The Study of Acoustic Emission Detection Based on Magnetoelastic Film

• Main Authors: Liu,Ming Kai, 劉明凱
• Other Authors: Chen, Jenq-Shyong
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/36996648362226680541

碩士 === 國立中正大學 === 機械工程學系暨研究所 === 99 === The study mainly applied magnetoelastic film to detect acoustic emission signals（AE）. Nowadays, AE sensors is used to detect AE signals that the frequency range of usually lay between 50kHz and 1MHz. Acoustic emission is the elastic energy that is spontaneously released by materials when they undergo deformation. In the paper, using pencil-breaking and ball-bumping methods to calibrate two piezoelectric AE sensor, which consist of piezoelectric ceramic and PVDF film respectively, based on the piezoelectric effect. Then, the surface wave signal was analyzed by FFT. In order to improve the AE circuit noise and reach a higher sensitivity, the study replaced the piezoelectric materials with magnetoelastic thin film for acoustic emission detection. The magnetoelastic film are amorphous alloy ribbons, fabricated from Metglas. It includes two types, 2826MB（Iron-Nickel base）and 2714A（Cobalt-based）, which have great permeability and low magnetostriction. When the strain was applied on the films, the permeability changed. In the study, surface wave signals were detected by single excitation-detection coil. For the purpose of understanding of the properties of the film, by the spectrum analysis and the impedance analysis, when the strain was applied on the film, it was indicated that the resonant frequency drifts and the output voltage changed. Compared with AE sensors, the magnetoelastic strain sensor was fabricated by a single excitation-detection coil and the inverting amplifier to detect surface wave. By Recording the frequency point and the voltage point at every strain, it showed that the resonant frequency was 2MHz for 2714A and 4~7MHz for 2826MB. From the impedance analysis, the impedance was changed 400% of 7cm magnetoelastic thin film. Eventually, the strain-sensitivity of magnetoelastic thin film（2714A）was 10-5V/με in the static strain experiment. The higher the excitation frequency, the lower the sensitivity. The measurement of the surface wave signals resulted that the signal bandwidth of PVDF AE sensor and Kistler AE sensor were 0~10kHz and 0~120kHz. The voltage of the former that the decay time of the Kistler AE sensor was 5ms in the measurement was more larger than the latter. Therefore, the peak-to-peak voltage of magnetoelastic thin film（3cm-2714A）was about 20mV in the dynamic experiment. However, if the coil shape was changed plane type, the variation of the voltage in the surface wave measurement was only about 8mV.