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Using the method of ultrasonic infrared thermography, it has been shown that 3D printing technology prevents cracking of the edges of access holes in composites during their machining. It is expedient to evaluate the impact strength of composites by the relative change in the thermophysical characteristics in the zones of impact damage, based on the assumption that a higher impact energy leads to the more developed defects and, accordingly, to the greater relative changes in thermal inertia and thermal diffusivity. The impact resistances of Kevlar and carbon fiber composite specimens, as well as their hybrid, have been compared. The highest impact resistance was demonstrated by a hybrid sample of Kevlar and carbon fiber composite, in which the change in thermal inertia and thermal diffusivity after an impact with an energy of 15 J was 4 and 8%, respectively, compared with 10 and 9% for the CFRP and 15 and 11% for the Kevlar.

We propose a combined method for thermal nondestructive testing using optical and ultrasonic stimulation by means of combining individual thermograms obtained at the corresponding time points. The resulting sequences of infrared thermograms provide more efficient identification of defects of various types and can also be processed using well-known algorithms, for example, thermographic signal reconstruction, principal component analysis, etc. We obtained experimental results on a composite CFRP sample imitating aircraft ribs using a robotic manipulator.

Purpose Active infrared (IR) thermography, because of its high productivity and illustrativeness, is a promising technique in nondestructive testing (NDT). The purpose of this paper is to discuss a concept and practical implementation of a portable experimental unit intended for IR thermographic NDT of corrosion in metallic shells. Design/methodology/approach The basic theory relates to the analysis of heat conduction in a plate with rear-surface material loss subjected to pulse, thermal wave or arbitrary heating. Findings The amplitude of temperature anomalies over defects and their characteristic observation times depend on material loss, size and shape of corrosion defects. A flexible architecture of the inspection unit is proposed to include flash tubes, halogen lamps and laser-emitting diode (LED) panels as sources of stimulating thermal radiation. In particular, LED heaters might be perspective due to their narrow spectral band, which is beyond a spectral sensitivity of modern IR imagers. It has been found that the IR thermographic technique is convenient for detecting material loss of up to 15–20 per cent in uniformly painted steel shells with thickness up to 8 mm. The concept of signal-to-noise ratio has been applied to evaluate efficiency of data processing techniques, such as Fourier transform and principal component analysis. Originality/value The developed equipment and inspection guidelines can be used for detecting hidden corrosion in metallic objects, such as above-ground tanks, pipes, containers, etc.

Recent developments in electronics have demonstrated some advantages of using carbon fibres in manufacturing flexible PCBs thus requiring to elaborate some new approaches for checking PCB quality. Barely visible impact damage (BVID) represents a typical type of defects in carbon-based composites. In this study, the two inspection techniques, namely active infrared thermography and laser vibrometry, were comparatively used for detecting BVID in composite materials manufactured by three-dimensional printing from kevlar and carbon fibres. The comparative analysis of the composite resistance towards multifold impacting with the total energy of up to 15 J has demonstrated advantages of the hybrid configuration obtained by using the technology of additive manufacturing. The measurement of damping characteristics of the composites in the 50–100 kHz frequency range has also confirmed the ability of the hybrid composite to absorb more energy than classical single component materials.

The purpose of this study has been to develop a multivariate model for predicting body fat mass in women by using the technique of infrared (IR) thermography. Sixty-nine healthy women, aged from 16...

The algorithm makes it possible to simplify the procedure for processing results of the thermal testing aimed at both revealing latent defects and evaluating their transverse dimensions and shape. Applying this algorithm requires certain participation and experience of the thermography operator, as well as preliminary preparation of initial data by using techniques that increase the signal-to-noise ratio. The algorithm includes selection of defective zones on the thermogram of the test object, automated identification of points with extreme signals, and a pixel-by-pixel threshold analysis of the zones adjacent to these points, culminating in the construction of binary defect maps.

