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Application of fiber Bragg gratings for strain measurement in historic textiles and paintings on canvas

Zawadzki W., Bartosik M., Dzierzega K., Bratasz L., Lukomski M., Peacock E.

Optica Applicata

2012

Vol. 42, nr 3

503-517

The aim of this work was to evaluate the applicability of optical fiber Bragg grating (FBG) sensors to the monitoring of deformation in historical textiles and paintings on canvas. Fibers with a ceramic coating were selected for strain investigation in textiles due to both their almost perfect strain transfer and much shorter relaxation times compared to fibers with an acrylate coating. FBG sensors were attached to fabrics in a non-destructive manner using specially designed magnetic clamps. Local strain measurements using these sensors were consistent with general strains measured using either a universal testing machine (UTM) or a laser triangulator when varying external load or relative humidity. However, strain magnitudes measured by the different methods were comparable only after correction for the influence of the fiber on the textile under study. Strain measurements in model paintings on canvas were carried out using uncoated fibers embedded in the gesso layers on the canvas. Despite some drawbacks, the FBG sensors were found to be useful in monitoring strain in historic textiles and consequently, for the assessment of environmental risk of these works-of-art.

Simple digital speckle pattern interferometer (DSPI) for investigation of art objects

Lasyk L., Lukomski M., Bratasz L.

Optica Applicata

2011

Vol. 41, nr 3

687--700

Technical development and practical evaluation of a simple digital speckle pattern interferometer (DSPI) for the non-invasive, non-contact detection and characterization of early-stage damage of painted objects of art, like fracturing and layer separation, are reported. One of the most important features of the presented measuring system is a possibility to progress stepwise from the simplest version of the instrument based on the digital image correlation (DIC), to more advanced and accurate ones: DSPI for thermally- and sound-induced surface deformation. Analysis of the resonant frequency of a vibrating delaminated paint layer was, for the first time, used to detect the damage progress in polychrome wood and proved to be extremely sensitive and accurate. This method, together with two other presented in the article makes the multilevel analysis of the preservation state of the object's surface possible and provides information on the damage on a desired level of complexity and accuracy.