Figure 4

(a) Diagram of the transversal profile assumed in the FE model for the characterization of the treated side of the specimen. (b) Distribution of penetration depths \(h_l\) making the FE model best approximate the modal frequencies of plates 1-3, only sized. (c) Distribution of penetration depths \(h_l\) making the FE model best approximate the modal frequencies of plates 4-6, pre-treated with KOH. (d) Distribution of penetration depths \(h_l\) making the FE model best approximate the modal frequencies in plates 7-9, pre-treated with \(\hbox {NH}_{3}\). Histograms are evaluated when plates are only pre-treated (\(t=p\), dashed lines) and after the application of the complete primers (\(t=s\), solid lines). Colored regions highlight the ranges of preferential values characterizing each combination of treatments.