Three nondestructive testing techniques, namely, optically- and ultrasonically stimulated infrared thermography, ultrasonic laser vibrometry and laser ultrasonics, have been comparatively investiga...

Detecting delaminations in the stringer foot areas of “T -joints” made of carbon fiber reinforced polymer (CFRP) composite is a challenging task for standard nondestructive testing (NDT) techniques. In this study, several methods of thermal NDT (TNDT) have been used to inspect eight CFRP T-Joint specimens with polyolefin film implants which represent subsurface defects. Both one- and two-sided TNDT procedures were used. Thermal modeling was performed to predict the results of TNDT tests. The potential of laser vibrometry was also investigated, and UT (ultrasonic) phased array C-scan was used for verification of test results. Two-sided TNDT was able to detect simulated defects throughout the entire thickness of the test material. Thermal images of defect-free T-Joints clearly establish baseline thermal patterns of “good” stringers, and subsurface defects may create an identifiable distortion to the baseline patterns. The ability of one-sided TNDT to detect defects depends strongly on their depth and size. Ultrasonic (“sonic”) infrared thermography was not successful in detecting the implants, due to the formation of standing waves and complicated thermal patterns observed on the stringers. And laser vibrometry has proven to be ineffective in the detection of the implants. Phased array ultrasonic C-scan testing has also been successful in detecting polymeric implants located outside the ultrasonic “dead zone” but the best sensitivity of UT is achieved in immersion techniques, with water between the ultrasonic transducer and a part to be tested. In all cases, the use of advanced data processing techniques has been indispensable to provide reasonable test results.

The influence of the average size of the structure elements on the deformation and thermal behavior of the Zr-1 wt.% Nb (Zr1-Nb) alloy under quasi-static tension was investigated using the digital image correlation and infrared thermography methods. It is shown that with increasing average size of the structural elements in the range 0.2–2.0 µm the physico-mechanical properties, such as yield strength, microhardness, maximal true strain, and maximal temperature increment during deformation decrease, while longitudinal and transverse strain increase. According to the obtained results, correlations between the mentioned deformation characteristics and the average size of the structural element d–1/2 can be described by linear functions.

Pulsed thermography is a common technique for nondestructive testing (NDT) of materials. This study presents the apparent effusivity method for the quantitative evaluation of coating thickness in a one-sided thermal NDT procedure. The proposed algorithm is based on determining a threshold value of apparent effusivity, which can be found for particular coating-on-substrate structures. It has been found that the square root of the time at which the apparent effusivity curve reaches this threshold is proportional to the coating thickness. The efficiency of the proposed approach is demonstrated by analytical modeling and experimentation performed on thermally-sprayed coatings.

The use of drones is constantly increasing while prices of high-performance drones has fallen. Nowadays, drones can accommodate various complementary optical measuring instruments, such as thermal imagers and photographic imagers. Advanced data communication systems enable real-time wireless data transfer and data processing. .Drones have expanded capabilities for thermography and other optical measurements,. There is a need to develop interpretation keys and data processing techniques. Especially the use of drones is effective when scanning high-rise buildings, but the all the influencing factors must be known and taken into consideration. In this presentation,results and experiences of multi-story apartment houses and other buildings in Finland are presented, along with an evaluation of restrictions and conditions of UAV-based thermal scanning. Also some case studies from USA and the use of outdoor thermography in Russia have been discussed.

Ultrasonic infrared thermography is a rapid and informative method of nondestructive testing, used to inspect materials and products in aviation and rocket and space industries. High-power piezoelectric emitters stimulate various materials by ultrasound and help revealing hidden flaws by local temperature changes, which can amount to tens of degrees. The possibility of optimizing the procedure of ultrasonic infrared thermography by choosing the frequency of acoustic waves so as to match the frequencies of local resonances of defects of different sizes has been investigated.

