Showing papers on "Thermography published in 2012"

Infrared thermal imaging in medicine

Abstract: This review describes the features of modern infrared imaging technology and the standardization protocols for thermal imaging in medicine. The technique essentially uses naturally emitted infrared radiation from the skin surface. Recent studies have investigated the influence of equipment and the methods of image recording. The credibility and acceptance of thermal imaging in medicine is subject to critical use of the technology and proper understanding of thermal physiology. Finally, we review established and evolving medical applications for thermal imaging, including inflammatory diseases, complex regional pain syndrome and Raynaud's phenomenon. Recent interest in the potential applications for fever screening is described, and some other areas of medicine where some research papers have included thermal imaging as an assessment modality. In certain applications thermal imaging is shown to provide objective measurement of temperature changes that are clinically significant.

Monitoring mechanical damage in structural materials using complimentary NDE techniques based on thermography and acoustic emission

Abstract: This work deals with nondestructive evaluation (NDE) of the fracture behavior of metallic materials by combining thermographic and acoustic emission (AE) characterization. A new procedure, based on lock-in infrared (IR) thermography, was developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue. The thermography results on crack growth rate were found to be in agreement with measurements obtained by the conventional compliance method. Furthermore, acoustic emission was used to record different cracking events. The rate of incoming signals, as well as qualitative features based on the waveform shape, was correlated with macroscopically measured mechanical parameters, such as load and crack propagation rate. Additionally, since the failure modes have distinct AE signatures, the dominant active fracture mode was identified in real time. The application of combined NDE techniques is discussed for characterizing the damage process which leads to catastrophic failure of the material, thereby enabling life prediction in both monolithic aluminum alloys and aluminum alloy/SiC particle (SiCp) reinforced composites.

Dissipated thermal energy and damage evolution of Glass/Epoxy using infrared thermography and acoustic emission

Abstract: In this paper, we present an experimental approach for characterizing energy dissipation and degradation evolution in a woven Glass/Epoxy (G10/FR4) laminate subjected to fully reversed bending fatigue test During cyclic loading, a fraction of the input mechanical energy is converted to thermal energy, which results in an increase in the temperature of the specimen By analyzing the surface temperature and its drop rate after halting the cyclic operation, the dissipated thermal energy (DTE) is estimated Infrared thermography is used to assess the temperature evolution and to various damage states Acoustic emission is also utilized to corroborate the thermography results in characterizing the degradation progression The results of these two non-intrusive techniques show similar evolutionary response revealing the existence of degradation stages Using calculated DTE, a damage growth model is developed that appropriately characterizes the three damage phases during fatigue process of Glass/Epoxy

Comparison of Nondestructive Testing Methods on Detection of Delaminations in Composites

Abstract: Delamination is one of the most common defects in carbon fibre reinforced plastic (CFRP) components, such as those used in aircraft and wind turbine blades. To detect delaminations, different NDT methods such as ultrasonic (UT), eddy current (EC) scanning, flash thermography, and recent developed pulsed-eddy-current-(PEC-) simulated thermography are conducted for comparison and evaluation of the new developed PEC thermography system at Nanjing University of Aeronautics and Astronautics (NUAA), China through UK-China collaboration. A PEC-stimulated thermography system is built at NUAA, extended from previous joint work between Newcastle and Bath Universities. Using these NDT systems, man-made, dedicated delaminations with varied diameters and depths are investigated and studied. Through this comparison, PEC-stumilated and flash thermography show relatively good indications of the shape of delaminations. The joint studies also show that PEC-stimulated thermography has unique advantage for fibre orientation evaluation.

