As important bearing units of bridges and buildings, the monitoring of the stress state of bridge cables and prestressing strands is essential to ensure the safe operation of the facilities. In this study, according to the characteristic of the existence of a great value of the force-induced magnetic induction intensity with the change of magnetic field in the Villari reversal, a stress characterization method based on force-induced magnetic induction intensity is proposed and reveals the relationship between the change of the force-induced magnetic induction intensity at the point of Villari reversal point and the applied stress. A stress characterization model based on Villari reversal was established for high-carbon steel wire. The results show that the force-induced magnetic induction intensity of steel wire is approximately linear with the stress. The results are helpful to further understand the influence of stress on the magnetic properties of ferromagnetic materials and have practical guiding significance for the stress characterization of ferromagnetic materials.

Bridge cables, as one of the critical load-bearing elements in cable-stayed bridges, are prone to hidden internal defects that are difficult to detect. In conventional magnetic flux leakage (MFL) testing, the magnetic field decays rapidly with depth, which hinders defect localization. To overcome this limitation, this study proposes a defect localization method based on multi-component MFL signals. Based on the magnetic dipole model (MDM) of a single broken wire, the spatial-domain summation preprocessing in the circumferential direction is proposed to enhance weak responses. For axial localization, cross-validation of the summed differential axial component and the radial component improves robustness. In addition, an asymmetric peak-valley full width at half-maximum (APV-FWHM) feature is introduced for depth localization, which reduces amplitude dependence and decouples depth localization from circumferential positioning. In order to validate the method, an experimental platform for bridge cable based on MFL testing was established. Experimental validation on a PECS7-127 cable successfully detected all broken-wire defects at depths of up to 42 mm with a 95% confidence interval of 97.9-100%. The axial localization results from different components indicated strong consistency, reaching 94.9% accuracy within a +/- 5 mm tolerance. In addition, circumferential defect regions were effectively identified, and radial localization achieved 97.7% accuracy when a tolerance of +/- 1 layer was permitted. These findings provide preliminary validation of the feasibility and reliability of the proposed method for testing and localizing a single broken wire defect in bridge cables using multi-component MFL signals.

Bridge cables, which serve as critical load-bearing components in cable-supported bridges, are highly susceptible to broken wires caused by corrosion and fatigue. Accurate quantitative evaluation of this type of damage is essential to ensure structural safety. This study presents a novel quantitative evaluation method for identifying the number of broken wires by employing the magnetic flux leakage (MFL) signal in three-dimensional (3D) space. The method first acquires the 3D spatial magnetic leakage field and generates 3D arrays of MFL signals for computational analysis. It then extracts two categories of features. The first is the global feature, defined as the L1 norm distance (L1D) between the measured 3D spatial MFL signal and the defect-free reference signal. The second is the local feature, consisting of multi-scale waveform features organized as a feature array. The multi-scale waveform feature arrays are compressed using Multilinear Principal Component Analysis (MPCA) to reduce computational redundancy. The compressed feature arrays are then introduced into the Elastic Net-Constrained Regression (ENCR) model to predict defect width. The number of broken wires is ultimately calculated as the ratio of the total L1D value to the L1D value corresponding to the predicted width of a single wire. For a given broken wire width, the L1D demonstrates linear superposition with respect to the number of broken wires, with goodness-of-fit values exceeding 0.999, enabling proportional quantification. Validation through simulations and experiments on PES7-127 cables (127 wires of 7 mm diameter) confirms the method's effectiveness. The simulations achieved 100 % accuracy in counting broken wires across varying widths and distributions, while experimental results verified 100 % quantification accuracy (within a tolerance of +/- 1 wire) for defects involving <= 4 broken wires. This performance is obtained using a training dataset of only 30 samples. This study provides a practical and efficient approach for bridge cable assessment.

