Abstract: The characteristics of sandstone localized deformation have been studied by visual triaxial compression servo control test system under different loading rates. By the use of the 3D-DIC (3 dimensional digital image correlation) test system, we obtain the axial and radial strain field nephogram, as well as the crack evolution process of sandstone under triaxial stress. The influence of loading rate on the localized deformation of sandstone has been analyzed. The results show that: before the peak strength, the surface deformation of sandstone is relatively uniform. The strain concentration phenomenon occurs at the peak strength, and it expands rapidly in the post-peak stage, and finally forms a deformation localized zone that penetrates the sample surface. As the load rate increases, the peak strength, elastic modulus, Poisson's ratio, peak axial strain and peak radial strain of sandstone all increase. When the loading rate increases from 1×10–6 s–1 to 1×10–3 s–1, the starting stress of localization of deformation also increases. Besides, the ratios and , which describe the levels of the starting stress of axial and radial deformation localization, have changed from 92.00% and 93.75% after the peak to 97.17% and 96.00% before the peak, respectively, indicating that the deformation localization of sandstone has relatively obvious loading rate effects.

Key words: sandstone, 3D-DIC, strain field nephogram, deformation localization, rate effect