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Study on Eddy Current Imaging System for Crack Testing at Train Brake Beam Axle

Author: GuoYun
Tutor: YanRengChun；LouMinZhu
School: Research Institute of Mechanical
Course: Measuring Technology and Instruments
Keywords: train brake beam-axle crack eddy current testing array probe pseudo color imaging
CLC: U270.35
Type: Master's thesis
Year: 2008
Downloads: 147
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Abstract


In our country, train brake braking and shedding caused by the cracks in brake beam axle is a hidden trouble to the safety of trains. Magnetic particle test used nowadays to inspect the cracks at beam axle is inefficient and with personal failure of defects report caused by the complicated testing procedure and long term defect viewing. So it is in urgent need of a new efficient, quick and easy operation testing method. For this reason, eddy current testing technique is used to test the cracks at beam axle in this paper with improvement and advance in some techniques such as: using eddy current array probe scan instead of single probe rotation scan for the reason that static scan has higher accuracy with shorter lift-off and simpler scan mechanical device than the single probe scan, using Pseudo color image display directly showing the crack in the surface of beam axle and using linear interpolation process to improve the quality of image. All these improve the ability of inspection cracks.1. Adding the scan circuit into the traditional eddy current instrument circuit, the multi-channel scan circuit which is built with several CMOS dual 4-channel analog multiplexer and Mod 8091 SCM achieves function of 16 channel probe coils shared-time scanning. In addition, the system collects data in scan synchronization and position synchronization based on the communication between data acquisition and SCM. The system is the production of upgrading an eddy current instrument to multi-channel eddy current imaging instrument. 2. Through the analysis of the object’s characters and its crack feature, by derivation the magnetic core pancake coil’s Impedance analytical expression and analysis from experience, coil’s character the coil’s parameters is determined and the array probe is produced. 16 channel eddy current array probe has both the advantage of high sensitivity of surface crack and large area quick scanning. The difference between the coils is eliminated to minimum by coil adjustment one by one. The software will subtract the residual voltage of the coil and solve this problem completely.3. The eddy current scan imaging software is designed based on the new LabVIEW platform. The software realizes the functions of parameters control through IO control card and inherits the traditional eddy current display including eddy current impedance and XY value display. However, the software have the new way of display like C-scan imaging display.4. In addition, the author designs the digital process algorithm according to the character of eddy current signal character and processing efficiency. The algorithm includes digital denoising based on the increment abnormity judge method and signal maximum compression. In image process, pseudo color technique is used to enhance the image vision resolution and the image interpolation process algorithm is designed to improve the image quality.The research in this paper provides not only the conference to further research of eddy current imaging system but also a technical fundament to develop the special instrument which is used in train brake beam axle crack inspection.

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CLC: > Transportation > Rail transport > Vehicle Engineering > General issues > Body construction and equipment > Brake
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