Reliable Non-destructive Testing Research Articles

The Potential for Material Property Characterization Using Physics-Informed Neural Networks and Ultrasonic Wave Data

ABSTRACT There is a need for reliable nondestructive test methods that can collect data from structural members and analyze the results in a rapid and efficient manner. Large amounts of test data are needed to achieve such characterization, which provides additional challenges because of their heterogeneity and complexity. Advances in machine learning, in particular physics-informed neural networks (PINN), offer potential to address these problems. PINN is a particular form of artificial neural networks (ANN) and portends notable advantages over traditional measurand analysis or purely data-driven approaches. Here, we explore the potential of heterogeneous material property characterization using PINN and ultrasonic wave data. First, several types of 1-D ultrasonic wave data are numerically simulated for a spatially heterogeneous material, and then PINN is applied to predict wave velocity, defect location, and energy dissipation. Then, three different types of defects are simulated and all defects are detected using the corresponding 2-D ultrasonic wave data and PINN. The presented results demonstrate the promise of PINN to assist with heterogeneous material characterization methods.

Characterization of Microchannels Produced by Friction Stir Channeling: An Experimental Study

Friction Stir Channeling (FSC) is a recent and innovative solid state manufacturing technology that allows, in a single pass, the opening of continuous internal channels in monolithic components and can be used in the mold and heat exchanger industries. However, the development of reliable Non-Destructive Testing (NDT) for the characterization of the channels is a major challenge. The focus of this work is the non-destructive characterization of micro channels, and the main goal was to experimentally validate which NDT techniques can be used to identify the presence of microchannels, their regularity along the section, and also their location, size, and path. Five NDT techniques were studied: digital radiology; eddy currents; ultrasounds; thermography; and dye penetrants. These techniques were applied to specimens with linear and curvilinear channels. The specimens were produced using tool pins with 0.5 mm diameter which obtained channels with 0.4 mm width and depths of 0.53 mm. Digital radiology and ultrasounds were effective in detecting channels regardless of its dimensions. Eddy currents did not allow to confirm the exclusive presence of the channels due to microstructural changes caused by the FSC process. Thermography using cold fluid injection was not successful in the channel’s characterization due to the extremely low flow. The dye penetrants confirmed the presence of the channels of all dimensions due to the liquid having traveled along the entire path of the curvilinear channel without reaching the surface.

Application of Non-destructive Testing in Quality Control of Manufactured Aluminium Metal Matrix Composite Components for the Automotive Industry

The manufacturing of automotive components using aluminium metal matrix composites (Al-MMCs) is progressively gaining a relevant place in the automotive industry. Due to the increasing competition in the automobile sector, there is a great need to supply efficient, stable, and high-quality products. Generally, following automotive standards is voluntary, which means that businesses and other organizations are not legally obliged to apply them. Nevertheless, in certain cases standards may facilitate compliance with legal requirements, such as those contained in European directives and regulations. IATF 16949:2016 is the current version of the IATF 16949 Standard and outlines the requirements an organization must maintain in their quality system for IATF 16949 certification. This new application of manufacturing Al-MMCs requires additional procedures to guarantee the quality of the components manufactured. Because the manufacturing process may generate various defects, such as cracks, voids, lack of fusion, inclusions, porosities, and other metallurgical aspects, non-destructive testing (NDT) techniques should be used for guaranteeing the quality of the components manufactured. The development of reliable NDT methods for aluminium metal matrix composite parts is thus a major challenge. This aspect is related to how NDT procedures need to be optimised or developed to address the singular structures of the processes, such as complex geometry, anisotropic material properties, special internal structures, and the presence of nanoparticles. The main objective of this work is to summarize and present the relevant potential of different NDT techniques used in quality control of manufactured Al-MMC components in the automotive industry, to be explorer in the European FLAMINGo project (Fabrication of Lightweight Aluminium Metal Matrix Composites and Validation in Green Vehicles). This study is very significant because the NDT techniques present different probabilities of detection of the defects, principally of the microdefects.

Application of Terahertz Nondestructive Testing Technology in the Detection of Polyethylene Pipe Defects.

