Non-destructive Examination Methods Research Articles

Momentum informed muon scattering tomography for monitoring spent nuclear fuels in dry storage cask

Development of an effective monitoring method for spent nuclear fuel (SNF) in a dry storage cask (DSC) is important to meet the increasing demand for dry storage investigations. The DSC investigation should provide information about the quantity of stored SNF, and quality assurance of materials should be possible without opening the cask. However, traditional nondestructive examination (NDE) methods such as x-rays are difficult to deploy for DSC investigation because a typical DSC is intentionally designed to shield against radiation. To address this challenge, cosmic ray muons (CRMs) are used as an alternative NDE radiation probe because they can easily penetrate an entire DSC system; however, a wide application of muons is often hindered due to the naturally low CRM flux (~104 muons/m2/min). This paper introduces a newly proposed imaging algorithm, momentum-informed muon scattering tomography (MMST), and presents how a limitation of the current muon scattering tomography technique has been addressed by measuring muon momentum. To demonstrate its functionality, a commercial DSC with 24 pressurized light water reactor fuel assemblies (FAs) and the MMST system were designed in GEANT4. Three noticeable improvements were observed for MMST system as a DSC investigation tool: (1) a signal stabilization, (2) an enhanced capability to differentiate various materials, and (3) statistically increased precision to identify and locate missing FAs. The results show that MMST improves the investigation accuracy from 79 to 98% when one FA is missing and 51% to 88% when one-half FA is missing. The advancement of the NDE technique using CRM for DSC verification is expected to resolve long-standing problems in increasing demand for DSC inspections and nuclear security.

Investigation on the modeling and simulation of hydrodynamics in asymmetric conduction laser micro-welding of austenitic stainless steel and its process optimization

Laser micro-welding is a joining technology utilized across various high-value industries, like medical, automotive, e-mobility, and aerospace. A trial-and-error process to identify welding parameters does not necessarily lead to optimized quality levels. Furthermore, offline non-destructive examination methods often launched to verify welding quality may inadvertently trigger excessive costs and time delays, ultimately failing to guarantee defect-free welds. In response to these challenges, this article introduces an advanced multiscale model designed to unravel the intricate dynamics of hydrodynamics and the overarching physics within laser micro-welding melting pools. Developed using the COMSOL software package, the model adeptly demonstrates how surface tension gradients shape the geometry of welds, thus influencing their quality. This knowledge allows the mapping of welding defects. One of the novelties of the article is to introduce geometric dissimilar welding conditions by simulating an asymmetric edge joint. It shows a study on a new, unstudied way to laser weld with many applications in the field. The model further establishes its utility in design experiments to determine parameter, tolerance, and system design. Moreover, the insights garnered from understanding and controlling these drivers have far-reaching implications for the advancement of subsequent methodological research and the development of in-situ quality control practices by characterizing the welding defects. Finally, the results shows that the discouragingly high computational costs restrict its potential application to support a Digital Twin.

Finite element modelling of ultrasonic backscattered waves for improving creep void detection

ABSTRACT Ultra-supercritical coal-fired power plants in Japan and globally experience creep damage in the welded parts of their high-chromium steel assets. As the creep damage advances, voids develop at depth by preference and become dense and cause accidents. The voids cannot be detected using existing non-destructive methods, causing the unreasonable and uneconomic management of plants. To establish a non-destructive examination method that can be used for practical and economic maintenance, a detection method for dense creep voids using ultrasonic backscattered waves is proposed herein. The creep-damaged structures are modelled using a transducer and the transmission and reception characteristics are discussed. These characteristics are considered using the finite element method, as they cannot be measured through normal experiments. The results show that without a focusing process at the time of reception, changes in the amplitude of backscattered waves cannot be confirmed; thus, the contribution of transmission focus to creep void detection is limited. Conversely, it is confirmed that when the received backscattered waves in the direction normal to the transducer are integrated and the phase matching is reflected, the amplitude of the scattered waves increases with creep void density. The reception focus considerably contributes towards dense creep void detection.

