An inter-laboratory study of the calibration of optical full-field systems for measuring deformation

Abstract

A calibration of optical full-field systems for measuring deformation is performed using a physical Reference Material that reproduces fields of strain and deformation. Traceability of the measurement results is established by applying a calibrated transducer at a selected point and using an analytic description of the deformation field to extend traceability to the entire gauge area. A Reference Material based on a cantilever together with a protocol for its use had been suggested for both static and dynamic calibrations in a CEN Workshop Agreement. They have been challenged in an inter-laboratory study of calibration conducted on an international scale. We report results of this inter-laboratory study of calibration which prove that the Cantilever Reference Material is sufficiently stable and reproducible to be used as a calibration artefact for displacement and strain fields in static and dynamic loading. Participants applied the Cantilever Reference Material in a range of tip deflections from 2 μm to 4.7 mm. Deformation from static bending is shown to be linear in the tip deflection up to the highest loads applied thus providing evidence that the reference values of the calibration artefact are appropriate. In dynamic loading, the first resonant bending mode has proven especially useful for the purpose of calibration. While the calibration procedure proved to be viable, the feed-back of the participants led to a number of modifications to the relevant chapter of the CEN Workshop Agreement, for example, as to the estimation of calibration uncertainty.