At present, polyethylene pipeline is widely used in urban gas projects, but a relatively mature and reliable nondestructive testing technology has not been formed. Therefore, it is urgent to develop a new nondestructive testing technology to meet the increasing demand for inspection of non-metallic pipes. The terahertz testing technology and related equipment have played an increasingly important role in the nondestructive testing of many nonmetallic structures, but they have not been applied to polyethylene (PE) pipes. In this work, terahertz time-domain spectroscopy was used to detect prefabricated defects inside the PE pipe specimens. The results show that the terahertz nondestructive testing technology can be used to detect common defects in nonblack PE pipes with a detection error of less than 10%. Higher-power terahertz devices can detect defects in black PE pipe, while lower-power terahertz devices cannot. Because the black PE pipe contains carbon and has a strong absorption of terahertz waves. The penetration of lower-power terahertz devices to the black PE pipe is not enough, resulting in a low resolution of the imaging. The results of this work may promote the progress of the nondestructive testing technology of nonmetallic pipelines.

A non-destructive test method for assessment of cement-sand mortar quality on blockwalls finishes: A short-cut method for achieving acceptance criteria

Monitoring quality of cement-sand mortars used for plastering/rendering masonry surfaces has not been given utmost attention thereby adversely encouraging damp rising and other defects in walls. An attempt is made in this paper to propose a methodology for monitoring the quality of mortars using non-destructive testing method. It enables categorization of the quality of mortar mixes for making decision on acceptance criteria for short-term and long-term strengths of the composite mixture. Firstly, a factorial experimental design using the Central Composite Design (CCD) was used, to design the mix and compressive strengths at 28-day was obtained within the design domain considered. Secondly, a hardness test using the Mohs’ hardness scale was used on both the laboratory specimens and field tests on plastered walls of some selected housing estates. The method clearly exhibited defect patterns on the blockwall finishes which are closely related to the quality of the mix which also varied based on heights above ground level. The Mohs’ hardness test has proven to be a reliable non-destructive test method which can be used to reveal quality and categorization of cement mortar mix used on blockwall finishes. Consequently, the upper bound mix with ratio 1:4 cement to sand mortar remains a reliable mixture proportion based on the scale of hardness and strength performance both in the short-term and long-term values measured. This method would enable a reward system measurement/assessment on contractors and consultants on various building projects.

Nondestructive Testing of 3D Printed Fiber-Reinforced Polymeric Composites: An Experimental Critical Comparison.

Polymer matrix composite (PMC) materials produced by additive manufacturing are a promising solution with several applications in industry. The presence of defects due to fabrication could undermine the performance of the component structure. PMC performance has been extensively studied using destructive tests, but reliable nondestructive testing (NDT) techniques are essential. In this study, PMC with unidirectional fibers were 3D printed with an adapted conventional fused filament fabrication printer. The matrix material was polylactic acid, and three different reinforcement fibers were used: Kevlar®, carbon, and glass fibers. The samples were 3D printed with artificial defects, to simulate delamination's 0.5 mm thick. Four NDT techniques were explored, benchmarking the inspection of PMC envisaging an automated noncontact imaging inspection for easier result interpretation. Active pulse thermography, air-coupled ultrasounds, continuous wave terahertz, and digital X-ray were the techniques chosen, and a critical comparison is presented, evaluating the performance of each technique in the detection of defects. NDT technique diversity, complementarity, and redundancy improve inspection reliability, as there is not a single inspection technique that can cover all material defects or characteristics.

Intelligent Hardness Prediction of Bearing Rings Using Pulsed Eddy Current Testing

Bearings are central components of rotating machinery. Original equipment manufacturers must utilize high-quality bearings for desirable performances and safety of the equipment. Hardness, which is directly linked to product performance and reliability, is, thus, an essential mechanical property of bearings. As a result, it is necessary to evaluate the hardness during the manufacturing process. However, because of the complicated transformation of microstructures during heat treatment, there is no an established noncontact, quick, and affordable method for measuring the hardness of bearings. This article describes a pulsed eddy current testing (PECT)-based novel method utilizing deep learning for reliable nondestructive testing of bearing rings. The continuous wavelet transform (CWT) was used to combine the time-frequency information in the PECT signals, and the deep learning models were trained to predict hardness. In addition, we compared and optimized the network’s performance in feature maps, the number of convolutional kernels, and the learning rate. The results indicate that the developed novel method has an average error of 1.37% and a maximum error of 1.89%, exhibiting good hardness prediction accuracy and stability.