Non-Destructive Evaluation and Damage Determination of Fiber-Reinforced Composites by Digital Image Correlation

The trend in recent years shows that fiber-reinforced polymer composites (FRPCs) are steadily replacing traditional engineering materials in the aerospace, automotive, and sports equipment industries, where the safety and reliability of structures are of crucial importance. The increasing popularity of FRPCs is explained by their favorable mechanical properties. However, a serious problem of FRPCs is their catastrophic failure under overload and lack of ductile behavior. This issue makes it necessary to develop a non-destructive examination method that can estimate the structural integrity and predict the remaining properties of a composite structure even after its partial damage. In this paper, we propose a Digital Image Correlation (DIC)-based new method, which is able to meet all the requirements of Industry 4.0, thus this method can be automated, is fast, accurate, and excludes the human factor. To prove the efficiency of the proposed, Non-Destructive (NDT)-DIC method, we created specimens with known impact damage, and tested them firstly by infrared thermography to get a basic reference to compare the subsequent results. Then we performed the NDT-DIC tests, where through the practical example, we presented the steps and the logical deduction of the method. Firstly, the test load limit is determined, proven by AE testing to be in the non-destructive range for the examined composite system. In the case of a simple tensile test setup, the obtained result is the principal strain field from which we calculate our indicator, the X value. The X value can indicate the existence of damage by itself, furthermore, a correlation can be established that defines the X value’s relationship with the reduction of strength, based on preliminary experiments. The use of the correlation enables a higher level of health monitoring than the use of the DIC method without this information because the effect of a random impact damage is predictable for the given composite. In our case, the correlation is already strong with a 0.1% strain/elongation test load, but when the test load is increased to 0.15%, the coefficient of determination (R2) slightly increases from 0.979 to 0.997.

Information Value of the Results of Examining Metallic Products by the X-Ray Computer Tomography Method

The information value of X-ray computer tomography (X-CT) lies in the quality and accuracy of its results. Despite indisputable advantages of X-CT in comparison with other non-destructive examination methods, it has not received widespread use in the industry in view of its high cost and low throughput capacity. In addition, in Russia there is no regulatory and technical framework that would stipulate a standard procedure for selecting the tomographic examination parameters, nor are there standard techniques for estimating the quality of X-CT results. In view of this circumstance, the article analyses the US standard ASTM E 1695 Standard Test Method for Measurement of Computed Tomography (CT) System Performance. This standard stipulates a procedure for quantitatively assessing the quality of tomograms of a cylindrical test specimen, namely, spatial resolution and contrast sensitivity. The standard describes methods and a mathematical tool for calculating the modulation transfer function (MTF), contrast discrimination function (CDF), and constructing a contrast-detail diagram (CDD), which takes into account the influence of both unsharpness and noise on the possibility of detecting a flaw of certain size and morphology. The MTF values obtained under specific scanning and reconstruction conditions are a quality indicator of the X-CT results for objects examined under the same scanning conditions and made of materials similar in terms of attenuation coefficient, and can be used to assess the sensitivity of examination by the X-CT method. The article defines artifacts as any discrepancy between the object’s reconstructed volume and real attenuation factors. The reasons why artifacts appear are explained, their images on tomograms are shown, and recommendations for minimizing them are given. Factors affecting the information value of the X-ray tomographic examination results are pointed out.

Multi-Output Gaussian Processes for Inverse Uncertainty Quantification in Neutron Noise Analysis

In a fissile material, the inherent multiplicity of neutrons born through induced fissions leads to correlations in their detection statistics. The correlations between neutrons can be used to trace back some characteristics of the fissile material. This technique, known as neutron noise analysis, has applications in nuclear safeguards or waste identification. It provides a nondestructive examination method for an unknown fissile material. This is an example of an inverse problem where the cause is inferred from observations of the consequences. However, neutron correlation measurements are often noisy because of the stochastic nature of the underlying processes. This makes the resolution of the inverse problem more complex since the measurements are strongly dependent on the material characteristics. A minor change in the material properties can lead to very different outputs. Such an inverse problem is said to be ill posed. For an ill-posed inverse problem, the inverse uncertainty quantification is crucial. Indeed, seemingly low noise in the data can lead to strong uncertainties in the estimation of the material properties. Moreover, the analytical framework commonly used to describe neutron correlations relies on strong physical assumptions, and is thus inherently biased. This paper addresses dual goals. First, surrogate models are used to improve neutron correlation predictions and quantify the errors on those predictions. Then the inverse uncertainty quantification is performed to include the impact of measurement error alongside the residual model bias.

