Experimental Study On The Strain Rate Effect Of Granite Mechanical Properties From Creep To Super Dynamic Strain Rate

The source of the difference between the dynamic behavior and the static behavior of rock is the loading rate and the strain rate.The strain rate has a significant influence on the mechanical and deformation characteristics of the rock.However,the current research on the strain rate effect of rock is concentrated within a small strain rate range,and the test methods as well as the rock samples adopted in different strain rates are quite different,leading to different research results which is difficult to compare and analyze.Therefore,a complete and systematic study of rock mechanical behavior within a wide strain rate range is of high scientific interest and high application value in fields such as blasting engineering,protection engineering,and earthquake engineering.Considering different loading rate tests demanding,three-axis rheometer,rigid hydraulic servo testing machine,MTS815 testing machine,Instron Vhs high-speed test system,Hopkinson pressure bar device as well as light gas gun testing device were applied on high repeatability granite samples which were taken from the same core,to carry out the rock uniaxial compression test within the strain rate range of 10-7~104s-1.The stress-strain curve of granite at different strain rates was obtained,and the strain rate of mechanical characteristics,i.e.,strength and elastic modulus,were analyzed.The average particle size,fractal dimension as well as RR model of the fragmentation distribution function were adopted to quantitatively describe the fracture degree of granite samples,revealing the strain rate effect of granite fracture degree;The law of energy dissipation of the granite under different strain rates was analyzed,and the dependence of energy dissipation on the strain rate was quantitatively characterized.The test results show that the strength and elastic modulus of granite both increase with the increase of strain rate.Within the strain rate range of 10-7~10-1s-1,the increase in strength and elastic modulus is small and remains stable.At the strain rate range of 100~104s-1,the changing trend of strength and elastic modulus is relatively large with an increasing trend.The average particle size decreases first and then increases with the increase of strain rate,while the fractal dimension presents a roughly opposite trend.The changing trend of the m parameter in the RR function of the fragmentation distribution function is inconsistent with that of the degree of granite fracture,indicating it cannot be adopted to describe the degree of fragmentation.The average particle size is greatly affected by the change of the large particle size.The quality of different particle size ranges does not contribute to the average particle size,while the fractal dimension of the same particle size range has the same contribution to the average particle size.Therefore,the fractal dimension describes the degree of rock fragmentation more accurately.The energy consumption in the compression process of granite increases with the increase of the strain rate.At the strain rate range of 10-7~10-1s-1,the increment of the dissipated energy is small and remains stable,while the dissipated energy varies greatly and shows an increasing trend within the strain range of 100~104s-1.Energy dissipation is the direct reason to rock fragmentation,and a good corresponding relationship between these two parameters can be found at high strain rates while it is not obvious at low strain rates.