Thermal Nondestructive Testing Research Articles

Stabilization system for solar loading thermography applied on cultural heritage objects exposed outdoors: the contribution of advanced algorithms and dual-branch U-Net

AbstractThis study investigates the use of solar loading thermography (SLT) for thermal non-destructive testing (TNDT) and image stabilization of cultural heritage objects, specifically focusing on a century-old ancient book. The irregular contours and deteriorated areas of the book posed significant challenges for feature extraction due to non-uniform temperature variations. To address these challenges, a convolutional neural network (CNN) based dual-branch network of U-Net was used to stabilize the dataset across three degrees of freedom with the ancient book. The stabilization process involved tracking feature lines across each frame of the time-domain datasets, correcting for frame misalignment caused by sample movement during prolonged data acquisition. The effectiveness of this stabilization technique was evaluated by comparing the results of principal component analysis (PCA), fast Fourier transform (FFT), and fast iterative filtering (FIF) algorithms before and after stabilization. Significant improvements were observed, particularly in the clarity and accuracy of defect detection, indicating that this technique provides a robust foundation for further analysis and processing of SLT datasets in cultural heritage preservation. This research demonstrates the potential of combining advanced image processing techniques with SLT to enhance the quality and reliability of NDT in preserving valuable historical artifacts.

Efficient algorithm for thermal nondestructive testing and evaluation by considering the heteroscedastic nature of noise sources in infrared thermography

Abstract Thermal Imaging is a promising Non Destructive Testing & Evaluation (NDT & E) approach to monitor the health
of composite materials. Among various post processing approaches adopted in thermal imaging for NDT & E, statistical
analysis schemes gained importance due to their reliability and data reduction capabilities. This paper provides an insight
to a factor analysis-based statistical approach to detect the hidden defects in the Glass Fiber Reinforced Polymer (GFRP)
sample. The proposed approach models the observed data covariance into combination of temporal signal covariance
and noise covariance matrices. The modeling of the diagonal covariance matrix (with different elements) is motivated by
the presence of heterogeneity in the experimental data obtained from GFRP sample. This novel method is based on the
coordinate descent technique, which estimates the covariance matrix of the noise variances iteratively by minimizing the
negative log likelihood function. The obtained results from the chosen GFRP samples compared with the widely used
statistical Principal Component Thermography (PCT) technique illustrate the improved performance in terms of defect
detection with the proposed technique.

Thermal testing of corundum ceramics: Classical techniques for optical heating

The types of defects and ways of their formation in the production of tiles from corundum ceramics are considered. The integrity of tiles containing artificial defects has been investigated by the method of active thermal non-destructive testing using optical heating. Single- and double-sided thermal control schemes are applied, as well as various methods of software processing of thermograms. It has been established that the best results in detecting internal defects in ceramic tiles with a thickness of 10 mm during thermal stimulation using halogen lamps are obtained by the method of unilateral thermal testing.

Golay coded thermal wave imaging for inclusions inspection in titanium alloy (Ti-6Al-4V): an analytical study

Detecting and characterizing inclusions in metallic materials is crucial in nondestructive testing (NDT) and imaging to ensure structural integrity and reliability. In the field of nondestructive material assessment, infrared thermographic imaging is a well-established technology. This approach analyzes the thermal profile collected over a test specimen to find surface and sub-surface abnormalities. Infrared thermography has demonstrated rising interest in coded thermal excitation techniques and the accompanying data processing technologies in recent years. However, using coded excitations in thermal NDT is still uncommon. This research investigates the viability of using complementary Golay-coded excitation in active thermography. This unique method displays its usefulness in improving the detection sensitivity and resolution by efficiently minimizing the side lobes of the compressed pulse. The current analytical study demonstrates the flaw detection capability of Golay-coded thermal wave imaging (GCTWI) for analyzing titanium alloy materials with anomalies such as inclusions. The research replicates thermal wave propagation and interaction with various inclusion geometries and sizes at the same depths. Furthermore, a comparison study is done between GCTWI analytical and simulation models to validate these models. The correlation coefficient is used as a figure of merit to assess GCTWI’s ability to identify and precisely localize these inclusions. The results show that GCTWI has better fault detectability and spatial resolution capabilities, making it a viable approach for inclusion inspection. Overall, this study advances NDT and imaging approaches by proving the capability of GCTWI for the reliable and efficient identification of inclusions in Titanium Alloy (Ti-6Al-4V). The study’s findings can help to develop more effective inspection procedures for assuring and maintaining the structural integrity of Ti-6Al-4V components in various sectors, including aerospace, automotive, and biomedical engineering.

