantitative heat-loss analysis of district heating pipes by means of IR surface-temperature measurements
Heimo Zinko, Bengt Perers
The aim of this study is to investigate the possibility of analyzing the temperature profile at the ground surface above buried district heating pipes in such a way that enables the quantitative determination of heat loss from the pair of pipes. In practical applications, it is supposed that this temperature profile is generated by means of thermography. For this purpose, the principle of the TX-model has been developed, implementing that the heat losses from pipes buried in the ground has a temperature signature on the ground surface. A qualitative analysis of this temperature signature is very well known and in practical use for detecting leaks from pipes. These techniques mostly makes use of relative changes of the temperature pattern along the pipe. In the quantitative heat loss analysis, however, it is presumed that the temperature profile across the pipes is related to the pipe heat loss in Watt/m. The basic idea is that the integral of the temperature variation across the pipe, called TX, is a function of the heat loss, but affected by some other parameters such as depth, heat diffusivity and so on. In order to analyze the parameters influencing the TX-factor, a simulation model for the energy balance at the ground surface has been developed. This model includes the heat flow from the pipe to the surface and the heat exchange at the surface with the environment due to convection, latent heat change, solar and long wave radiation. The simulation gives the surprising result that the TX factor is relatively unaffected during the course of a day even when the sun is shining, as long as other climate conditions are relatively stable (low wind, no rain, no shadows). The results from the simulations were verified at a testfield in Studsvik, Sweden, with electrically controlled pipe heat losses and long term monitoring of the surface temperature profile and TX factor with temperature sensors at the ground surface. The quantitative TX model for heat loss determination was also tested with IR thermography in a district heating network in Vasteras. The work was performed under the IEA District Heating Programme, Task III, and is continued under Task IV.
Air-leakage effects on stone cladding panels
This paper looks at the effects of air leakage on insulated stone clad precast panels used in present day construction of large commercial buildings. The building investigated was a newly built twenty story office building in a high density urban setting. Air leakage was suspected as a possible cause for thermal comfort complaints at isolated locations within the perimeter zones of the building. During the warrantee period the building owner asked for a quality control inspection of the air barrier assembly of the building envelope. Infrared thermography was used to locate areas of suspected air leakage within the building envelope. In order to differentiate thermal patterns produced by air leakage, conduction and convection as well as radiation from external sources, the building was inspected from the exterior; (1) after being pressurized for three hours, (2) one hour after the building was depressurized and (3) two and a half hours after total building depressurization was maintained by the building mechanical systems. Thermal images from similar locations were correlated for each time and pressure setting to verify air leakage locations within the building envelope. Areas exhibiting air leakage were identified and contractors were requested to carry out the necessary repairs. The pressure differential across the building envelope needs to be known in order to properly carry out an inspection to identify all locations of air leakage within a building envelope. As well the direction of the air movement and the density of the cladding material need to be accounted for in the proper inspection of these types of wall assemblies.
Infrared survey of 50 buildings constructed during 100 years: thermal performances and damage conditions
Sven-Ake Ljungberg
Different building constructions and craftsmanship give rise to different thermal performance and damage conditions. The building stock of most industrial countries consists of buildings of various age, and constructions, from old historic buildings with heavy stone or wooden construction, to new buildings with heavy or light concrete construction, or modern steel or wooden construction. In this paper the result from a detailed infrared survey of 50 buildings from six Swedish military camps is presented. The presentation is limited to a comparison of thermal performance and damage conditions of buildings of various ages, functions, and constructions, of a building period of more than 100 years. The result is expected to be relevant even to civilian buildings. Infrared surveys were performed during 1992-1993, with airborne, and mobile short- and longwave infrared systems, out- and indoor thermography. Interpretation and analysis of infrared data was performed with interactive image and analyzing systems. Field inspections were carried out with fiber optics system, and by ocular inspections. Air-exchange rate was measured in order to quantify air leakages through the building envelope, indicated in thermograms. The objects studied were single-family houses, barracks, office-, service-, school- and exercise buildings, military hotels and restaurants, aircraft hangars, and ship factory buildings. The main conclusions from this study are that most buildings from 1880 - 1940 have a solid construction with a high quality of craftsmanship, relatively good thermal performance, due to extremely thick walls, and adding insulation at the attic floor. From about 1940 - 1960 the quality of construction, thermal performance and craftsmanship seem to vary a lot. Buildings constructed during the period of 1960 - 1990 have in general the best thermal performance due to a better insulation capacity, however, also one finds here the greatest variety of problems. The result from this study is to be incorporated in planning of short- and long term maintenance programs of the Swedish Defence. In general the military buildings are expected to have better status than civilian buildings, due to the more rigorous control during the building process, performed by military building authorities.
