Current Nondestructive Testing Research Articles

Resonant frequency tracking mode on eddy current pulsed thermography non-destructive testing

Eddy current pulsed thermography (ECPT) has been widely used in the field of non-destructive testing due to its safety, non-contact detection, high spatial resolution and intuitive results. Inductive excitation source is an important component of ECPT and provides high-frequency alternating current to drive the excitation coil. However, a resonant frequency distortion phenomenon exists in the excitation source during the detection process, which seriously affects the output power of the excitation source and the sample detection effect. This paper presents a fast resonant frequency tracking loop for full bridge series resonant inverter which is used to search the resonance frequency in real time through direct digital synthesizer (DDS) and all-digital phase-locked loop. Theoretical analysis and simulation are presented to explain the working principle of the loop. Then, an experimental prototype is manufactured which serves as an excitation source for the ECPT experimental system. Compared with traditional excitation sources, the prototype does not need a water-cooled device and the tracking speed can be adjusted by modifying the parameters of DDS. Finally, experiments have been conducted on both artificial slot of 45# steel and natural cracks of rail and stainless steel to investigate the influence of resonant frequency tracking speed on the crack detection. The results revealed that reducing the resonant frequency tracking time can efficiently improve defect detectability and the manufactured prototype showed more application potential. This article is part of the theme issue 'Advanced electromagnetic non-destructive evaluation and smart monitoring'.

Wireless power transfer-based eddy current non-destructive testing using a flexible printed coil array.

Eddy current testing (ECT) has been employed as a traditional non-destructive testing and evaluation (NDT&E) tool for many years. It has developed from single frequency to multiple frequencies, and eventually to pulsed and swept-frequency excitation. Recent progression of wireless power transfer (WPT) and flexible printed devices open opportunities to address challenges of defect detection and reconstruction under complex geometric situations. In this paper, a transmitter–receiver (Tx–Rx) flexible printed coil (FPC) array that uses the WPT approach featuring dual resonance responses for the first time has been proposed. The dual resonance responses can provide multiple parameters of samples, such as defect characteristics, lift-offs and material properties, while the flexible coil array allows area mapping of complex structures. To validate the proposed approach, experimental investigations of a single excitation coil with multiple receiving coils using the WPT principle were conducted on a curved pipe surface with a natural dent defect. The FPC array has one single excitation coil and 16 receiving (Rx) coils, which are used to measure the dent by using 21 C-scan points on the dedicated dent sample. The experimental data were then used for training and evaluation of dual resonance responses in terms of multiple feature extraction, selection and fusion for quantitative NDE. Four features, which include resonant magnitudes and principal components of the two resonant areas, were investigated for mapping and reconstructing the defective dent through correlation analysis for feature selection and feature fusion by deep learning. It shows that deep learning-based multiple feature fusion has outstanding performance for 3D defect reconstruction of WPT-based FPC-ECT.This article is part of the theme issue ‘Advanced electromagnetic non-destructive evaluation and smart monitoring’.

Smart crawfish: A concept of underwater multi-bolt looseness identification using entropy-enhanced active sensing and ensemble learning

With the rapid development of the oil industry, more and more subsea pipelines enter into service, and thus we are facing the challenge of safe operation and maintenance of these underwater infrastructures. For instance, as a common component to connect subsea pipelines, the flange is prone to losing sufficient integrity due to severe working conditions and harsh environments under the sea. However, most of the current structural health monitoring (SHM) and nondestructive testing (NDT) techniques are targeted at onshore structures, and we require a more practical method for multi-bolt looseness identification of subsea flanges. In this paper, attempting to solve the above difficulty, we propose the “Smart Crawfish”, which is a concept that employs a subsea robot equipped with a gripper and a pair of Lead Zirconate Titanate (PZT) transducers to implement the active sensing method. Particularly, the main computational contribution of this paper is that we develop two new entropy indexes, i.e., multiscale range entropy (MRangeEn) and multiscale bubble entropy (MbEn) to enhance the current active sensing method (i.e., the entropy-enhanced active sensing method). To detect underwater multi-bolt looseness, we first obtain stress wave signals under different categories (i.e., different cases of multi-bolt looseness) by the active sensing and then compute their MRangeEn and MbEn to construct the feature dataset. Subsequently, via the dataset, a stacking-based ensemble learning classifier is trained to classify different categories. Finally, we conduct a lab-level experiment to demonstrate the effectiveness of the proposed method, which outperforms the current entropy-enhanced active sensing. To the best of our knowledge, this paper is the first attempt to address the detection of underwater multi-bolt looseness, which has great potential for future industrial applications.

