Final Report - Strategic Environmental Research and Development ...

Predicted TTF
The BFM method, introduced by Haruyama et al. [29] and later modified by Mansfeld and Tsai
has been proposed as an estimator of the area of delaminated metal without the need of modeling
EIS spectrum into an equivalent circuit [30, 31]. The original or modified BFM model relates
the frequency at 45º (f 45º ) or minimum phase-angle (f min ), to the delaminated coated area. An
increase in both, f 45º or f min , is associated with an increase in the defect area and therefore to a
decrease in the corrosion protection.
The phase angle response at the frequencies given by the fuzzy sensitivity analysis can be used to
predict evolution on the defect area coating response. Figure 6.23 shows the phase angle
response of commercial samples 7075-BDP and 7075-BHN. Although both samples showed no
signs of corrosion at the end of the experiment (TTF = 1000 h), sample 7075-BDP shows twice
the difference in the phase angle between 2 and 600 hours of exposure when compared with
7075-BHN. This difference suggests a markedly larger increase in the defect area for sample
7075-BDP than 7075-BHN.
1.2
1
y = 0.8512x + 0.0629
R 2 = 0.9195
0.8
0.6
0.4
0.2
0
0 0.2 0.4 0.6 0.8 1 1.2
Measured TTF
Figure 6.24. P-normalized predicted vs. measure data. Prediction was done by a 7 hidden
neurons ANN fed with phase angle information collected before 48 hours exposure to ASTM
B117.
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