Additional Paper
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Nondestructive testing: use of IR and acoustics methods in buildings pathology
Walter Esposti, Italo Meroni
In the paper the authors present some experiences made using IR and acoustics methods in a non destructive way for the evaluation of situations of degradation in building materials and components. Two studies are presented: (1) detection of the delamination of wall renderings, especially those supporting frescos, by means of IR and sonic investigation; (2) use of infrared thermography for the visualization of fracture zones of walls and steel components under cyclic loads. The possibility of detecting rendering delaminations is based on the different path of the heat diffusion in part of the wall affected by the delamination, compared to the rest of the wall. The difference is caused by the presence of small pockets containing still air. The case study showed makes reference to the analysis of adhesion conditions of a rendering dating back to the IV century, applied on the bell towers of the ancient basilica dedicated to S. Lorenzo in Milan, Italy. The use of infrared thermography for detecting the strength status of materials and components is based on the fact that the strength status of parts of building components can become evident because of heat losses which appear where the component is weaker. The IR observation was made on steel bars subject to traction testing and on lightweight concrete prismatic samples subject to compression testing. The experiences indicate that there is room for this NdT technique to provide some useful answers. Nevertheless it is sure that more experimental work is needed in order to increase the full comprehension of the phenomena which are the basis of their applications for alternative uses.
Buildings and Infrastructures
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Crawling spot thermal nondestructive testing (NDT) for plaster inspection and comparison with dynamic thermography with extended heating
Paolo Giulio Bison, Alberto Braggiotti, Chiara Bressan, et al.
Defects in building materials located parallel to the front surface, like plaster detachment, or perpendicularly, such as cracks, are detected creating a space-varying heat flux. A variant of the `flying spot' technique called `crawling spot' was developed in order to fit requirements of these materials. This nondestructive method is performed with a localized radiant heating of the surface and synchronized local temperature measurement in the IR band. The identification of delaminations and cracks was theoretically and experimentally studied using two different procedures. Results obtained for plaster detachments were compared with dynamic thermography, applied with an extended excitation of the surface and analysis of the normalized thermal contrast both in amplitude and time. Another technique requires a continuously moving spot to heat the surface while a sequence of thermograms is recorded. The temperature profile of each pixel has to be reconstructed according to the spot speed and trajectory. This procedure was applied to stone crack detection. The experimental apparatus is thoroughly described.
Predictive Maintenance
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Application of differential infrared thermography in power generation facilities
Herbert Kaplan, Paul A. Zayicek
Improvements in commercial IR thermal imaging equipment and advances in the related data and image processing capacities make differential infrared thermography (DIT) a highly promising tool for condition monitoring and predictive maintenance of electronic, electrical, and mechanical elements. The controlled and systematic application of DIT can dramatically improve the reliability, maintainability, and operational life of these elements throughout the power generation and distribution community. This paper describes a program initiated by the Electric Power Research Institute (EPRI) Nondestructive Evaluation (NDE) Center to apply DIT to operating elements within a power generating station environment. It traces the selection of candidate elements at some of EPRI's member facilities, the implementation of exploratory measurements on selected candidates using available on-site infrared imaging equipment and the analysis of significant findings on one specific critical element. Finally, a summary of the advantages and limitations of DIT is provided along with a description of several variations of the technique.
Problems inherent to quantitative thermographic electrical inspections
The primary value of using infrared thermography to inspect electrical systems is to find problems made apparent by their thermal differences. Thermographers have also begun collecting radiometric temperature data as quantitative imaging systems have become more reliable and portable. Throughout the industry the use of temperature data has become a primary means of prioritizing the severity of a problem. The validity of this premise is suspect for several reasons, including the lack of standard data collection methods; the often poor understanding of radiometric measurements by maintenance thermographers; field conditions that vary widely enough to defy standardization; and the almost total lack of scientific research on the relationship between heat and time with regard to the failure of the components being inspected. Several possible solutions to the problems raised, as well as other suggestions for improving the usefulness and reliability of qualitative inspections, are offered.