Application of Dirichlet-to-Neumann Map Boundary Condition for Low-Frequency Electromagnetic Problems

In this article, we present a differential formulation combined with an exact boundary condition based on a Dirichlet-to-Neumann (DtN) operator, and its applications to eddy current problems. A numerical model for the eddy current problem is derived using a reduced vector potential formulation combined with analytic expression of a DtN operator on an appropriate canonical boundary. The main advantage of this method is the improved accuracy and reduced computational cost compared to conventional approaches. The effectiveness of the proposed formulation is demonstrated in eddy current nondestructive testing applications for predicting the induced current density distribution. The numerical results for two model problems are presented: a conducting sphere in a uniform magnetic field and an eddy current probe inspection of a conducting plate with a volumetric defect.

Enhancement in Quality Estimation of Resistance Spot Welding Using Vision System and Fuzzy Support Vector Machine

The current nondestructive testing methods such as ultrasonic, magnetic, or eddy current signals, and even the existing image processing methods, present certain challenges and show a lack of flexibility in building an effective and real-time quality estimation system of the resistance spot welding (RSW). This paper provides a significant improvement in the theory and practices for designing a robotized inspection station for RSW at the car manufacturing plants using image processing and fuzzy support vector machine (FSVM). The weld nuggets’ positions on each of the used car underbody models are detected mathematically. Then, to collect perfect pictures of the weld nuggets on each of these models, the required end-effector path is planned in real-time by establishing the Denavit-Hartenberg (D-H) model and solving the forward and inverse kinematics models of the used six-degrees of freedom (6-DOF) robotic arm. After that, the most frequent resistance spot-welding failure modes are reviewed. Improved image processing methods are employed to extract new features from the elliptical-shaped weld nugget’s surface and obtain a three-dimensional (3D) reconstruction model of the weld’s surface. The extracted artificial data of thousands of samples of the weld nuggets are divided into three groups. Then, the FSVM learning algorithm is formed by applying the fuzzy membership functions to each group. The improved image processing with the proposed FSVM method shows good performance in classifying the failure modes and dealing with the image noise. The experimental results show that the improvement of comprehensive automatic real-time quality evaluation of RSW surfaces is meaningful: the quality estimation could be processed within 0.5 s in very high accuracy.

Optimal design of remote field eddy current testing probe for ferromagnetic pipeline inspection

Remote field eddy current (RFEC) nondestructive testing has its unique advantages in defect detection of metal pipelines, such as being unaffected by skin effect and material properties, but the size of RFEC probe is large and the signal received by the detection coil is weak. In this paper, a shielding plate is introduced between excitation and detection coil, and a ferromagnetic ring is introduced outside the ferromagnetic pipeline. Both theoretical analysis and finite element method (FEM) simulation are carried out. The result of FEM simulation shows that the distance between the excitation and the detection coil can be shortened after adding a shielding plate; particularly, setting a 1 mm-thick shielding plate 5 mm away from the excitation coil has an optimum optimization effect, which could shorten the distance between the excitation coil and the detection coil by 2 times. The ferromagnetic ring can strengthen the detected signal, and the closer it gets to the detection coil, the stronger magnetic flux density will be detected in the latter. Therefore, it provides a direction for the structural optimization of RFEC testing device.

Research on an Improved Metal Surface Defect Detection Sensor Based on a 3D RFID Tag Antenna

Structural health monitoring (SHM) technology is a monitoring process and early warning method for the health status or damage of special workpiece structures by deploying sensors. In recent years, there have been many studies on SHM, such as ultrasonic, pulsed eddy current, optical fiber, magnetic powder, and other nondestructive testing technologies. Due to their sensor deployment, testing environment, power supply, and transmission line wiring mechanism, they bring problems such as detection efficiency, long-term monitoring, and unreliable systems. The combination of wireless sensing technology and intelligent detection technology is used to solve the above problems. Therefore, this paper studies the tag antenna smart sensor, which is used to characterize the extension of metal defects in SHM. Then, it presents a wireless passive three-dimensional sensing antenna, and simulations verify the feasibility of the antenna. The simulation results show that the antenna can characterize the two extension directions of depth and width of the metal surface structure smooth defect. At the same time, the antenna can characterize the position of smooth defects on the surface of metal structures relative to the antenna and then realize the smooth defect positioning.