Quasi-static ultrasound elastography of ex-vivo porcine vocal folds during passive elongation and adduction

Objectives. The elastic properties of the vocal folds have great influence on the primary sound and thus on the entire subsequent phonation process. Muscle contractions in the larynx can alter the elastic properties of the vocal fold tissue. Quasi-static ultrasound elastography is a non-destructive examination method that can be applied to ex-vivo vocal folds. In this work, porcine vocal folds were passively elongated and adducted and the changes of the elastic properties due to that manipulations were measured. Methods. Manipulations were performed by applying force to sewn-in sutures. Elongation was achieved by a suture attached to the thyroid cartilage, which was pulled forward by defined weights. Adduction was effected by two sutures exerting torque on the arytenoid cartilage. A series of ten specimens was examined and evaluated using a quasi-static elastography algorithm. In addition, the surface stretch was measured optically using tattooed reference points. Results. This study showed that the expected stiffening of the tissue during the manipulations can be measured using quasi-static ultrasound elastography. The measured effect of elongation and adduction, both of which result in stretching of the tissue, is stiffening. However, the relative change of specific manipulations is not the same for the same load on different larynges, but is rather related to stretch caused and other uninvestigated factors. Conclusion. The passive elongation and adduction of vocal folds stiffen the tissue of the vocal folds and can be measured using ultrasound elastography.

Deep Learning-Enriched Stress Level Identification of Pretensioned Rods via Guided Wave Approaches

By introducing pre-compression/inverse moment through prestressing tendons or rods, prestressed concrete (PC) structures could overcome conventional concrete weakness in tension, and thus, these tendons or rods are widely accepted in a variety of large-scale, long-span structures. Unfortunately, prestressing tendons or rods embedded in concrete are vulnerable to degradation due to corrosion. These embedded members are mostly inaccessible for visual or direct destructive assessments, posing challenges in determining the prestressing level and any corrosion-induced damage. As such, ultrasonic guided waves, as one of the non-destructive examination methods, could provide a solution to monitor and assess the health state of embedded prestressing tendons or rods. The complexity of the guided wave propagation and scattering in nature, as well as high variances stemming from the structural uncertainty and noise interference PC structures may experience under complicated operational and harsh environmental conditions, often make traditional physics-based methods invalid. Alternatively, the emerging machine learning approaches have potential for processing the guided wave signals with better capability of decoding structural uncertainty and noise. Therefore, this study aimed to tackle stress level prediction and the rod embedded conditions of prestressed rods in PC structures through guided waves. A deep learning approach, convolutional neural network (CNN), was used to process the guided wave dataset. CNN-based prestress level prediction and embedding condition identification of rods were established by the ultrasonic guided wave technique. A total of fifteen scenarios were designed to address the effectiveness of the stress level prediction under different noise levels and grout materials. The results demonstrate that the deep learning approaches exhibited high accuracy for prestressing level prediction under structural uncertainty due to the varying surrounding grout materials. With different grout materials, accuracy could reach up to 100% under the noise level of 90 dB, and still maintain the acceptable range of 75% when the noise level was as high as 70 dB. Moreover, the t-distributed stochastic neighbor embedding technology was utilized to visualize the feature maps obtained by the CNN and illustrated the correlation among different categories. The results also revealed that the proposed CNN model exhibited robustness with high accuracy for processing the data even under high noise interference.