The paper describes experimental results of determining scales of turbulent eddies in diffusion flames. The results are obtained by analyzing a set of 2D cross-sections cut from 3D semi-transparent flames. The comparison of data obtained by using the particle image velocimetry (PIV) method and infrared (IR) thermography is presented to demonstrate similarity between hydro- and thermodynamic parameters.

The quality control of composite materials remains an important topic of research in nondestructive testing (NDT) of modern materials, in particular, the ones intended for aerospace industry. Over the last decade, there has been a noticeable increase in interest to the ultrasonic stimulation of tested materials and analysis of dynamic temperature distributions. This method is commonly implemented with two techniques, viz. high-power stimulation at a fixed acoustic-signal frequency and low-power resonant ultrasonic stimulation. Results are provided on comparing the above ultrasonic NDT methods using the example of an impact damage in a graphite epoxy-filled composite. The comparison is made based on the criteria of temperature signals, revealed flawed zone, and productivity of testing.

Results of analyzing the infrared thermograms of flawed carbon-, glass-fiber reinforced composites steel, and aluminum samples obtained in active thermal-testing procedures are described. The reproducibility of the results of testing conducted by thermography operators using manual and automated image-processing procedures has been evaluated. The advantage of an automated thermogram-analysis algorithm that halves the spread in informative parameters over manual data processing has been demonstrated.

The history of thermal nondestructive testing and infrared thermography is briefly reviewed. The state-of-the art of thermal testing with a focus on its applications to testing of composite materials in aerospace industry is described.

Composite materials are widely used in aerospace engineering, shipbuilding, and automobile industry due to their high durability, relatively low mass, and corrosion resistance. Composites are vulnerable to impact damages that may occur during production and service (e.g., as a result of dropped tools, bird strikes and luggage hits in aviation, hail, and other similar factors). Often unnoticeable on the affected composite surface, low-energy damages (below 20–40 J) can, however, lead to the emergence of significant flaws (such as complex combinations of cracks, exfoliations, fiber ruptures, etc.) inside the material. Results of applying ultrasonic infrared thermography to the detection of impact damages with an energy of 5–30 J in a carbon-carbon composite are presented.

Heat generation in steel samples with discontinuity-like defects subjected to tensile loading is analyzed by using the technique of infrared thermography. It is shown that the heat is predominantly generated in shear bands where one observes a considerable rise in temperature. The sample mean temperature is conditioned by the sum of all heat sources (shear bands), as well as the thermal properties of the material and the magnitude of the heat exchange with the environment. It also depends on the mass of elastically deformed material adjacent to the shear bands.

Application of active infrared thermography to assessing the internal structure and functioning of hyperthermoconductive panels used in on-board electronics is described. Effective thermal- diffusivity maps of hyperthermoconductive panels, obtained using the pulsed Parker method, are presented. The peculiarities of heat transfer in hyperthermoconductive panels are illustrated using experimental modeling in which a local thermal-load source is placed on the surface of hyperthermoconductive panels.

The use of infrared thermography for quantitative evaluation of water ingress in aviation honeycomb cells is discussed. Numerical modelling has been performed by analysing a 3D panel model where water fully or partially occupies honeycomb cells. Calculation of several test cases has allowed better understanding of how the thickness of the water layer affects surface temperature anomalies and times of their appearance in active one-sided thermal tests. Experimental results have been obtained on both reference samples and real honeycomb panels.

Numerous mathematical techniques to enhance the signal-to-noise ratio in IR image sequences are discussed. It is shown that the most efficient method is to use temporal phenomena accompanied by the time evolution of pixel-based temperature functions. Standard image processing algorithms are summarized. Also, advanced processing techniques including pulse phase thermography, thermal wave lock-in technique, principal component analysis, polynomial fitting, correlation analysis, thermal tomography, neural networks and more exotic methods, are discussed. Some novel TNDT techniques, including vibrothermography, eddy current, and electromagnetic IR thermography are described. Particular attention is paid to the analysis of thermo-mechanical phenomena in solids.

