EDDY CURRENT THERMOGRAPHY FOR DEFECT DETECTION AND CHARACTERISATION IN NDT APPLICATION
Eddy current thermography is one of the active thermography technique that can provide application in non-destructive testing for defect detection and characterisation. The method for defect detection in eddy current thermography has become reliable due to its mode of interactions i.e. eddy current heating and heat diffusion, acquired via an infrared camera. Such ability has given the technique the advantages for non-destructive testing applications. An overview of the eddy current thermography technique is presented which covers the physical principles of the technique, associated systems and its applications. The experimental parameters and settings which contributed towards optimum heating and defect detection capability are highlighted as the focus of research associated with the technique. In addition, the knowledge and understanding of the characteristics heat distribution surrounding a defect as an important factor for successful inspection results are discussed by experimental and 3D FEM simulation results. Thus, detection and the quantitative characterisation of defects by this technique are possible based on the changes of the induced eddy currents flow and the resultant temperature distribution captured by the infrared camera.
Uncooled detectors for high sensitivity synchronous thermography
Thermal detectors are seldom considered a viable alternative to cooled photon detectors for scientific thermographic applications. Their inferior noise equivalent temperature difference (NETD) and slower dynamic response are generally assumed to militate against good performance in applications requiring high sensitivity and speed, and for the most part that assessment is true. For the measurement of weak high-speed transients in flash thermography for instance photon detectors are unarguably superior. The same however cannot be said of all synchronous thermographic methods, several of which fulfil important roles in non-destructive inspection and experimental mechanics, e.g. optical lock-in thermography and thermoelastic stress analysis (TSA). For such methods, the signal of interest is not transient but persistent and oscillatory and often so weak as to be undetectable without synchronous averaging. In such cases the ultimate sensitivity achievable by a detector is determined not by its random temporal noise floor for which the NETD is a good figure of merit, but the fixed pattern noise floor a parameter which is seldom specified by manufacturers or measured by the user. This presentation will outline how this distinction explains why microbolometers can achieve performance levels comparable to cooled photon detectors for thermoelastic stress analysis, a finding that has had significant practical implications for the aircraft fatigue community. Case studies are given to illustrate how microbolometer-based TSA applied to airframe full scale fatigue testing has enabled a significant improvement in one of the underpinning elements of aircraft structural certification practice.
INFRARED THERMOGRAPHY WITH OPTICAL AND ULTRASONIC EXCITATION: PROMISING TOOLS FOR THE CHARACTERIZATION OF VERTICAL CRACKS
Active infrared thermography is nowadays recognized as an efficient nondestructive evaluation tool to detect defects such as cracks, delaminations, or voids in a wide variety of materials. In this presentation we will focus on the characterization of vertical cracks using optical and ultrasonic excitation of the sample, as complementary techniques for open and kissing cracks, respectively. We will show that, for open cracks, optically excited thermography with a focused illumination is very well suited to characterize the thermal resistance (opening) and size of open vertical cracks. We present analytical calculations of the surface temperature distribution produced by infinite cracks, we analyze the optimum experimental conditions to characterize them and we point out a new methodology to deal with finite and thin cracks, based on discontinuous Galerkin finite elements. In the second part, we will show that ultrasound excited thermography is a very appropriate choice to characterize kissing cracks, as the rubbing of the contacting surfaces produces heat at the crack. We will describe the methodology we have developed to retrieve the geometry of the heat source distribution produced at the crack from surface temperature vibrothermography data. Experimental verification of the potential of infrared thermography with optical and ultrasonic excitation to characterize calibrated open and kissing vertical cracks will be presented.
INFRARED THERMOGRAPHY IN CIVIL ENGINEERING:
FROM NON DESTRUCTIVE TESTING IN LABORATORY TO OUTDOOR THERMAL MONITORING
Being able to perform full field easily noninvasive diagnostics for surveillance and monitoring of transport infrastructures and structures is a major preoccupation of many technical offices. Among all the existing electromagnetic methods, active infrared thermography  up to long-term thermal monitoring using uncooled infrared cameras is a promising technique .
Anyway, except for vision applications , there is few results available in literature (mainly on buildings) for outdoor measurements by infrared thermography. So, to complete, a review of specificities and constraints for in situ measurements on large scale structures is proposed. Key points identified are analyzed versus infrared system technological potential solutions available on the shelf or at laboratory level.
To introduce transfer from laboratory conditions to real field, we will lean on some laboratory works on active thermography applied to quality control of reinforcement operations by gluing composite (CFRP) plates or tissues on concrete structure  or voids in pavement . First, we will introduce and discuss the benefit of using numerical heat transfer modeling to optimize the control process [6,7] or generate virtual thermal image sequences to test post-processing methods [8_,9]. It will be followed by presentation and discussion on experiments carried out using laboratory specimen. Then, some post-processing analysis approaches will be discussed. Finally, considerations on requirements to move from laboratory conditions to real site field measurements will be proposed.
Following the laboratory level presentation, a review of various experiments carried out, with an adapted infrared system, on different transport infrastructures or large scale element of Civil Engineering structures in outdoor conditions is given [10,11]. Raw results analysis is proposed. Processed data, obtained from few thermal images  to few days of experiments [10-11,13] up to several month of experiments, are presented and discussed. Lessons learned from in situ outdoor experiments are then addressed. In particular, field expertise acquired was used to initiate the development of a new infrared system architecture “Cloud2IR” dedicated to long term monitoring . An overview of this new architecture is proposed and discussed. In particular, benefit of using standards for measured data, but not only, is addressed.
Finally, a summary of results obtained and current limitations of studied solutions  is given. Perspectives in term of in-situ inspection solutions by active infrared thermography (i.e. under natural solicitations) or by coupling techniques  are proposed .
RECENT ADVANCES IN MEASUREMENT TECHNIQUE OF
In order to analyze the recent problems in thermal management, micro-scale thermography has been utilized to measure the thermophysical properties of energy materials and to detect the localized failure in semiconductors in the electronic industrial parts. Our equipment is widely applicable in the field of microscale thermography to achieve high-quality thermal imaging. The Infrared (IR) optical lens design has been optimized to each wavelength band of the photon type and the thermal type detectors of IR FPA. Typical applications to observe the freezing biological cells and the crystallization of organic mlecular crystals are reviewed together with the microscale laser flying spot method using the superimpose technique. The recent instrumentation of thermospectroscopy and the high temperature imaging systems are introduced with regard to the exothermic heat of chemical reaction in polymerization in microfluidics and the chemical heat storage process with molten salt to be utilized as the energy carier for the solar power plant.