Increasing predictive program effectiveness by integrating thermography and lubricant analysis
Jeffrey P. Evans, Thomas J. Jarc, Richard Norman Wurzbach
As today's marketplace becomes more competitive, companies are continually searching for more efficient ways to maintain plant equipment. As a result, predictive maintenance (PDM) techniques are frequently utilized to help reduce maintenance costs and increase equipment reliability. Two PDM technologies that have enjoyed widespread success in many different industries are lubricant analysis and infrared thermography. Lubricant analysis is a very effective technique in the identification of both machine and lubricant deficiencies. Problems such as bearing wear, gear wear, lubricant contamination and degradation are identified utilizing technologies like ferrography and physical properties testing. Infrared thermography has likewise enjoyed much success in various electrical, mechanical, and process applications. High resistance electrical connections, excessive friction, insulation degradation, and roofing deterioration are just a few of the more common problems detectable utilizing infrared thermography. Although each PDM technology has its own distinct area of specialization, the greatest benefits come from the integration of each technology into a comprehensive PDM program. This paper focuses on the interrelationship between lubricant analysis and infrared thermography and successful applications where these two PDM technologies have been used together to identify and solve equipment specific problems.
Thermal instability observation in power transistors by radiometric detection of temperature maps
Sergio Pica, G. Scarpetta
In this paper the thermal instability problems in semiconductor power devices are briefly presented. Experimental observations about these phenomena can be achieved by using infrared radiometry to obtain a temperature mapping of the surface of the devices. Our system, based on a radiometric microscope with an automatic scanning and elaboration system, is described. Finally, some results of our system, consisting in dynamic temperature maps obtained on two different devices, are presented, and the causes of their different thermal instability are briefly discussed.
Electrical fault location for surface-mounted feeders in metallic conduit
Sean Finneson
Manufacturing, warehouse and process control facilities utilize surface mounted metallic raceways to serve as electrical distribution in service entrance, feeders and subfeeds. This network of power distribution is susceptible to electrical faults through the breakdown of the conductors insulation. Typically, due to the high power associated with these circuits, faults produce explosive events creating shorted phases. Though these conductors are protected by devices rated for their ampacity, during a fault, a short circuit generates instantaneous current limited only by the primary source, system impedance and the time required for the protective device to respond. As a result the fault creates a high resistance junction, an artifact left behind by the fault event. Once this circuit has been identified and both the primary and secondary lifted, the path through the conductors and/or conductor to ground needs to be marked. After verification, a constant current dc source, not to exceed the ampacity of the conductor, is connected to the circuit. Energizing the junction generates heat due to its greater resistance. The heat is transferred to the surrounding raceway, yielding the fault's location when thermally scanned.
Use of an infrared sensing technique in the regular monitoring of incinerators and a kiln
Jukka P. Varrio, Seppo Kesanto, Tapio Heikkinen
Thermal imaging is a promising technology in the field of predictive maintenance. However, the effective use of infrared sensing techniques in predictive maintenance necessitates (1) good preliminary preparations, (2) regular imaging of the targets, (3) an infrared imaging system equipped with a floppy-disk drive, and, (4) an effective computer program for making analyses and drawing conclusions. At present, due to the lack of suitable software, there are not many practical applications of this technique in this field. In this paper, a functioning maintenance program for an industrial plant using a thermal sensing technique is presented. The strategy for constructing this program and the problems involved in this work are introduced. Also the main results, which clearly indicate the usefulness of thermal sensing techniques in predictive maintenance, are presented. This maintenance program has been constructed and been in use in the modern hazardous waste plant, EKOKEM Ltd., for the last two years. This program uses an Inframetrics model 760 infrared thermal imaging radiometer and a Thermonitor thermal image processing program by Thermoteknix Systems Ltd. The maintenance consists of (1) regular thermal imaging of the critical parts of the incinerators and (2) thermal image computer analysis. Also, a large table (arrays of thermal images) illustrating visually the target temperature behavior as a function of time has been constructed. This table together with the data from the computer analysis show both slow and rapid temperature variations clearly. The hot spots and limited hot areas which are indications of abnormal wear, are easily observed in our analyses. There is no way to observe these local hot spots using any other method. Thus unnecessary shutdowns, in some cases, can be prevented.
Professionalism
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U.S. market for infrared thermography equipment
The market for infrared thermography is undergoing dramatic changes. Focal plane array technologies previously dominated by the military are being opened up to the commercial sector, new uncooled technologies are advancing rapidly and entirely new applications are emerging. Maxtech International has carried out its second in-depth analysis of these markets within two years. In 1994, the U.S. market for commercial (and dual-use) infrared thermography equipment reached $100 million and is expected to grow to $250 million by 1999. As part of the analysis, a survey of over 3,900 users of infrared thermography equipment has been completed. Included are segmentation by end-user industry and expected spending projections in various market segments.