Comparison of Rail Head Checks Using Destructive and Non-Destructive Examination Methods

The development of railway transportation requires increased vehicle speeds and axle loads. The enhanced effects from the vehicle side and the new harder steel rails used in tracks lead to increased Rolling Contact Fatigue (RCF) crack initiation and propagation. One of the most frequently occurring RCF defects is the Head Checks (HC) around the rails’ gauge corner. These defects cause severe economic and safety issues. In-use maintenance is based on corrective and preventive approaches, which are neither cost-effective nor reliable. The development of new predictive methods and the improvement of the existing corrective and preventive approaches offer a solution to this issue. In this investigation, an HC-infected rail sample was examined with non-destructive Dye Penetration Testing, Eddy-current Testing, and Visual Microscopic Testing after the sectioning of the sample. In the future, an extensive HC database can be created from the results of the developed evaluation process, which may serve as the base validation tool for newly developed predictive maintenance methods.

Research on Nondestructive Examination of Jacket Section for CFETR TF Coil

The Chinese Fusion Engineering Testing Reactor (CFETR) is aiming to bridge the gap between the International Thermonuclear Experimental Reactor (ITER) and the first commercial fusion power plant, a necessary complement of the ITER. The requirement for sustaining long burn duration as specified in the duty time CFETR mission necessitates the use of superconducting magnets. Totally 16 toroidal field (TF)D-shaped coils which are of cable-in-conduit conductor type are designed. All the subcomponents have very demanding requirement to withstand the severe environments. This paper gives the nondestructive examination (NDE) method developed for the jacket of TF conductor which is made of 316L stainless steel. Based on the linear elastic fracture mechanics, maximum acceptable defect sizes in the TF jacket material have been defined. Phased array ultrasonic testing(PAUT)method and eddy current test (ECT) method were developed for the circular-in-square jacket inspection. For PAUT method, focus laws were calculated and optimized. For ECT method, specific ECT probe was designed and manufactured. Benchmark experiments were carried out to study the NDE reliability.

Adhesive Joint Integrity Monitoring Using the Full Spectral Response of Fiber Bragg Grating Sensors.

Although adhesive joining has many advantages over traditional joining techniques, their integrity is more difficult to examine and monitor. Serious structural failures might follow if adhesive joint degradation goes undetected. Available non-destructive examination (NDE) methods to detect defects are helpful in discovering defective joints during fabrication. For long-term monitoring of joint integrity, many of these NDE techniques are prohibitively expensive and time-consuming to carry out. Recently, fiber Bragg grating (FBG) sensors have been shown to be able to reflect strain in adhesive joints and offer an economical alternative for on-line monitoring. Most of the available works relied on the peak shifting phenomenon for sensing and studies on the use of full spectral responses for joint integrity monitoring are still lacking. Damage and disbonding inside an adhesive joint will give rise to non-uniform strain field that may chirp the FBG spectrum. It is reasoned that the full spectral responses may reveal the damage status inside the adhesive joints. In this work, FBGs are embedded in composite-to-composite single lap joints. Tensile and fatigue loading to joint failure have been applied, and the peak splitting and broadening of the full spectral responses from the embedded FBGs are shown to reflect the onset and development of damages. A parameter to quantify the change in the spectral responses has been proposed and independent assessment of the damage monitoring capability has been verified with post-damage fatigue tests.

Technical Evaluation of Construction and Operational Spillways Using a Set of Non-Destructive Examination Methods

Technical Evaluation of Construction and Operational Spillways Using a Set of Non-Destructive Examination Methods

Determining loss tangent values of dry granite for potential S‐band applications

AbstractExamination of the historical buildings and the modern buildings for varying applications and specific absorption rate (SAR) reduction for certain applications from security to health concerns find significant attention in both engineering and science. Applications related to an electromagnetic field and material interaction require the determination of the dielectric coefficients of materials. Both ground‐penetrating radar, which is one of the nondestructive examination methods used during the examination of the historical and modern buildings, and SAR techniques manipulating materials' properties for reduction of specific absorption rates use complex dielectric permittivity of materials. The proposed study as a novelty deals with complex dielectric permittivity in the S‐band region for nine different types of granite commonly used in the construction industry. The standard waveguide method is used as a measurement method. The mean εr for granite is measured as 4.49, and the mean tangent loss is measured as 0.45. Correspondingly, unlike the literature, a model that calculates the relative dielectric constant and dielectric loss value is obtained.

