The multiple applications of infrared thermography, a tool ...

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Short course on infrared thermographyShort course on infrared thermographyapplicationsapplications IntroductionIntroduction

The multiple applications of infrared thermography, a tool forThe multiple applications of infrared thermography, a tool formeasurement, characterization and monitoringmeasurement, characterization and monitoring

Organizing institutions and contributorsOrganizing institutions and contributorsDepartment of ContinuingEducation & Development

IR thermography basisAppl. to fluids mechanicsAppl. to solids mechanicsAppl. to NDEAppl. to electromagnetismAppl. to environment problemsDaniel Balageas

IR thermography basisAppl. to solids mechanicsAppl. to thermal properties characterization

Jean-Claude KrapezAppl. to electromagnetism

Patrick Levesque

IR thermography basisAppl. to solids mechanics

Pierre Brémond

Detectors for IR thermography

Jean-Luc Tissot

Plate 0-1-01

The present short course of continuing education entitled "Multiple Applications of Infrared Thermography, a tool formeasurement, characterization and monitoring" results from the collaboration of two institutions : The Ecole NormaleSupérieure of Cachan, a top level French academic institution and the ONERA, the French National Center for AerospaceResearch & Development. This course was first given live, at the ENS-Cachan, in French in 2001, and then in 2003 and 2004 in English.Considering the positive reaction to the course, the ENS-Cachan decided to transform it into a Web-based course to allow awider public to take advantage of this very original and very complete state-of-the-art thermographic technique. This coursemay be of particular interest to engineers and scientists.Daniel Balageas (Dipl. Eng., HDR), is the author, architect and major contributor to this course. He holds the position ofSenior Scientist and Deputy Head of the Structure and Damage Mechanics Department of ONERA and has 40 years ofexperience in aerospace research and nearly 20 years of experience in infrared thermography. Author of more than 80publications or communications on IR thermography, he created the QIRT (Quantitative InfraRed Thermography)Conferences in 1992 and the QIRT Journal in 2004. Since 1999, he has been a Part-Time Assistant Professor at ENS in theApplied Electronics and Electricity Department. In this course, he wrote the chapters on Applications to Fluid Mechanics, toNon Destructive Evaluation, to Electromagnetism and to Environment, and participated in writing the chapters on the Basisof IR Thermography and on the Application on Thermal Properties Measurement. Dr. Jean-Luc Tissot, has nearly 30 years of experience in infrared focal plane arrays. He joined the Infrared Laboratoryof CEA/LETI in 1979 to take part in the development of HgCdTe based 2nd generation IRFPA technology transferred toSofradir. In 1986, he became head of the silicon technology line in order to develop a new CCD technology for IR andvisible applications. In 1992, he was in charge of the development of uncooled IR detectors. In 1999 he became head ofImaging Sensor Technologies Programs at CEA/LETI. In 2002, he joined the new ULIS Company, a spin-off of Sofradir, asDirector of the R&D Division for Uncooled Microbolometer Industrialization. He wrote the lessons on Detectors in thechapter devoted to the Basis of Infrared Thermography. Dr. Jean-Claude Krapez, presently research engineer at the Department of Theoretical and Applied Optics, has nearly20 years of experience in IR thermography, photothermal radiometry, and in non-destructive characterization. He joinedONERA in 1992 after having spent 6 years in Canada working in these fields. At ONERA he has been involved in thedevelopment of new measurement methods using thermography, shearography, as well as in the thermal transfer modeling(conduction, radiation). He is author of more than 90 papers or communications on infrared thermography and photothermalradiometry. He is co-author of the course chapters on the Basis of Infrared Thermography, on the Applications to SolidMechanics and to Thermal Properties Measurement. Dr. Patrick Levesque, research engineer at ONERA, in the Structure and Damage Mechanics Department, is aspecialist in Electromagnetism. He joined the Physics Direction of ONERA in 1988 to work in the field of Electromagnetism.At the beginning of the 90's, with Daniel Balageas, he developed the ElectroMagnetic-InfraRed (EMIR®) technique whichallows visualizing quantitatively electromagnetic fields using IR thermography. He is currently applying this technique toseveral fields, in particular non-destructive evaluation and electromagnetic compatibility. He participated in the elaboration ofthe chapter on the Application to Electromagnetism. Dr. Pierre Brémond, presently Industrial Sales and Product Manager of CEDIP Infrared Systems, has 25 years ofexperience in research, marketing and thermography. He obtained his PhD in Mechanics in 1982, developping a thermalstress analyser applied to crack mechanics at the CNRS. He joined SNECMA as a test engineer working on thedevelopment of new measurement technologies in IR signature, stress and temperature analysis using IR cameras. From1987 to 1997 he worked for AGEMA and ADDITIONAL, as sales engineer and participated to the French Training Center.He joined CEDIP in 1998 as a product manager to sell, promote and assist in product design and development for stressanalysis systems. He participated in the writing of the chapters on the Basis of Thermography and on the Application toSolid Mechanics.

