This PDF file contains the front matter associated with SPIE Proceedings Volume 11004, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The purpose of this work is to introduce a new analytical inversion method for three-dimensional (3D) sub-surface imaging beneath the skin from time sequenced infrared (IR) thermography images. The work was motivated by advances in thermal nondestructive evaluation methods. Using relationships between wave propagation and thermal diffusive propagation, transformation from diffusive propagation into an equivalent wave field is performed. This transformation results in well-defined reflections with time delay proportional to the distance. We apply the algorithm to a dynamic thermogram of histologically confirmed breast carcinoma obtained from the Brazilian breast thermal imaging set. Inversion of the raw data reveals intensities that correspond to heat conduction, most notable is presence of hyperintense, aberrant vascularization in the diseased breast in comparison with the non-diseased breast. Equivalent wave field transform (EWFT) serves as a computationally efficient method of extracting depth resolved anatomical and physiological information from skin surface thermogram data for research purposes.

A software tool was developed for application to thermographic images of canines to identify syrinx or no-syrinx classes in dogs exhibiting Chiari malformation. The MATLAB CVIP Toolbox was used to create a Graphical User Interface (GUI) for feature extraction and pattern classification. The thermographic images were obtained from the Long Island Veterinary Specialists (LIVS). Histogram and texture features were extracted from the images and used for pattern classification. Efficacy of the new development tool is shown by this initial investigation and the potential of such custom software tools in automating the research and development of medical diagnostic procedures makes it a valuable approach.

Periodic thermal imaging inspection of air-insulated substations can lead to false negatives due to the heating effects of solar radiation and cooling effects of wind and precipitation. This work aims to characterize the effects of wind on thermal images of thermally loaded equipment, allowing thermal response forecasts to be made. Data is collected in two load patterns from an indoors experiment, comprising a current loop of two overhead- line conductors energized by a high-current DC power supply. Wind is emulated by an industrial fan. Infrared images, environmental data (ambient temperature, humidity, pressure, wind speed and direction) and electrical load data are all captured periodically. A further dataset from an in-service substation is used. Models are created using vector autoregressive and long short-term memory recurrent neural network models in order to further develop the methods presented by Bortoni et al. The results display a clear improvement over those found in the literature, highlighting the utility of modern data-processing techniques. These results present an opportunity to extract meaningful information for long term thermal condition monitoring of power substations.

This paper presents an inspection methodology for high-temperature furnace tubes by IR thermography based on the acquisition and analysis over the time of a sequence of thermographic images. With this aim, a set of IR data has been collected during a furnace inspection (operated in steady-state condition) using a high-speed IR camera manufactured by TELOPS (3.0 - 5.4 μm with filter BBP-3670-4020 nm, 320×256 pixels, 3100 Hz). The stacks of IR images have been processed using multivariate statistical analysis – more specifically, partial least squares regression (PLSR), which decomposes the thermographic data sequence into a set of latent variables. Since each latent variable is orthogonal to each other and is characterized by its variance, it is possible to separate the noise affecting the IR signatures through a careful analysis of each component. A qualitative comparison between the processed and non-processed images will be made in order to evaluate the effectiveness of the proposed inspection method.

A new design and its characterizations for use in thermal-infrared radiation thermometer and sensors are described. This new design uses an optical configuration where critical optical elements such as the field stop, Lyot stop, collimating lens, and detector, are placed inside a thermally stabilized assembly that is controlled using thermo-electric coolers and feedback from thermistors. The optical components have been incorporated into an operational system and calibrated using both variable-temperature fluid-bath and heat-pipe blackbodies from -45°C to 75°C. The radiation thermometer has been calibrated using modified Planck function and these blackbodies. This new design has been characterized to determine noise-equivalent temperatures and long-term stability. This new design, without the need for cryogenic cooling, demonstrates sub-millikelvin temperature resolution with the possibility of weeks-long and extended-length stable operations while measuring room-temperature objects with few millikelvin stability.

In the foundry industry the typical casting process is done by pouring the liquid (fused) metal on a mold shape and left until solidification. The inner part of the mold gets in contact with the liquid, high temperature metal. The mold is generally coated with a special refractory varnish that improves the flow of the liquid metal inside the mold and allows to obtain smoother surfaces of the solidified object. In the process of optimizing the performance of such refractory coatings, new recipes are experimented and the thermal properties of such new materials are paramount in the process of qualification of the product. In this work, three different kind of coatings varnishes are tested. These coatings are deposited on a metallic substrate and the thermal diffusivity is evaluated by one side thermal test. The laser shots the surface of the coating with a short pulse and the temperature variation is measured by an infrared camera. Knowing the density, and measuring the specific heat by Differential Scanning Calorimeter, it is then possible to derive the value of the thermal conductivity.