As a critical load-bearing component in many infrastructures, the tension status of steel strand serves as a key indicator for infrastructure safety assessment. This study focuses on estimating the tension of steel strands and proposes a multi-feature fusion approach based on Pulsed Eddy Current (PEC) testing. Firstly, the mechanism of PEC-based tension estimating for steel strand is analysed in detail, and PEC experiments on steel strand under different tension are carried out. The response of the PEC signals to tension is consistent with the results of the theoretical analysis. Subsequently, five features are extracted from the PEC signals for estimating the tension of steel strand, and their characteristics and performance in tension estimation are analysed. Finally, based on these features, a Principal Component Analysis (PCA)-based method for multi-feature fusion is developed to improve the accuracy of tension estimation. Compared with the features without using fusion method, the performance in tension estimation of the significant principal component with fusion feature has been significantly enhanced. The Root Mean Square Error (RMSE) of the estimation results with multi-feature fusion is 0.73% of Full Scale (FS), and the maximum is 1.41% FS.

Non-destructive testing (NDT) of cable-supported bridges is crucial for ensuring their safe and reliable operation. However, detecting internal broken wires using traditional Magnetic Flux Leakage (MFL) testing remains a challenge due to the low Signal-to-Background Ratio (SBR). To address this issue, this paper proposes a novel sensor composed of multilayer-arranged Hall elements (MAHE) based on the Radial Differential Magnetic Flux Leakage (RDMFL) principle, aiming for effective detection of broken wires at various depths within the cable. The RDMFL method detects damage by superimposing the differences in magnetic flux density measured at multiple radial points and identifying local peaks in the combined signals. A theoretical expression for the RDMFL signal is derived, and the influence of MAHE sensor structural parameters on both SBR and amplitude enhancement of broken wire signals is analyzed. Finite element simulations are used to verify performance improvements and identify the optimal structural parameters. Experimental results on a cable specimen demonstrated that the MAHE sensor-equipped testing system effectively detected single broken wires positioned in layers 1-7 of a PES7-127 specification cable (comprising 127 steel wires, each with a 7 mm diameter). Meanwhile, a preliminary image of all broken wires within the cable specimen was generated, providing a clear magnetic field visualization of the damages. Finally, the detection capability of the MAHE sensor was analyzed using a Receiver Operating Characteristic (ROC) curve, and the optimized threshold for identifying broken wires was determined.

With the development of modern industry, the types and quantities of industrial equipment are increasing. In the long-term production process, various failure modes such as corrosion and cracks will occur, therefore the workload of inspection will increase dramatically. It is extremely urgent to study the combined non-destructive testing (NDT) technology and develop corresponding multi-functional instruments to achieve rapid inspection. In this paper, an electromagnetic testing principle based on the varied frequency domain is proposed. In the first place, spatial uniformity and spatial periodic static fields are generated by the arrangement of the permanent magnetizers, these static fields are fields with different spatial frequencies. In the second place, dynamic fields with different frequencies are generated by different frequencies excitations. Under the time-space electromagnetic field coupling, a new combined electromagnetic testing principle of magnetic flux leakage (MFL), guided wave (GW) and electromagnetic acoustic transducer (EMAT) is proposed. The MFL testing method can be realized based on the uniform static field, GW based on the interaction of spatial periodic static field and low frequency dynamic field, while EMAT based on the combination of uniform static field and high frequency dynamic field. According to the above principle, a multi-functional instrument is developed, which includes a medium-low frequency excitation unit for GW, a high frequency excitation unit for EMAT, corresponding receiving amplifiers for GW/EMAT/MFL, and USB-based data transmitters. Finally, the relevant performance tests are carried out, which laid the foundation for field application.