Marquetry method is important in the culture of the Italian community as can be witnessed from the large quantity of artworks that have been realized in this way. The monitoring of the integrity of such pieces poses a great challenge given the need for a reliable and nondestructive technique able to detect surface and subsurface defects. In this work, two ancient marquetry samples containing natural defects were inspected thanks to active thermography by using time-tested, safe, and resilient advanced signal processing algorithms (i.e., principal component thermography, correlation contrast, pulsed phase Fourier transform amplitude and phase, cold image subtraction contrast, and polynomial fitting). The latter have been applied to provide a 2D map of the defects. Anyway, in the cultural heritage field, one of the main interests of restorers is the volume of the subsurface defects for structural analyses. The emphasis in this study is placed on the use of dynamic thermal tomography (DTT) as an advanced technique of active thermal nondestructive testing. The main concepts of DTT are illustrated in the manuscript, while a special technique for defect thermal characterization has been used during the second analysis to validate tomographic results. Finally, the position of the main defects retrieved by means of the established techniques applied during the first analysis has been confirmed by DTT.

Thanks to its good strength/mass ratio, a glass fibre reinforced plastic (GFRP) composite is a common material widely used in aviation, power production, automotive and other industries. In its turn, active infrared (IR) nondestructive testing (NDT) is a common inspection technique for detecting and characterizing structural defects in GFRP. Materials to be tested are typically subjected to optical heating which is supposed to occur on the material surface. However, GFRP composite is semi-transparent for optical radiation of both visual and IR spectral bands. Correspondingly, the inspection process represents a certain combination of both optical and thermal phenomena. Therefore, the known characterization algorithms based on pure heat diffusion cannot be applied to semi-transparent materials. In this study, the phenomenon of GFRP semi-transparency has been investigated numerically and experimentally in application to thermal NDT. Both Xenon flash tubes and a laser have been used for thermal stimulation of opaque and semi-transparent test objects. It has been shown that the penetration of optical heating radiation into composite reduces detectability of shallower defects, and the signal-to-noise ratio can be enhanced by applying the technique of thermographic signal reconstruction (TSR). In the inspection of the semi-transparent GFRP composite, the most efficient has been the laser heating followed by the TSR data processing. The perspectives of defect characterization of semi-transparent materials by using laser heating are discussed. A neural network has been used as a candidate tool for evaluating defect depth in composite materials, but its training should be performed in identical with testing conditions.

International audience; This study has illustrated the potentials of optical and THz infrared thermography in the identification of inserts of different nature in glass fiber reinforced polymer. The inspection efficiency has been comparatively evaluated by applying the Tanimoto criterion. The best test procedure has proven to be one-sided stationary thermal nondestructive testing (TNDT) implementing optical heating with Xenon lamps (Tanimoto criterion 87%). Close values of the Tanimoto criterion have been achieved by using the optical and THz line-scanning procedures. A more subjective evaluation of test procedures has been performed by comparing eight parameters of test performance. The line-scanning TNDT procedure implementing optical heating with halogen lamps seems to be optimal in practical applications.

This review paper describes in short the application areas of infrared thermography and thermal testing, such as civil and electrical/thermal engineering, petrochemistry, military, aerospace and others.

Potentials of a novel non-destructive testing technique called ultrasonic infrared thermography (UIT) have been widely recognized for the last decade. This technique is promising for many practical industrial applications being of interest for academic researchers who deal with thermomechanical problems. Significant improvements in the performance of infrared imager have also contributed to increasing popularity of this inspection technique. This paper presents an introduction to the use of UIT in NDT, combining a review of earlier and later research with some experimental illustrations.

