Study On Laser-Acoustic Emission Identification And Localization Method For Metal Weld Joint Damages

Welding is extensively used for structural connections in modern production systems.Early damage detection for welded joints will aid in preventing failure of the structure and reducing the cost on maintenance of replacement and ensuring the structure operates safely and efficiently during its whole intended life.There are many non-destructive testing methods for weld joint damage,but no one can detect static damage in weld joints with long distance.The objective of this work is to identify,locate static damage in the weld joint with long distance by a new detection means which developed by laser technology and acoustic emission.(1)Principle of laser-acoustic emission detectionTheoretical research methods has used in this part.Fist,the principle of laser excitation acoustic signal,lamb wave theory and acoustic emission detection were described in detail.Second,the basis of laser excitation technology and acoustic emission technology was given.Finally,the process of laser acoustic emission in damage detection was summarized.(2)The propagation rule of laser-acoustic emission signalsIt is great important to understand rule of laser-acoustic emission signals before the damage detection.This part studied four factors that affect the laser-acoustic emission signal,including excitation energy,propagation distance of laser beam,propagation distance of signal and change of medium structure.The results provide guidance for detection of static damage in the weld joint with laser-acoustic emission technique.(3)The identification of damage characteristics in weld jointThe detection of damage was carried out in the weld joint with four different types of damage by laser-acoustic emission technique.First,the characteristics of different acoustic emission signals are distinguished by acoustic emission parameter analysis.Then,the K-means clustering method is used to classify the signals,and the signal characteristics of the different categories are compared with results of the acoustic emission parameters.Finally,the relationship between the failure modes and AE parameters was built.(4)The localization of damage in weld jointMore accurate signal analysis methods are proposed for locating the damage in weld joint.First,the signal of the particular frequency is proposed based on the EMD combined with the lamb wave theory.Then,an energy compensation method is used in the signal energy calculation.Finally,the damage position is determined according to the signal propagation path.