On the ratio of rock fracture parameters in static and dynamic conditions

Abstract

This paper presents the methods and results of experiments on contact fracture and splitting of sandstone plates (f = 4 points Protodyakonov scale, scompr = 82–112 MPa) with a thickness of d = 10, 15, and 30 mm, when tested using a hemispherical indenter in quasi-static (v ~ 1 mm/min) and dynamic (vmax ~ 2.2 m/s) loading conditions. It has been found that the dependence between force N and penetration of an a-indenter during contact fracture of the rock under quasistatic conditions is close to N = gsta at the system stiffness coefficient of gst ~ 1.1·107 N/m, and the work and specific energy consumption of the splitting process under these conditions are significantly lower than they are under impact. Assuming the load characteristic of indenter penetration at impact is described by the same function as it is in the static conditions and that only about half (54 %) of the impact energy is used for rock fracturing, equations of the V. B. Sokolinsky two-element classical impact system may be used to calculate the maximum penetration depth am, maximum impact force Nm, and the time to reach the maximum force on impact tm with contact surface fracturing and splitting of the plates. The reliability of the calculation is confirmed by the closeness of the calculated values of am and tmto their values that had been established experimentally based on the depth of the indenter impressions ai and oscillogram trends. It has been established that the forces required to split sandstone plates upon impact are approximately two times higher than the forces required under static loading conditions.