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Course structureCourse structure

Plate 0-1-02

This course is organized into 8 chapters. Six chapters (from chapter 2 to chapter 7) correspond to agiven field of application: fluid mechanics, solid mechanics, thermal properties measurement, non-destructive evaluation, electromagnetic phenomena characterization, environmental problems. Theyare preceded by a chapter devoted to the basic knowledge required to understand the course (chapter1) and followed by a chapter giving extra information to go further than this course (chapter 8). Each chapter is made up of lessons, which can be considered as the basic units of the course.Each lesson includes between just a few to a considerable number of plates.

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Introductionof the chapter

The tree-structureThe tree-structure


Course structureCourse structure

Plate 0-1-03

The course has a tree structure which allows easy and completely accessiblenavigation. The user can reach any of the 800 plates in any order he wishes,providing a quick flash-back feature.

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Course structureCourse structureTutorialsTutorials

More than 800 transparenciesdistributed into 47 Lessons

grouped into 6 chapters

Arborescent structure allowingan easy navigation in the

full course

Various possibilities:• Live courses thanks to audiocomments and illustration bysome video sequences• on-line reading of the coursedocuments combining both fullplates and their comments• Loading of the coursedocuments under pdf form to beprinted at home

PrintablePrintableshort course short course documentsdocuments

More than 800 pages, in full colorEach page presents

a plate with its comments

The arborescent structure

ExperimentalExperimentaldemonstrationsdemonstrationsIllustrative video sequences

ForumForumYour questions on thermographyanswered by experts and collected inFAQ pages

We will consider first the passive method of determining the convective heat transfer to which a model

embedded in a flow is submitted. The method is passive in that sense that the model temperature evolution

is only due to the action of the flow.

The problem consists to identify the convective heat transfer from the time evolution of the model surface

temperature (called the "wall temperature",Tw). (!) .

A First assumption consists to consider the transfer as unidirectionnal, which means that the spacedistribution of the convective transfer along the surface (x and y directions) is nearly uniform. (!)

Let us consider a control volume of very small thikness lying along the model surface. The heat fluxbalance is the following and must consider three fluxes: (F ) .

- the first heat flux correspond to the energy entering in the control voume due to the convection. Let be!c the convective heat flux at the wall. It is supposed to be proportionnal to the temperature gap between thewall and the flow gas recovery temperature Tr (this is theboundary layer theory). The proportionnalitycoefficient is the heat transfer coefficient, h. Both parameters, Tr and h fully characterize the boundarylayer and the heat transfer. They have to be identified from the thermographic experiment.(F ) .

- the second flux, !r, is due to the radiation losses from the wall toward the environment It is proportionalto the difference between the fourth power of the wall and environment temperatures and to "#, " being theemissivity and # the Stefan constant. Generally, radiation is neglectible, or can be considered as a

correction term (F )

- the third flux; !cond, is linked to the conduction from the wall to the inner part of the model. This flux is

given by the Fourier law relating the temperature gradient in the z direction to the conductive heat fluxthrough the thermal conductivity, k. The conduction heat flux is modeled depending on the nature of the wall,which can be thin or thick, conductive or isolating (F ) .

At every moment, these three heat fluxes are in equilibrium and we can state: !cond = !c + !r.

Plate 0-1-04

Most of these plates are animated and accompanied by an audio comment. Youare always free to choose between :- following the live course (animated and commented plates),- on-line reading of the course by simultaneously viewing the plates and reading thecomments, -loading the course documents as pdf files, printing them and reading them off-line.Each plate and its comments are given on the same page, providing for easyconsultation. The full collection is a real full color book of more than 800 pages. Furthermore, some video sequences are attached and render the user’sunderstanding of some important experimental procedures much easier than would beotherwise possible. The course will be periodically updated and improved with the addition of newmaterial as techniques progress. Finally, your questions concerning thermography will be answered by ourexperts. Questions and answers will be searchable and consultable in a FAQdocument.

