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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.

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.

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.

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.

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 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.

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.

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.

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.

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 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 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.

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.

Results of using powerful LED matrices to inspect metal articles for hidden corrosion by active thermal-wave method are described. The effect of the color of paint-and-lacquer coating on the efficiency of heating with LED and halogen emitters is analyzed. The possibility of using powerful LED panels as thermal stimulation sources in portable flaw detectors is described.

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.

The mechanical behavior of coarse- and ultrafine-grained (CG/UFG) Zr–1Nb alloy specimens under quasi-static tensile testing, the distribution of exx, eyy, exy strains and the evolution of temperature patterns have been studied using the techniques of digital image correlation and infrared thermography. The microstructure of the Zr–1Nb alloy in the initial CG and UFG states, as well as after deformation at the prefracture stage, has been investigated. A study of the accumulation and dissipation of energy in these materials under tensile load has demonstrated the influence of the alloy heat capacity on these processes. It has been found that, under tensile testing, the Zr–1Nb alloy in the UFG state is characterized by a stage with constant temperature, which takes place up to e t r u e ≈ 0.04 thus indicating that UFG materials, unlike CG ones, more efficiently use the structural energy absorption channel during deformation. The prefracture stage of the Zr–1Nb in the UFG state is characterized by the sharp temperature increase up to 60 °C. At this stage, the strain hardening coefficient becomes negative reaching values up to -6.5 GPa thus indicating local material softening before fracture. The formation of large local areas with disoriented mesh structure of dislocations is another feature of structural transformations in the Zr–1Nb alloy in the UFG state before fracture that also indicates a local material softening.

Dynamic thermal tomography is a technique that allows the display of “slices” of solids by analyzing the evolution of surface temperature as a function of time. This paper presents the principles of one-sided thermal tomography using reference points and also introduces a technique of thermal tomography that does not require the use of reference point. The diffusion nature of heat conduction in solids causes lateral diffusion, which modifies and complicates the heat flow that is needed to detect defects. In the case of anisotropic composite materials the heat will diffuse more readily in one direction than another. Lateral diffusion can make it difficult to detect (visualize) deep defects, especially those located under shallower ones. Artifacts can be reduced by thresholding timegrams but this may hide small defects. The effectiveness of thermal tomography in detecting impact damage (cracks/delaminations) in composites has been confirmed by numerous experiments.

This paper summarizes the basics of pulsed thermal nondestructive testing (TNDT) including theoretical solutions, data processing algorithms and practical implementation. Typical defects are discussed along with 1D analytical and multi-dimensional numerical solutions. Special emphasis is focused on defect characterization by the use of inverse solutions. A list of TNDT terms is provided. Applications of active TNDT, mainly in the aerospace industry, are discussed briefly, and some trends in the further development of this technique are described.

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.

Deformation of steel parts is accompanied by either heating or cooling of particular zones depending on deformation mechanism. The use of infrared thermographic equipment allows analyzing spatial/temporal temperature distributions on the surface of steel parts thus allowing the evaluation of heat release caused by deformation in bulk material. Determination of stressed state in critical parts by analyzing infrared thermograms can be most simply conducted for components subjected to uniaxial tension–compression. The paper describes some potentials and problems of nondestructive testing of steel parts and constructions based on the analysis of heat release caused by deformation. By analyzing this methodology, it is possible to better evaluate the life expectancy of critical parts in steel structures (components of offshore oil platforms, seismic-resistant buildings, frames of large mining trucks, etc.).

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.

Composite materials are being increasingly used in high-tech industries, such as aerospace, automotive manufacture and building inspection. Thermal nondestructive testing (TNDT) has become an accepted method for composite inspection. However, the majority of investigations have dealt with flat or slightly-curved composite components with a thickness of up to 5 mm. Particular studies have been devoted either to NDT modeling with an emphasis on some theoretical issues, or they have been based exclusively on experimental results. There has been some recent interest in the use of composite materials in the nuclear industry. Some critical parts, including centrifuge components, have been made of carbon fiber reinforced polymer (CFRP) composites. The working conditions in a centrifuge include radioactivity and high rotational speed, and the composites used in centrifuges must have very uniform thermal properties and must be free of defects. This paper describes a complex approach to the TNDT of cylindrical parts made of CFRP by starting from thermal properties measurement, theoretical modeling and preliminary experiments, and finishing with the technical requirements for the development of practical equipment capable of operating in both laboratory and industrial conditions. The objects tested were CFRP cylinders with a diameter of 150 mm and a wall thickness of 4–6 mm, and they contained some artificial defects of varying size and depth. Both one- and two-sided test procedures have been analyzed for spot, line and uniform heating. Ultrasonic excitation has also been used as an alternative stimulation technique. In a one-sided test, the depth detection limit has been about 4 mm. Similar results have been observed in the case of ultrasonic stimulation, but the practical implementation of ultrasonic IR thermography to the inspection of cylindrical parts requires further exploration. In a two-sided test, even fairly mild heating resulted in the reliable detection of all defects independent of their size and depth. In all test cases, the highest signal-to-noise ratio occurred after applying the technique of principal component analysis.