Active infrared (IR) thermography is a non-contact, fast and wide-area nondestructive testing (NDT) technique that has been increasingly used in aerospace applications to detect both manufacturing and in-service environment-induced defects. The classical pulsed IR thermographic testing suffers from the problem of false indications due to surface clutter conditioned by uneven optical properties across a test sample surface. To some extent, this problem can be relaxed by using a technique called ‘normalization’. A simple normalization algorithm, conventionally called 1D, involves the division of all images in a sequence by a chosen single image, often captured immediately after a flash. The novel technique of 3D normalization is implemented in this study to overcome the problems arising due to non-uniform heating and lateral heat diffusion in the case of pulsed IR thermographic NDT. In this case, normalization is carried out by dividing an experimental IR image sequence by the synthetic sequence which is calculated by solving the corresponding 3D problem of heat conduction. As a result of 3D normalization, the artefacts appearing due to uneven heating and absorption can be subdued through data normalization (division). Furthermore, fully automatic defect detection becomes possible as defining a reference point for sound area is not required as opposed to thermal contrast methods. In this work, the effectiveness of proposed 3D normalization approach is demonstrated for different heating conditions applied to glass and carbon fiber reinforced composites.

This work presents a non-destructive analysis based on infrared thermography (IRT) and speckle inspection methods performed on a helicopter blade. In both cases, thermal stresses are needed in order to provoke the visualization of defects. The sample possess fabricated defects, and three techniques were selected, namely, long-pulse thermography, flash thermography, and digital speckle photography (DSP) to retrieve their positions. The first two techniques belong to the group of infrared imaging, that are inherent to the analysis of the infrared thermal patterns to detect internal anomalies in the material, whilst the last one corresponds to the optical imaging group that requires visible light to measure the material response under a thermal stimulus. The active approach, useful to produce a gradient in either, thermal and/or displacement field of the material, was used. In all cases, heat lamps were used to generate the required thermal stresses. Post-processing algorithms were applied to raw data in order to improve the defect detection. Results are finally compared to evaluate pros and cons of each method.

The efficiency of eight algorithms of defect depth characterization (pulse phase thermography – PPT, thermographic signal reconstruction by analyzing the first and second derivatives– TSR, early observation – EO, apparent thermal inertia – ATI, thermal quadrupoles - TQ, non-linear fitting - NLF and neural networks – NN) has been comparatively analyzed on both theoretical and experimental IR image sequences obtained in the inspection of CFRP composite. Synthetic noise-free image sequences have been calculated by means of the ThermoCalc-3D software, while experimental results have been obtained by applying a one-sided procedure of pulsed thermal NDT to the inspection of artificial defects in CFRP. A relative error in the evaluation of defect depth has been chosen as a figure of merit. It has been demonstrated that a simple and robust processing technique is the use of the Fourier transform resulting in phase-domain data (PPT). The technique of TSR ensures maximal values of signal-to-noise ratio and is less susceptible to uneven heating and lateral heat diffusion. The calculation of ATI has allowed the characterization of defects at depths up to 1.5 mm, but it is sensitive to uneven heating thus requiring to carefully choose a non-defect area. The EO method, as well as the technique of TQ, have revealed inferior results in defect depth identification because of a noisy character of raw signals. Non-linear fitting is a convenient processing technique allowing simultaneous characterization of some test parameters, such as material thermal properties, defect depth and thickness, etc., but this technique is time-consuming and can hardly be applied to full-format images. In the whole defect depth range, minimal characterization errors have been ensured by the use of the NN that is a promising tool for automated identification of hidden defects.

This study is devoted to the analysis of impact damage in composite samples by applying techniques of IR and Terahertz imaging. The samples made of high-density homogeneous particleboards of sugarcane bagasse and castor oil polyurethane resin were subjected to impacts with the energy from 5 to 30 J. The impact damage defects were evaluated by applying one- and two-sided thermal non-destructive testing. Both the apparent thermal effusivity and diffusivity were determined to analyse their relationship to impact energy. In the above-mentioned range of impact energies, the thermal effusivity varied from 5 to 18%, while the variations in thermal diffusivity were from 4 to 24%. The algorithm of dynamic thermal tomography was used to demonstrate that predominant subsurface cracking occurred at depths up to 1 mm. In addition, the defect areas were tested by applying the Terahertz technique, whose results qualitatively matched the IR thermographic ones to show that the damaged areas were larger than they appeared visually. However, both inspection techniques have revealed no significant dependence of analysed parameters on impact energy. This is believed to prove that non-uniform composite structure is the decisive factor in producing structural defects under impacting.

