The finite element framework for nonlocal digital image correlation (NL-DIC) for discontinuous displacement fields

Abstract

A numerical procedure of finite element (FE) method for nonlocal displacement measurement from digital images is proposed. The method is a two-scale model of displacement measurement, which constitutes the classical FE displacement, and a nonlocal displacement measured from the attenuated relative displacement of the neighboring pixels. The traditional finite element-based digital image correlation (FE-DIC) method suffers from noisy and overestimated displacement fields near singularities, analogous to the Gibbs phenomenon. Due to its selective displacement adjustment, the proposed Nonlocal DIC (NL-DIC), detects the displacement jump with reasonable accuracy and smoothen the noise in the vicinity of discontinuity. The algorithm does not require input regarding the affected region from the discontinuity and works as an automated system. The method’s de-noising property helps to decrease the displacement uncertainty for finer meshes. A robust, three-parameter Discontinuity Resolution Index (DRI) is introduced to assess the metrological performance of DIC algorithms for discontinuous displacement measurement. The proposed framework is validated on three numerical experiments exhibiting discontinuities. Practical guidelines are provided, underscoring its applicability in capturing sharp kinematic features with improved robustness.