Numerical and experimental studies on the localization of a small crack with optimized spatial wavelet analysis and windowing
Date
2017
Authors
Ghanbari Mardasi, Amir
Journal Title
Journal ISSN
Volume Title
Publisher
World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering
Abstract
In this thesis, a high sensitive spatial wavelet-based crack localization technique is presented on a cracked beam structure. Due to the crack existence in the beam structure, a perturbation/slop singularity is induced in the displacement profile. Spatial wavelet transformation works as a magnifier to amplify the small perturbation signal at the crack location to detect and localize the damage. This technique is studied both theoretically and experimentally. Theoretical model and vibration analysis considering the crack effect are first proposed and performed in MATLAB based on the Timoshenko beam model. Wavelet scale in spatial wavelet transformation is optimized to enhance crack detection sensitivity. As the outcome of the simulation, optimal ranges are obtained for wavelet scale factor. The experimental part of the thesis is based on the obtained ranges. The experiment is then carried out on a cracked cantilever beam subjected to a certain displacement at the free end. The profile of a deflected aluminum cantilever beam is obtained for both intact and cracked beams by a high-resolution laser profile sensor. Gabor wavelet transformation is applied on the subtraction of intact and cracked data sets. To improve crack localization sensitivity, scale factor optimization process in spatial wavelet transformation is conducted. Furthermore, to detect the possible crack very close to the measurement boundaries, wavelet transformation edge effect, which is large values of wavelet coefficient around the measurement boundaries, is efficiently reduced by introducing different windowing functions. The result shows that a small crack with the depth of 10% of the beam height can be localized with a clear perturbation. Moreover, a perturbation caused by a crack 0.85 mm away from one end of the measurement range, which is covered by wavelet transform edge effect, emerges by applying proper window functions.
Description
Keywords
Small crack detection, Crack localization, Spatial wavelet transformation, Optimization, Edge effect, Windowing
Citation
Mardasi, A. G., Wu, N., & Wu, C. (2017). High Sensitivity Crack Detection and Locating with Optimized Spatial Wavelet Analysis. World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, 11(5), 817-822.