Novel Multifrequency Eddy Current NDT Signal Inversion Scheme for Aerostructures

Abstract Flaw profile characterization from nondestructive evaluation measurements is a typical nondestructive testing (NDT) inverse problem. Flaw profiling, particularly in aerospace industry, is important, as it is a decision tool to evaluate the air worthiness of the aerostructures. Accurate flaw profiling thus ensures aircraft safety through the timely implementation of cost-effective replacement/repair actions. Eddy current (EC) NDT data acquired at multiple frequencies contain complementary information about the flaws due to the skin effect phenomenon. However, finding the exact contribution of each measurement mode while determining the solution to the inverse problem is considerably challenging. In the reported research work, a novel multifrequency EC data-based polynomial model is formulated to solve the inverse problem. The weight (coefficient) of each measurement mode in the polynomial model is computed using nonlinear optimization techniques. Actual NDT data of a retired aircraft containing mutually exclusive training and test databases has been used as a case study. Data fusion (DF)-based inversion results are compared to the results acquired using individual measurement mode data. The improved results with DF indicate the efficacy of the proposed technique.

Research on the detection of curved ferromagnetic materials by flexible eddy current array sensor based on ldc1614

Flexible eddy current array nondestructive testing technology has the advantages of large single scanning area and fast scanning speed in the defect detection of conductive materials, so it becomes a common research hotspot of sensor and nondestructive testing technology. The performance of the array probe on the sensor is an important factor to determine the performance of the sensor, and the detection circuit and excitation mode are another important factor. In this paper, the array coils with different parameters are simulated and analyzed, and the resonant detection circuit based on ldc1614c digital inductance conversion chip is used to detect the high permeability materials on curved surface. Through the digital imaging technology, the defect image of the tested material is obtained to verify the selection of the probe coil and the reliability of the detection circuit.

A novel magnetic force transmission eddy current array probe and its application for nondestructive testing of defects in pipeline structures

Eddy current nondestructive testing (ECT) method is an efficient method based on electromagnetic induction for quantitative nondestructive evaluation of defects in the pipeline structure, due to its advantages of high detectability, non-contact and quick scanning. How to realize the probe scanning is a key issue for the long distance pipe inspection when the probe is located inside the tube. To address this problem, in this paper, a novel type of magnetic force transmission eddy current array split type probe has been proposed and developed to detect the defects in the pipeline structure. Firstly, the magnetic force transmission eddy current probe is proposed and designed, which includes excitation device outside the pipe and pickup device inside the pipe. The whole probe can simultaneously move along the pipe under the function of magnetic force. Secondly, the advantage of this proposed split type probe is validated through numerical simulation and experiment, which is that the detection signal cannot be saturated for deep buried defect, compared to the reflection type probe. Thirdly, the array structure pickup probe is designed and its merit is verified through simulation and experiment, which is that the detection sensitivity and efficiency are improved significantly. Finally, the proposed magnetic force transmission eddy current array probe is applied to detect one aluminum pipe with crack defects. The depth, axial position and circumferential position of the cracks can be successfully determined according to the proposed novel probe in this study.

Effects of voltage on the components of surface integrity of Al2O3 ceramic coatings on AA2024 by plasma electrolytic oxidation

It is said that plasma electrolytic oxidation (PEO) is considered as an effective technique to boost the surface properties of light materials by means of forming ceramic films on their surfaces. In this study, three different voltage values were applied to the PEO process to AA2024 so that Al2O3 ceramic coatings were directly supplied for AA 2024 substrates by PEO and it is focused on the adhesion of interface between coating and substrate. All of the cases such as microstructure, phase composition, thickness, roughness and hardness of Al2O3 ceramic coatings were assayed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Atomic-force microscopy (AFM), Eddy Current Non-destructive testing and microhardness test, respectively. The results showed that roughness, hardness and thickness of the coatings were increased as we increased the voltage. Therefore, it could be claimed that the voltage parameters have an important role in the unified coating on the metal surface as it is directly connected with the morphologies of the PEO coating.