An analytical–numerical formulation to modelling wave propagation in double-cased oil wells

A reliable non-destructive test to assess the integrity of double-cased wells is still an open task. In the present work, we introduce an analytical–numerical formulation for modelling the wave propagation in such structures. The formulation was developed with the aid of the invariant embedding technique and is numerically unconditionally stable even for high frequencies. Usually, the invariant embedding technique is employed in cases of solid stratified media. Here, due to the nature of the structure under investigation, we had to extend the technique to accommodate fluid layers as well. We illustrated the use and relevance of the developed formulation modelling the wave propagation in a typical double-cased pipe and identifying the frequencies and angles of incidence that most strongly interact with defects placed at the critical casing layer/cement sheath interface. Based on a robustness analysis, we further indicated what would presumably be the best inspecting field. In that sense, we hope our formulation can help in the optimum experiment design of strategies aimed at assessing the structural integrity of double-cased wells.

Pulsed eddy current testing for gap measurement of metal casing

A pulsed eddy current testing (PECT) method is proposed to measure the gap of non-ferromagnetic metal casing. Firstly, the detection sensitivity to the casing gap of the voltage signal induced respectively by time-harmonic excitation current and by pulsed excitation current are calculated theoretically and compared. Then the advantages of PECT method for gap measurement are discussed. Secondly, the difference curve of the time-domain induced voltage signal between two gaps near the nominal value is presented. And the value of the induced voltage signal corresponding to the peak time of the difference curve is extracted to serve as the signal characteristic. Furthermore, using a calibrated casing, the function relationship between the signal characteristic and the casing gap is derived by curve fitting. Finally, the casing gap can be determined rapidly through the induced voltage at the peak time. This paper provides a reliable non-destructive testing method for the casing gap measurement, and compared with the existing sinusoidal ECT method, the PECT method can significantly improve the signal-to-noise ratio and the detection sensitivity to the casing gap.

Ultrasonic inspection of curved structures with a hemispherical-omnidirectional ultrasonic probe via linear scan SAFT imaging

A reliable non-destructive testing technique that enables effective detection and quantification of defects within safety-critical curved structures is highly demanded both in manufacture and service. Conventional Ultrasonic Testing (UT) methods usually adopt planar ultrasonic probes and it is preferable to adjust the probe axis direction perpendicular to the curved surface, because both the transmitting and receiving sensitivities in the probe axis direction are the highest. This paper proposes a new UT method using a hemispherical-omnidirectional ultrasonic probe. This probe has an omnidirectional directivity pattern and can cover curved surfaces with normal incident ultrasounds at different scan positions without the necessity of adjusting the probe attitude and position to follow the curved surface profiles. A surface reconstruction algorithm is firstly proposed to estimate curved surface profiles, which is based on a fast-imaging algorithm for ultra-wideband radar called the Shape Estimation Algorithm based on the Boundary scattering transform and Extraction of Directly scattered waves (SEABED). This method only uses surface reflection echoes, and thus can inspect curved structures without knowing the surface profiles a prior. Further, the Synthetic Aperture Focusing Technique (SAFT) is implemented to generate a focused image of internal defects by performing delay-and-sum beamforming on defect echoes based on the reconstructed surface profile. The proposed UT method is eventually experimentally verified on a curved plexiglass specimen with 29.4 mm surface curvature radius containing three Ø 3.5 mm Side Drilled Holes (SDHs) at different depths. Results show that compared with the planar ultrasonic probe, the reconstructed surface profile via SEABED is much wider and accurate with a relative error ≤ 0.47%. All SDHs are not only clearly positioned with relative errors ≤ 7.43%, but also can be accurately quantified from the curvature radius of SDH indications in the SAFT images with relative errors ≤ 8.60%. This work proves that the UT method based on the hemispherical-omnidirectional ultrasonic probe can emerge as a promising technique to inspect curved structures with high efficiency and accuracy, which has great potential in practical applications.