The use of drones has almost exploded almost in the last five years in Finland. The utilization of drones has increased and more and more applications have emerged. In addition to video cameras, thermal cameras and hyperspectral cameras have been used as well as their combinations. The use of thermography has been more qualitative, as in case of thermography in general when devices became more common and the prices lowered. The progress of optical measurement devices and image processing software will give more and more opportunities for R&D. It is essential to convert data obtained from a given object to information that is beneficial to the parties - the question is about the interpretation of the images and also how to combine the information from different wavelengths. This will require knowledge of the phenomenon or subject and factors affecting it. Drones provide better opportunities to observe large areas. The most important result should be, anyway, to increase information about the subject. In this presentation some applications will be introduced: Visible video and thermography in built environment evaluation, surveillance, firefighting and thermography and hyperspectral in agriculture. The possible future applications will be will be evaluated. Dealing with building thermography, drones give better possibilities to scan the whole building and especially looking at the top floors and especially the roofs. The structures be known in advance and several measurements are often required under different conditions. In surveillance, people have been searched by thermography for a long time, but drones can be used more effectively than in case of airplanes or helicopters. Interesting application is thermography combined with hyperspectral scanning in agriculture. Scheduled methods, processes and routines are needed.

In order to improve the performance of infrared system, both infrared detector and readout circuit must be packaged together and work at low temperature. A great deal of research has been done on the readout circuits of infrared detectors internationally, but there are some universal disadvantages such as unstable performance at low temperature, excessive noise of output signal and oscillation at low temperature. To improve the performance of infrared detector system, a design with a cascode CTIA and phase self compensation capacitor before CDS is developed, which is able to ensure that the circuit has a larger phase margin and a stable operating status at low temperature. Through simulation analysis, the compensation capacitance benefit is to reduce output overshoot voltage from 76 mV to 4.9 mV, the signal stability time can be decreased to 1/10 of the former. The performance of the readout circuit is tested after design and tapeout, the output noise of circuit becomes lower, the value is less than 0.5 mV. The circuit can work normally from room temperature to low temperature. The signal swing is greater than 2 V. After being interconnected with IR detector, the readout circuit can work well at low temperature and overcomes the defect of oscillation phenomenon at low temperature. The system’s electrical cross-talk is also improved obviously.

We show successful printing of chalcogenide glass using two different techniques. Additive manufacturing is still a fairly new field, but is increasing rapidly. We compare some of the first tests of selective laser melting and direct laser processing techniques to chalcogenide glass.

Passive thermography is used to monitor small increases in temperature resulting from delamination damage formation in a composite hat-stiffened panel during quasi-static loading. The heating is composed of two heat generation components. The first component is an instantaneous response due to a strain release during quasi-static loading. The second component is mechanical heating, at the interface of failure, due to fracture damage. This second component produces a transient rise in temperature that is a function of the damage depth and thermal diffusivity. The first component defines the thermal start time for the transient response. A one-dimensional thermal model is used to determine the damage depth. The results are compared to ultrasonic and X-ray CT data. The advantages and limitations of the thermal technique for damage depth detection are discussed.

Thermography has been shown to be a viable technique for inspection of composites. Impact damage in composites typically contains multiple overlapping delaminations at different depths. Understanding the limitations of the thermographic inspection is enhanced by performing simulations of the technique. Most simulations of composite thermographic inspections have focused on simulations of a single delamination at a fixed depth. The quadrupole method has been shown as a viable technique for rapid three-dimensional thermographic simulations of a delamination. This method is expanded to enable rapid simulation of multiple overlapping delaminations at different depths. Quadrupole simulations are compared to finite element simulations of multiple delaminations at different depths. The simulations are also compared to the thermographic measurements on impacted composites where shape and depth of the delaminations are known from x-ray computed tomography data.

Thermosonic imaging is a new nondestructive testing (NDT) technique capable of provide full-field, rapid inspection of crack-type of defects in materials or structures. Conventional thermosonic imaging system employs an ultrasonic welder, which is designed of a single frequency to generate high-power ultrasonic excitation in a work piece, and an infrared (IR) camera to capture thermal images of surface and subsurface defects under ultrasonic excitation. Most thermosonic imaging NDT is applied for metallic materials to detect crack-like defect, since the heat is generated from the rubbing surfaces of a defect. The inspection of composite structures using thermosonic NDT remains challenging due to their high acoustic attenuation and low surface hardness. In this paper, we present the development of a thermosonic imaging system, which is capable of exciting the ultrasonic transducer at different frequencies for Thermosonic NDT to overcome the limitations associated with single frequency power source as well as the spring loaded transducer design. One particular application of this new thermosonic imaging system is for rapid inspection of composite structures. Various composite structures have been tested to verify and valid the new thermosonic imaging system performance.