Developments of NDE method of jacket welds for ITER In-Vessel coil joints

The ITER facility currently incorporates two types of In Vessel Coils (IVC) as a method of stabilizing “Edge Localized Modes” (ELM) and providing “Vertical Stabilization” (VS). To withstand the severe conditions, the IVCs are made of stainless steel mineral insulated conductor (SSMIC). The jacket of the SSMIC is modified stainless steel 316LN. The diameter is 59mm and thickness is only 2.5mm. In order to join the IVC coils, it is necessary to develop the joints manufacturing. Jacket welding is an important process of the joints manufacturing. Based on the structural analysis, the maximum acceptable defect sizes inside the jacket weld were defined. This paper presents the non-destructive examination (NDE) development of the jacket weld NDE is the thin thickness which will cause the scattering of sound waves and lead the difficulty of effective identification of defects. Phased Array Ultrasonic Test (PAUT) and eddy current test (ECT) were developed for the jacket welds inspection. The results indicated the feasibility of the PAUT and ECT method could solve the problem of the thin thickness tube weld inspection.

Nondestructive Internal Defect Detection Using a CW–THz Imaging System in XLPE for Power Cable Insulation

The demand for internal nondestructive testing and inspection techniques is rapidly increasing. Using a continuous wave (CW) terahertz (THz) imaging system, we demonstrate that the internal defects in cross-linked polyethylene (XLPE) plates for power cable insulation can be detected. In a coherent detection scheme based on photomixers, which serve as the THz emitters and receivers, the change of phase occurring with the defects inside the XLPE plates is distinctly measured by the change in the amplitude of the transmitted THz waves. According to the two-dimensional images of THz waves transmitted through the XLPE plates, defects of up to 0.5 mm size located inside the XLPE plates can be detected by the internal nondestructive examination method based on CW–THz waves. This technique will be useful for internal nondestructive testing and inspection of insulation materials that require high resolution in various industries, including the automobiles, electronics, and electrical power industries.

Grain size characterization of aluminum based on ensemble empirical mode decomposition using a laser ultrasonic technique

In this study, an effective approach was presented for the decomposition and reconstitution of ultrasonic signals and the creation of a prediction model to characterize the average grain size of materials via a nondestructive on-line evaluation technique. Aluminum specimens with diverse grain sizes were handled by different thermal treatments and detected using a laser ultrasonic technique. The ultrasonic signals were decomposed into intrinsic mode functions that were characteristic of high to low frequencies by empirical mode decomposition and ensemble empirical mode decomposition methods, and the results were compared. The ensemble empirical mode decomposition method was adopted due to its ability to reduce mode mixing. After the correlational analyses between the intrinsic mode functions and the signal, the high-frequency noise and the linear trend terms were discarded, and the remainder of the useful constituents was chosen to rebuild the ultrasonic signal. Finally, a grain size characterization model was established by an energy attenuation coefficient. This novel approach is a rapid and precise method for grain size evaluation and laser-ultrasonic technology is a promising nondestructive examination method due to its advantage of noncontact and online evaluation.

Computing in Railway Engineering

The articles in this special section focus on computing applications in railway engineering, with particular emphasis on the dynamic service performance of railway systems, especially of the high-speed trains. All of the six selected papers are from the Southwest Jiaotong University, the leading Chinese research institute in railway engineering, especially from the State Key Laboratory of Traction Power at the university. Furthermore, with the rapid network expansion of Chinese high-speed railways, more publications on better maintenance strategies and nondestructive examination methods for higher safety and reliability in operation may also come in the future if possible.