Carbon-carbon composites, or more precisely, carbon fibre reinforced carbon (C/C) are composed of carbon fibres in a carbon matrix. They are lightweight materials that can perform structurally at extreme temperatures and have superior thermal shock, toughness, ablation, and high-speed friction properties. C/C is widely use in aerospace and defence industries. However, like other composite, it is also sensitive to impact damage, therefore detecting damages in C/C is important for ensuring the structural integrity and safety. This paper presents an application of a novel non-destructive testing called Ultrasonic-stimulated Infrared Thermography (UIT) for a real-time impact damage detection in C/C. In this study, a short ultrasonic pulse (15 s) is applied to C/C plate which contained 6 artificial low energy impact damages. An infrared (IR) camera is used to observe and record the temperature change. From a sequence of thermogram, the defective area can be detected easily. The study demonstrates that UIT can successfully reveal the low energy impact damage in carbon composite structure or component.

This paper reports both theoretical predictions and experimental results of the use of infrared thermography for determining the scale of turbulent vortices in flames of burning liquid hydrocarbon fuels and flammable vegetation. The size of flames, as indicated by temperature instabilities observed in infrared thermograms, agrees fairly well with the size of turbulent vortices calculated by analyzing the spectra of flame temperature pulsations.

One-sided thermal non-destructive testing (TNDT) is of vital importance in aerospace composites to monitor structural degradation, as well as to detect subsurface defects. The objective of this study is to evaluate simultaneously the thermal diffusivity and to characterize the defects within carbon fiber reinforced polymer (CFRP) composites. In this paper, a novel one sided TNDT technique is presented which relies on creating an artificial inflection point by multiplying front-surface temperature evolution by n th power of time, where 0 n n . An analytical solution of the diffusivity calculation and defect characterization in the case of CFRP composite plate is discussed. The characterization of low velocity impact damage is also investigated with the help of theoretical and experimental results. Some key research points which need further exploration are also discussed.

The concept of “dynamic thermal tomography” (DTT) was suggested in the 1980s. At that time, there was a wave of interest in the tomographic analysis of materials by active thermal nondestructive testing (TNDT). Unlike particles and quanta of electromagnetic radiation, thermal energy propagates in solids by diffusion. Therefore, a purely geometrical approach, that is characteristic of computed X-ray tomography, is replaced in DTT with the analysis of the evolution of temperature versus time. DTT is based on the fact that, in one-sided TNDT, deeper material layers are characterized by longer time delays of the thermal response. The DTT algorithm is relatively stable when used in the inspection of certain materials. Thermal waves experience damping by amplitude and retardation in time. This limits the detection depth and produces certain artifacts that can be suppressed by thresholding maxigrams. DTT can also be considered as a specific way of data presentation that has proven to be useful in many practical cases, including surface and volumetric thermal stimulation of both metals and non-metals. Thermal tomograms appear similar to binary maps of defects, thus enabling more reliable defect detection in comparison to conventional IR thermograms. In this paper, a “reference-free” approach to DTT is proposed being based on some mathematical manipulations with a front-surface temperature response. Also, the possibility of using the DTT principles for processing the results of ultrasonic infrared thermography is demonstrated.

The results of applying three nondestructive testing techniques to the inspection of parts of a new Russian TVS-2DTS airplane made of carbon fiber reinforced plastic are presented. A basic technique implemented in workshop conditions implements optical stimulation of inspected parts. The usefulness of ultrasonic infrared thermography combined with laser vibrometry in the evaluation of parts with complicated geometry is illustrated. Samples with artificial and real defects have been tested in workshop conditions.

