Analysis of Vibroacoustic Modulations for Crack Detection: A Time-Frequency Approach Based on Zhao-Atlas-Marks Distribution
Figure 7
The separate damage indices (sDI) based on the (first row), the MAX-MIN range (second row), the corresponding standard deviation (third row) of the ZAM transform, and the normalized FFT magnitude (fourth row) at the corresponding VAM frequencies, that is, 31208 Hz (left column), 31300 Hz (middle column), and 31392 Hz (right column), respectively. Note that, for the FFT-based analysis, only the 31208 Hz (left column) and 31392 Hz (right column) were considered, since the FFT amplitude at the central high-frequency (31300 Hz) was used as a normalization factor. Moreover, in the ZAM-based analysis, all values were estimated for the time span of 0.006–0.036 sec to avoid edge effects, while all data samples acquired (92001) were used in the FFT-based analysis to increase its frequency resolution.