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Basis of

thermography

Appl. to fluids

mechanics

Appl. to solids

mechanicsAppl. to thermal

properties

measurement

Appl. to NDE

Appl. to

electromagnetism

Appl. to

environmental

problems


Relative importance of the various chapters in the courseRelative importance of the various chapters in the course

Plate 0-1-05

This plate presents the relative importance given to each chapter of the course.The surfaces are proportional to the number of plates devoted to the given topic.

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Before starting Focal plane array cameras are the very dominant part of the infrared thermographymarket nowadays.

Nevertheless, this course presents numerous examples illustrating some of the possibleapplications obtained with single detector cameras. What we want to show you is how tocorrelate a thermal phenomenon to other physical phenomena, regardless of which type ofcamera is used. These examples may be as different as laminar-turbulent transition on a modelin a flow, fatigue in a steel coupon, interaction of microwaves with aircraft components or thedebonding of two parts of a structure.

Examples of applications using single detector cameras are given because this course is acompendium of the experience of several active research scientitt who have been working onthis for more than two decades. Of course, these experiments can be duplicated with focalplane array cameras which yields better thermal and space resolution, but never forget that:

The most important thing is not the camera itself, it is HOW you use it !

Plate 0-1-06

Normally, this plate does not need a comment. All the information is written on it.We make the present comments just to give you an example of a "mute" plate. Fromtime to time you will find plates like this. They are often used as transition betweentwo sequences, or to summarize conclusions. They are presented like this : short texts explaining the story in the style of old-fashioned silent movies. When you see a plate with this format, don't be surprised bythe absence of audio and written comments !

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Before starting …

Some reflections about howthermography is used

Plate 0-1-07

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Thermography is not a new techniqueThermography is not a new technique

Invention of thermography by Invention of thermography by Hippocrates (- 460, - 377 B.C.)Hippocrates (- 460, - 377 B.C.)

Hippocrates, Diseases III, Part 16: on pleurisys,traduction by Paul Potter in Hippocrates, vol. 6,Harvard University Press, Cambridge (MA), 1988.

This experiment was repeated by twoJapanese researchers, Kimio Otsuka andTatsuo Togawa 24 centuries later

Kimio Otsukai and Tatsuo Togawa, Hippocraticthermography, Physiol. Meas. 18 (1997), 227-232.

"Soak a piece of fine linen in warm moist finely trituratedEretrian earth; then wrap this all the way around the thorax,and, wherever it first dies, that is were you must cauterize orincise, as close to the diaphragm as possible, but sparingthe diaphragm itself. If you prefer, apply the Eretrian earthdirectly and look for the place the same way you would inthe linen; let many people apply the earth simultaneously, inorder that the first applied does not become dry".

Plate 0-1-08

We would like to show you an efficient way to use thermography and at the sametime remind you of or tell you an old story which demonstrates that the invention ofthermography is very ancient. We can consider that the inventor of thermography is … Hippocrates who livedin Greece from 460 to 377 B.C. Of course the technique proposed by this famousphysician was not based on infrared radiometry. Hippocrates’ method appears in a section of his work on Diseases on pleuraleffusion. The object is to locate where the pus is in the chest of the patient sufferingfrom pleurisy and consequently, where the physician has to operate. The presence ofpus, like any infection, causes local overheating. Hippocrates describes his thermal -let say thermographic - method as follows : "Soak a piece of fine linen in warm moist finely triturated Eretrian earth; then wrapthis all the way around the thorax, and, wherever it first dies, that is were you mustcauterize or incise, as close to the diaphragm as possible, but sparing the diaphragmitself. If you prefer, apply the Eretrian earth directly and look for the place the sameway you would in the linen; let many people apply the earth simultaneously, in orderthat the first applied does not become dry". This experiment was repeated by two Japanese researchers, Kimio Otsukaand Tatsuo Togawa 24 centuries later. We will present this interesting experiment inthe following plate.

