Quantitative Measurement of In-plane Strain of Canvas Paintings Using ESPI

摘要

This paper reports on an experimental investigation into the application of electronic speckle pattern interferometry to characterise and quantify the mechanical behaviour of paintings on canvas. It is difficult to apply standard engineering measurement techniques to paintings because of their complex composite structure and therefore the use of interferometric analysis is particularly appropriate. Additionally, non-contact, non-destructive, in-situ measurement of genuine paintings is one long-term aim of this project, as their inherent stochastic nature makes it difficult to obtain repeatable data. A fibre optic electronic speckle pattern interferometer (ESPI) has been built to operate in conjunction with a custom designed biaxial tensile tester and environmental chamber. It has been used to investigate the potential of ESPI to map non-uniform biaxial strain of paintings on canvas. The measurements have shown that non-uniform strain does occur and that ESPI is an effective method of investigating discontinuities such as paint delamination or structural repairs of the canvas. Comparison with strain gauge measurements has shown that although ESPI is a difficult technique to apply to flexible specimens, quantitative measurements of the biaxial mechanical properties of the anisotropic composite are achievable.