Active Thermal Nondestructive Testing Research Articles

Detecting and evaluating water ingress in horizontally oriented aviation honeycomb panels by using automated thermal nondestructive testing

Results of applying active thermal nondestructive testing for the detection of water ingress in horizontally oriented aviation honeycomb panels and quantitative evaluation of water content are presented. Unlike ultrasonic inspection, thermal testing allows detecting water and evaluating its quantity in the presence of air gaps between water and inspected honeycomb skin. The proposed algorithm based on using an artificial neural network has enabled estimating water content with errors under 15 % in the cases where water contacts with a honeycomb skin, as well as in presence of air gaps between skin and water.

Thermal testing of corundum ceramic plates

A review of the methods of production of corundum ceramics with specified characteristics is carried out and possible causes of hidden defects are indicated. Ceramic samples for research were obtained by the method of slip casting and their physical properties were determined. The possibility of diagnosing the integrity of corundum ceramic plates was investigated by the method of active thermal non-destructive testing. Various testing schemes and sources of thermal stimulation of the studied samples were applied. As a reference method, X-ray inspection was used, which confirmed the characteristics of the defect detected by the thermal method in the control sample.

Efficiency of using different types of infrared imagers in active thermal nondestructive testing of delaminations in non-metals

Six types of infrared imagers characterized by different technical performance (arrays from 160×120 to 640×512 and temperature sensitivity from 25 до 110 mK) and cost were used in active thermal nondestructive testing of delaminations with size from от 5×5 to 45×45 mm located at the depth of 3,1 mm in a reference sample made of polymethylmetacrilat. The efficiency of TNDT was evaluated by 9 thermographers to demonstrate that reasonable inspection results can be achieved by using IR imagers and modules of an economic cost segment.

The novel procedure of active thermal ndt: combining heating and forced cooling

A novel technique of active thermal nondestructive testing is proposed. It involves consecutive heating and forced cooling of the surface of test objects. The results of numerical modeling and experiments have demonstrated efficiency of this technique in case of test materials, which are characterized by a high level of emission/absorption noise. Optimization of such test procedure requires correctly choosing power and turn-on time of forced cooling to stimulate increase of temperature contrast over defects at particular times. An additional advantage of forced cooling is decrease of a thermal load on test materials that may be important in case of composites.

ОПРЕДЕЛЕНИЕ ПОПЕРЕЧНЫХ РАЗМЕРОВ ДЕФЕКТОВ РАССЛОЕНИЯ БИМЕТАЛЛИЧЕСКОЙ ПЛАСТИНЫ ПРИ АКТИВНОМ ТЕПЛОВОМ НЕРАЗРУШАЮЩЕМ КОНТРОЛЕ

Various methods of nondestructive testing, including active infrared thermography, are used to detect latent subsurface defects in the contact of layers in multilayer products. One of the main difficulties using this method consists in processing and interpreting the thermal image data. The peculiarity of investigated defects of bimetal plate layers continuity violation is that the depth of defect location is known and the main task is to determine its size. Some methods are used for this purpose including analysis of spatial temperature profiles. Aim. To analyse the use of various approaches to determining the transverse dimensions of a delamination between metals in simulating active thermal non-destructive testing of steel-aluminium plates. Materials and methods. Mathematical and computer simulating methods, numerical differentiation are used. The delamination size is determined by projections of half the height of the amplitude signal and the extremum of the derivative of the temperature signal function. Calculations and graphical constructions are performed using the mathematical package GNU Octave. Results. Numerical simulation is carried out for different values of heat flow power, heating and cooling time. The temperature signal distribution over the surface of a multilayer bimetallic plate has been plotted. The values of the defect radius according to the projections of the characteristic points are determined. Conclusion. The results of simulation allow us to conclude that using the projection of the extremum of the temperature signal derivative function allows us to accurately estimate the defect size, while in the case of the point projection cor¬responding to half of the signal amplitude height, the result is underestimated. The obtained results can be used for further experimental studies of processes of active thermal non-destructive testing of products made of multilayer bimetallic materials.

Machine learning based models for defect detection in composites inspected by Barker coded thermography: A qualitative analysis

Machine learning and artificial intelligence have evolved as enablers for automation in various industrial applications. Barker-coded thermography is an active thermal non-destructive testing technique for examining subsurface features in industrial components. This article introduces supervised and unsupervised machine learning models for automatic defect detection in composite specimens inspected by the barker-coded stimulus. This work provides supervised and unsupervised machine learning methods to detect defects in composite specimens examined with a barker automatically coded stimulus. The suggested technology is tested using a carbon fiber-reinforced polymer sample with synthetically reproduced flat bottom hole flaws. The one-class Support vector machine is chosen for the unsupervised class of operation, whereas the supervised technique modifies the traditional Support Vector Machine (SVM). The qualitative comparison suggests that the unsupervised approach presents a less than 1% marginal difference in defect detection from its supervised counterpart.