Look at the inside the American Society for Nondestructive Testing (ASNT) Level III certification program
Edward R. Schaufler
The American Society for Nondestructive Testing (ASNT) has historically provided guidelines to qualify NDT personnel for employer certification. In recent years, ASNT has provided certification of Level III NDT personnel by qualification based on experience, training, and examination. This certification program is administered by the National Certification Board (NCB). Guidelines for certification are available for ten (10) test methods, including thermal/infrared (TIR). ASNT certification requires qualification based on experience, training, and examination. The written examination consists of multiple choice questions developed by volunteers in the Personnel Qualification Council and utilized by the NCB. The examination data base is confidentially controlled with ParTEST computer software. Recently, a major task for the NCB has been the development of the Generic Practical Examination, which is available in 1995. This examination tests the ability of the Level III to prepare written test methods. This paper describes the mechanics of the ASNT Level III certification program with emphasis on the examination process.
American Society for Nondestructive Testing (ASNT) certification of thermographers
Robert W. Spring
As the United States and the rest of the world's industrialized nations work together to nurture the emerging world economy we must insure manufacturing and service products meet the scrutiny of global standards. Qualification and certification of personnel who provide nondestructive testing (NDT) services are vital if infrastructures and products of industry and commerce are to be functional, reliable, safe, and long lived. This paper explains the process of certifying thermal/infrared testing (T/IRT) personnel under the guidelines of the American Society of Nondestructive Testing (ASNT).
Nondestructive Testing I
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Imaging the early time behavior of reflected thermal wave pulses
Lawrence D. Favro, Xiaoyan Han, Pao-Kuang Kuo, et al.
We describe the early time behavior of reflected thermal wave pulses, and relate that behavior to schemes for making depth images.
Methodology of processing experimental data in transient thermal nondestructive testing (NDT)
Noise which occurs in space and time temperature evolution is analyzed using three informative parameters: temperature signal over defect, running contrast, and normalized contrast. It is shown that the choice of optimum informative parameter depends on the kind of noise which dominates in a particular experiment. Decrease of noise by passing into time domain is demonstrated. A methodology for creating images of signal-to-noise ratio and probability of correct detection is proposed. Experimental validations were performed for plaster specimens. The proposed methodology allows us to compare various thermal NDT techniques.
Differential thermography applied to structural integrity assessment
Jon R. Lesniak, Bradley R. Boyce
A dual-function for differential-thermographic devices is discussed. It is shown that differential thermographic cameras can be used for rapid inspection of structures as well as for stress analysis. Reviews of forced diffusion thermography (FDT), thermoelastic stress analysis (TSA), and differential thermographic cameras are offered. A new stress intensity measurement technique using TSA data in the vicinity of cracks is described in more detail.
Thermal wave nondestructive testing (NDT) of ceramic coatings
Steven M. Shepard, Lawrence D. Favro, Robert L. Thomas
A description of preliminary experimental work, in which thickness of ceramic coatings is measured using pulse echo thermal wave imaging, is presented. The thermal wave measurement technique uses the time (relative to flash heating) at which the peak slope of the contrast curve occurs to determine the thickness of the coating layer, based on reflection of the thermal wave from the coating/substrate interface. Thermal wave thickness measurements are compared to measurements made (destructively) with a drill micrometer. Repeatability and precision of measurements are discussed.
Microwave-source time-resolved infrared radiometry for monitoring of curing and deposition processes
Robert Osiander, Jane W. Maclachlan Spicer, John C. Murphy
Thermal wave methods employing optical heating sources have been used successfully in the past to determine layer thicknesses or thermal diffusivities. However, monitoring of curing or deposition processes can be difficult with such techniques due to changes in the sample surface properties such as optical absorption during processing. The method introduced in this paper, microwave-source time-resolved infrared radiometry (TRIR) in conjunction with intentionally embedded carbon or metal fibers allows the determination of surface layer thickness and thermal diffusivity almost independently of the surface properties of the layer. This suggests the use of fibers as embedded sensors in applications where layer thickness or thermal properties need to be controlled during processing.