Infrared Thermography has been successfully used as an experimental, non-destructive, real-time and non-contact technique both to perform non-destructive evaluations and to study the fatigue behaviour of materials. However, the temperature is a very sensitive parameter to the environment conditions such as the thermal heat exchanges. It follows that, heavy and time expensive algorithms have to be setup to accurately filter out the overall ‘disturbing’ heat sources. Otherwise, an in-depth analysis of thermal signal allows the assessment of different indexes related to physical processes of fatigue damage and failure. Theoretical and experimental framework becomes complicated in case the material is a composite due to the layups of lamina or due to the viscous properties of the bulk of the matrix, or due to the pattern described by the yarns or fibers making difficult any quantitative and qualitative analysis. In fact, anisotropy and heterogeneity of composites influences unavoidably the mechanical response of the material to external excitation and the failure mechanisms. In all the cases, the study of thermal heat sources related to dissipative phenomena becomes complicated. Thermal signal analysis provides a localised analysis for assessing qualitatively and quantitatively the state of degradation of material in terms of stiffness or in term of damage detection, by extracting temperature components related to the appearance of plastic zones or cracks or in general to dissipative heat sources. The focus of the present research is to provide an innovative method and algorithm for processing the signal from innovative composites obtained by Automated Fiber Placement process in order to assess the fatigue behaviour and damaged regions qualitatively and quantitatively.

Transient thermography is a method used successfully in the evaluation of composite materials and aerospace structures. It has the capacity to deliver both qualitative and quantitative results about hidden defects or features in a composite structure. Aircraft must undergo routine maintenance – inspection to check for any critical damage and thus to ensure its safety. This work aims to address the challenge of NDT automated inspection and improve the defects’ detection by suggesting an autonomous thermographic imaging approach using a UAV (Unmanned Aerial Vehicle) active thermographic system. The concept of active thermography is discussed and presented in the inspection of aircraft CFRP panels along with the mission planning for aerial inspection using the UAV for real time inspection. Results indicate that the suggested approach could significantly reduce the inspection time, cost, and workload, whilst potentially increase the probability of detection of defects on aircraft composites.

We present a methodology to measure the in-plane thermal diffusivity of (an)isotropic samples using flying spot thermography. We obtain an analytical expression for the surface temperature distribution when a continuous wave laser spot scans the sample surface at constant velocity. By analyzing this expression, we propose three simple methods to measure the thermal diffusivity in the directions parallel and perpendicular to the motion. The methodology can also be applied in the case where the laser spot is at rest, and the specimen moves at constant velocity. This configuration is interesting for in-line evaluation of industrial products. Finally, we present a set-up allowing the inspection of large and complex parts, by means of a robotic arm used to displace the part and orient the region of interest perpendicular to the optical axis of the camera.

We present a methodology to characterize the width of infinite vertical cracks using flying-spot thermography. We present the calculation of the evolution of the surface temperature distribution when a continuous wave laser spot scans at constant velocity the surface of a specimen containing an infinite vertical crack. The presence of the crack is revealed by a discontinuity on the surface temperature. By analyzing this temperature contrast between both sides of the crack, we determine the optimum experimental conditions to size width of the crack. We propose to fit the temperature profile perpendicular to the crack through the center of the laser spot to assess the thermal resistance associated to the crack. In order to check the validity of the method, we present experimental flying-spot data obtained on samples containing artificial and calibrated vertical cracks. The results confirm that, although detecting wide cracks is easy, it is not always possible to assess the width of wide cracks. The technique is better adapted to evaluate narrow cracks, which is the most challenging situation for other nondestructive evaluation techniques.

Carbon fiber reinforced plastic (CFRP) specimens, charged with defined loads in impact tests, have been examined with flash and inductive thermography from the front and the rear side. In the case of inductive thermography, eddy currents are induced in electrically conductive materials, usually in metals. But it can be also excellently used for inspection of CFRP, as eddy current can be induced in the carbon fibers. The fiber’s orientation regarding the magnetic field of the induction coil also has an influence on the detection results. The sequence of the temperature images, recorded during and after the short inductive heating pulse, is evaluated with a Fourier Transform, and the obtained phase image is used for localizing the impact damages. The flash thermography tests in transmission and reflection mode were evaluated using PPT and TSR methods. The results of the flash and inductive inspection techniques are compared for samples with different degrees of damage, in order to learn more about the capability of induction thermography for detecting impact damages.