Nondestructive Bridge Deck Testing with Air-Coupled Impact-Echo and Infrared Thermography

Abstract: Two different nondestructive test (NDT) methods, air-coupled impact-echo (IE) and infrared (IR) thermography are evaluated on a full-scale simulated reinforced concrete bridge deck containing simulated delamination and cracking defects. The IE data are presented as two-dimensional frequency maps and spectral B-scan lines. The IR data are presented as temperature maps on the concrete surface. The lateral boundaries of the detected delaminations are also indicated in the images. The results obtained from each of the individual NDT methods show reasonably good agreement with most of the actual defects. The advantages and limitations of each method to characterize defects are discussed. The consistency and sensitivity of each method are also investigated. Finally, a simple data fusion technique is proposed to improve effectiveness of the individual test data. The findings from this study demonstrate that the combination of air-coupled IE and IR thermography tests is a practical option for consistent and rapid in situ evaluation of reinforced concrete bridge decks.

Infrared Thermography for Thermo-Fluid-Dynamics

Abstract: Introduction and historical groundings - Physical background - Infrared scanner - Heat flux sensors - Restoration of thermal images - Some practical considerations - Applications.

Defect characterisation using pulsed eddy current thermography under transmission mode and NDT applications

Abstract: Pulsed eddy current (PEC) thermography has been successfully applied to detect cracks in metal alloy and carbon fibre reinforced plastic (CFRP) in previous works. In these applications, an inductor and infrared camera are on the same side of components, named reflection mode. In this work, the transmission mode, where the inductor and infrared camera are on opposite sides of component is investigated for defect characterisation through the analytical analysis and experimental studies. The studies show that the detection mechanisms for impact and delamination in CFRP are totally different. Carbon structure can be observed on the early stage of heating phase and impact leading to decreasing conductivity can be also detected in heating phase. However, delamination can be characterised using late stage of cooling phase. Combing the detection mechanisms, principal components analysis and independent components analysis, image reconstruction method is used to improve the sensitivity.

Computational water stress indices obtained from thermal image analysis of grapevine canopies

Abstract: Thermal imaging of crop canopies has been proposed more than a decade ago as a sensitive methodology to determine the water status of different crops. This paper describes the development of a semi-automated and automated methodology using MATLAB® programming techniques to analyse the infrared thermal images taking into consideration the pitfalls pointed out previously in the literature. The proposed method was tested in an irrigation reduction and recovery trial for Chardonnay in the 2010–2011 season and in the 2009–2010 season from seven varieties in field conditions. There was a clear separation (assessed by principal component analysis) between control and recovery compared to stress treatments using leaf area index (LAI), stomatal conductance, stem water potential and indices derived from canopy temperatures measured by infrared imaging. High and significant correlations were found between canopy temperature indices and other measures of water stress obtained in the same vines that were independent of LAI. Furthermore, a fully automated analysis method has been proposed using ancillary weather information obtained from the same locations of infrared thermal images. This paper is a first step towards automation of infrared thermography acquisition and analysis in the field for grapevines and other crops.

Eddy-current induced thermography—probability of detection study of small fatigue cracks in steel, titanium and nickel-based superalloy

Abstract: Eddy-current induced thermography (induction thermography, hereon referred to as eddytherm) is an active thermographic method which is capable of rapid and non-contacting detection of out-of-plane cracks in electrically conductive parts. In an eddytherm inspection, the part is induction heated; cracks cause localised changes in the induced eddy-current flow and the associated Joule heating is imaged at the surface of the part with an infrared camera. In this study the detectability of fatigue cracks in steel, titanium and Waspaloy is quantified by novel but simple image processing routines which are specifically applicable to eddytherm inspection. The quantitative detection data is then input into a cumulative log-normal probability of detection model to estimate the probability of detecting the fatigue cracks as a function of crack length. a90,95 (i.e., the crack length which can be detected 90% of the time with 95% confidence) is found to be 0.60 mm for steel, 0.78 mm for titanium and 1.50 mm for Waspaloy (a nickel-based superalloy), showing eddytherm to be an extremely sensitive method.

