Characterization of coating processes in Moiré Diffraction Gratings for strain measurements

This paper analyses the influence of the coating process in the optical efficiency of replicated Moiré Diffraction Gratings (MDGs), which are applied on real field applications for measuring both the surface displacements and strains. The Moiré diffraction technique is an experimental full-field, non-contact and high resolution optical method, which can reveal to be very useful in extreme harsh environments. The optical efficiency of the replicated MDGs plays an important role in the quality of the experimental measurements. Two processes were used to obtain the metallic coatings: sputtering and aluminum vaporization. A good coatings quality with high optical efficiency was achieved for both processes (e.g., 17%–28%). However, for the replicated gratings a slight decrease in the optical efficiency was found (e.g., 14%–21%). The MDGs were successfully used for the experimental measurements of displacement and strains in a single lap joint. The measurements also showed that high quality of measurements allowed the identification of unbounded regions.

► The influence of coating process in the optical efficiency of replicated MDGs. ► Metallic MDGs were fabricated (by sputtering and aluminum vaporization). ► MDGs in aluminum with high reflection index were replicated and tested. ► A case study for demonstrating the concept and application in the real field is presented.