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.