The problem of moisture accumulation in airplane honeycomb panels is so serious that perspective aviation constructions could become monolithic or filled in with special foam. However, the number of airplanes with plentiful honeycombs under exploitation will keep very high in the few next decades. Therefore, quantitative water detection remains an actual task in aviation. The qualitative aspect of this problem can be solved by using the remote and fast technique of infrared thermography. Hidden water can be detected for a certain period of time after landing, or some stimulation heat sources can be used to enhance water visibility in honeycomb panels. However, quantitative evaluation of moisture content is typically achieved by applying a point-by-point ultrasonic technique which allows measuring the height of the water bar in single cells thus compiling maps of water distribution. This technique is contact and can be enough informative when applied to the water which is in contact with the panel skin because of gravitation. The use of solely infrared thermography for evaluating accumulated water mass based on the analysis of temperature patterns is difficult. Recently we found that there is a certain promise in the thermographic determination of water content, but the question is how precise (or how approximate) can be such estimates. The paper contains modeling and experimental results obtained in this direction.

Some optical phenomena observed in the flames from the burning of flammable vegetation materials and ethyl alcohol are analyzed. Recommendations on the optimal spectral bands for temperature measurements of hot objects obscured by flames are given. Frequency spectra of temperature pulsations in flames are obtained, thus revealing a spatial structure in the flow of combustion products, as well as the degree of turbulence in a high temperature fluid medium.

Ultrasound-stimulated IR thermography, thanks to its large-area imaging capability, high test productivity and safety, is a powerful tool for the inspection of cracks in heavy aluminum structures. In thick aluminum parts, the most important defect detection parameters are the differential temperature signal and signal-to-noise ratio (SNR), which typically reach their maximums at shortly (under 1 s) after the beginning of the ultrasonic excitation. In the IR inspection of non-metals, the ultrasonic excitation may be relatively long, while in the case of highly-conductive aluminum, short-pulse (burst) stimulation (from 0.4 to 1 s) is sufficient The crack detectability can be improved by evaluating temperature images at the times when maximum SNR values occur. Further enhancement of test results can be achieved by applying some data processing algorithms which can be 1D, i.e. applied to temperature evolutions in time, or 2D, i.e. applied to spatial coordinates, or a single image.

The use of wide frequency band piezoelectric transducers in ultrasonic infrared thermography allows analyzing material structural defects under low power ultrasonic stimulation compared to single-frequency stimulation which is performed, for example, by means of powerful magnetostrictive stimulation. Defect resonance frequencies can be determined through the detailed analysis of material surface vibrations by using a technique of laser vibrometry in a wide range of frequencies. This paper describes the approach to analyze ultrasonic resonances in samples with hidden defects by using resonant piezoelectric transducers. The effectiveness of the method is assessed by discussing some key examples of impact damaged graphite/epoxy composite samples hybridized with flax fibers. Optical and powerful ultrasonic stimulation have been also used as alternative inspection techniques.

The usage of terahertz infrared thermography for assessing the humidity of wooden samples is described. Terahertz radiation transmitted through a sample is imaged by means of a tera-thermoconverter. The temperature field of the converter is analyzed with an infrared imager. The possibility of using the technique for testing the nonuniformity of drying of timber is illustrated.

This study is devoted to the comparison of strength characteristics in the process of deformation and damage of axially strained VT1-0 titanium in the ultrafine-grained (UFG) and coarse-grained (CG) states. The temperature distributions on the surface of titanium specimens were recorded by means of IR thermography. The VT1-0 titanium in UFG state formed by applying severe plastic deformation is characterized by twice the yield stress and strength limit but half the deformation limit compared to CG titanium. The fracture of CG titanium is accompanied by local powerful generation of heat, while, in UFG titanium, the damage nuclei are less intense and more evenly distributed over the fracture cross-section. The titanium in UFG state, being deformed, utilizes structural channels of energy absorption more efficiently than in the CG state by involving the whole deformed volume in the fracturing process.