Thermal nondestructive testing of cracks in turbine blades by using ultrasonic stimulation

The results of nondestructive testing (NDT) of a turbine blade made of a heat resistant alloy with a ceramic coating were obtained by using ultrasonic infrared (IR) thermography. The purpose of the study was to determine possibilities of this NDT technique in detecting cracks in the blade and the coating. Image processing was performed by using principal component analysis, which allows to underline defect indications in IR images. The obtained test results were in a good accordance with the results obtained by means of penetrants with a considerably shorter inspection time. Potentials of IR ultrasonic thermography in the detection of “kissing: cracks and cracks located in difficult to reach sites was demonstrated.

Heat flow density measurement during non-destructive testing

The object of the study is the development of a device capable of accurately and reliably measuring heat flux density in various environments. The development of a heat flux density meter designed for non-destructive analysis of thermal processes in various fields of application is presented. The developed device is intended for evaluating the thermal insulation condition of underground pipelines. The functionality of the heat flow device relies on comparing standard temperature values with experimental ones measured on the soil surface. To ensure accurate and reliable measurement of heat flux density, the basis is a thermoelectric battery converter, which uses the auxiliary wall method. The heat flow density measuring device is constructed in the shape of a restricted cylinder, with one base serving as the working surface, while the second base establishes thermal contact with the body at ambient temperature. Embedded heaters enable the generation of heat flow through the thermoelectric sensor in directions perpendicular to its base. For calibrating the heat flux device, experiments were conducted using a standard copper-constantan calibration table. Temperature increments were determined from thermo electromotive force, and tests were performed on an existing heating network. The conducted measurements validate the fundamental feasibility of employing the proposed device for implementing the non-destructive thermal testing method on underground heating mains. The results of the experiment can be used not only for research, but also for monitoring and regulating processes in various fields of science and technology. The developed heat flux meter promises a significant contribution to the development of modern methods for analyzing thermal processes. The dimensions of the thermoelectric battery converter are also determined and the coefficient (kq) should be in the range from 4.0 to 12.0 W/(m2⋅mV), and the electrical resistance should be in the range of 12–20 kOhm

Review of methods and devices for determining the resistance to heat transfer under natural conditions

The purpose of this study is to review modern methods of determining the resistance to heat transfer of building envelopes under natural conditions using experimental equipment. Methods for experimental determination of the resistance to heat transfer given in regulatory documents have been considered. Golunov S.V. and co-authors developed a method of determining the resistance to heat transfer based on thermal imaging examination with the placement of sensors on the surfaces of the building envelopes. Abramova E.V. together with other researchers created a method of thermal non-destructive testing using a thermal imaging system, temperature and heat flow sensors. The possibility of experimentally determining the reduced resistance to heat transfer of external building envelopes under summer operating conditions using the device developed by A.E. Rusanov’s with co-authors has been described. Wang Xin et al. proposed a device for determining the resistance to heat transfer of building envelopes with improved accuracy. As a result of the analytical review, it was concluded that the presented methods make it possible to measure the resistance to heat transfer of external building envelopes when modeling various stationary and non-stationary heat transfer processes.

A novel reference-free technique for processing one-sided thermal NDT results in the time domain

In this study, simple analytical and numerical solutions were used to introduce a novel technique of processing thermal nondestructive testing (TNDT) results using a one-sided test procedure to determine material apparent diffusivity and represent TNDT results in the time domain without identifying non-defect areas. The technique is based on establishing dimensionless levels in the temperature decay functions that describe the cooling profile of a test sample after pulsed heating. The times when such levels cross the front-surface response curves may serve as specific heat transit times and may reduce the temperature-related noise. The corresponding level images are not associated with any reference point and allow determining apparent diffusivity thus providing more contrast representation of defect indications than raw infrared images.