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Kimio Otsuka and Tatsuo TogawaKimio Otsuka and Tatsuo Togawaexperience of Hippocratic thermographyexperience of Hippocratic thermography

aa

bb

cc

dd

ee

ff

gg

hh

Subject's back photographies: a) 5 min after application ofthe earth-soaked cloth. Arrow indicates the first part to dry,b) 2 min later, c) 4 min later… h) 14 min later.

IR thermography of thesubject's back justbefore the earth soakedcloth was applied

Images taken from Kimio Otsukai and Tatsuo Togawa, Hippocratic thermography, Physiol. Meas. 18 (1997), 227-232.

Plate 0-1-09

There are some differences between the Kimio Otsuka and Tatsuo Togawaexperience of Hippocratic thermography and the Hippocrates experience itself: i) the subject is not suffering from a pleural infection, but from a compress soakedwith an acqueous solution of red pepper extract which was applied for one hour onthe left side of his back. At the end, the skin-temperature of this compressed areawas 3 to 4 degrees higher, as seen on the infrared thermographic image of thepatient’s back taken just before the earth-soaked cloth was applied. ii) the cloth was made of silk (used for insect nets) and not of linen.iii) the earth was not from Erethrea, but was given by a potter from Kyoto. The photo of the patient’s back five minutes after application of the earth-soakedcloth is shown on the right. The wet parts of the earth-soaked cloth are dark grey,whereas the dry part, which appears at the location pointed to by the arrow, isgreyish white. A blue arrow indicates the location of the hottest spot given in the infraredthermographic image and the spot given by the Hippocrates procedure. Every two minutes following this first picture, a new photo was taken, the lastone being 14 minutes later. This series of photos shows the progressive extention ofthe dry part of the cloth. Regions drying later and later correspond to parts of theback where the heat source is weaker and weaker.

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Synthetic Hippocraticthermographic image

Infrared thermographic images


Kimio Otsuka and Tatsuo Togawa experience of Hippocratic thermographyKimio Otsuka and Tatsuo Togawa experience of Hippocratic thermography

9 min after application ofthe earth-soaked cloth

Just before the applicationof the earth-soaked cloth

Plate 0-1-10

Then, with the use of computer imaging, if we superimpose the successiveimages of this series of photos and if we colour the dry (greyish white) part of the a)image in red (5 min) and in the next hue of the light spectrum the dry part of thesubsequent photographies, we obtain a synthetic image, which we can call a "Hippocratic" image. In this image, colour change borders correspond to :- lines where the total energy given by the skin to the cloth to make it dry is equal tothe latent heat of evaporation of water trapped in the cloth,- isotherm lines at any moment during the drying process, - isotherms before the application of the cloth, since we can suppose that the heattransfer of the skin with the environment is linearly related to the temperature gapbetween the skin and the air.

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The space- and time analysis of the the thermalmethod defined by Hippocrates leads to results similarto those of "active" infrared thermography.The Hippocratic technique does not aim to measure theskin temperature, as classical "passive" infraredthermography does,nevertheless, it allows to locateinfection and to give a certain evaluation of its extent.

IR thermography of thesubject's back just beforethe earth soaked cloth wasapplied

Synthetic hippocraticthermographic image


Kimio Otsuka and Tatsuo Togawa experience of Hippocratic thermographyKimio Otsuka and Tatsuo Togawa experience of Hippocratic thermography

Plate 0-1-11

If we analyze the experiment performed by Hippocrates, we see that it is in fact acomplex time and space analysis of a thermal phenomenon, which is provoked togain information on the internal structure and temperature of a complex structure (asick human body). This approach is similar to present Non destructive Evaluationtechniques. We can qualify the process as "active thermography" in which the aim isnot to measure surface temperature distribution, but to locate the infection and toassess its extent.

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Generally, the thermographist is not interested in knowing the temperature foritself, but for infering information on very different things like structurearrangement and properties, heat sources intensities… The observed temperatureis just an intermediary between the observer and the examined phenomenon.

This is frequently achieved by active (or stimulated) thermography : theexperimenter not only records the distribution and/or evolution of thetemperature, but provokes an imbalance of the observed system throughstimulation.

Time and space are closely connected in thermographic analysis. Both spacedistribution (thermographic images) and time evolution (thermograms, or time-grams) are jointly used for the thermographic data reduction.

This Hippocratic experiment is a paradigmillustrating the fundamental ideas which underlie everything

that will be presented throughout this short course

Plate 0-1-12

The multiple applications of infrared thermography, a tool ...

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