Моделирование нестационарной теплопередачи в многослойной биметаллической пластине

When using the method of active thermal non-destructive testing to detect latent defects in multilayer bimetallic products, the adequate choice of technological modes of testing is of great importance. One of the important parameters is the optimum observation time, at which a sufficient amplitude of the temperature signal over the defect is provided. This value depends on the controlled object geometry, its thermophysical characteristics, and also selected testing modes and procedures. Various experimental stu-dies are used to determine the optimum observation time. Preparing bimetallic plates samples for full-scale experiments is a technologically complex and expensive task. Therefore, a large amount of preparatory research is carried out in the form of a numerical experiment, during which, with certain assumptions, changing the thermal state of the control object is simulated. Aim. Determination of optimal parameters of the thermal NDT process for a three-layer steel-aluminum plate with a planar delamination defect between the metal layers. For different variants of mutual location of the temperature registration device and source of heat flux of different power it is necessary to determine the heating time at which the sufficient amplitude of temperature signal is observed. Materials and methods. The methods of mathematical and computer modeling were used. Solving the task by the finite element method with the Agros2D code is given. Results. The calculation data have been obtained, which are used as the basis for constructing the temperature signal distribution over the bimetallic plate surface above the defect under different heating modes, heat flux rate, relative position of the heat stimulation source and temperature registration device, as well as determining the temperature signal dependence over the defect on the heating time. Conclusion. On the basis of modeling the temperature dependences necessary for interpretation of the results of thermal NDT of multilayered bimetallic plates have been determined, as well as the relations between the parameters of the heating process, which contribute to obtaining a temperature signal of sufficient amplitude. The results can be used for further experimental studies of the active thermal NDT processes of multilayer bimetallic materials.

Исследование поверхностного окисления циркония активным тепловым методом

The possibility of testing the surface oxidation of zirconium has been investigated by the method of one-way active thermal non-destructive testing based on the analysis of radiation temperatures. The emissivity of the oxidized surface of zirconium samples obtained at different annealing temperatures was estimated at various stages and heating temperatures in the infrared wavelength range. It is shown that there is a principal possibility to remotely test the oxidation process of zirconium alloys used in the nuclear industry for the manufacture of fuel elements operating in the core of nuclear reactors.

Efficient pulse compression favourable thermal excitation scheme for non‐destructive testing using infrared thermography: a numerical study

Active thermal non-destructive testing (TNDT) has emerged as a swift, robust and cost-effective non-contact inspection method used to detect the surface and sub-surface defects present in a wide verity of solid materials. To further increase the efficacy of the process, various pulse-compression-based post-processing techniques are in use. However, the applicability of pulse compression-based thermographic methods has limited due to the presence of side lobes that degrades the energy concentration capabilities within the main lobe. In order to address this limitation, this work proposes a poly-phase code (P4-code). P4 codes are very efficient and robust in the reduction of distribution of energy in side lobes by concentrating on the main lobe. This Letter proposes a numerical study on the applicability of P4 codes-based pulse compression favourable thermal wave imaging approach for TNDT for testing and evaluation of steel specimen for identification of flat-bottom hole defects located at different depths. Further performance of the proposed method is compared with the widely used linear frequency modulated thermal wave imaging by considering the signal-to-noise ratio as a figure-of-merit.

Программное обеспечение для тепловых дефектоскопов

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.

Evaluating quality of marquetries by applying active IR thermography and advanced signal processing

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.

АКТИВНЫЙ МЕТОД ТЕПЛОВОГО КОНТРОЛЯ ТЕПЛОПРОВОДНОСТИ СТРОИТЕЛЬНЫХ МАТЕРИАЛОВ И ИЗДЕЛИЙ

Thermal control refers to non-destructive testing methods. There are passive and active thermal non-destructive testing. With passive thermal control, the test object is characterized by a temperature field formed during its operation. With active thermal control, an additional source of thermal stimulation of the controlled object is used. Thermal control is widely used in various sectors of construction, energy, engineering and transport. The paper proposes a variant of active thermal non-destructive control of thermal conductivity coefficient of building materials and products on the example of a fragment of a building structure made of silicate bricks. The controlled object is subjected to thermal stimulation by an external source of thermal energy until the fixed thermal regime. Thermography of the test object surfaces is performed. The average values of surfaces temperature or individual sections of controlled object are calculated. The heat equation determines a controlled parameter - the heat coefficient of the object under control. The thermal resistance (heat transfer resistance) of the controlled object is calculated with a known coefficient of thermal conductivity. The heat transfer coefficient is calculated with a known coefficient of thermal resistance (heat transfer resistance). The method is implemented in the laboratory. It can be used in field and operating conditions for accurate and rapid determination of the key thermal properties of building materials and products.

