Research On Acoustic Emission Signal Analysis And Source Localization Technology Based On Fiber Bragg Gratings

Acoustic Emission (AE) is the phenomenon of transient elastic-wave generation due to a rapid release of local energy in a material and it is also known as stress-wave emission. There is AE occurring when most materials undergo deformation and frac-ture. AE technology is very useful in real-time damage monitoring for materials and equipments. Fiber Bragg Grating (FBG) is known for its characteristics such as high sensitivity, anti-electromagnetic interference, small size and light weight. The Com-bination of FBG sensors with AE technology is a hotspot in current research. Based on a survey of present AE technology, this thesis focused on AE technology and did a series of research in mainly four aspects which are stated as follows.First, the theory of the interaction between FBG and AE elastic waves is studied. It is demonstrated that the FBG wavelength can be modulated as static case when the grating length is much shorter than the AE wavelength. Based on this, an AE detect-ing system which used FBG sensors as AE sensors is proposed and tested.Second, a detailed introduction of AE technology is presented, which includes the mechanism of AE phenomenon, the rule of AE waves’ propagation and the basic principle of AE detection. Meanwhile, important parameters of AE in time domain are introduced and AE analysis based on these parameters is studied.Third, time-frequency analysis of AE signal is presented using wavelet transform based on Gabor function. And it is demonstrated that the arrival time of AE signal to each sensor can be attained using this method. Based on this, auto-pick of arrival time difference (ATD) between different sensors can be realized. In addition, principle of AE source localization is deeply studied, thus location area and sources of errors are represented. The method proved to be useful by both linear source localization and planar source localization experiments.Finally, a new AE source localization method is represented. In this method, op-timization method is used to locate the AE source.By using weighted generalized cross-correlation method to attain ATD, we can get the location of AE source by us-ing a genetic algorithm. Planar source localization experiments are conducted using the FBG sensing system. It is proved that by using this method, accurate source local-ization can be realized without knowing the velocity of AE wave, and location area is not constrained to the sensor array. The FBG AE detection system proposed in the thesis provided a new way for AE detection. Through deep study in linear source localization and planar source localiza-tion, the thesis mainly provided two AE localization methods which can improve the localization accuracy and localization scope. The work of the thesis have important significance in both theory and application in future AE study.