Full-field characterization of thermal diffusivity in continuous-fiber ceramic composite materials and components
J. Scott Steckenrider, William A. Ellingson, Scott A. Rothermel
Continuous-fiber ceramic matrix composites (CFCCs) are currently being developed for various high-temperature applications, including use in advanced heat engines. Among the material classes of interest for such applications are silicon carbide (SiC)-fiber-reinforced SiC (SiC(f)/SiC), SiC-fiber-reinforced silicon nitride (SiC(f)/Si3N4), aluminum oxide (Al2O3)-fiber-reinforced Al2O3 (Al2O3(f)/Al2O3), and others. In such composites, the condition of the interfaces (between the fibers and matrix) are critical to the mechanical and thermal behavior of the component (as are conventional mechanical defects such as cracks, porosity, etc.). For example, oxidation of this interface (especially on carbon coated fibers) can seriously degrade both mechanical and thermal properties. Furthermore, thermal shock damage can degrade the matrix through extensive crack generation. A nondestructive evaluation method that could be used to assess interface condition, thermal shock damage, and to detect other `defects' would thus be very beneficial, especially if applicable to full-scale components. One method under development uses infrared thermal imaging to provide `single-shot' full-field assessment of the distribution of thermal properties in large components by measuring thermal diffusivity. By applying digital image filtering, interpolation, and least-squares-estimation techniques for noise reduction, we can achieve acquisition and analysis times of minutes or less with submillimeter spatial resolution. The system developed at Argonne National Laboratory has been used to examine the effects of thermal shock, oxidation treatment, density variations, and variations in oxidation resistance coatings in a full array of test specimens. Subscale CFCC components with nonplanar geometries have also been studied for manufacturing-induced variations in thermal properties.
Infrared inspection of advanced army composites
Thomas S. Jones, Eric A. Lindgren, Charles G. Pergantis
The development of a field portable infrared inspection system, complete with infrared imager, data recording, digital image processing and analysis, and heat source for introduction of a thermal gradient, is described. The system provides excellent portability with minimal reliance on on-site electric power while maintaining excellent sensitivity to a variety of defects in typical U.S. Army composite structures. The portable system has demonstrated considerable flexibility in the nondestructive evaluation of a diverse assortment of composite structures for both aircraft and ground vehicle applications.
Thermographic nondestructuve testing (NDT) technique for delaminated defects in composite structures
Yuwen Qin, Nai-Keng Bao
Thermographic non-destructive testing (NDT) based on the thermal resistance effect of defects is developed for the inspection of delaminated and sandwiched defects embedded in composite structures. The resolution is examined for the artificial delaminated defects in carbon fiber honeycomb structures using the conventional infrared radiation heating. Experimental results demonstrate that the radiation heating is effective for the accurate defect inspection of composite structure samples. We have developed an experimental and computational hybrid system which can be applied to detect defects in various composite structures. The system consists of an infrared thermal video system by which the temperature distribution of body surface can be measured, a computer with a PIP-1024B image board carrying out image processing of thermograms, and a HP ink jet XL printer. By applying the system to honeycomb sandwich structures and delaminated composite structures, various types of defects lying between the honeycomb core and the surfaces as well as between the internal layer and the surface of delaminated structures have been examined. It is found that the method is extremely applicable to defect detection of honeycomb sandwich structures and composite materials delaminated structures.
Nondestructive Testing II
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Quantitative thermal imaging of aircraft structures
Aircraft structural integrity is a major concern for airlines and airframe manufacturers. To remain economically competitive, airlines are looking at ways to retire older aircraft, not when some fixed number of flight hours or cycles has been reached, but when true structural need dictates. This philosophy is known as `retirement for cause.' The need to extend the life of commercial aircraft has increased the desire to develop nondestructive evaluation (NDE) techniques capable of detecting critical flaws such as disbonding and corrosion. These subsurface flaws are of major concern in bonded lap joints. Disbonding in such a joint can provide an avenue for moisture to enter the structure leading to corrosion. Significant material loss due to corrosion can substantially reduce the structural strength, load bearing capacity and ultimately reduce the life of the structure. The National Aeronautics and Space Administration's Langley Research Center has developed a thermal NDE system designed for application to disbonding and corrosion detection in aircraft skins. By injecting a small amount of heat into the front surface of an aircraft skin, and recording the time history of the resulting surface temperature variations using an infrared camera, quantitative images of both bond integrity and material loss due to corrosion can be produced. This paper presents a discussion of the development of the thermal imaging system as well as the techniques used to analyze the resulting thermal images. The analysis techniques presented represent a significant improvement in the information available over conventional thermal imaging due to the inclusion of data from both the heating and cooling portion of the thermal cycle. Results of laboratory experiments on fabricated disbond and material loss samples are presented to determine the limitations of the system. Additionally, the results of actual aircraft inspections are shown, which help to establish the field applicability for this technique. A recent application of this technology to aircraft repairs using boron/epoxy patches is shown illustrating the flexibility of the technology.
Transient thermal nondestructive testing (NDT) of defects in aluminum panels
Xavier P. Maldague, Vladimir V. Shiryaev, E. Boisvert, et al.
This paper describes results of the inspection of aluminum specimens by transient infrared thermography. The inspected specimens contain various defects: internal and external corrosion, delaminations and water between two sheets. The accent is made on comparison between scanning IR radiometer and FPA camera, verification of theoretical data by experiment, discrimination between different defects and simple inversion method for corrosion data.