On-line Monitoring by Acoustic Emission of Butt Joint Structure on the Composite Fuselage Frame

Acoustic emission (AE) technique is an online and dynamic non-destructive testing technology by diagnosing sounds, applicable to damage identification of all sorts of materials and structures. In order to fulfill the requirement of on-line monitoring for butt joint structure on the composite fuselage frame in static loading, Acoustic Emission (AE) is employed in this article. The experiment research is focused on examining the damage evolution process of the specimen subjected to mechanical tests by constantly monitoring the AE and strain responses. Combined with strain results, the recorded acoustic signals are analyzed using AE characteristic parameters such as AE amplitude and AE accumulative energy to identity five different damage stages and conclude the corresponding damage style during the entire test. The outcomes of this article can be available for supplementation and improvement of the current on-line non-destructive testing research for composite structures.

A Novel Perturbed Matrix Inversion Based Method for the Acceleration of Finite Element Analysis in Crack-Scanning Eddy Current NDT

Non-destructive testing (NDT) has a promising capability for crack detection. In this paper, a novel method for accelerating eddy current calculation for crack detection using the finite element method (FEM) is presented. This method exploits the fact that, due to the presence of a small defect, the stiffness matrix in FEM for a sample plate with the defect can be regarded as a summation of the stiffness matrix Q from the sample plate without the presence of the defect and the perturbation matrix D from the defect. The inversion of the stiffness matrix for a sample plate with the defect can, therefore, be obtained using the perturbed matrix inversion (PMI) method. PMI method only requires the inversion of a much smaller matrix and therefore improves the speed of the computation process. Numerical tests verified the effectiveness of the proposed method in shortening the computation time for crack scanning in FEM.

An Examination on Queuing Classification in Non-Destructive Testing

Nondestructive testing (NDT) is the way toward assessing, testing, or assessing materials, segments or gatherings for discontinuities, or contrasts in attributes without pulverizing the usefulness of the part or framework. Today current nondestructive tests are utilized in assembling, creation and in-administration investigations to guarantee item uprightness and unwavering quality, to control fabricating forms, lower generation costs and to keep up a uniform quality dimension. Amid development, NDT is utilized to guarantee the nature of materials and joining forms amid the manufacture and erection stages, and in-administration. NDT assessments are utilized to guarantee that the items being used keep on having the honesty important to guarantee their value and the security of the general population .Test strategy names regularly allude to the kind of entering medium or the hardware used to play out that test. One of the every now and again utilized test techniques is Liquid infiltrating test. The procedure is carried out in such a way that, to begin with, the penetrant is connected on the specimen which is to be tried, next the utilization of developer is done. In any case, before this designer procedure, there is a delay where other distractive procedure to be discounted. Next after the developer procedure, the procedure is rehashed if the aftereffect of the item isn't true to form. Following, maintenance work, for example, pre cleaning process like showering, brushing, inundating and so on is done. At last if in need another primer nondestructive test is additionally done for the item got. The above procedure is totally changed into a Queuing procedure in which the issue is all around concentrated by hypothesis of lining and it is illuminated by beneficial variable strategy. By the utilization of the above strategy, all the presentation proportions of the line in this procedure can be determined. Numerical delineation and graphical portrayal still amplify the model to a great extent.

Analytical solution for magnetic field of cylindrical defect in eddy current nondestructive testing

In metal components, a defect frequently causes the failure of the components and results in serious accidents consequently. Eddy current nondestructive testing method is one of the most effective testing approaches to quantitatively monitor the defects both in non-ferrite metal and in ferrite metal. Therefore, knowledge of the magnetic field is necessary to deeply understand the mechanism of eddy current nondestructive technique in defect characterization. In this paper, an analytical expression for the magnetic field for a cylindrical defect in metal in eddy current testing system is proposed by solving the partial differential equations. Firstly, a conductive metal plate with a cylindrical defect is modeled for the cylindrical coil with rectangular cross-section, and the analytical expression to the magnetic potential vector is obtained. Then, the series form expressions are extended to calculate the axial component of magnetic induction intensity Bz and is computed on the MATLAB platform. Finally, a finite element model is setup to validate the proposed analytical expression for the magnetic field. The results show that the magnetic field calculated by the analytical method is in good agreement with that calculated by finite element method, and the calculation efficiency of the analytical method is higher than that of FEM. The proposed expressions not only can be readily used to investigate the quantitative relationship of the cylindrical defects in a conductive metal, but also it is expected to be extended to seek the theoretical expression for the elliptic defect and also for the natural defect in key structures (e.g. oil pipe, rail track, iron bridge, oil tank, ocean ship) by using (pulsed) eddy current nondestructive technique.

