Application of the digital image correlation technique in wide width tensile test of geogrids

Abstract

This paper aims to explore the DIC technique for use in wide width tensile testing of geogrids, from specimen preparation to selection of DIC parameters required for analysis to provide a guide for a proper use. A series of monotonically loaded wide width tensile tests were conducted on a PET geogrid to investigate the effects of specimen surface preparation methods and the user-defined DIC parameters. An additional set of tests under cyclic loading was conducted to investigate the effect of the image sampling rate. The results indicate that the speckle pattern (image texture) has a significant effect on the DIC results such that the larger is the speckle size, the greater is the uncertainty level, eventually leading to increased nonuniformity in the calculated strains. Also, it was revealed that a subset size smaller than optimal, typically 20–30 pixels, results in highly localized strain distribution. A similar trend was observed in step size. In addition, the image sampling rate was found to have a significant effect on the DIC-calculated cyclic strains, such that the lower is the image sampling rate, the lower is the calculated cyclic strain.