Accurate Reconstruction of High-Gradient Strain Field in Digital Image Correlation: A Local Hermite Scheme
High-gradient strain field measurement is attracting more attention from both engineering and scientific domains, where digital image correlation (DIC) is widely adopted to recover the dramatically changing displacement fields of stressed samples. Accurate reconstruction of reliable strain field from noisy displacement field is one of the key issues, since the strain calculation is highly sensitive to the displacement noise. The formally proposed improved Hermite finite element smoothing method  (IHFESM) and fast Hermite element method (FHEM)  are effective global Hermite method based on Tikhonov regularization. However, complex meshing process and high computation burden are inevitable downsides. In this work, we present a local version of FHEM, i.e. the local Hermite method, in which the Hermite element is taken as a smoothing window centered on one displacement data, and the whole field is handled point-wisely. The smoothed displacement and strain are consequently computed from the regularized local surface as in FHEM. The proposed method can deal with arbitrarily shaped region of interest, and is especially suitable for high gradient strain measurement due to the rich high gradient components contained in C2 continuous Hermite element. Experiments show that the local Hermite method is more accurate than global Hermite method such as FHEM and IHFESM.
KeywordsDigital image correlation High-gradient strain Displacement smoothing Hermite element