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Air-coupled ultrasonic excitation is a relatively poorly studied method of nondestructive testing of polymer and composite materials. The combination of noncontact ultrasonic stimulation in conjunction with laser vibrometry can provide an assessment of the quality of the product without external influence on the tested material. This work is devoted to the study of an ultrasound diagnostic system based on the combined use of a noncontact magnetostrictive transducer and scanning laser Doppler vibrometry for nondestructive testing of polymer and composite materials. We believe that such combination can provide sufficient power for rapid detection of defects, while the optimization of the experimental conditions increased the efficiency of testing results. Measurement of the directional diagram of the magnetostrictive transducer has made it possible to determine the features of the radiation of the magnetostrictor in an assembly with a titanium step-type waveguide.

The technique of 3D scanning laser Doppler vibrometry has recently appeared as a promising tool of nondestructive evaluation of discontinuity-like defects in composite polymers. The use of the phenomenon of local defect resonance (LDR) allows intensifying vibrations in defect zones, which can reliably be detected by means of laser vibrometry. The resonance acoustic stimulation of structural defects in materials causes compression/tension deformations, which are essentially lower than the material tensile strength, thus proving a nondestructive character of the LDR technique. In this study, the propagation of elastic waves in composites and their interaction with structural inhomogeneities were analyzed by performing 3D scanning of vibrations in Fast Fourier Transform mode. At each scanning point, the in-plane (x, y) and out of plane (z) vibration components were analyzed. The acoustic stimulation was fulfilled by generating a frequency-modulated harmonic signal in the range from 50 Hz to 100 kHz. In the case of a reference plate with a flat bottom hole, the resonance frequencies for all (x, y, and z) components were identical. In the case of impact damage in a carbon fiber reinforced plastic sample, the predominant contribution into total vibrations was provided by compression/tension deformations (x, y vibration component) to compare with vibrations by the z coordinate. In general, inspection results were enhanced by analyzing total vibration patterns obtained by averaging results at some resonance frequencies.

Abstract The robotic equipment for and the technique of combined thermal nondestructive testing (NDT) of large-sized products by zones with subsequent data synthesis are described. The effectiveness of the combination of two methods, infrared and ultrasonic thermographic testing, is shown by the example of the developed complex-shaped reference sample with 18 simulators of production and operational defects. The developed algorithms for the synthesis of test results, including spatial “matching” of a set of thermograms and automated flaw detection and defect characterization with the use of neural networks have illustrated the effectiveness of the proposed approach for practical application.

The results of a study of thermal conductivity and specific heat capacity of Zr – 1 wt.% Nb and Ti – 45 wt.% Nb alloys in coarse-grained and ultrafine-grained states are presented. The influence of the utrafinegrained state on the thermophysical properties and the processes of energy dissipation and accumulation during deformation of the alloys are estimated. It is shown that the formation of an ultrafine-grained state in a Zr – 1 wt.% Nb alloy by abc-pressing and subsequent rolling leads to a decrease in its thermal conductivity and specific heat capacity by 10 and 20%, respectively, due to substructural strengthening under severe plastic deformation. It is found out that thermal conductivity and specific heat capacity of the ultrafine-grained Ti – 45 wt.% Nb alloy increase by 7.5 and 5%, respectively, due to dispersion hardening of the ω phase by nanoparticles and formation of a new α phase. It is established that the ultrafine-grained structure has a significant influence on the energy dissipation and accumulation during plastic deformation, which in turn depend on their thermophysical characteristics and on the structural and phase states.

This article is devoted to the analysis of the results of mathematical modeling, and experimental investigations of the structure of a turbulent flame arising from the combustion of diesel fuel. A estimation of the turbulence scale in a diffusion flame by using infrared thermography and the fast Fourier transform (FFT) approach by temperature spectra was carried out. Flow field was modeled by using Reynolds-averaged Navier–Stokes (RANS) equations. The turbulence characteristics have been determined by the Menter Shear Stress Transport (SST model). The heat balance, diffusion, and chemical reactions are described by the heat-transfer and mass-balance equations. The chemical reaction in the laminar flow is determined by the Arrhenius kinetics. For fully developed turbulence combustion was modeled on the basis of eddy dissipation model. In the intermediate regime when turbulence intensity is small takes into account the influence of turbulent pulsations on combustion rate. The comparison results of numerical modeling and experimental investigation show a good match between the parameters of flame turbulence structure. Results of investigation demonstrate that in the initial part of the flame near the fuel surface appear turbulent temperature pulsations, but the gas flow and combustion occur in a laminar mode with curved streamlines. Turbulent combustion in the basic area of the flame on the outer jet boundary occurs in the regime of micro-volume burning.

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.