STATISTICAL ANALYSIS OF THERMAL NONDESTRUCTIVE TESTING DATA

The features of processing of active thermal nondestructive testing results are considered. Proved the necessity of search and introduction of new informative parameters in evaluation of thermograms in order to improve the reliability of control. Task of detecting and estimating the relationships between defect parameters and optimal testing time and the maximum value of temperature signal is set. Computer simulation of active thermal testing of two samples with artificial defects with known characteristics was performed. Also obtained the sequences of thermograms and formed the sets of initial data during simulation for correlation, regression and dispersion analysis of testing results. The method of dynamic thermal tomography was used to determine the levels of maximum differential temperature signal and optimal testing time. The estimates of correlation coefficient for various informational parameters of thermal control obtained. There is a high level of relations between the optimal control time and depth of defects. A high correlation also observed between the maximum value of temperature signal and depth of defects. The nature of relationships between various informative parameters of active thermal control established by the regression analysis. A one-factor dispersion analysis of the influence of defect parameters on optimal testing time and maximum value of the temperature signal was performed. High degree of mutual influence of all informative parameters is established. The conclusion made on the necessity of developing new modern methods for analysis the data of thermal testing. Revealed patterns in relationships between data show low efficiency of traditional statistical methods in tasks of active thermal testing. Alternatively, proposed to use the artificial intelligence technologies, in particular, neural networks.

Digitised Frequency Modulated Thermal Wave Imaging for Non-destructive Testing and Evaluation of Glass Fibre Reinforced Polymers

ABSTRACTThe active thermal non-destructive testing and evaluation techniques have gained wide acceptance in health monitoring of various solids materials such as metals, composites and semiconductors. The most popular active infrared thermographic methods for non-destructive testing and evaluation applications are pulse based thermography and lock-in thermography techniques. But the usage of these techniques is limited due to their inherent limitations. To overcome the limitations of the existing approaches, the present work demonstrates the effectiveness of digitized frequency modulated thermal wave imaging technique for detection of different shaped defects in a glass fibre reinforced polymer specimen. Further, the usage of post-processing scheme facilitates defect detection with high resolution and also preserves the shape of defects.

Determining the lateral size of subsurface defects during active thermal nondestructive testing

A practical implementation of a technique for determining the lateral size of subsurface defects by analyzing the spatial temperature derivative is described. The technique is illustrated by inspecting a graphite epoxy composite sample that contains an impact-damage defect.

Comparing thermal stimulation techniques in infrared thermographic inspection of corrosion in steel

Remote detection of corrosion in metals is a developing application area of active thermal nondestructive testing. In this study, emphasis is made on the optimization of heating techniques that is of a major interest in practical surveys. Some popular data processing techniques, such as Fourier transform, correlation and principal component analysis, are also quantitatively compared in application to corrosion detection in 1-2 mm thick steel by applying a criterion of signal-to-noise ratio. The best inspection results have been obtained by using powerful halogen lamps and air blowers. Material loss of about 25% with lateral dimensions greater than 10×10 mm can be reliably identified in practical tests. The use of Xenon flash tubes is inefficient because of significant steel thickness. LED panels have not provided expected results due to low absorption of LED quasi-monochromatic radiation.

Dynamic thermal tomography: Recent improvements and applications

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.

Thermal NDT: historical milestones, state-of-the-art and trends

The first practical attempts of sensing our world in the infrared spectrum were undertaken in the nineteenth century. One of the first implementations of the active thermal non-destructive testing (TNDT) was the inspection of Polaris rocket motor cases in 1965 but by the end of the 1970s applications of IR thermography inspired by successful developments of IR technology in military were still rather qualitative thus preventing the progressive competition of TNDT with other inspection techniques. A new level of TNDT was achieved after the wider use of elements of the heat conduction theory. Nowadays, IR thermographic diagnostics and TNDT represent mature high-technology fields which combine achievements in the understanding of heat conduction, material science, IR technology and computer data processing. The high interest to the IR/thermal inspection technique is related to its universal character, high testing productivity and in-service safety. The purpose of this review is to briefly review the basics of TNDT, which include elements of many disciplines of science and technology, such as heat conduction, IR engineering, optoelectronics, image processing and statistics.

Applications of non‐stationary thermal wave imaging methods for characterisation of fibre‐reinforced plastic materials

The active thermal nondestructive testing and evaluation method is a rapidly growing testing procedure for a quick and remote inspection procedure for fibre-reinforced plastics. Conventional modulated lock-in thermography significantly contributed to this field by allowing usage of low peak power controlled stimulations followed by phase based detail extraction procedures. But demand of repetitive experimentation required for depth scanning of the test object limits its applicability for realistic critical applications and demands multi-frequency low power stimulations for better resolution and sensitivity for sub-surface defect detection. Frequency modulated thermal wave imaging and coded excitation thermal wave imaging methods permitting multi-frequency stimulations cater for these needs and facilitate depth scanning of the test object in a single experimentation cycle. Recently introduced three-dimensional pulse compression is an alternative to phase based analysis for these stimulations by providing enhanced defect detection even in noisy environmental and experimental conditions. Defect detection capability and sizing by these non-stationary thermal wave imaging methods are highlighted using the pulse compression approach. The present experimental study has been carried out on a carbon fibre reinforced plastic specimen with flat bottom holes.

Processing of active thermal nondestructive testing results by the method of wavelet analysis

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.