Issue 61

S.M. Firdaus et alii, Frattura ed Integrità Strutturale, 61 (2022) 254-265; DOI: 10.3221/IGF-ESIS.61.17

defect locations, as shown in Fig. 5 and Fig. 6. This obviously indicated that the highest peaks were within the range of 6 s to 8 s due to the expected region of specimen failure.

a) 85 % UTS

b) 80 % UTS

c) 75 % UTS

d) 70 % UTS

e) 65 % UTS

f) 60 % UTS

g) 55 % UTS h) 50 % UTS Figure 7: Time base magnetic flux leakage signals from UTS loads of; a)85%, b)80%, c)75%, d)70%, e)65%, f)60%, g)55% and h)50%. Then, after the conversion of the dH(y)/dx signals from length-based to time-based, the MMM signals were transformed into the time-frequency domain since the Morlet wavelet transform was chosen as the basic function for the transformation. As illustrated in Fig. 8, the estimation of wavelet coefficients was the first step in a wavelet analysis, as the matrix row (x axis) represents the time parameter and the matrix column (y-axis) represents the scale parameter, which is inversely

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