Chapter 18 Feasibility of Using Fringe Projection System for Corrosion Monitoring in Metals of Interest in Cultural Heritage C. Casavola, P. Pappalardi, G. Pappalettera, and G. Renna Abstract Cultural heritage is affected by degradation processes related to intrinsic factors, environmental or human activities. Corrosion is one the most deteriorative phenomena and it can introduce huge damages. Patina or thick corrosion crust formed on artifacts, may display complex products and structures. The identification of the corrosion products or characterization of the patina on artifacts is an essential task to acquire a better knowledge about the condition of ancient objects, corrosion processes and conservation treatment or preventive procedures for long-term, stable preservation. These considerations show that corrosion monitoring is a very important aspect for the evaluation of the degradation of cultural heritage. It is important to have a system that could be used for easy monitoring of the surface condition to put in evidence the beginning of dangerous localized corrosion phenomena. Nowadays optical methods allow detecting and representing, with remarkable accuracy, three-dimensional objects such as sculptures and archaeological finds, as well as large items such as architectural structures. One of the most powerful approaches is the Fringe Projection System (FP) based upon the projection of a complex pattern of light on the object to be reconstructed. In the following work, Fringe Projection is proposed for monitoring and to make quantitative evaluations of the corrosion process occurring on surfaces. The corrosion tests have been performed. Before starting the test, a fringe pattern is projected and the frequency spectrum of the recorded image is analyzed. Successively the samples are submerged in a solution of synthetic acid rain. At different time intervals the specimens were extracted from the solution and analyzed. Fringe pattern is projected again on the surface and new analysis of the frequency spectrum is run. Moreover surface analyses by microscopy and weight loss measurements were performed. At the end of the test, the specimens extracted from the solution were studied by surface analyses and weight loss measurement. The corrosion behavior of the bronze sample has been checked by fringe projection and optical microscopy observation during the exposure to synthetic rain. The average weight loss values were calculated using weight of sample measured before and after exposure to synthetic rain to quantify the corrosion rate of the sample in the corrosive solution. Keywords Bronze Alloy • Corrosion • Cultural Heritage • Fourier Transform • Fringe Projection 18.1 Introduction The cultural heritage is the man’s identity. Its preservation and enhancement require an extensive documentation, which includes the physical characteristics of position, shape, color and geometry, and the restoration operations. Nowadays technology based on 3D reconstruction on 3D prototyping can give a great support in restoration planning [1–4] The cultural heritage is affected by degradation processes related to intrinsic factors, environmental or related to human activities, because of their composition and chemical reactivity of the materials that constitute them. These processes alter the appearance and the mechanical and structural characteristics including fatigue behavior [5–12]. Corrosion is one the most detrimental processes [13]. It is a complex chemical-physical phenomenon involving degradation of the materials driven by the environment in which they are exposed. The damage caused by corrosion can be huge. In general the corrosive damage often is not limited to the simple replacement of the affected component (direct costs), but it may include a series of indirect damages. Furthermore, the corrosion is an insidious and a slow process as it displays its negative effects on monthly or yearly base time. One of the most invasive corrosion mechanisms is certainly the one that occurs in marine environments [14, 15]. Another type of very dangerous corrosion is due to exposure to the urban environment, most significantly urban pollution. Several studies have examined the properties of pollutants (water solubility, chemical reactivity, acidity, deposition C. Casavola • P. Pappalardi • G. Pappalettera ( ) •G. Renna Dipartimento di Meccanica, Matematica e Management, Politecnico di Bari, Bari, Italy e-mail: giovanni.pappalettera@poliba.it © The Society for Experimental Mechanics, Inc. 2018 L. Lamberti et al. (eds.), Advancement of Optical Methods in Experimental Mechanics, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-63028-1_18 111
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