The specialized software intended for active thermal nondestructive testing (NDT) is developed. The software is oriented toward both commercial and laboratory thermal NDT systems including heat sources and infrared imagers of various types. A modeling module is an essential part of this software allowing optimization of test procedures. Experimental data is treated by using a processing and defect characterization modules intended for enhancing signal-to-noise ratio and identifying lateral size, depth and thermal resistance of hidden defects.

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.

This paper describes research in the field of fiber optic nondestructive testing and structural health monitoring (SHM) of carbon fiber reinforced polymers (CFRP) by the use of integrated optical fiber sensors (OFS) based on fiber Bragg gratings (FBG). Basic mathematical expressions that represent optical SHM of composites are presented. Some new relationships are derived by considering the non-linear character of the FBG-sensor response and the combined effect of temperature and deformation. Both linear and non-linear coefficients of the sensor elements, as well as combined strain–temperature coefficients before and after the sensors are embedded into the composite panels, have been obtained. Experimental results on the strain state of CFRP under static and dynamic loads demonstrate the effectiveness of the proposed non-linear model for evaluating deformation in composites. It is shown that integrated OFS’s allow SHM of composite parts when mechanically loaded to failure, and that they can provide the actual level of strain in the composite parts in real time. SHM improves the operational safety of highly loaded and/or critical aerospace structures by providing real-time stress data, which would permit data-based decisions on overload conditions or imminent failure. Additionally, actual stress data from CFRP samples, or from real parts in use, could show whether the design of the parts should be changed to improve safety margins or to reduce weight.

Natural fibres present ozone-friendly solutions in the field of construction. The attenuation of the sound and heat losses is an important feature in such type of materials above all, when used in non-woven fabrics and fibre-reinforced composites. Hemp fibres show robust insulation performance, this research work should be considered beneficial to the development of a non-destructive thermographic methodology, which can address the thermal barrier (typically applied on multi-layer panel) effects. The intent is to assess the integrity of the sub-surface reinforcing glass fibres, such integrity state will help confer the rigidity and the resistance to mechanical stresses. The testing proposed in this study can be further developed in a laboratory right after the manufacturing process of similar type of components. The testing needs preliminary numerical simulations to help guide the selection of the appropriate pre- and post-processing algorithms combined with or without segmentation operators. A set of numerical and experimental tests were performed through controlled thermal stimulation while recording the thermal responses. The study also highlights the advantages, disadvantages, and future development of the presented technique and methodologies.

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 results of studying the thermal conductivity and specific heat capacity of Zr-1 wt.% Nb and Ti-45 wt.% Nb in coarse-grained and ultrafine-grained states are presented. The influence of the utrafine-grained state on the thermo physical properties and the processes of dissipation and accumulation energy during deformation of the alloys are estimated. It is shown that formation of the ultrafine-grained state in the Zr-1 wt.% Nb alloy by abc -pressing and subsequent rolling leads to a decrease in its thermal conductivity and specific heat capacity by 10 and 20%, respectively, due to substructural hardening under severe plastic deformation. It is found that thermal conductivity and specific heat capacity of the ultrafine Ti-45 wt.% Nb alloy increase by 7.5 and 5%, respectively, due to dispersion hardening of the ω phase by nanoparticles and formation of a new α phase. It is established that the ultrafine-grained structure has a significant influence on the regularities of the dissipation and accumulation energy during plastic deformation, which in turn depend on their thermo-physical characteristics and on the structural and phase state.

The mechanical and thermo-mechanical damage mechanisms of a multi-layer woven polymeric fabric ballistic body armor are analyzed. A proposed two-stage model takes into account the wave interaction between an impacting element and an armor package at the initial stage of the collision. The model allows the prediction of initial fabric compaction and the estimation of velocities and displacements. These can then be used to predict the response of a layered flexible barrier and the contribution of stresses and frictional forces in causing permanent deformation.

The stage-like character of the stress-strain curves and microstructure in the fracture zone of coarse-grained and ultrafine-grained specimens of the VT1-0 and Zr–1Nb alloy specimens under quasistatic loading are investigated using the temperature curves obtained by the method of IR-imaging. New experimental data are obtained, which provide evidence on a considerable influence of the ultrafine-grained state on the evolution of plastic deformation and fracture in the VT1-0 and Zr–1Nb alloys.

Nondestructive quality control of small-thickness composites is an important scientific and technical problem due to significant damage inflicted on materials even with minor impact loads. The stability of a 1-mm–thick CFRP composite to impact damage with an energy of up to 10 J has been investigated. Special attention has been paid to the analysis of the “visible” area of defects formed as a result of successive striking with increasing and decreasing energy in the range from 1 to 5 J. The area of defect indications was estimated by analyzing the images of vibrations at the surface of the composite produced by its acoustic stimulation and laser vibroscanning.

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...