Magnetic flux leakage (MFL) is one of the most popular techniques for detecting broken wire in bridge cables. MFL sensor array has attracted a lot of attention in recent years due to its capacity to measure the spatial distribution of the magnetic field of bridge cable. More sensors in the array lead to increased useful information extraction from the MFL field, allowing for more precise quantitative evaluation of bridge cable damage. This study reports the development of a cable MFL testing system capable of synchronous acquiring up to 512 channels of MFL sensors signal. Radial sensor arrays (RSA) composed of vertically placed magnetic sensors spaced at equal intervals are developed to be arranged around the bridge cable. They record the spatial distribution of the magnetic leakage field of the broken wire by collecting the MFL signal at various lift-offs. To solve the problem of multi- channel MFL signal synchronous acquisition, this study develops a MFL signal acquisition card based on multiplexing technology, capable of synchronous acquisition of up to 512 channels of MFL signal. Multiplexers are used to switch sensor channels, followed by multi-channel A/D conversion chips to convert the transmitted data. The converted data are temporally stored in the First-In-First-Out (FIFO) buffer of the Field Programmable Gate Array (FPGA) and transferred to the computer through the network port for display, storage, and signal processing. Finally, the motion control circuit, mechanical structure, and control software of the bridge cable MFL testing system are fully customized. Experiment results reveal that the system can be used in multi-channel MFL testing, laying the foundation for further multi-channel signal processing and bridge cable health evaluation.

The large storage tank is one of the major infrastructures. Once a leak occurs, it often causes environmental pollution and even catastrophic accidents. In the early years, the method of emptying tanks and cutting plates for defects inspection was adopted to avoid leakage. However, there exist some deficiencies such as large blindness, long downtime and high cost. Since there are many problems in the traditional testing, inspection without emptying the tank and without stopping production is an indispensable technical means to ensure the safe operation of the tank. An in-service non-destructive testing (NDT) system for storage tanks without emptying is developed in this paper, which mainly includes sensors, the signal processing module, the testing crawler, the winding and releasing mechanism and control module et. al. The sensors, signal processing module and testing crawler need to be placed into the tank from the roof man-hole by the crane, while the control module is located outside the tank. The sensor can realize the combined inspection of magnetic field leakage (MFL) and electromagnetic acoustic transducer (EMAT). The laboratory experiments indicate that the system can realize in-service inspection of the corrosion defects on the bottom and works well in water. The new testing system will overcome the shortage of off-line service inspection methods that emptying and cleaning tanks are needed before inspection and environmental risks are involved. These research works guarantee the safe operation of storage tanks and provide an alternative NDT system for storages related industrial projects.

Period-permanent-magnet (PPM) electromagnetic acoustic transducer (EMAT) has been widely used in shear horizontal (SH) ultrasonic guided wave testing owing to its advantages, such as non-contact coupling, and convenient to excite SH waves. However, its poor transduction efficiency leads to weak signals and limits the lift-off performance. This article investigates how to improve the signal amplitude by adjusting the number of turns of the racetrack coil. The inductive coupling process of the PPM-EMAT receiver is first studied using the equivalent circuit method, and the corresponding equivalent model is obtained. Aiming at the effects of coil configurations, the equivalent impedance parameters of multilayer racetrack coils are analyzed by calculations and measurements. The proposed model can be used to predict the receiving frequency response of PPM-EMAT receivers with different coil structures, and it has been verified experimentally. It can be obtained that by choosing an appropriate coil configuration and matching resistance, the SH wave signal amplitude can be increased by 3 times.

直角弯管是石油化工行业中管道运输系统的重要组成部分.与直管相比,直角弯管的弯头部分更容易遭受磨损和腐蚀,对其进行无损检测具有重大意义.提出了一种基于开放式磁致伸缩导波传感器的直角弯管检测方法,在含多种类型人工缺陷的弯管上进行了试验.试验结果表明:基于该传感器的检测方法能够识别出直角弯管的所有人工缺陷,具有良好的检出能力和定位精度,其定位误差绝对值不大于3.74%.该研究为磁致伸缩导波检测技术应用于现场弯管检测提供了参考和依据.