Thermal/infrared non-destructive testing (T/I NDT) is a particular application of IR thermography. T/I NDT is typically classified for passive and active, as well as for steady-state (stationary) and transient (non-stationary, or dynamic). Active T/I NDT can be classified by: (1) the type of thermal stimulation, (2) the arrangement of a sample and a thermal stimulation source, and (3) the size and shape of stimu l ated area. T/I NDT has proven to be a convenient technique for the detection of impact damage in composite materials due to the following: (1) graphite-based composites are similar to a blackbody by absorption/radiation properties in the infrared (IR) wavelength band, (2) their thermal conductivity is lower than that of metals but higher than of many non-metals thus ensuring reasonable temperature signals at convenient observation times, (3) impact damage leads to thin but laterally-extended air-filled defects which produce considerable thermal resistance to the in-depth heat flux, and (4) T/I NDT is a fast, remote and illustrative technique which, unlike ultrasonic inspection, does not require immersing a sample into water. This paper describes some approaches to thermal detection and characterization of impact damage in carbon fiber reinforced plastic (CFRP) of whose inspection is an important issue in several industrial areas, first of all, in aero space where subsurface defects might lead to catastrophic consequences. Realistic solutions of T/I NDT theoretical problems can be obtained by using 3D numerical models of heat conduction. Direct solutions allow better understanding of heat propagation in defect areas while inverse solutions ensure the evaluation of defect parameters, such as defect depth, size and thickness. Several characterization algorithms are available, with a one-sided T/I NDT procedure being better suited for the characterization of defect depth, while defect thickness is best evaluated in a two-sided procedure. In the case of CFRP composites, the defect characterization approaches are well developed, including the technique of dynamic thermal tomography, which enables a considerable reduction of surface clutter and allows the imaging of separate layers of a composite test sample.

Thermal/infrared non-destructive testing (T/I NDT) appeared in the 1970s as a mainly experimental technique. In its active implementation, T/I NDT is inherently related to some methods and technical means of thermal stimulation, such as optical, convective, eddy current, microwave and ultrasonic heating. Therefore, the mechanism of defect detection in T/I NDT is governed by heat conduction laws. The paper contains the analysis of analytical and numerical solutions to typical T/I NDT models where defective materials are subject to thermal stimulation. The comparison between 1D, 2D and 3D models is presented to illustrate the accuracy of particular solutions. Both ‘classical’ and advanced models are comparatively studied to illustrate the influence of material anisotropy and optical semi-transparency, as well as some other factors, on observed temperature signals.

In this study, high-power ultrasonics has been used for non-contact nondestructive testing of composites. Air-coupled magnetostrictive ultrasonic transducers provide reasonable amplitudes of horn oscillations even if this type of ultrasonic stimulation is close to the idle mode. Four types of ultrasonic horns have been designed and manufactured in order to choose an optimal horn configuration. For each horn, the dependence of vibration amplitude on ultrasonic unit power has been found to exhibit a good match between the theoretical and experimental results. The resonance frequencies and amplitudes of oscillatory velocity were experimentally evaluated by using the technique of scanning laser vibrometry and modeled by means of the Autodesk Inventor software. An air-coupled magnetostrictive transducer, in conjunction with an optimized horn, has been used in the evaluation of impact damage in a graphite epoxy composite and detection of water and excessive epoxy adhesive in an aviation honeycomb panel. It is expected that the technique of air-coupled ultrasonics may be useful for inspecting thin, fragile and hydrophilic materials.

A comparative study of the effectiveness of algorithms for processing infrared images, namely, Fourier and wavelet analysis, analysis of principal components, polynomial fitting, and other types, has been performed with active thermal testing of metals and nonmetals and using optical, convective, ultrasonic, and eddy-current stimulation.

An apparatus that works on the thermal-testing principle involving infrared thermal imagers of different types and optical and convective heating devices is described. The main purpose of the apparatus is to detect hidden corrosion in 1- to 2-mm-thick steel containers that are intended for temporary storage of radioactive wastes.

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.

Thermal nondestructive testing (TNDT) may be considered to be a more widely applicable method than many traditional techniques, such as X ray, ultrasonic, eddy current, liquid penetrant, etc. It can be applied to both metals and non-metals containing subsurface defects such as cracks, foreign inclusions, disbonds, delaminations, variations in thermal properties, etc. This is especially true for composite materials, and TNDT is very appropriate for screening purposes. TNDT test results may be analyzed by advanced image processing algorithms. This paper provides a concise review of composite NDT using TNDT in combination with other inspection techniques, providing an opportunity for data fusion.

Experimental results on the thermal nondestructive testing (NDT) of corrosion simulators in 6- and 10-mm-thick steel products are presented. The need for the processing of infrared thermal images via a Fourier transform and principal component analysis (PCA) is demonstrated. The ultimate capabilities of the thermal method are estimated at a level of 20% material loss.

It has been experimentally found that composite materials are characterized by partial transparency, particularly in the range of 0.2–0.14 μm, with the coefficient of the Bouguer absorption from 1000 to 2500 m−1. This yields deterioration of the conditions for revealing undersurface flaws using the active thermal method.

The results of the processing of experimental data on the inspection of a carbon-fiber composite with the use of two neural networks that provide both the qualitative detection of latent flaws and the elements of flaw metering are considered.

Wavelet transforms can be used for active thermal nondestructive testing for the identification of flaws that are located at different depths and produce Gaussian-like signals characterized by a time shift on a heated surface. The results of the application of scalar and complex wavelet analysis for increasing the signal/noise ratio in the active thermal inspection of flaws in composite materials and thermal-barrier coatings, as well as also for revealing the corrosion in metals, are described. Parent Morlet, Paul, and Mexican-hat wavelets were used.