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Purpose – The purpose of this study is to study the quantitative evaluation method of contact wire cracks by analyzing the changing law of eddy current signal characteristics under different cracks of contact wire of high-speed railway so as to provide a new way of thinking and method for the detection of contact wire injuries of high-speed railway. Design/methodology/approach – Based on the principle of eddy current detection and the specification parameters of high-speed railway contact wires in China, a finite element model for eddy current testing of contact wires was established to explore the variation patterns of crack signal characteristics in numerical simulation. A crack detection system based on eddy current detection was built, and eddy current detection voltage data was obtained for cracks of different depths and widths. By analyzing the variation law of eddy current signals, characteristic parameters were obtained and a quantitative evaluation model for crack width and depth was established based on the back propagation (BP) neural network. Findings – Numerical simulation and experimental detection of eddy current signal change rule is basically consistent, based on the law of the selected characteristics of the parameters in the BP neural network crack quantitative evaluation model also has a certain degree of effectiveness and reliability. BP neural network training results show that the classification accuracy for different widths and depths of the classification is 100 and 85.71%, respectively, and can be effectively realized on the high-speed railway contact line cracks of the quantitative evaluation classification. Originality/value – This study establishes a new type of high-speed railway contact wire crack detection and identification method, which provides a new technical means for high-speed railway contact wire injury detection. The study of eddy current characteristic law and quantitative evaluation model for different cracks in contact line has important academic value and practical significance, and it has certain guiding significance for the detection technology of contact line in high-speed railway.

The electromagnetic eddy current non-destructive testing system enables the non-destructive analysis of surface defect information on tested materials. Based on the principles of eddy current detection, this paper presents a digital eddy current detection method using high-speed sampling based on STM32. A differential eddy current coil is used as the detection probe, and the combination of a differential bridge and a differential amplifier circuit helps to reduce common-mode noise interference. The detection signal is collected via an STM32-based acquisition circuit and transmitted to the host computer through Ethernet for digital demodulation processing. The host computer performs operations such as smoothing averaging, sinusoidal fitting, and outlier removal to extract the amplitude and phase of the detection signal. The system also visually displays the condition of the tested object's surface in real time through graphical visualization. Testing showed that this system can operate at frequencies up to 8.84 MHz and clearly identify defects as narrow as 1 mm on the surface of the tested steel plate. [ABSTRACT FROM AUTHOR]

The electromagnetic eddy current non-destructive testing system enables the non-destructive analysis of surface defect information on tested materials. Based on the principles of eddy current detection, this paper presents a digital eddy current detection method using high-speed sampling based on STM32. A differential eddy current coil is used as the detection probe, and the combination of a differential bridge and a differential amplifier circuit helps to reduce common-mode noise interference. The detection signal is collected via an STM32-based acquisition circuit and transmitted to the host computer through Ethernet for digital demodulation processing. The host computer performs operations such as smoothing averaging, sinusoidal fitting, and outlier removal to extract the amplitude and phase of the detection signal. The system also visually displays the condition of the tested object’s surface in real time through graphical visualization. Testing showed that this system can operate at frequencies up to 8.84 MHz and clearly identify defects as narrow as 1 mm on the surface of the tested steel plate.

Prepreg is used as the raw material for the preparation of carbon fiber reinforced plastic（CFRP）, and its quality will directly affect the performance of the finished material. Eddy current detection technology is applied to the damage detection of prepreg. Aiming at the problem that the eddy current in the prepreg is small, the damage signal is more likely to be lifted off by the transmit-receive（T-R）probe composed of double circular coils, and the probe is not sensitive to the damage direction detection, we design a rectanglecircular（R-C）probe. In theory, no matter how the probe is lifted off, it will not affect the received signal. Through three-dimensional electromagnetic finite element simulation, the size of the rectangular coil is optimized and the feasibility of the R-C probe is verified. Experimental research shows that compared with the original T-R probe, the lift-off effect of the R-C probe is significantly reduced and it has a good characterization of the fiber bending direction on the prepreg, and it also has a unique characterization method for cracks；but the signal received under the same excitation is smaller than the original probe. [ABSTRACT FROM AUTHOR]

In this study, an eddy current (EC) detector is integrated in an additive/subtractive hybrid manufacturing (ASHM) process. The detector facilitates in-process inspection and repair operations through material deposition, defect detection, and removal processes layer by layer. A feasibility test is carried out on eddy current detection of subsurface defects in additively manufactured parts by using an EC detector. The study compares the results obtained from the EC detection with those by the X-ray computed tomography and the destructive methods. Experiments and simulations are conducted to investigate the effect of excitation frequency on intensity of the eddy current signal. The effects of residual heat of an additively manufactured specimen and lift-off distance of an EC probe on impedance changes are also investigated. In addition, the effect of defect width on EC signal is analyzed. The study shows that the EC method is capable of detecting subsurface defects in the ASHM parts. It is promising to integrate the EC detection and subtractive manufacturing into additive manufacturing to produce parts with improved quality and better performances. [ABSTRACT FROM AUTHOR]

In pebble-bed high temperature gas-cooled reactors (HTGRs), spherical fuel elements move inside pipelines of a handling system, which should be controlled precisely. A detecting method for these elements is proposed in this paper, which is achieved by a detecting system with self-diagnosis function. Detecting signals are obtained by sensors installed outside pipes. A signal identification algorithm was designed for graphite ball detection. Electromagnetic simulations and detecting experiments were performed for system optimization and development of the method. The results show that the proposed method is capable for spherical fuel elements detection, and can be successfully used in practical application. [ABSTRACT FROM AUTHOR]

A new nondestructive eddy current technique is described for testing for incipient creep damage in austenitic steel boiler tubing in power plants. It is used because as incipient creep damage is formed, a magnetic oxide scale forms on the outside of the boiler tube in concentration proportional to the incipient creep damage; simultaneously in the base metal under the scale, a magnetic ferrite phase also forms in the grains and grain boundaries, which is in smaller concentration, but which is also in concentration proportional to the incipient creep damage. The eddy current signal can be processed in such a way that it varies monotonically and nearly linearly with the magnetic phase concentration and monotonically and nearly linearly with the incipient creep damage. Various aspects of the measurement are analysed and discussed—for example, liftoff, wall thickness, and diameter dependence. Using a zero point value to assess oxide layer permeability and dependence on conductivity is also discussed. Comparison is made between measurements and finite element modelling results. [ABSTRACT FROM AUTHOR]