Detection-depended parameters of internal defect mapping in fringe-based analysis

As it is well known an important application of holographic non-destructive testing (HNDT) is found in the investigation of structural condition of artworks, especially in defect localization, as well as in detection of deformation responses and stress concentration. The detection is realized through the generation of visual interference fringe patterns of low frequencies and the analysis is performed through a qualitative or quantitative assessment of their distribution. In this paper the aim is primarily towards the establishment of the experimental parameters dominating the fringe pattern formation process and their significance on the results obtained along with their inherent limitations in the interpretation procedure. Relevant experimental results obtained using the basic principle of double-exposure holographic interferometry from specifically constructed defects in samples are presented in support of the above goal. It should be underlined that there are fringe pattern similarities in relation to experimental parameters. Finally it is suggested that the most specific the investigating conditions are, the most precise defect characterization is achieved leading to accurate metrology on the artwork.