Non-Destructive Multi-Method Assessment of Steel Fiber Orientation in Concrete

Integration of fiber reinforcement in high-performance cementitious materials has become widely applied in many fields of construction. One of the most investigated advantages of steel fiber reinforced concrete (SFRC) is the deceleration of crack growth and hence its improved sustainability. Additional benefits are associated with its structural properties, as fibers can significantly increase the ductility and the tensile strength of concrete. In some applications it is even possible to entirely replace the conventional reinforcement, leading to significant logistical and environmental benefits. Fiber reinforcement can, however, have critical disadvantages and even hinder the performance of concrete, since it can induce an anisotropic material behavior of the mixture if the fibers are not appropriately oriented. For a safe use of SFRC in the future, reliable non-destructive testing (NDT) methods need to be identified to assess the fibers’ orientation in hardened concrete. In this study, ultrasonic material testing, electrical impedance testing, and X-ray computed tomography have been investigated for this purpose using specially produced samples with biased or random fiber orientations. We demonstrate the capabilities of each of these NDT techniques for fiber orientation measurements and draw conclusions based on these results about the most promising areas for future research and development.

The photothermal wave field and high-resolution photothermal pulse compression thermography for ceramic/metal composite solids

Pulse compression thermography has been recently developed to increase the signal-to-noise ratio (SNR) and enhance depth resolvability. However, a distinctively high SNR and depth resolvability is usually required for the accurate characterization of the (thin) topcoat thickness and defects of multilayer ceramic/metal composite solids (CMCSs). To this end, based on the Green function approach, a photothermal wave model for three-layer CMCSs consisting of a semitransparent ceramic coating and two-layer opaque metal solids is first derived, where a spatially varied volumetric heat source and an interior interface heat source described as the Dirac delta function are considered. The dependence of the thermal wave behaviors on both the thickness and photothermal properties of the semitransparent coating is investigated using the model. Inspired by high-precision radar target detection, two nonlinear frequency modulation (NLFM) waveforms, whose instantaneous frequency curves are respectively convex and concave quadratic function, are explored. Results indicate the NLFM waveform with the instantaneous frequency curve of concave quadratic function outperforms conventional LFM and Barker waveforms in terms of the SNR and depth resolvability. Finally, we reveal that a proper window function can further significantly improve the pulse compression quality. Our investigation can provide direct guidance for the accurate and reliable non-destructive testing and evaluation of multilayer CMCSs.

К вопросу повышения безопасности эксплуатации промышленных конструкций по результатам неразрушающего контроля

The main methods of assessing critical defects of industrial structures are considered and analyzed, among which special attention is paid to the method based on the verification of non-destructive testing techniques in operating conditions of industrial structures close to real ones, as well as the method of assessing defects by risk criteria. It is shown that the main disadvantage of the known methods is the lack of a link between the types and characteristics of real defects and non-destructive testing methods that are optimal by one criterion or another for the control of industrial structures. A comprehensive experimental technique for determining the parameters of minimum defects in a real industrial structure made of polymer composite materials is proposed, which combines the advantages of using traditional methods and means of non-destructive testing with a probable approach, which together allow to identify the entire range of critical defects that directly affect the resource and operational safety of industrial structures. As the defects of the composite structure used to study the developed technique, spatial defects in the form of delamination between layers of reinforcing filler were considered, as the most critical from the point of view of the resource of the structure and the safety of its operation. Based on the results of experimental studies, it is established that for a specific structure it is advisable to determine the minimum values of defects geometric parameters. This, in turn, allowed to manufacture an appropriate standard sample with similar artificial defects, adjust the flaw detector to its parameters, and conduct non-destructive testing. It is experimentally confirmed that this approach allows to increase the reliability of non-destructive testing of industrial structures by identifying the entire spectrum of defects characteristic of the case under consideration, which directly affect the reliability, resource, and safety of their operation.

