Digital image correlation (DIC) is used to monitor strain in a representative textile material and an historic tapestry. The validity of a ‘map function’ that allows 3D DIC displacement measurements to be obtained when the reference data are collected with a camera set‐up different from that of the deformed data is assessed. An experiment was devised to study the effects of DIC processing parameters (interrogation cell size and overlap) on strain measurements, and to investigate if the textile contains adequate contrast for DIC to operate. The study shows that the textile’s weave pattern can be used as the device for correlation. Long‐term tests for monitoring creep strain using DIC both in the laboratory and in situ are presented. The results show good correspondence between strain changes in the tapestry and relative humidity.
The engineering techniques used for inspecting structural damage are not widely known in the conservation sector. Techniques are available based on deformation or strain measurement that have the ability to provide quantitative data. This paper reviews currently available techniques, covering point-strain measurements using resistance strain gauges and fibre-optic sensors, as well as full-field optical measurement approaches such as holography, electronic speckle pattern interferometry, photoelastic stress analysis and photogrammetry. The underlying technology of each of the techniques is described for the non-specialist. The relevance of each technique is established from a conservation perspective through accounts of usage. The application of the techniques to a wide range of artwork, including panel paintings, statues, murals and mosaics is described and the results critically reviewed. The paper also provides an insight into possible future applications of the techniques and identifies areas for further investigation.
The findings of a year-long programme carried out by a multidisciplinary
engineering/conservation team are described. A mass-produced textile material that can be used to
represent tapestries is identified and mechanical tests are detailed which demonstrate it behaves in a
similar way to tapestry. The feasibility of using optical fibre sensors, full-field optical strain
measurement techniques and thermography for monitoring tapestry degradation is assessed. The
results of preliminary findings are presented and a rationale is developed for in-situ quantitative
strain monitoring of tapestries.
Fibre Bragg gratings (FBGs) in polymer optical fibres (POFs) have been used to measure the strain in a woven textile. FBGs in both POFs and silica optical fibres were attached to a woven textile specimen, and their performance characterised. It was demonstrated that the POF FBGs provide improved strain transfer coefficients and reduce local structural reinforcement compared to silica FBGs and therefore make a more suitable proposition for textile monitoring.
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