As an essential load-bearing component of a bridge,problems such as internal steel wire breakage may occur in main ca-ble after long-term operation,requiring regularly testing.To address the issues in magnetic flux-leakage(MFL)testing caused by the large diameter of the main cable and the orthogonal arrangement of the main cable steel wire and wrapping wire,the feasibility of MFL testing applied in main cable was first investigated using finite element simulation.Based on the simulation results and modular design idea,a MFL detection system for bridge main cable was developed,including the modules of drive,sensor,signal processing,WIFI communication,etc.Finally,the main cable detection experiment was carried out.The results show that the system can identify 3 and 5 broken-wire defects in the surface-layer steel wires of the main cable specimen,which is consistent with the simulation results.And the system is able to crawl on the main cable of a bridge in service while maintaining a steady signal.The research results provide a new method for the detection of bridge cables.

Guided wave based non-destructive testing technique has been widely used in many engineering structures. Accurate characterization of defects by extracting defect-related features from the guided wave testing signals is very important for the condition evaluation of the tested specimen. In this paper, a topological feature for defect characterization is extracted from the topological domain of the guided wave testing signal. Specifically, the topological feature is extracted from the 2-dimensional phase space of the testing signal based on persistent homology. The steel wire notch experiments show that there is an exponential relationship between the topological feature and the cross sectional area loss ratio of the steel wire, and the goodness of fit is 0.9962. This paper confirmed that the persistent homology is a useful tool to analyze guided wave testing signals to investigate the defect characterization.

Corrosion of steel wires in cables is a frequent occurrence and is a major factor affecting the durability and safety of cables. Magnetostrictive guided waves have been employed to detect steel wire corrosion. However, due to the complexity of the geometry of the corrosion area, it is difficult to interpret the magnetostrictive guided wave testing signals. Hence, extracting features from testing signals to characterize the corrosion condition is a great challenge. This study proposes a topological feature for corrosion characterization of steel wire, which is extracted from the two-dimensional point cloud with optimal geometry structure of the testing signal based on persistent homology theory. Corrosion experiments were carried out on 30 galvanized steel wires. The experimental results indicate that the topological feature increases roughly linearly with the corrosion depth. Furthermore, compared to other features obtained from the time domain, frequency domain, and joint time–frequency domain, this topological feature can reflect the progression of corrosion more accurately.

针对储罐底板在役检测过程中遇到的难题,研制可以实现漏磁、电磁超声、导波和脉冲涡流 4种检测方法的复合检测仪器.提出结合继电器和电源稳压模块的电源供电方案,解决复合仪器研制相关的硬件电路中多电平、多频率复合时所引入的串扰问题.其中复合仪器的电磁超声测厚采用基于阈值电平的脉冲计数法全硬件实现厚度测量,需要对部分硬件参数进行调节,开发基于现场可编程逻辑门阵列和数字电位器的程控调节方案,使增益、阈值、时延等电路参数可以实时调节从而实现基于阈值电平脉冲计数法的电磁超声测厚.最后,在室内实验平台上对系统的检测性能进行了测试,结果表明:电-磁-声复合检测仪器可以实现导波、漏磁、电磁超声以及脉冲涡流检测,各检测模块工作正常.

针对缆索磁性检测中大直径缆索深层次钢丝磁化的难题,建立了缆索闭合磁化解析模型,研究缆索磁化规律.提出一种穿过闭合式磁化器的轴对称模型,采用等效面磁荷法对永磁体进行等效,并应用截断区域特征函数展开法和传递矩阵求解磁标位方程,得到磁场的空间解析表达式,该模型可用于求解缆索内部磁场分布.与有限元仿真结果的对比显示:当使用解析模型计算磁化器两磁极中间区域磁场时,轴向磁感应强度的相对计算误差不大于3％,径向磁感应强度不大于12％,表明使用该模型计算缆索内部磁场是可行的.

