Sensitivity Analysis Of Crack Detection In Beams By Wavelet Technique

Defects are almost unavoidable in structures, and their existences will decrease the mass, stiffness, strength and safety of structures. How to diagnose the existence and position of defect is an important and promising problem. Currently, a lot of researchers devote their attention to detect the damage in structure by means of the ultrasonic method and vibration-based method. Because the ultrasonic wave decays very quickly during the propagating process in structure, it can only detect the damage in its near field for the case that the vicinity of damage must be. known in advance. The vibration-based method utilizes the vibration characteristic of structure to diagnose the damage, which can only give global information on the structure. Therefore, a new detective method needs to be proposed.Wavelet transform (WT) is the local transform of space and time. Time -frequency window of WT has self-adaptability, which is suitable for detecting the abrupt information from signal. Inoue et al. firstly applied the Morlet wavelet transform to the analysis of flexural wave in Euler beam. Onsay and Haddow determined the location of the impact by analyzing the flexural wave of Timosenko beam based on Gabor wavelet. However, the above works are not related to the damage detection.This paper examines the sensitivity of wavelet technique in the detection of cracks in beam structures. Specifically, the effects of different crack characteristics, boundary conditions, and wavelet functions employed are investigated. Crack characteristics studied include the height and orientation of slit. The two different boundary conditions considered are simply supported and fixed end support, and the four types of wavelets compared in this study are the Haar,Gabor,Morlet and Mexican hat wavelets. The results show that the wavelet transform is a useful tool in detection of cracks in beam structures.