Parametric study of anomaly detection models for defect detection in infrared thermography

In the current NDT 4.0 revolution, machine learning and artificial intelligence have emerged as the major enablers for non-destructive testing and evaluation (NDT&E) of industrial components. However, recent developments in active thermal NDT (TNDT) support its use as a practical method for checking a range of industrial components. Additionally, recent post-processing research in TNDT has developed several machine learning models to replace human interaction and offer automatic defect detection. However, the smaller area of the flaws and their related few thermal profiles than the wide sound area, leading to imbalanced datasets, make it difficult to train a supervised deep neural. Recently added to TNDT are anomaly detection models and one-class classifiers, both of which are commonly applied machine learning models to real-world issues. The accuracy and other important metrics in autonomous defect detection are influenced by the hyper-parameters of these models, such as contamination factor, volume of training data, and initialization parameter of the relevant model. The current paper investigates how initialization parameters affect these models’ TNDT capabilities for automated flaw detection. Using quadratic frequency modulated thermal wave imaging (QFMTWI), a carbon fiber-reinforced polymer specimen with variously sized artificially produced back-holes at different depths is examined. A good hyper-parameter for automatic flaw identification is chosen after qualitatively comparing testing accuracy, precision, recall, F-score, and probability.

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.

DETECTION OF HAZARDOUS STATES AND FAULT CONTROL
 IN STRETCHED STEEL ELEMENTS BY THERMAL METHOD

The article discusses the areas of effective application, the features of heat generation and the main possibilities
 of the passive method of thermal non-destructive testing of steel elements and products. The basic requirements
 for passive thermal control equipment are formulated. The mechanism of heat generation in steel is described and
 the structure of the formula for changing its temperature during deformation is substantiated. It is shown that
 the diagnostics of steel elements in the passive mode should be carried out with the functioning of heat sources in them,
 arising as a result of force effects on structures. The features of determining the stress state in steel elements by
 the passive thermal method are considered.
 
 It is shown that the passive method of thermal non-destructive testing of steel structures, loaded with
 continuously increasing or decreasing forces in time, under the influence of which internal deformation heat sources
 and surface temperature fields function in potentially dangerous zones of elements, makes it possible to control the
 operability in elastic, elastic-plastic stages of steel operation, the origin and development of destruction. The power
 of thermal deformation sources, the places of their occurrence and the kinetics of development depend on the conditions
 of force loading, external temperature influences, material and structural shape of the elements.

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.

Thermal nondestructive testing: traditional approaches and novel trends (review)

In the last years, thermal testing has shown up as a quickly growing nondestructive evaluation technique. This is explained by wide implementation of composite materials in many industrial spheres, first of all, aviation and aerospace. Inspection of composites by means of traditional nondestructive testing (NDT) methods encounters some difficulties, which can successfully be overcome by using thermal NDT. Moreover, an overwhelming progress in development and commercialization of infrared imagers also took place in the last two decades. On the basis of earlier reviews in the field of thermal NDT, the author has attempted to summarize recent achievements in this field, including inspection methodologies and data processing, as well as development of thermal NDT equipment and applications of this technique. The review describes both national achievements and international approaches, which have been lately proposed in thermal NDT thus making this technique a very promising in NDT of some classes of materials and constructions.

Effect of internal defects on the thermal conductivity of fiber-reinforced polymer (FRP): A numerical study based on micro-CT based computational modeling

Use of fiber-reinforced polymer (FRP) composite in structural and aerospace fields is often restricted in a heated service condition. The thermal-induced degradation of FRP can be complicated by the internal defects with geometrical irregularities. This highlights the need for new characterization methods capable of revealing the thermal conduction process of FRP with different types of defects. To this end, the present study establishes a state-of-the-art methodology, namely micro computed tomography based finite element analysis (μCT-based FEA), for evaluating the influence of internal defects on the thermal conductivity of FRP. The modelling work through μCT gains an insight into the actual three-dimensional (3D) meso-scale structures for various species of defects (void, needle-like cavity, air pocket/unfilled bug hole, and delamination) in FRP. From the numerical ‘virtual’ experiments, the simulated through-thickness thermal conductivities range from 0.2196 to 0.2270 W/(m·K), which are comparable with the experimental data from literature. The investigation also discovers that the unfilled bug hole and delamination decrease the effective thermal conductivity of FRP, while these defects can cause sub-surface heat concentration. In contrast, the needle-like cavity has negligible effect on the through-thickness thermal conductivity. Increasing the water saturation degree of defects leads to an exponential increase in the thermal conductivity of FRP, especially when a large air cavity or delamination is incorporated into the composite. Based on transient analysis, the relationship among temperature, heat flux intensity and exposure time is numerically determined. The research findings can motivate the applications of μCT-based FEA in quality inspection/control of manufactured polymer composite products and even in improving the thermal non-destructive testing methods for defect detection of field composite structures.

