Investigation of the Uncertainty of DIC Under Heterogeneous Strain States with Numerical Tests

In this research, numerical 2D digital image correlation (DIC) tests are carried out to assess the uncertainty of DIC under heterogeneous strain states. DIC is implemented to measure the deformation of the numerically deformed images with respect to the undeformed counterparts, which are taken from the real tensile specimens. The tensile specimens are made of three materials, i.e. steel DC06, steel DX54D+Z, and aluminium alloy Al6016, and cut into three different geometries, namely one standard design and two complex designs. The specimens are all painted manually with random speckle patterns. The original images are deformed by imposed displacement fields, which are obtained by simulating uni-axial tensile tests of the specimens with finite element analysis (FEA). In this way, the errors sourcing from the hardware of the image system are excluded. According to the geometries of the specimens, homogeneous and heterogeneous strain states are achieved by FEA. The optimum mesh sizes of the models are identified in order to minimize theirs influence on the imposed fields. The impacts of sub set sizes, step sizes and strain window sizes are studied for an optimum correlation. Finally, the influence of the strain state is in vestigated. It is found that the DIC accuracy and precision decrease under highly heterogeneous strain states.