An ultrasonic signal reconstruction algorithm of multilayer composites in non-destructive testing

With the wide application of composite materials in various fields, efficient and reliable non-destructive testing technology has been developed in a general manner. Due to the technical constraints and environmental changes in the composite material preparation process, there are many defects, such as debonding and unequal thickness. Ultrasonic testing, being a non-destructive testing method, has been widely used in many areas because of its convenience and effectiveness. In this paper, a new self-interference cancellation algorithm based on the matching pursuit algorithm is proposed, which can eliminate the waveform generated by multiple reflections in the echoed signal. A two-dimensional finite element model with multiple defects of composite materials is established to simulate the actual process of damage detection. The calculated damage location is compared with the model's actual parameters, which shows that the algorithm can be applied to the defect location of multilayer composites. A multilayer structure ultrasonic experiment is established and the good performance of the algorithm has been verified.

Ultrasonic and acoustic pulse velocity methods for nondestructive detection of early decay in wood poles

Wood poles are widely used to support overhead distribution and transmission power lines in North America and the world. These poles are vulnerable to internal deterioration due to extreme weather conditions, requiring a large number of poles to be inspected every year. This paper presents a comparative study of four stress wave-based nondestructive testing (NDT) methods commonly used for condition assessment of wood poles. These include the traditional approaches of sounding, sonic pulse velocity, and ultrasonic pulse velocity tests; and a new approach that considers the orthotropic characteristics of wood, uncertainties in the elastic properties, ultrasonic wave velocity and attenuation. Two poles with an internal hole of 4% of the cross-section are evaluated and compared by each method. Ultrasonic measurements of wave velocity and attenuation considering orthotropic characteristics of wood and uncertainties in the elastic properties provide a reliable wave-based NDT method for the detection of early decay in wood poles.

A pulsed eddy current testing method for relative thickness of ferromagnetic components considering local hysteresis characteristics

A pulsed eddy current testing method is proposed for the assessment of the relative thickness of ferromagnetic components with uneven external insulation layer and remanence. By establishing a least squares problem of theoretical and measured value of induced voltage based on the time-domain analytical expression to pulsed eddy current testing model of a ferromagnetic plate, unknown parameters including the thickness, conductivity and relative permeability are determined by inversion algorithm. Then, the coupling relationship among parameters in the inverse problem is verified by experiments on a steel plate, and the detection method for relative thickness is proposed. Furthermore, the function relationship between the inversion results of the thickness and the relative permeability under different amplitudes of the pulsed current is obtained through the linear fitting. Finally, the suppression method is discussed for the influence of the variation of permeability. It is suggested that the reference value of the thickness should be dynamically corrected by this function, as to improve the accuracy and reliability. This paper provides a reliable non-destructive testing method for wall-thinning corrosion detection of coated ferromagnetic tubes or tanks in industry.

Numerical investigation on the fracture failure of a railway axle

Railway axles are designed to be highly reliable so as to ensure even more than 30 years of service. Even though they are periodically inspected by scheduled Non Destructive Testing (NDT) inspections to detect the potential initiation of cracks, failures with disastrous consequences for railway vehicles and human beings can occur.This paper reports an investigation concerning the failure of an axle of a passenger coach due to fatigue crack propagation. Calculations indicated that the need for reliable NDT inspection methods is of crucial importance for the upfront detection of potentially critical cracks. The presented investigation was useful to support the application of the crack propagation simulation for the determination of reliable axle NDT inspection intervals so as to prevent future accidents.

