In this study,the effect of loading rate on shale fracture behaviors was investigated under dynamic and static loading conditions.Cracked straight through Brazilian disc(CSTBD)shale specimens were tested with a split ...In this study,the effect of loading rate on shale fracture behaviors was investigated under dynamic and static loading conditions.Cracked straight through Brazilian disc(CSTBD)shale specimens were tested with a split Hopkinson pressure bar(SHPB)setup and INSTRON1346 servo-testing machine under pure mode I loading conditions.During the test,the crack propagation process was recorded by high-speed(HS)camera,and the acoustic emission(AE)signal generated by the fracture was collected by acoustic emission(AE)system.At the same time,crack propagation gauge(CPG)was used to measure the crack propagation velocity of the specimen.The results show that the crack propagation velocity and fracture toughness of shale have a positive correlation with the loading rate.The relationship among the crack propagation velocity,the fracture toughness and the loading rate is established under the static loading condition.In addition,the characteristics of AE signals with different loading rates are analyzed.It is found that the AE signals generated by microcrack growth decrease with the increase of loading rates.Meanwhile,the turning point of cumulative counting moves forward as the loading rate increases,which shows that the AE signal generated by shale fracture at low loading rate mainly comes from the initiation and propagation of microcracks,while at high loading rate it mainly comes from the formation of macro large-scale cracks.The fracture mechanism that causes shale fracture toughness and crack propagation velocity to vary with loading rate is also discussed based on the analysis results of AE signals.展开更多
Cracked straight-through Brazilian disc(CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700℃. Uniaxial splitting experiments were performed using an automatic...Cracked straight-through Brazilian disc(CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700℃. Uniaxial splitting experiments were performed using an automatic electro-hydraulic servo press to study the evolution laws of physical and fracture properties of different deep rock materials under high-temperature geological conditions. The fracture characteristics were measured using an industrial camera and digital image correlation technology to analyze the effect of high temperature on fracture properties and failure modes of the CSTBD samples after different thermal treatments. The micro-damage properties of green sandstone and granite materials were obtained using a scanning electron microscope(SEM). The following conclusions were drawn from the test results:(1) With the increasing temperature, the fracture characteristics of green sandstone and granite change from brittle fracture to plasticity fracture, the longitudinal wave velocity of granite decreases sharply at 600℃, and the damage factor reaches 0.8748 at 700℃.(2) The fracture toughness of green sandstone and granite decreases with increasing temperature;however, the decreasing range of granite is larger than that of green sandstone.(3) As the temperature increases, the fracture morphologies of green sandstone and granite materials become rougher, whereas thermal damage cracks of granite and intergranular fractures inside sandstone as well as pores of sandstone increase.(4) The crack tip opening displacement and peak strain corresponding to peak load increase with the temperature.展开更多
基金Project(41630642)supported by the National Natural Science Foundation of China。
文摘In this study,the effect of loading rate on shale fracture behaviors was investigated under dynamic and static loading conditions.Cracked straight through Brazilian disc(CSTBD)shale specimens were tested with a split Hopkinson pressure bar(SHPB)setup and INSTRON1346 servo-testing machine under pure mode I loading conditions.During the test,the crack propagation process was recorded by high-speed(HS)camera,and the acoustic emission(AE)signal generated by the fracture was collected by acoustic emission(AE)system.At the same time,crack propagation gauge(CPG)was used to measure the crack propagation velocity of the specimen.The results show that the crack propagation velocity and fracture toughness of shale have a positive correlation with the loading rate.The relationship among the crack propagation velocity,the fracture toughness and the loading rate is established under the static loading condition.In addition,the characteristics of AE signals with different loading rates are analyzed.It is found that the AE signals generated by microcrack growth decrease with the increase of loading rates.Meanwhile,the turning point of cumulative counting moves forward as the loading rate increases,which shows that the AE signal generated by shale fracture at low loading rate mainly comes from the initiation and propagation of microcracks,while at high loading rate it mainly comes from the formation of macro large-scale cracks.The fracture mechanism that causes shale fracture toughness and crack propagation velocity to vary with loading rate is also discussed based on the analysis results of AE signals.
基金funding support from the Sichuan Science and Technology Program (Grant No. 2021YJ0511)the State Key Laboratory for Geo-Mechanics and Deep Underground Engineering,China University of Mining&Technology (Grant No.SKLGDUEK2111)the Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province (Grant No. ZJRMG-2020-01)。
文摘Cracked straight-through Brazilian disc(CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700℃. Uniaxial splitting experiments were performed using an automatic electro-hydraulic servo press to study the evolution laws of physical and fracture properties of different deep rock materials under high-temperature geological conditions. The fracture characteristics were measured using an industrial camera and digital image correlation technology to analyze the effect of high temperature on fracture properties and failure modes of the CSTBD samples after different thermal treatments. The micro-damage properties of green sandstone and granite materials were obtained using a scanning electron microscope(SEM). The following conclusions were drawn from the test results:(1) With the increasing temperature, the fracture characteristics of green sandstone and granite change from brittle fracture to plasticity fracture, the longitudinal wave velocity of granite decreases sharply at 600℃, and the damage factor reaches 0.8748 at 700℃.(2) The fracture toughness of green sandstone and granite decreases with increasing temperature;however, the decreasing range of granite is larger than that of green sandstone.(3) As the temperature increases, the fracture morphologies of green sandstone and granite materials become rougher, whereas thermal damage cracks of granite and intergranular fractures inside sandstone as well as pores of sandstone increase.(4) The crack tip opening displacement and peak strain corresponding to peak load increase with the temperature.