Pulsed thermography is a commonly used infrared thermal technique for non-destructive evaluation of engineering materials and components. The quality of the obtained results, in terms of sizes and depths of the researched defects depends mostly on the data processing methods and the observed time intervals. This work is focused on the algorithms used for processing the thermal data after a pulsed test: Pulsed Phase Thermography (PPT), Principal Component Thermography (PCT), Thermographic Signal Reconstruction^® (TSR^®), Slope and R². The work focuses on an aluminium sample with shallow imposed defects and regards the post-processing analysis with different algorithms by considering different lengths of the cooling sequence (time interval or number of frames) and the investigation of the correlation between the signal contrast and the aspect ratio of defects. This correlation represents a first attempt for estimating the size and the depth of the defects, with a new empirical approach. Results show as the influence of the truncation window size changes according to the algorithm used for data analysis and the depth and the size of the detected defects. Moreover, each algorithm has its own peculiarities and capabilities and a synergic action in defects detection and characterization can be obtained if more algorithms are applied on the same thermal sequence.

Resistance Spot Welding is one of most used method to weld two sheet material thanks to its reliability and rapid production that makes it economical. The quality of the produced joints is related to the process parameters such as current, time, electrode pressure and surface condition and generally, destructive tensile tests are used to investigate the effect of each parameter on the quality of joints. However, these latter are time consuming and do not allow for a complete check (100%) of joints. In this work, a non-destructive thermographic technique and a new procedure was used to assess the quality of joints. In particular, different steel joints were obtained by varying two process parameters: current and cycle time. These joints were tested with the pulsed thermography technique adopting a transmission set-up. Thermographic data were acquired by means of a cooled infrared camera capable to acquire thermographic sequences at 400 Hz with a geometrical resolution equal to 0.062 mm/pixel. A flash lamp has been used to produce a thermal pulse of 3000 J with duration 5 ms. The thermal signal was investigated in the time domain with the aim to obtain different features related to the investigated process parameters. Proposed approach allows for detecting the typical defects that affect the joints such as stick and expulsion of material.

The Thermoelastic Stress Analysis (TSA) is a contactless technique able to determine the superficial stress of a component subjected to a dynamic load in a linear elastic field. In these conditions the thermoelastic effect shows the generation of small reversible temperature variations. In this work, a general equation was obtained for the evaluation of the thermoelastic signal. The proposed equation is valid under adiabatic and isentropic conditions, for generalized homogeneous and anisotropic materials in any load condition. By using the proposed generalized equation, TSA sensitivity to the variation of the physical and mechanical material characteristics and TSA sensitivity in the determination of residual stresses were studied. The case studies for performing numerical simulations were represented by AA6082 and Ti6Al4V non-ferrous metals. The results were then compared with the data obtained from experimental tests performed on AA 6082 samples.

As thermography has evolved to become a widely used method for Nondestructive Testing, strategies and tools for interpretation of results have evolved similarly. While early stage efforts relied on direct visual interpretation of IR camera output, modern practice increasingly relies on signal processing to extend the range and sensitivity, perform quantitative measurement and enable automation. The most widely used methods, Thermographic Signal Reconstruction (TSR), Pulse Phase (PP), Lock-In (LI) and Principal Component Analysis (PCA) have all been demonstrated to outperform unprocessed results. However, the methods are quite different in their underlying mathematical approaches and in how results are presented to, and must be interpreted by, the end-user. In the past few years, several papers have attempted to provide comparative analysis of some, or all of these techniques. However, each paper defines its own benchmark samples and performance metrics, and defines the equipment and experimental procedure to be used for all of the methods studied. It is not surprising that results vary widely, and may be confusing to one trying to select an approach to implement. In this paper, we will evaluate several recent studies and compare their specific objectives, evaluation criteria, procedure, results, an analysis and conclusions, and identify strengths and pitfalls specific to thermography that should be considered in future comparative studies.

By using relationships between wave propagation and thermal diffusive propagation, it was shown that that one can transform from diffusive propagation into an equivalent wave field. The transformation results in sharper reflections with time delay proportional to the distance. I have built a low cost system based on IR camera designed as a smartphone add on. I have tested the performance of the system on flat bottom holes both in polycarbonate and carbon composite samples using incandescent quartz halogen light bulb as excitations. The images are as good as or better than any of the common techniques in use. Application of delay and sum back projection was also demonstrated. The combined use of the equivalent wave field transform and delay and sum back projection improves both depth and lateral resolution above any existing methods. The technique is very efficient in term of computational load.

Infrared thermography (IRT) is a well-established and well-documented nondestructive evaluation (NDE) technique which has been proved as one of the critical assessment tools providing not only qualitative but also quantitative results useful for various applications. Even though many post processing methodologies have been used for thermal imaging analysis, there is still a need for a methodology that could possibly reduce the noise, improve the Signal to Noise Ratio (SNR) and focus on a specific area of interest reconstructing automatically the thermal image. This work deals with fine-tuning the IRT method in order to assess the detectability of damage in composite materials.