Defense and illustration of time-resolved pulsed thermography for NDE

Abstract: After defining a good usage of pulse thermograms, in particular their ‘rectification’ thanks to log-log plot, and fitting by the TSR (thermographic signal reconstruction) technique, it is demonstrated that a simple and efficient normalisation is possible. The optimisation of pulse thermography is proposed based on two complementary approaches: the early detection of contrasts and the use of the TSR technique with logarithmic derivation. It is shown that in these conditions the quality of thermal images is greatly enhanced (reduction of blurring) and the accuracy of the identified defect parameters (depth and thermal resistance) is better. Based on experimental and simulated results it is shown that to optimise pulse stimulated thermography it is necessary to consider two parameters: the signal-to-noise ratio of the defect contrast and the precociousness of its exploitation. It is shown that this second parameter, which has been neglected by most of the users of pulse thermography who identified the defect...

Crack sizing by laser excited thermography

Abstract: Active thermography is a nowadays widely used NDT method making use of thermal material properties for defect detection. Basically, the sample is heated and the resulting surface temperature is recorded by an IR camera. For laser thermography a laser is used to heat the sample locally. The resulting spherical heat flow allows the detection of voids in arbitrary orientation. In this work, a method is presented which is suitable for the quantitative characterization of depth and angle of surface cracks. The main idea is to evaluate the crack-caused asymmetries of the laser's thermal footprint. The heat is introduced at fixed reference positions relative to the crack. In this paper a data analysis procedure is presented which allows the crack depth and angle to be described by only two characteristic scalar parameters. By investigating artificial test specimens with spark eroded notches, the feasibility of this method is validated. Furthermore, the behavior of the characteristic parameters with variations of crack angle, depth and experimental conditions is studied systematically by FEM simulations, showing that these parameters are well behaved.

Thermography study of skin response due to whole‐body cryotherapy

Abstract: Purpose: Thermography and contact thermometry were used to study the influence of body mass index (BMI) on the lowering of skin temperature caused by whole-body cryotherapy. Methods: The study was performed using the Thermovision Camera AGEMA Type 470 and A40. The thermograms of the chosen regions of interests were performed before and immediately after whole-body cryotherapy in a research room outside a cryogenic chamber where the temperature was stabilized. As an additional measurement technique during whole-body cryotherapy, contact thermometry was performed using thermocouples Ni–Cr–Ni–Al stacked to the skin surface. Results: The results obtained showed differences in the decrease of skin temperature of predetermined body parts. The largest temperature decrease was observed on the lower extremities. Some differences in the thermal response of similar body parts influenced by the extremely low temperature, with regard to the BMI of volunteers, were observed. This was also found in the results of contact thermometry studies. The statistical analysis confirmed the results of thermography and thermometry studies. Conclusion: The magnitude of skin temperature decrease due to the extremely low temperature used in whole-body cryotherapy may be connected to a patient's BMI.

An analytical study of the pulsed thermography defect detection limit

Abstract: A simple modification of the one-dimensional expression for the thermal contrast of a layer provides a useful prediction of peak contrast temperature and contrast peak time for defects of all aspect ratios. The new analytical results have been shown to agree with numerical modelling. The thermographic nondestructive evaluation (NDE) rule-of-thumb that defects are detected if aspect ratio exceeds two is shown to have no general validity as peak contrast is found to depend critically on defect depth and absorbed excitation energy as well as defect aspect ratio. The effects of thermal diffusivity anisotropy are included in the analysis and illustrated by simulations of defect image contrast in composite materials.

Measurement of Excitation Winding Temperature on Synchronous Generator in Rotation Using Infrared Thermography

Abstract: A new measurement method for infrared (IR) surface temperature measurement of excitation winding in rotation is presented. The method is experimentally verified on a 400-kVA salient pole synchronous generator. This method uses an industrial IR thermometer which represents an alternative to expensive fast IR thermometers or cameras. The target application of this method is the determination of the dynamic limit in the P-Q diagram of a synchronous generator due to excitation winding overheating. The measurement error model which shows the way how to minimize measurement error has also been derived. The effect of the interpolar surface can be cancelled if the IR thermometer is positioned at a certain angle with respect to the machine's main axis. Digital temperature sensors have been mounted on the rotor to measure the excitation winding surface temperature for comparison.