Pulsed eddy current testing (PECT) is widely used to detect corrosion in industrial pipelines with coatings; however, the energy dissipation caused by liftoff limits the detection capability for small-sized pipes, especially the non-ferromagnetic pipes recently installed in various industrial scenarios. Since the magnetic field is not concentrated within non-ferromagnetic pipes due to their low permeability, energy dissipation is particularly large, which makes the PECT challenging. Aiming at such energy dissipation problem, this article investigates the excitation process of PECT and proposes an optimization method for excitation coils. The proposed optimization aims to increase the incident field intensity, which is then decoupled from the PECT analytical solution, thereby allowing the solution to have only electromagnetic coupling relationship between the excitation coil and the specimen. Theoretical calculations are verified by the finite-element method (FEM) simulations, followed by the experimental validation of optimized coils, which verified their advantages in enhancing the specimen-related components in signals. Furthermore, the PECT performance improvement is also discussed when the average incident field of different surfaces is enhanced. Results show that the coils designed based on the average incident field of modified footprint have good performance.

针对埋地长输管道检测需求,基于洛伦兹力机理,研制管道电磁超声周向导波内检测系统.详细论述了系统主机、传感器和检测软件等部分.实验室管道试件检测实验表明,该系统可以有效检出管道通孔、模拟腐蚀等缺陷,可应用于现场管道的检测,为管道安全运营提供一种有效检测方法.

Multi-wire cables are widely used in suspension bridges and cable-stayed bridges as primary load bearing structural elements. Broken Wires in cables can lead to catastrophic accidents such as bridge collapse. Magnetostrictive guided wave testing technology has been employed to detect the broken wire defects in multi-wire cables, and the defect size is estimated by analyzing the defect echo signals. However, there are many studies on the guided wave testing for the seven-wire steel strands but fewer for the bridge cables which have a large number of wires. Moreover, the relationship between the guided wave testing signal features and the defect size of multi-wire structures is imprecise, which means the defect size estimated by the features may deviate significantly from the real defect size. In this paper, large-scale topological features are extracted by using persistent homology from the dynamical reconstruction topology of the guided wave testing signals to characterize broken wire defects in the bridge cable. The broken wire experiments were performed on a 61-wire cable. The experimental results show a good linear relationship (the goodness of fit 0.9946) between the large-scale topological features and the number of broken wires in the cable. It indicates that it is feasible to extract topological features from the topological domain of the testing signals to characterize the broken wire defects of bridge cables.

Magnetic flux leakage (MFL) is one of the most commonly used techniques for detecting broken wires of bridge cables. In practical testing, the sensor and magnetizer lift-off variations caused by mechanical vibration, sheath surface roughness and thickness nonuniformity significantly affect the accuracy of the estimated defect size. To address this problem, the theory of ratio of adjacent peaks (RAP) is developed based on the magnetic dipole model, which reveals the nonlinear relationship between RAP vector and broken-wire width. Based on the RAP theory, a radial sensor array (RSA) configuration and an evaluation method are further proposed in this paper. The RSA consists of four sensors along the bridge cable radial direction with a fixed interval and is employed to acquire RAP vector, which is identified as a spatial characteristic of MFL signal. An artificial neural network (ANN) algorithm is employed to develop the nonlinear defect width evaluation method based on the RAP vector. The effectiveness of the RSA configuration and the evaluation method is verified by finite element method (FEM). The results indicate that the broken-wire width can be accurately estimated utilizing RAP vector obtained by RSA without considering the lift-off variation.

储罐是石油、化工等领域的重要储存容器,底板腐蚀是储罐最为常见的安全隐患之一.储罐底板腐蚀类型多样,目前广泛应用的储罐底板漏磁检测系统难以识别出均匀壁厚减薄缺陷且难以进行精确厚度测量.为此,根据电磁超声具有测厚精度高、不需要耦合剂、非接触等优点,研制了一套储罐底板电磁超声测厚系统.该系统主要包括储罐底板扫查器、信号激励接收控制器、运动控制器和计算机分析处理系统.通过探头线圈和硬件电路优化设计,使得该系统具有无A/D采样、低频激励时回波信号分辨率高的特点.实验室内厚度7～20 mm的16MnR阶梯钢板上测试结果表明,该系统能够实现储罐底板扫查式高精度、高灵敏度测厚.