Flash infrared thermography for nondestructive testing (NDT) I/E of naval aircraft
Paul J. Kulowitch, Ignacio M. Perez, Dianne M. Granata
In this effort we have used thermographic techniques to inspect several structures of interest to naval aviation, with the purpose of determining the effectiveness of these techniques in finding flaws/defects. The structures/materials used in this study included metals with metallic and nonmetallic coatings, graphite/epoxy bonded assemblies, ceramic matrix composites, and a boron/epoxy panel. The results that were obtained indicate that IR thermography works well identifying disbonds in coatings and bonded assemblies, quantifying porosity in ceramic matrix composite materials, identifying delaminations, and identifying large amounts of material loss (> 10%). It was not reliable for identifying small amounts of material loss (< 10%), however, efforts are continuing to improve our detection limits and reduce false indications.
Thermal sensing and imaging of the dry-sliding contact surface using IR thermomicroscope
Takahide Sakagami, Keiji Ogura, Masahiro Shoda
A new experimental technique using an infrared (IR) thermography combined with IR transmitting materials is proposed for the visualization of the contact surface temperature of two solids. A dry sliding contact between a pin and a disk is investigated. IR transmitting solids such as sapphire, alumina ceramics and silicon are employed for the disk material. The temperature distribution on the contact surface is measured by the IR thermography through the IR transmitting disk. It is found that the temperature rise on the contact surface as well as the contact area is accurately analyzed from the obtained thermal images. The influence of contact pressure and sliding velocity on the contact surface temperature is discussed. Further, the dynamic process of wear of bearing steel against sapphire is investigated under dry sliding contact by the new type IRCCD thermography. Transient temperature distribution around the frictional heat spot was computed by the FEM analyses in order to estimate the magnitude of flush temperature from the experimental result in the dry sliding contact. All the results show that the proposed technique is useful for examining the successive process of the tribological phenomena.
Inspection of low-density polyethylene using near-infrared imaging
Michael W. Jones, James M. Chandler, Steven Bernstein
We report on the development of techniques for imaging the interior of a volume of low density polyethylene. Images are acquired using both near infrared and visible illumination and inexpensive silicon-based CCDs. An application, using these techniques is currently being developed for the inspection of high reliability undersea seals. The system is capable of imaging flaws that are smaller than 1/1000 inch. In addition to image acquisition, the system supports database and image processing functions. Remote manipulation of camera and part positioning is also provided.
Thermal image study of detecting nearly underground structures by means of infrared radiometer
Yoshizo Okamoto, Zuofen Fan, Chanliang Liu, et al.
An infrared radiometer is used to detect several flaws of industrial structural elements, as one remote sensing device. The thermal image method (TIM) was carried out to analyze location and dimension of the internal flaws of mechanical components, like piping, vessel, slab and pile. Internal flaws were detected by visualizing abnormal behavior of radiation temperature distribution of the tested surface by solar and artificial heat injection. The induced nonuniform temperature shows the existence of the internal flaws imaged on the CRT display of the infrared radiometer. As one application subject, the TIM method was extensively applied to near-underground buried materials of ancient remains; such as corner stone, stone settlement, shell mound, and tomb. The paper represents basic experimental and analytical results of preliminary and demonstration model tests of the buried materials in the soil and rock by solar, direct, and indirect combustion heaters. After continuous irradiation heating, we measured and recorded transient radiation temperature distribution of the tested ground surface which inserts the model near-underground tests plates of stylene, concrete, stone and gravel, changing width and depth of the test plates. Nonuniform and discontinuous temperature distribution of the tested surface above the inserted plates shows the existence of near- underground buried materials. Furthermore, transient temperature and heat flow behavior was numerically analyzed by solving a transient two-dimensional heat-balance equation. Calculation results were quite useful to analyze the experimental heat flow behavior around the buried object.
Novel applications of thermal imaging in the steel industry
John Chen, Ross Barrow
Near infrared (NIR) thermal imaging using Si CCD cameras is a cost-effective technique for generating thermographs of hot objects having temperatures above 350 degree(s)C. The relatively low cost and the favorable performance of the technique makes it the preferred thermal imaging technology for solving many measurement problems in the steel industry. In recent years, a number of systems have been developed by BHP Research and installed within BHP's steelworks to fulfill various measurement tasks. This paper provides an overview of the technique together with a description of several industrial applications that BHP Research has developed.
