Accuracy of Quasi-Static Bending Strain Measurement using Scanning Laser Doppler Vibrometry (SLDV)

This paper presents an investigation into the use of 1D scanning laser Doppler vibrometry for the measurement of quasi-static bending strain, on a beam, from measured out-of-plane deflections. To calculate the bending strain from measured deflections, a Savitzky-Golay differentiation filter is used. An experimental investigation was conducted to determine how the strain estimate would be affect by the spatial interval between measurement points, amplitude of loading, and the numerical parameters used within the Savitzky-Golay differentiation filter. A number of findings, from the investigations undertaken are presented. The bending strain measurement technique is best approximated by using a third-order polynomial in the Savitzky-Golay differentiator filter. An accurate bending strain measurement can be produced at any spatial interval, as long as the filter width spans a fixed distance. In addition, changes in applied load have no effect on the accuracy of the technique. This technique has significant application for the measurement of localised bending strain on the surface of structures or materials that are cyclically loaded and subjected to harsh environmental conditions, such as elevated temperatures.