Evaluation of the fused silica thermal conductivity by comparing infrared thermometry measurements with two-dimensional simulations

Abstract: A self-consistent approach is proposed to determine the temperature dependent thermal conductivity k(T) of fused silica, for a range of temperatures up to material evaporation using a CO2 laser irradiation. Calculation of the temperature of silica using a two-dimensional axi-symmetric code was linked step by step as the laser power was increased with experimental measurements using infrared thermography. We show that previously reported k(T) does not reproduce the temporal profile as well as our adaptive fit which shows that k(T) evolves with slope discontinuities at the annealing temperature and the softening temperature.

Non-destructive evaluation of thick glass fiber-reinforced composites by means of optically excited lock-in thermography

Abstract: Optically excited lock-in thermography (OLT) has been exploited for quantitative assessment of simulated subsurface defects in thick glass fiber reinforced polymer (GFRP) composite laminates routinely employed for the manufacturing of luxury yachts. The paper investigates the detection limits associated to defects geometry and depth as well as recognition of barely visible impact damage over the external gel-coat finish layer. The obtained results demonstrated the effectiveness of lock-in infrared thermography as a powerful and non-contact full-field measurement technique for the inspection of large GFRP structures. In particular, results showed that, by using a transmission set-up instead than a reflection one, accurate assessment (standard uncertainty

Emissivity estimation for accurate quantitative thermography

Abstract: In this paper an emissivity measurement method is proposed; it relies on individual calibration functions, and is based on the spectral response of a specific IR sensor. The reflected temperature is kept constant during the test, and its knowledge is not required. Results of measurements on materials commonly used as emissivity references in quantitative thermography are reported. Computer simulations of indoor and outdoor thermographic inspections show the differentiated influence of emissivity and surroundings temperature on the measurement accuracy. Finally experimental results of absolute and differential temperature measurements are discussed.

Defect characterisation based on heat diffusion using induction thermography testing

Abstract: Pulsed eddy current (PEC) thermography (a.k.a. induction thermography) has been successfully applied to detect defects (corrosion, cracks, impact, and delamination) in metal alloy and carbon fiber reinforced plastic. During these applications, the defect detection mechanism is mainly investigated based on the eddy current interaction with defect. In this paper, defect characterisation for wall thinning defect and inner defect in steel is investigated based on heat diffusion. The paper presents the PEC thermography testing, which integrates the reflection mode and transmission mode by means of configuring two cameras on both sides of sample. The defect characterisation methods under transmission mode and reflection mode are investigated and compared through 1D analytical analysis, 3D numerical studies, and experimental studies. The suitable detection mode for wall thinning and inner defects quantification is concluded.

Infrared thermography applied to the analysis of material behavior: a brief overview

Abstract: The characterization of material behavior under various loading conditions involves two closely related aspects, namely mechanical and thermal, that can be grouped into one general thermomechanical framework. The goal of this paper is to briefly review specific applications of infrared techniques, over a range of loading conditions, such as quasi-static and polycyclic, for various types of material. Some experimental and theoretical issues are discussed to highlight the additional knowledge that can be gained through the application of these techniques to the mechanical characterization of materials.

Temperature maps measurements on 3D surfaces with infrared thermography

Abstract: The use of the infrared camera as a temperature transducer in wind tunnel applications is convenient and widespread. Nevertheless, the infrared data are available in the form of 2D images while the observed surfaces are often not planar and the reconstruction of temperature maps over them is a critical task. In this work, after recalling the principles of IR thermography, a methodology to rebuild temperature maps on the surfaces of 3D object is proposed. In particular, an optical calibration is applied to the IR camera by means of a novel target plate with control points. The proposed procedure takes also into account the directional emissivity by estimating the viewing angle. All the needed steps are described and analyzed. The advantages given by the proposed method are shown with an experiment in a hypersonic wind tunnel.