"Classical" IR ultrasonic thermography is based on applying a relatively powerful ultrasonic stimulation to test objects. Attempting to expand an inspection area by further increasing ultrasonic power may lead to sample damage, particularly, at a stimulation point. The recently proposed low-power resonant ultrasonic vibrothermography method involves an individual approach to the inspection of materials being based on a detailed analysis of vibrations on the sample surface in a wide range of acoustic frequencies. The determination of defect resonance frequencies enables efficient transfer of acoustic wave energy into a defect area and further transformation of this energy into heat due to intensive plastic deformations and internal friction. This paper contains the results of applying low-power ultrasonic IR thermography to detecting impact damage in graphite epoxy composite by using techniques of laser vibrometry and IR thermography.

It has been shown that the estimates obtained for the heat losses in buildings and structures with the use of infrared thermography can be accompanied by 30.0–100.0% error levels, thus dictating the necessity of revising the specified requirements for indoor-to-outdoor temperature drops.

Active infrared thermography has been applied for the evaluation of the internal structure and operation quality of hyperconductive flat mini heat pipes used in satellite electronics. The distribution of effective transverse thermal diffusivity in heat pipes has been obtained by means of the Parker technique to exhibit areas with low content of fluid in the porous structure. The lateral components of thermal diffusivity were determined by placing a slit mask between a flash heater and a heat pipe. Peculiarities of heat pipe operation in a working regime have been experimentally studied by placing a local heat source on the pipe surface and following the surface temperature dynamics.

The theoretical and experimental results of a thermal testing technique for corrosion detection in 2-mm-thick duralumin and 10-mm-thick steel are given.

We have used infrared thermography to study water trapped in aviation honeycomb panels, namely: 1) possibility of quantitative evaluation of trapped water, 2) influence of honeycomb panel orientation on the efficiency of water detection, and 3) discrimination between honeycomb cells filled with water and adhesive. It is shown, both theoretically and experimentally, that it is difficult for TNDT to discriminate between the presence of water and epoxy trapped in honeycomb cells, by analyzing only the surface temperature patterns. It has been demonstrated that water trapped in honeycomb cells can be reliably detected by an increase in effusivity starting from the inflection time. This process is referred to as the “concept of apparent effusivity”.

The proposed algorithm is based on the analysis of an artificial front-surface pixel-based function which includes temperature and time. This function experiences certain extremums, and the corresponding times can be used for determining thermal diffusivity by the formula similar to the known Parker expression. In thermal NDT, such approach being applied to defect areas, provides diffusivity variations which can be used for the evaluation of defect severity in a particular specimen. In this study, both the theoretical basis and the some experimental implementations of the proposed data processing algorithm have been explored to illustrate its validity in thermal properties measurement and thermal NDT, including thermal tomography.

Several reviews and summary papers describing the history and the current status of pulsed thermal nondestructive testing (TNDT have been published recently. However, some of the theoretical possibilities cannot easily be implemented in practical applications. This paper contains useful tables and formulas that are illustrated with typical IR thermograms to provide a general overlook of pulsed TNDT.

A methodology, based on the solution of the inverse heat transfer problem, for the detection and evaluation of flaws in buildings is discussed. The temperature varying in space and time is recorded by a thermographic equipment and each point belonging to the inspected area is analysed quantitatively. Data are processed to give a map of defects of the wall, based on the most suitable local thermal parameter. The thermal-physical aspects of different defects are studied, along with the description of simplified models to interpret surface temperature data. The building envelope is examined mainly in transient thermal regime. Testing procedures using periodic or pulse heating of the surface are described. The theoretical analysis is used to predict temperature evolution and properly design the test. A detectability comparison among different procedures is performed. Experimental results are reported for insulation deficiencies and thermal bridges evaluation, air leakage detection and moisture content mapping.