Thermal Nondestructive Testing: Development of Conventional Directions and New Trends (A Review)

Thermal Nondestructive Testing: Development of Conventional Directions and New Trends (A Review)

INCREASING THE ACCURACY OF DEFECTOSCOPY BY THE METHOD OF ACTIVE THERMOGRAPHY OF PRODUCTS MADE OF NON-METALLIC HETEROGENEOUS MATERIALS AND USED IN ENGINEERING

Nowadays, non-metallic heterogeneous materials are widely used in mechanical engineering, which is primarily due to their unique properties, such as strength, light weight, corrosion resistance, and high vibration, sound, and heat insulation characteristics. At the same time, non-destructive control methods that would allow to obtain the most complete picture of the defective state of products made of such materials are of great importance. The main task of the work is the development of optimal algorithms for determining each defect of a product made of non-metallic heterogeneous material with the establishment of its exact location, including the depth of occurrence, as well as its geometric parameters. The method of thermal non-destructive testing is considered promising. Studies of the accuracy of determining the parameters of defects in non-metallic heterogeneous materials by the specified method have been carried out.

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.

Detection of hidden defects of thermal protection of buildings and determination of some thermal properties of structural building materials by Non-destructive Thermal Imaging method

Objective. The purpose of the work is the practical approbation of a nondestructive thermal imaging method to identify hidden (invisible) defects and qualitative analysis of the thermal protection of a complex of construction objects in the city of Vologda, as well as the study of some physical (thermophysical) indicators (coefficients of thermal conductivity, thermal resistance (thermal insulation) and heat transfer) of structural building material in the form of silicate brick.Method. The fundamental laws of the theory of heat transfer, thermal nondestructive testing, infrared and technical diagnostics, the current domestic regulatory and technical and regulatory documentation, field experiments on real objects and laboratory samples.Result. The results of the practical determination of hidden defects in the thermal shells of the complex of civil and industrial buildings functioning in the urban environment, thermophysical properties (coefficients of thermal conductivity, thermal resistance (thermal insulation), heat transfer) of modern building materials by methods of thermal non-destructive testing are presented. The locations of identified invisible defects of thermal protection of the surveyed construction objects are determined and recommendations for their elimination are proposed. The obtained values of thermophysical characteristics for the studied structural building material are consistent with the data of current regulatory documents.Conclusion. The features of the nondestructive method of infrared thermography in determining the hidden defects of the heatshielding shells of operated buildings of various functional purposes and the complex of thermophysical parameters of modern structural building materials are shown. The demand for thermal imaging during energy and technical surveys of construction objects, their individual structural elements, life support engineering systems, as well as studies on the refinement, quantification and prediction of various thermal properties of building materials and products has been experimentally confirmed.

Perspective on pulse compression favorable infrared imaging techniques for non-destructive testing and evaluation of solids

Abstract Inspection reliability of sub-surface defects is imperative for safer functionality of critical components/materials/structures used in a wide variety of applications in various industries. The need for reliable, fast, remote, safe inspection and evaluation methods for detection of hidden defects increases in parallel with the demand for more sustainable solutions which helps in inherent modifications in design and manufacturing specifications. During in-service operation, the hidden defects are typically originated from various loading conditions leading to catastrophic failure. This perspective explores the best possible reliable, fast, remote, safe, and easy to implement for field inspection and evaluation experimental method and the associated post-processing approach using InfraRed Imaging (IRI) for Thermal Non-Destructive Testing and Evaluation (TNDT&E) of Glass Fibre Reinforced Polymer (GFRP) materials having delamination defects. This perspective further explores the state-of-the-art infrared imaging modalities used in TNDT&E by highlighting their advantages and limitations in terms of the detection sensitivity and depth resolvability to detect the subsurface defects located at interior of material. Most of the proposed experimental and post-processing techniques presented in the literature for TNDT&E, explore the observed spatial thermal contrast over the defective region of sample to provide the depth resolvability from the reconstructed thermograms even though it is obtained from the temporal data processing on the captured image sequence. This perspective provides an insight on the state-of-the-art research in the field of thermal/infrared non-destructive testing and evaluation and associated post-processing approaches to visualize the hidden subsurface defects not only resolved by spatial thermal gradients but also simultaneously provide temporal thermal gradients to locate defective regions.