Strain fields measurement using frequency domain Savitzky–Golay filters in digital image correlation
Rong Wu, Yanbing Li, Shuiqiang Zhang
Abstract
Abstract Savitzky–Golay (SG) filter is an effective and convenient gradient calculation method employed for full-field strain measurement in digital image correlation (DIC). Currently, the strain field can be conveniently obtained by moving smoothing filtering with SG filters. This is a method of spatial filtering, which offers the advantages of easy implementation and high accuracy. This study proposed a strain calculation method based on frequency domain SG (FD-SG) filtering. Prior to performing FD-SG filtering, data extension operations involving outer-boundary padding and zero-padding were performed on the displacement field data. Similarly, the SG filters template was extended with zero-padding and circularly shift operations. Subsequently, FD-SG filters were generated by applying the fast Fourier transform (FFT) to the expanded SG template. Thereafter, FD-SG filtering was implemented through the multiplication of the displacement in the Fourier-domain by an FD-SG filter. Finally, the strain field was obtained via inverse FFT and valid data interception operation. The simulation and practical experiments confirmed the equivalent accuracy exhibited by FD-SG and spatial domain SG filtering. Thus, the proposed FD-SG filtering method has great potential for real-time strain measurement in DIC.