The evolution of temperature fields and the deformation behavior of samples of VT1-0 titanium and zirconium Zr–1 wt % Nb alloys in coarse-grained and ultrafine-grained states is investigated under quasistatic stretching using infrared thermography. It is shown that the nature of the evolution of the temperature field in the process of deformation and the dependence of the maximum temperature on the strain in the working area differ for VT1-0 titanium and Zr–1 wt % Nb and depend on their structural and phase states, mechanical characteristics, and thermal diffusivity. It has been established that upon transition to the ultrafine-grained state, thermal diffusivity decreases by 6.5 and 9.3% for VT1-0 titanium and Zr–1 wt % Nb alloy, respectively. Differences in the deformation behavior of samples of VT1-0 titanium and Zr–1 wt % Nb alloy in the coarse-grained and ultrafine-grained states are associated with substructural hardening of the matrix phases of α-Ti and α-Zr and solid-solution hardening caused by the dissolution of β-Nb particles as the alloys under study are transferred into the ultrafine-grained state by severe plastic deformation.

The high reliability of modern 3D printing technologies makes it possible to create structural elements for aerospace and rocket industry products. Currently, the team of authors are developing a system for designing and additive manufacturing of composite and polymer structures for high-tech applications. In this paper, we studied the body of a Tomsk-TPU-120 CubSat satellite, the first Russian spacecraft to contain additive manufactured elements. Device quality control was carried out using resonant ultrasonic stimulation in conjunction with the use of scanning Doppler laser vibrometry, as well as experimental modal analysis. The testing results made it possible to reveal a defect at the butt end surface of the satellite body by analyzing the amplitude-frequency characteristic of surface vibrations. Experimental vibration-scanning data were used to verify a mathematical model developed using the ANSYS software.

We describe possibilities offered by active thermal testing when detecting delaminations of heat-shielding coatings from a metal base using an optical thermal-stimulation source that implements heating in a scanning mode. Results of numerical simulation of thermal processes are given for various defective situations. The thermophysical characteristics of heat-shielding materials have been experimentally determined, and the limits of the thermal method have been estimated for heat-shielding thickness and defect size.

It is common on space vehicles to have thermal insulation adhesively bonded to a metal structure. A typical defect in such structures is an interlayer disbond, which may occur either between the insulation and the metal substructure or between the layers of multilayer thermal insulation. One-sided thermal nondestructive testing (TNDT) using surface optical heating, such as Xenon flash or quartz tube, may detect disbonds if the thermal insulation thickness does not exceed a few millimeters and disbonds are not very small. In thicker insulation, the effectiveness of the inspection can be improved by using electrical induction to heat the metal base. In both cases, thermal excitation can be areal heating, which is heat projected over an area by a stationary heat source, or scanned linear heating (SLH), which is a linear heater scanned across the test subject. In the latter, either the linear heater is moved across a stationary test subject, or the linear heater is stationary and the test subject is moved. The SLH method usually provides a higher inspection rate (inspected area unit time). In this research, both the theoretical and experimental features of both optical and induction heating have been investigated and compared in the application to non-metallic insulation adhesively bonded to a metal structure. The effectiveness of using neural networks (NN) for characterizing defects has also been studied to demonstrate that optimal NN training should involve 4–5 points selected in defect areas close to non-defect areas, and the NN input data should be prepared by applying the known technique of Thermographic Signal Reconstruction (TSR). Since SLH provides more uniform heating, it provides higher quality IR thermograms than those obtained from areal (flash) heating and this improves the detectability of defects in thermal insulation to a depth of 4–6 mm. Other advantages of SLH for TNDT testing are (1) an inspection rate that is twice as high as an area heating technique and (2) a better potential for fully automated (robotic) testing.

Studie se zabývá kvantitativním stanovením hloubky defektů pomocí flahs pulzní termografie. Nová metoda vyhodnocení navržená v této práci zohledňuje 3D difuzi tepla, konečnou velikost defektů a koeficient tepelné reflexe mezi materiálem a defekty. Metoda je založena na kombinaci známých analytických modelů a procedury nelineárního fittingu (NLF). Algoritmus je ověřen numericky a experimentálně na vzorcích z PLA plastu vyrobených pomocí 3D tisku. Přesnost metody a její efektivcita byla hodnocena porovnáním s referenční metodou založenou rekonstrukci termografického signálu. This study is focused on the quantitative estimation of defect depth by applying pulsed thermal nondestructive testing. The majority of known defect characterization techniques are based on 1D heat conduction solutions, thus being inappropriate for evaluating defects with low aspect ratios. A novel method for estimating defect depth is proposed by taking into account the phenomenon of 3D heat diffusion, finite lateral size of defects and the thermal reflection coefficient at the boundary between a host material and defects. The method is based on the combination of a known analytical model and a non-linear fitting (NLF) procedure. The algorithm was verified both numerically and experimentally on 3D-printed polylactic acid plastic samples. The accuracy of depth prediction using the proposed method was compared with the reference characterization technique based on thermographic signal reconstruction to demonstrate the efficiency of the proposed NLF method

