Experimental and numerical simulation study on crack propagation of fractured fine sandstone under the influence of loading rate

For the study of crack Angle and loading rate influence on rock crack propagation and failure mode,the center drilling method is adopted in 50 mm×50 mm×100 mm fine sandstone samples on precast transfixion crack width range of 0°-90°,and carries on the acoustic emission monitoring and photography order axial compression test and PFC numerical simulation research,comprehensive analysis of the evolution regularity of crack and deformation and failure characteristics.Results show that the fracture failure mode in the sandstone sample containing the tensile failure and shear failure and tensile/shear mixing three kinds of damage,based on the mechanism of crack crack and refine its trajectory can be divided into T1-4(tensile),S1-3(shear),M1-2(mixed) 9 types,such as crack initiation can be divided into the wing crack,crack,resistance to pull coplanar/non coplanar secondary crack,transverse crack,such as five types,and are closely related to the sample loading failure process.The crack propagation and failure mode of rock sample is controlled by the crack angle α.With the increase of α,the crack initiation stress increases,the crack initiation location transfers from the center of the prefabricated crack to the tip,the number of crack initiation decreases in the early stage,and the rock sample failure mode transfers from shear failure to tensile failure.Loading rate and the initial crack extension and failure mode effect,with the increase of loading rate,crack initiation type changed from wing crack to crack resistance,and not to other types of crack,crack crack a shorter time,to make the transition to tensile failure of failure by shear failure mode by sample surface macroscopic crack down.The damage process of the rock sample is closely related to its acoustic emission characteristics and the acoustic emission location information accurately reflects the internal damage of the rock sample.PFC numerical simulation experiment results support the indoor physical experiment conclusion effectively,and reflects the rock crack initiation and extension and transfer is the root cause of the change of stress field,and the compressive stress is mainly concentrated in the prefabricated crack tip,and the tensile stress concentrated near the crack initiation,to some extent,the distribution of tensile stress field reveals that the main trend of crack initiation.