Investigation of the properties correlation of physical and mechanical characteristics of ferromagnets based on magnetoelastic sensors of mechanical stresses

The determination of the stress condition is a topical issue. At present, various non-destructive examination methods, such as strain gauge, magnetic, ultrasonic methods, and others are used to analyze pipelines stress condition. Each of them has its advantages and disadvantages. There is often the need to use several experimental non-destructive methods simultaneously. In this regard, the magnetic inspection holds a unique position. In this case a significant role is played by primary transducers, which directly perceive the effect of mechanical stresses and turn it into the electrical signal for further processing of the input information. The change of magnetic characteristics is closely connected with the physical effect on the monitored object. The advantages include the high mobility of equipment, the ability to perform control without the direct contact of transducer with the object under study. At the same time, there are several disadvantages inherent particularly in the magnetic methods – magnetoelastic hysteresis, in which there is the divergence of induction values during loading and unloading. The greatest divergence occurs in the lead-off cycle and decreases during repeated cycles. The best way is to embrace the complete information available in the hysteresis loop. Another method is not only to take measurements at one point (even if this measurement is carried out in two mutually perpendicular directions), but to perform surface sounding of the object in a certain plane. Therefore, the most efficient method is to compare the magnetic relief of loaded (in the structure) and unloaded (in reserve) pipes of one manufacturer and from one lot. Thus, using the examination method of pipelines stress condition, based on the evaluation of metal magnetic properties of pipes, creates the complex solution to the problems of reliability improvement of pipeline systems.

Manufacturing and testing of ITER-like divertor plasma facing mock-ups for DEMO

One of the most critical parts of a high heat flux plasma facing component of a Tokamak divertor is the armour to heat sink joint. R&D activity has been launched in the frame of the EUROFUSION Power Plant Physics & Technology programme and in particular in the Divertor project area in order to investigate the possibility of using the International Thermonuclear Experimental Reactor (ITER) design and fabrication technology in an EU-DEMO tokamak.ENEA is being involved in the R&D ITER activities since several years developing suitable joining technologies for divertor plasma facing components fabrication. In fact, Hot Radial Pressing technique was used for the manufacturing of several small and medium scale prototypes that have been successfully tested by e-beam thermal fatigue testing.A new furnace was designed and installed at ENEA labs with the objective to extend the Hot Radial Pressing (HRP) manufacturing technology to EU-DEMO relevant divertor plasma facing components. This new furnace uses the pipe heat sink of these components as heater, speeding up the heating phase and allowing a better control of the pipe temperature. Considering that in EU-DEMO the thermo-hydraulic operative conditions of these components are different from ITER a FEA parametric optimization was performed and the geometry of the small mock-up to be manufactured was defined accordingly. The six manufactured mock-ups were examined by Ultrasonic and SATIR non-destructive examination methods in order to check the quality of the joining before their delivering to the high heat flux tests facility GLADIS for the thermal fatigue testing at high heat flux.

Non-Destructive Testing of Archaeological Findings by Grating-Based X-Ray Phase-Contrast and Dark-Field Imaging

The analysis of archaeological findings reveals the remaining secrets of human history. However, it is a challenging task to investigate and simultaneously preserve the unique remains. Available non-destructive examination methods are limited and often insufficient. Thus, we considered X-ray grating interferometry as a non-destructive and advanced X-ray imaging method to retrieve more information about archaeological findings. In addition to the conventional attenuation image, the differential phase and the dark-field image are obtained. We studied the potential of the scattering-sensitive dark-field and the phase-shift sensitive differential phase image to analyse archaeological findings. Hereby, the focus lies on organic remnants. Usually, the organic materials have vanished due to decomposition processes, but the structures are often preserved by mineralisation and penetration of corrosion products. We proved that the combination of the attenuation and the dark-field image in particular, enables a separation of structural properties for fabric remnants. Furthermore, we achieved promising results for the reconstruction of sub-pixel sized fibre orientations of woven fabric remnants by employing the directional dark-field imaging method. We conclude from our results that a further application of X-ray dark-field imaging on wet organic findings and on the distinction of different types of organic remnants at archaeological findings is promising.