116 C. Casavola et al. Fig. 18.7 OM micrographs showing the microstructure of sample corroded 20 h (a), and 110 h in synthetic rain (b) Fig. 18.8 Corrosion rate as a function of exposure time 18.4 Conclusions Damages introduced by corrosion are huge and, due to this reason, monitoring of the corrosion is a very important aspect for the evaluation of the degradation of materials andthose of interest in cultural heritage. It is important to have a system that can be used for easy monitoring of the surface condition and to put in evidence the beginning of dangerous localized corrosion phenomena, which can require reparation. In this research, a fringe projection system for detecting corrosion onset was tested. By performing a frequency spectrum analysis of the recorded images, in fact, the onset of corrosion determines the contrast reduction of the projected fringe frequency, due of the matting, and the appearance of off-axis orders frequency connected to shape variation introduced by the patina. In particular, it appears that after 20 h of exposure to synthetic rain there are no significant effects while the presence of the patina is evident after 110 h. This preliminary study shows that the approach can have the potential of providing rapid on-site inspection and it could be adapted to measurement of corrosion in a small area or on a large structure. Acknowledgements This research was co-funded by Fondo di Sviluppo e Coesione 2007–2013–APQ Ricerca Regione Puglia “Regional progam for Smart Specialization and Social and Environment sustainability” -FutureInResearch
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