Identification of breathing cracks in a beam structure with entropy

• Main Author: Senake Ralalage, Buddhi Wimarshana
• Other Authors: Wu, Nan (Mechanical Engineering) Wu, Christine (Mechanical Engineering)
• Published: 2016
• Subjects: Structural health monitoring; Breathing cracks; Crack identification; Sample entropy; Quantized approximation of sample entropy; Wavelet transformation; Frequency response function
• Online Access: http://hdl.handle.net/1993/31748

During vibration of engineering structures, fatigue cracks may exhibit repetitive crack open-close breathing like phenomenon. In this thesis, the concept of entropy is employed to quantify this bi-linearity/irregularity of the vibration response so as to evaluate crack severity. To increase the sensitivity of the entropy calculation to detect the damage severity, entropy is merged with wavelet transformation (WT). A cantilever beam with a breathing crack is studied to asses proposed crack identification method under two vibration conditions: sinusoidal and random excitations. Through numerical simulations and experimental testing, the breathing crack identification under sinusoidal excitation is studied first and proven to be effective. Then, the crack identification sensitivity under lower excitation frequencies is further improved by parametric optimization of sample entropy and WT. Finally, breathing crack identification under general random excitations are experimentally studied and realized using frequency response functions (FRFs) as an add-in tool with the proposed crack identification technique. === October 2016