High-Resolution Nondestructive Test Probes Based on Magnetoresistive Sensors

This paper discloses two high-sensitivity probes for Eddy Current Nondestructive Test (NDT) of buried and surface defects. These probes incorporate eight and 32 magnetoresistive sensors, respectively, which are optimized for high sensitivity and spatial resolution. The signal processing and interfacing are carried out by a full-custom application-specific integrated circuit (ASIC). The ASIC signal chain performs with a thermal input-referred noise of 30 nV/ $\sqrt{\text{Hz}}$ at 1 kHz, with 66 mW of power consumption, in a die with 3.7×3.4 mm $^2$ . NDT results are presented, showing that there is an increase in spatial resolution of surface defects when contrasted to prior art, enabling the probes to resolve defects with diameters of 0.44 mm, pitches of 0.6 mm, and minimum edge distance as low as 0.16 mm. The results also show that the probe for buried defects is a good all-round tool for detection of defects under cladding and multiple-plate flat junctions.

Development of Multi-Coils Circular Eddy Current Sensor for Characterization of Fibers Orientation and Defect Detection in Multidirectional CFRP Material

ABSTRACTThis article presents a study of a Multi-coils circular eddy current non-destructive testing sensor for determining the fibers orientation as well as the detection of defect in multidirectional carbon fibers reinforced polymer (CFRP). The developed sensor contains 16 rectangular coils connected in series and supplied by a single-phase sinusoidal source. This sensor allows the annulations of the mechanical rotation of the conventional sensors and it permits to reduce the inspection procedure duration. The electromagnetic phenomena are calculated by using 3D finite element method (FEM) based on the electromagnetic AV-A formulation. Finally, the Multi-coils circular sensor responses are analyzed through polar diagrams of the impedance variation, where the defect is taken into consideration. A great concordance between the obtained results and those of literatures has been noticed. The provided results show that the proposed sensor allows an efficient characterization of multidirectional CFRP and detection of defects in different layers.

Assessment of the Properties of AISI 410 Martensitic Stainless Steel by an Eddy Current Method.

Based on electromagnetic theory, metallurgical characteristics can be detected by eddy current nondestructive testing technology. In this study, the relationship between the surface microstructure and the eddy current output of martensitic stainless steel AISI 410 was studied using this technology at different quenching temperatures. The mechanical properties include material hardness, microstructure types and microstructural changes after thermal treatment was evaluated. Using Vickers hardness as the surface hardness index of AISI 410 steel, the relationship between eddy current output signal, in terms of impedance and inductance, and sample surface hardness was studied and the effects of different quenching temperatures on the steel’s surface hardness was examined. In addition, the change of microstructure types of AISI 410 steel after thermal treatment was detected by the eddy current nondestructive testing method, and the results were verified by metallographic microscopy.

Serial magnetic tunnel junction based sensors for detecting far-side pits in metallic specimens

The high sensitivity of magnetic tunnel junctions (MTJs) is independent of the field frequency, and sensors based on them have shown considerable potential in measuring secondary fields during eddy current nondestructive testing (ECT). In this study, sensors with 4, 16, 28, 40, and 52 serial MTJs were fabricated and characterized for detecting variations in magnetic fields. These micrometer-sized TMR sensors with serial MTJs exhibited low detectivities (2.0 ∼ 5.1 nT/Hz0.5 at 100 Hz). Furthermore, in ECT measurements, the sensors were used to detect far-side pits in a copper specimen, and the sensor with 28 serial MTJs offered the highest signal-to-noise ratios when detecting far-side pits with various diameters (2.5, 5.0, and 7.5 mm). In addition, the TMR sensors could detect millimeter-sized far-side pits having various depths and diameters, suggesting that they could detect buried defects in ECT.

Image-Based Feature Extraction Technique for Inclined Crack Quantification Using Pulsed Eddy Current

Existing eddy current non-destructive testing (NDT) techniques generally do not consider the inclination angle of inclined cracks, which potentially harms a larger region of a tested structure. This work proposes the use of 2D scan images generated by using pulsed eddy current (PEC) non-destructive testing (NDT) technique in the quantification of the inclination and depth of inclined cracks. The image-based feature extraction technique effectively identifies the crack axis, which consequently enables extraction of features from the extracted linear scans. The technique extracts linear scans from the images to allow the extraction of three novel image-based features, namely the length of extracted linear scans (LLS), the linear scan skewness (LSS), and the highest value on linear scan (LSmax). The correlation of the three features to surface crack inclination angles and depths were analysed and found to be highly dependent on the crack depths, while only LLS and LSS are correlated to the crack inclination angles.