Experimental study of rock with parallel cracks under different loading rates:energy dissipation and damage evolution
In order to study the effect of internal flaw on rock energy dissipation and damage change law under impact loading,intact granite specimens and specimens with different flaw inclination are tested by a modified split Hopkinson pressure bar(SHPB).The results of experiment and theoretical analysis show that the elastic strain energy of 0° flaw decreases first and then increases,while 45° and 90° flaws increases first and then decreases with increasing the loading rate.According to the principle of energy conversion and distribution,a function model is constructed considering the variation of strain energy density,which can well reflect the energy dissipation characteristics of rock before peak stress.In this study,the ratio of dissipated energy to elastic energy is used as the energy indicator of rock failure precursor.During the absorption,storage,and release of energy before the peak stress,there exists self-control of energy.The damage variable of rock under different loading rates is divided into two stages,damage stable development and damage acceleration.Besides,the damage variable shows obvious rate effect,which decreases first and then increases with the increase of crack angle,and it has a good nonlinear relationship with the loading rate and the energy dissipation density,respectively.Based on the mathematical derivation method,the damage evolution equation of the fractured rock under impact loading is constructed,the influence of different fracture angles and loading rates on rock damage curve are also studied.The slope of the damage curve first increases and then decreases,while the damage factor m0 increases and F0 gradually decreases.These conclusions should provide scientific basis for the practical projects of deep rock engineering design and improve the efficiency of rock excavation and rock breakage to some extend.
rock mechanicssplit Hopkinson pressure bar(SHPB)loading rateparallel crackenergy dissipationdamage evolution
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