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 paper considers the thermo-mechanical mechanism of interaction between the damage agents and armor protection made of polymer fabrics. A simplified mathematical model is proposed to describe the deceleration of a damage agent within an armor fabric due to the dissipation of energy expended on irreversible stretching deformations of fabric fibers, as well as fiber slipping friction and material heating. Woven fabric layers are replaced by solid layers characterized by averaged stiffness and viscosity. A discrete numerical model of a solid material is proposed to reduce a problem with a finite number of degrees of freedom; motion equations are obtained on the basis of the Lagrange equations of the second kind, and for their integration, a stable non-conservative difference scheme is used. The software implementation is based on a functional-object paradigm which allows the modeling of conjugated processes. The parameters of governing equations are identified by using the experimental data. Some illustrative examples of interaction between damage agents and armor barriers with different arrangement of fibers are presented. The proposed model can be used to predict the quality of armor protection with the changing number and location of fibers, as well as to test the armor protection by applying the technique of infrared thermography.

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.

The characteristics of microstructure, deformation and fracture of Zr – 1 wt% Nb and Ti – 45 wt% Nb bioinert alloys in the coarse- and ultrafine-grained states are investigated. It is shown that the ultrafine-grained structure formed in them ensures excellent mechanical properties of the alloys and affects the stages of the stress-strain curves and the behavior of the maximum temperature vs. deformation time plot. The formation of an α-phase in the Ti – 45 wt% Nb ultrafine-grained alloy suppresses the linear stage VI characterized by a constant strain hardening coefficient. In stage VII, the strain hardening coefficient rapidly becomes negative, which indicates the material softening prior to its failure.

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.

An approach is proposed to evaluate the depth and thickness of planar defects detected by thermal nondestructive testing (TNDT) methods. A 1D 3-layer thermal problem is solved by using the technique of thermal quadrupoles, and the solution of the corresponding inverse problem is presented in the polynomial form. The inverse solution involves a number of TNDT experimental parameters, in particular, differential temperature signals, dimensionless contrasts and their observation times. The accuracy of defect characterization is in the range of 2–15% in defect depth and from 10 to 40% in defect thickness. It is believed that the proposed defect characterization approach can be easily implemented in existing TNDT systems to provide approximate values of defect parameters.

The paper describes the mechanism of heat release during deformation and main features of passive infrared thermographic diagnostics of steel parts subjected to elastic, elastic–plastic and plastic deformation under quasi-static loading. A basic equation for evaluating temperature signals caused by quasi-static deformation is derived. It is stated that the evaluation of steel structures by passive thermal methods should be performed when the heat is generated by mechanical stresses appearing in structures subjected to mechanical loading. The analysis of the loading kinetics and temperature anomalies has shown that thermal nondestructive testing technique is a useful tool for determining stress state in steel structures during the initiation and evolution of fracture. It is shown that the quasi-static deformation of steel structures is accompanied by the formation of elastic clusters separated by shear bands, and the plastic deformation in shear bands causes heat release resulting in a temperature increase of 4–12.5 °C.

The flame structure and flow modes have been investigated in the process of diffusion combustion of a number of liquid fuels, such as ethanol, benzine, kerosene and diesel fuel, by using the technique of infrared (IR) thermography in the narrow spectral range (2.5–2.7 μm). IR thermography provides useful information on the thermal behavior of turbulent diffusion flames, which is the thermal representation of turbulent processes in the hydrodynamic structure of flames. By analyzing IR images and spectra of flame temperature fluctuations, seven characteristic zones with different flow modes have been identified in the flames. To estimate flame flow parameters, the turbulent Reynolds number has been used thus taking account the amplitude and frequency of the temperature fluctuations determined by processing IR images of flames. The Reynolds number strongly increases during the diffusion combustion of kerosene, in contrast to benzine, diesel fuel and ethanol. This can be explained by a more complex chemical composition of kerosene and a multi-stage character of chemical reactions.

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.

In this chapter, elements of statistical data treatment and decision making in TNDT are presented. Noise sources in TNDT are described, along with establishing defect detection limits based on an analysis of surface clutter in TNDT procedures.

This chapter presents the basics of classical heat conduction in solids. A mathematical formulation of typical TNDT problems is given, and direct and inverse inspection problems are discussed. Tables of solutions of heat conduction equations for various types of heating and for both a semi-infinite body and a plate are provided. Both amplitude and time (frequency or phase) TNDT parameters are introduced.

This chapter is an introduction to TNDT. It describes the terminology, general physics and common heating methods used in the TNDT inspection method.