Calibration of a Speckle Interferometry Full-Field Strain Measurement System

: This study describes the calibration of a full‐field speckle interferometry strain measurement system using the calibration specimen and protocol defined in the Standardisation Project for Optical Techniques of Strain measurement (SPOTS) standard. The specimen was based on the monolithic embodiment of a four‐point bending test and was manufactured from aluminium following the SPOTS design. Strain‐gauge rosettes attached to the upper and lower faces of the beam were used to derive two correction factors of an analytical expression that predicted the strains generated in the gauge section of the beam. Following the SPOTS protocol, the comparison of measured and predicted strains yielded two fit parameters and their associated uncertainties for each of three displacement‐load steps which indicated the closeness of the data sets. An acceptable calibration was achieved for the single normal component of in‐plane strain considered in this study, for each load step employed. For the highest load range, which generated a maximum strain of approximately 810 μstrain in the gauge section, the overall calibration uncertainty was found to be 35.3 μstrain, which in relative terms can be expressed as 2.2% of the strain measurement range for which the instrument was calibrated.