Evaluation of metallic bonded plates with nonlinear ultrasound and comparison with destructive testing

In the last decades, the use of structural adhesives has increased. Indeed, they are able to replace advantageously traditional assembly techniques such as riveting or bolting, and generally tend to reduce the global weight of the structure and/or improve the strength of the structure thanks to more homogeneous stress distribution. In addition, it allows the assembly of composite materials or materials having different nature, which is of great interest in the aeronautic industry. However, to be used for structural joining and critical application, reliable non-destructive testing techniques are compulsory for evident safety reasons, be it after fabrication or during the whole life of the structure. While linear ultrasounds have demonstrated their capability to detect easily decohesion or voids in a structure, their use for bond strength inspection is less straightforward. Another approach relies on the analysis of nonlinear signature of a bond defect inspected by high amplitude ultrasound. In the present paper, a Chaotic Cavity Transducer is used to inspect various metallic bonded plates (titanium or aluminum) with several bond defects. The defects were introduced by depositing localized surface pollution (introduction of PTFE spray, release agent, or fingerprints) before the adhesive is deposited on top of the surface. Combined with the pulse inversion technique, high amplitude plane waves were sent in the structure, leading to harmonic components observed in the defect region. Mechanical destructive tests were performed and display a good agreement with nondestructive tests.

Estimating the Concrete Compressive Strength by Using the Concrete Ultrasonic Pulse Velocity and Moduli of Elasticity

Developing a non-destructive method which delivers fast, accurate and non-invasive results regarding the concrete compressive strength, is an important issue, currently investigated by many researchers all over the world. Different methodologies, like using the simple non-destructive testing (NDT) or the fusion of different techniques approach, were taken into consideration in order to find the optimal, most suitable method. The purpose of this paper is to present a new approach in this direction. The methodology consists in predicting the concrete compressive strength through ultrasonic testing, for non-destructive determination of the dynamic and static moduli of elasticity. One important, basic assumption of the proposed methodology considers values provided by technical literature for concrete dynamic Poisson’s coefficient. The air-dry density was experimentally determined on concrete cores. The dynamic modulus of elasticity was also experimentally determined by using the ultrasonic pulse velocity (UPV) method on concrete cores. Further on, the static modulus of elasticity and the concrete compressive strength can be mathematically calculated, by using the previously mentioned parameters. The experimental procedures were performed on concrete specimens, namely concrete cores extracted from the raft foundation of a multistorey building; initially they were subjected to the specific NDT, namely ultrasonic testing, and the validation of the results and the proposed methodology derives from the destructive testing of the specimens. The destructive testing is generally recognized as the most trustable method. The precision of the proposed method, established with respect to the destructive testing, revealed a high level of confidence, exceeding 90% (as mean value). It was noticed that even the cores with compressive strength outside of mean range interval (minimum and maximum values) presented high rate of precision, not influencing the overall result. The high rate of accuracy makes this method a suitable research background for further investigations, in order to establish a reliable NDT methodology which could substitute the very invasive and less convenient, destructive method.

Virtual round robin – A new opportunity to study NDT reliability

Round robin exercises have traditionally been difficult to arrange in the field of non-destructive testing (NDT). To create a representative round robin exercise, representative mock-ups with representative flaws are needed. The mock-ups are costly and transporting them around the world to facilitate testing by numerous laboratories is difficult. The few round robins that have been completed have often contributed significantly to our understanding on the capability of the used NDT methods and procedures.Recently, the increased use of automated inspections together with the development of virtual flaws (independently by Trueflaw and EPRI) has enabled a new type of round robin, where instead of moving samples around the world, the round robin is focused on the data analysis and only pre-acquired data files are distributed. This makes conducting a round robin much more cost-effective both in terms of arrangement and in terms of inspection effort from the participating companies. In addition, the virtual flaw technology allows unprecedented number and variety of flaws to be included. With high number of flaws included, the results present statistically meaningful sample and can be further analyzed to estimate the probability of detection (POD) with standard statistical tools. In connection with the international project “PIONIC”, such a virtual round robin was arranged for the first time.The exercise showed, that virtual flaws and virtual round robins can be used to extract important information about NDT reliability and performance. Also, some points of development were identified for further studies: the sizing and detection files should be better optimized for their respective uses and the data could be further obfuscated to avoid any possibility of inspectors learning to recognize repeating signal patterns.12 inspectors submitted results to the virtual round robin. The results showed a90/95 ranging from 1.2 to 7.0 mm – a significant variation in performance. The difference was mainly attributed to different inspection strategies. In addition, an unexplained tendency to miss big cracks was noted on some result sets. One of the data files did not contain any flaws. None of the inspectors correctly identified the file as flawless.