Corrosion/erosion detection in steel storage vessels using pulsed infrared imaging
Maurice J. Bales, Chip C. Bishop
Historically, steel has been a material that has been shunned by the thermal imaging community because of its thermal characteristics and because in most applications it is relatively thick. A new approach to evaluate this material for thickness changes caused by corrosion/erosion is discussed within this presentation. Some of the structures that have been evaluated are above ground storage tank floors, boiler tubes used in power plant facilities, pipes, and 55 gallon drums. Thermal imaging techniques have been developed to locate areas of material thickness loss within these examples using a high resolution thermal imager and a `pulsed' or `stepped' heat source. The thermal energy from the heat source is directed toward the inspection surface and begins to conduct through the material thickness. Areas that have been reduced in thickness will form a thermal gradient on the inspection surface which is detected by the thermal imager.
Infrared scanning of failure processes in wood
Minh Phong Luong
The paper aims to illustrate the relevant use of infrared thermography as a nondestructive, noncontact and real time technique (1) to observe the progressive damage processes and mechanisms of wood failure, and (2) to detect the occurrence of intrinsic dissipation localization. The parameter investigated in this paper is the heat generation due to intrinsic dissipation caused by anelasticity and/or inelasticity of wood material. Thanks to the thermomechanical coupling, this useful technique offers the possibility of scanning mechanical phenomena of wood degradation before reaching the ultimate strength. It allows a measure of the limit of a progressive damaging process under loading beyond which the wood material is destroyed.
Research and Development
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Dynamic area telethermometry and its clinical applications
Michael Anbar
Dynamic area telethermometry (DAT) is a recent development in thermology, the science of biological heat generation and dissipation. DAT is based on monitoring changes in infrared emission, deriving from them information on the kinetics and mechanisms of biological thermoregulation. Remotely monitoring infrared emission is the most reliable technique to study bioenergetics, because it minimally perturbs the investigated system. Area monitoring of heat dissipating surfaces is needed because temporal changes in the spatial distribution of temperature conveys information on mechanisms of thermoregulation. DAT can be applied to biological systems ranging from single cells (microtelecalorimetry) to large areas of human skin (clinical thermology). DAT requires the accumulation of many (hundreds to thousands) thermal images followed by analysis of the thermokinetics of each pixel or group of pixels. In clinical thermology this analysis uses FFT to extract systemic, regional and local thermoregulatory frequencies (TRFs). DAT also extracts information on local thermoregulation from the temporal behavior of homogeneity of skin temperature (HST). Analysis of the relative contributions (FFT amplitudes) of the different frequencies allows distinction between vascular, neurological, and immunological thermoregulatory dysfunctions. This analysis, which can reveal the mechanism of the dysfunction, can be very useful in the diagnosis and staging of various disorders, ranging from diabetes mellitus and liver cirrhosis to breast cancer and malignant melanoma. From the engineering standpoint DAT requires highly stable imaging systems and effective display of the spatial distribution of TRFs to allow identification of thermoregulatory pathways and their dysfunction.
Multiple wavelength infrared cameras and their biomedical applications
Michael Anbar
There have been substantial advances in multiple wavelength infrared imaging systems that can measure emissivity and temperature of surfaces. Multiplewavelength measurements can be done (1) using an array of detectors, each sensitive to a different range of photon energies; (2) using a tunable filter in front of a broad-band infrared detector; or (3) by using a focal plane array of tunable detectors. In choosing a multiplewavelength infrared camera for biomedical research or for clinical practice, the parameters of importance include cost, spectral resolution, spatial resolution, and response time. For many biological systems the assessment of infrared emissivity and/or fluorescence must be done simultaneously with the temperature measurement, because these parameters may rapidly change independently from each other. In addition to providing accurate absolute temperature readings in any thermological study, the measurement of emissivity and fluorescence and the display of their spatial distribution can be especially helpful in dermatology, dermatological oncology, dermatological pharmacology (assessment of pharmacokinetics and of diaphoretic excretion of drug metabolites), skin toxicology, burns management, assessment of radiation overexposure and microtelecalorimetry of cells, micro-organisms and tissue cultures. The measurement of light induced cutaneous vasoconstriction pose novel biomedical research problems that require the use of multiplewavelength cameras. In addition to the use of more sophisticated cameras, precision clinical telethermometry requires a better controlled environment. One must take into account infrared fluorescence, photoreflectance and light induced vasoconstriction all of which are induced by environmental illumination.
Empirical calibration of infrared images of electromagnetic fields
John D. Norgard, Michael F. Seifert, Ronald M. Sega, et al.
