Study Of The Mechanical Properties And Damage Characteristics Of Structural Sandstone Under Impact Loading

Rock is a special geological material with a certain structure and structure composed of one or more minerals,inevitably there are different orders of initial micro-fractures,joints,faults and defects distributed inside the rock under the long-term repeated geological evolution.destabilisation affects the safety of the project.Based on this thesis,structural sandstone is used as the research object,and the modified separated Hopkinson compression bar system is used to conduct uniaxial impact load and cyclic impact load tests on structural sandstone under certain static envelope pressure conditions,while the damage wave velocity of structural sandstone is measured using a non-metallic ultrasonic detection analyser to study the damage characteristics,and the main research contents and conclusions of the thesis are as follows.The dynamic stress-strain curves of intact and structural sandstones under SHPB uniaxial impact loading tests were divided into three stages: elasticity,strengthening and destruction,and the dynamic mechanical properties of sandstones with different fissure angles were obtained.With the increase of fissure angle,the dynamic compressive strength and cut-line modulus of structural sandstones increased and the strain rate decreased,and the fissures would deteriorate the mechanical properties of the rocks to different degrees,and the structural sandstones The compressive strength,dynamic deformation modulus and peak strain of structural sandstone increase with the increase of impact air pressure,and there is an obvious strain rate effect.In the process of energy dissipation in structural sandstone,the ratio of reflected energy to incident energy decreases and the ratio of transmitted energy to incident energy increases as the fracture angle increases,and there is no obvious relationship between energy dissipation rate and fracture angle.The fracture angle does not affect the final form of damage of the specimens,but as the impact pressure increases,the number of small fragments of the specimens increases and the degree of fragmentation increasesUnder the SHPB cyclic impact load test,the dynamic stress-strain curves of structural sandstone under different static load enclosure pressure conditions can be divided into compression-density phase,elastic phase,internal crack expansion phase,unloading phase and rebound phase.As the number of cyclic impacts increases,the dynamic compressive strength and deformation modulus of structural sandstone gradually decrease,and the ratio of recovery strain to elastic strain gradually decreases,and the peak stress,elastic modulus and ratio of recovery strain to elastic strain of structural sandstone increase as the static load envelope pressure increases.A good linear relationship is shown.During the energy transfer process,as the number of cyclic impacts increases,the reflected energy of the structural sandstone gradually increases and the transmitted energy gradually decreases,and the energy dissipation rate,absorbed energy per unit volume and accumulated absorbed energy per unit volume all increase,reflecting that the internal damage of the specimen gradually increases under the cyclic impact,and there is a positive linear correlation between absorbed energy per unit volume and the average strain rate.and fracture angle are not significantly relatedThe damage to the structural sandstone was determined by measuring the wave velocity after damage,and it was found that with the increase in the number of cyclic impacts,the damage to the structural sandstone gradually increased as the wave velocity decreased,and the damage evolution pattern of the specimens differed under different static load envelope pressures.At the same enclosure pressure and number of cycles,the accumulated damage to the structural sandstone gradually decreases as the fracture angle increases,and the accumulated damage gradually decreases as the enclosure pressure increases.2MPa static load enclosure,0°,30°,45° and 60° fracture specimens are highly fragmented,with tensile and splitting damage patterns dominating,and 90° fracture specimens are mainly edge damage.6 MPa static load enclosure,macroscopic damage occurred in the 0° fractured specimens,end edge damage was dominant in the 30°,45° and 60° fractured specimens,and a ring-shaped damage surface was produced in the 90° fractured specimens along the loading direction through the specimens.10 MPa static load enclosure,no macroscopic damage occurred in the fractured sandstone specimens after four cycles of impact loading,and high strains were concentrated at the end to produce spalling.