Abstract: Strain localization is the warning sign of rock damage. In order to reveal the key mechanical factors that control its occurrence time, position and growth direction, digital image correlation method is used to obtain the whole deformation process of specimens under uniaxial compression tests. The maximum and minimum principal strain field, displacement field are then calculated. Combining with the axial load-displacement curve, the strain localization evolution characteristics of different specimens are compared and analyzed comprehensively. It is found that for brittle rock-like material under uniaxial compression the strain localization belt grows at the direction of maximum principal strain (maximum compressive strain) and deflects with the direction change of maximum principal strain; the position of the strain localization belt is controlled by minimum principal strain; the transient displacement field indicates that damage of brittle rock-like material in the strain localization belt is mainly caused by tensile deformation not shear deformation; strain localization not only occurs at the point close to peak load, but also at the inflection point where deformation accelerates but the load is low; the appearance of localization belt and opposite horizontal displacement vector along the belt are two proper failure prediction indices.

Key words: strain localization position, strain localization direction, early-warning criteria, principal strain