An infrared (IR) measurement technique has been developed to measure electromagnetic (EM) fields. This technique produces a two-dimensional IR thermogram of the electric or magnetic field being measured, i.e., an isothermal contour map of the intensity of the EM field. The intensity levels (equi-color levels) of the IR thermograms are empirically calibrated using standard gain horn antennas at several frequencies, angles of incidence, and polarizations in the near and far fields of the antenna. The results of the initial calibration test for electric field measurements are presented for a lossy Kapton detector screen developed to measure the absolute magnitude of the electric field in the plane of the detector screen. The accuracy of the technique is also discussed.
Infrared system for methanol-droplets temperature measurement on a monodisperse jet
Nicolas Naudin, Jean A. Farre, Gerard Lavergne
The first results of our work concerning the vaporizing methanol droplets temperature measurement on a monodisperse (i.e., monosized and equally spaced) droplets stream are presented. The purpose of this study is the development of an infrared system that is able to measure the temperature of a moving methanol droplet, in order to validate experimentally the models of fuel droplets heating and vaporization. Instead of tracking the droplet along its trajectory, we work with a monodisperse droplets chain and we measure the droplet temperature along the stream. An IR system composed of an extended blackbody, two off-axis parabolical mirrors, and a LWIR monodetector has been built. This paper describes the experimental setup, the measurement principle and presents the first results concerning the temperature measurement along a jet of methanol vaporizing droplets of 200 micrometers in diameter with injection speed up to 5.2 m/s.
Scanning telescope for the advanced polarized infrared imaging sensor (APIRIS)
Chen Feng, Anees Ahmad, Ye Li, et al.
An advanced polarized infra-red imaging sensor (APIRIS) has been designed and prototyped to acquire the polarization signature of targets in the far IR (8 - 12 microns) region with a field of view 4 degree(s) X 3 degree(s). The design (optical and optomechanical), fabrication and assembly issues of the scanning telescope for the APIRIS are discussed in this paper. The telescope is designed for diffraction limited performance using germanium lenses and Zerodur fold mirrors to minimize overall size of the telescope. The tolerance budgeting and thermal sensitivity analysis are also presented.
Infrared monitoring of plant damages and herbivore invasions
Jouni Takala, Matti Laehdeniemi, Juha T. Tanttu
Industrial maintenance is one of the main branches of infrared thermology applications. Our main studies are also concentrated on real time applications e.g., quality control automation. Environmental control is the branch which is strongly increasing. Plant damage is one of the most interesting things. The temperature changes is one feature which gives information about damage. At the beginning the necessary laboratory tests were done to study the possibilities of infrared monitoring of nature. After the preliminary tests the systematical studies were carried out. Using systematical measurements with infrared camera including image processing on plant leaves the clear changes were seen as a function of time. The studies were done applying the measurements on the fresh plant leaves. Later on the leaves were damaged by cutting and again monitored by infrared. After filtering and profile analysis the systematical changes were detected which show the changes of plant physiology after damage. The analysis of the above studies are given in this paper.
Increased image resolution of aerial thermography based on signal processing: distortion correction in line scanners
Ragnar H. Jonsson, Sigfus Bjornsson
Methods for correcting scanned remote sensing images for distortions due to undesirable aircraft motion are presented. The methods are intended for correcting distortions due to yaw and roll of the aircraft during image acquisition. The aircraft motion is estimated by analyzing the distortion of the scanned image. The correction of the distorted image is then based on the estimated motion. The correction is based only on the distorted image itself, and there is no need for any additional side information. This makes the methods presented well suited for correction of existing data, but the methods can also be used in real time correction during image acquisition. The effectiveness of the correction methods is demonstrated by examples using both real data, and synthetic data with known distortions.
Products and Processes
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Mathematical models for simulation of cooling processes using infrared surface-temperature measurement
Srecko Svaic, Igor Sundov
Mathematical models developed for the simulation of cooling processes are presented in the paper. The input parameters for the models are the data obtained by IR surface temperature measurement. The models enable the calculation of the temperature distribution inside the probe versus time, as well as the calculation of the local heat transfer coefficients. Also they can be used for the simulation of the cooling process. The developed software is given as an integral package intended for the analysis of quenching processes.
Nondestructive Testing II
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Nondestructive investigation by thermal waves of new aeroengine components
Laurent J. -P. Guazzone, Raphael Danjoux
It was found that infrared thermography (IT) gives satisfactory results to investigate air inlet nozzles and compressor casings. Interesting results were also obtained with this technique on insulated hubs as well as on samples of composite assemblies whereas difficulties were raised on real parts due to their complexity. As far as photothermal radiometry is concerned, improvements are necessary. All these results, compared to the ones obtained with traditional techniques, are presented in this paper.