In order to investigate the progressive failure process of brittle rock

the mechanical properties of red sandstone from south area of Shandong province are studied by the RMT-150C rock mechanical experimental system. The stress-strain curves of samples under different strain rates are recorded. The deformation and progressive failure process of rock samples is divided into several stages

including crack closure stage

linear elastic deformation stage

crack initiation and stable crack growth stage and unstable crack growth stage. Then the crack initial stresses and crack damage stresses are determined by the moving point technique according to the data of stress-strain curves and other deduced data. The influence of strain rate on the ultimate critical strength

the crack initial stress and the crack damage stress are also investigated. The results show that the ultimate critical strength first decreases and then increases as the strain rate increases; and the rate of crack initial stress and crack damage with the ultimate critical strength decreases. The mechanism of the experimental results are analyzed and explained by the stress concentration model of rock with nonuniformities. And the influence of strain rate on the progressive failure process is studied.