Digital Image Correlation - Resolution of DIC/DDIT

Resolution of DIC/DDIT

The resolution that one can achieve in practice using these image-based techniques depends on a number of factors, including but not limited to camera resolution, lens optical quality, and marker size and quality. To demonstrate the achievable resolution that one can achieve using the setup and techniques described herein using both DIC and DDIT, a tensile test performed on a brittle linear elastic submicrometre (t ~ 250 nm) freestanding Al-32 at%Mo specimen was analyzed for strain using both methods. This specimen was chosen because it exhibits small strains that are difficult to resolve and also because it is amorphous and thus minimizes any microstructural inhomogeneities. The initial raster grid that was applied for the DIC method and the automatically labeled markers (“good” markers are shown as circles) are shown in Figures 6 and 7 (missing figures), respectively. The representative stress strain response from this film is shown in Figure 8 (missing figure), where both longitudinal (shown in blue) and transverse (shown in green) strains were calculated using DIC with two subset image sizes (15 and 25 pixels) and DDIT. It is apparent from these results that the peak tracking algorithm works quite effectively at resolving the response of this film, even when tracking about 50 times fewer points. The insets of Figure 8 (??) show the typical strain variation that was achieved, where as low as 40 με was observed in the longitudinal direction using DDIT. It was concluded that either of these techniques were effective at measuring the Young’s moduli of these specimens, although the transverse strain resolution obtained using DIC is at the upper limit of what one would desire to measure Poisson’s ratio.