Study On Tensile Properties Of Prefabricated Defect Sandstone Under High Strain Rate

There are a large number of solid and fluid minerals in the rock.75%?85%of the world's total reserves of various resources are sedimentary and sedimentary metamorphism.Affected by diagenesis and cementation,there are initial defects in the rock.With the development of resource exploitation to the deep,the difficulty of mineral resources exploitation increases,and the surrounding rock is vulnerable to dynamic disturbances such as rock burst,blasting load and vibration generated by mechanical drilling.Numerous studies have shown that in the construction project of deep mine roadways,the initial imperfection of rock cannot be ignored under the dynamic effect,and the evolution law and criterion of crack initiation of defective rock will also change.Based on this,this paper selects the common sandstone in deep mine as the research object.Around the dynamic fracture behavior and crack evolution mechanism of defective sandstone,the dynamic tensile mechanical characteristics and dynamic initiation criterion of defective sandstone under impact load are studied by laboratory test combined with theoretical analysis.The main contents and conclusions are as follows:In order to study the dynamic failure mechanism of rock with hole defects under dynamic disturbance environment,a rock SHPB test system integrating ultra-dynamic strain test system and high-speed photography system is constructed by using a split Hopkinson pressure bar(SHPB)test platform with a rod diameter of 50mm and a high-speed photography device.The synchronous acquisition of high-speed photography and ultra-dynamic strain system is realized.The dynamic tensile mechanical properties,fracture characteristics,energy absorption effect law and crack evolution law of rock with circular hole defects under radial impact load were studied.The results show that:(1)For the central-hole sandstone,the sandstone sample has tensile failure,and the degree of fracture increases with the increase of emission pressure;The dynamic tensile strength decreases linearly with the increase of pore diameter length,and increases linearly with the increase of strain rate.Compared with strain rate,the influence of inner diameter on the dynamic tensile strength of sandstone is weak.The energy absorption rate decreases linearly with the increase of hole diameter length or emission pressure;In addition to the common splitting cracks,along with the increase of pore diameter length,the macroscopic cracks of sandstone also derive the secondary cracks which are approximately vertical main cracks.(2)For eccentric hole sandstone,the peak load increases linearly with the minimum distance from the center of the disc to the edge of the hole,and decreases nonlinearly with the increase of the hole diameter length.With the increase of the minimum distance from the center of the disk to the edge of the hole,the initiation position of the crack transfers from the hole surface to the diameter range of the disk load.The crack initiation within the loading diameter range of the disk load is the initiation of tensile failure.As the crack expands along the loading diameter,it gradually turns to the combined failure mechanism of tensile and shear.The crack initiation on the surface of the hole is driven by tensile stress,and the crack propagation process is mainly affected by tensile stress.In order to realize the experimental study on the failure mechanism of rock with fracture defects under dynamic disturbance environment,the radial compression test of fractured sandstone under radial impact load is carried out by means of rock SHPB test system.The results show that:(1)When the impact pressure is 0.2MPa,the peak load increases first and then decreases with the increase of prefabricated fracture angle,and the maximum value is 60°.When the impact pressure is 0.3MPa and 0.5MPa,the crack initiation time decreases first and then increases with the increase of prefabricated fracture inclination angle,and the maximum value is at 45°.When the emission pressure is the same,with the increase of fracture dip angle,the peak load decreases nonlinearly,and the minimum value is at 60°,and the crack initiation time increases nonlinearly,and the minimum value is at 45°.(2)When the fracture surface has a certain angle with the direction of impact load,the final failure mode is the tensile and shear combined failure composed of tensile failure and shear failure.In order to study the influence of strain rate and fracture dip angle on the dynamic fracture characteristics of sandstone under radial impact load,the dynamic fracture performance of fractured sandstone under radial impact load was analyzed.The fracture performance of sandstone samples under high strain rate was measured by using the maximum stress intensity factor criterion.The I-type crack initiation criterion of sandstone under different strain rates was established.The ?-type strength factor value and ?-type strength factor value of sandstone under different strain rates and different fracture dip angles were obtained.The study shows that the ?-type dynamic fracture toughness of sandstone increases with the increase of strain rate.Under the three kinds of pressure loading,the variation laws of type ? and type ? intensity factors with fracture dip angle are the same.The absolute values of type ? intensity factors decrease first and then increase with the increase of fracture dip angle.The absolute value is the smallest at 30°,and the values of type ? intensity factors increase first and then decrease.Figure[87]table[14]reference[168]...