TB872 99021143爆炸过程裂纹发展的高速摄影试验研究=On highspeed photograph test of fractures evolution during blasting[刊,中]/杨军(北京理工大学机电工程系.北京(100081))//北京理工大学学报.—1998,18(2).—243-246通过硼硅酸...TB872 99021143爆炸过程裂纹发展的高速摄影试验研究=On highspeed photograph test of fractures evolution during blasting[刊,中]/杨军(北京理工大学机电工程系.北京(100081))//北京理工大学学报.—1998,18(2).—243-246通过硼硅酸玻璃平面模型柱状装药高速摄影爆破试验,观察不同瞬间的裂纹分布图片并进行分形特征分析研究。随着应力波在介质中传播所产生裂纹的分维呈增长趋势,其增加幅度随着应力波作用及其自由面效应变化具有明显的起伏.图5参3(金友)展开更多
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
The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers...The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers have studied the interaction between TBM disc cutters and jointed rock mass.However,in most of these works,the effect of joint on rock fragmentation by double disc cutter has been scarcely investigated.Thus,the effects of joint orientation and joint space on rock fragmentation by double disc cutter are highlighted in this study.During the test,jointed concrete specimens are adopted to simulate jointed rock mass.Improved RYL-600rock shear rheological instrument was employed during the indentation process under disc cutters,and acoustic emission location system was used to analyze the rock damage and physical deterioration.The results show that there are four failure modes and three modes of crack initiation and propagation in jointed rock mass.It is concluded that the existing joint planes have obviously restrained the crack initiation and propagation during the rock fragmentation process.The results also indicate that samples are damaged most seriously when joint orientation equals60°,which is proved to be the optimum joint orientation in TBM penetration.展开更多
In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the...In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.展开更多
文摘TB872 99021143爆炸过程裂纹发展的高速摄影试验研究=On highspeed photograph test of fractures evolution during blasting[刊,中]/杨军(北京理工大学机电工程系.北京(100081))//北京理工大学学报.—1998,18(2).—243-246通过硼硅酸玻璃平面模型柱状装药高速摄影爆破试验,观察不同瞬间的裂纹分布图片并进行分形特征分析研究。随着应力波在介质中传播所产生裂纹的分维呈增长趋势,其增加幅度随着应力波作用及其自由面效应变化具有明显的起伏.图5参3(金友)
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Project(11772358) supported by the National Natural Science Foundation of ChinaProject(2013CB035401) supported by the National Basic Research Program of ChinaProject(2015zzts262) supported by the Fundamental Research Funds for the Central Universities,China
文摘The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers have studied the interaction between TBM disc cutters and jointed rock mass.However,in most of these works,the effect of joint on rock fragmentation by double disc cutter has been scarcely investigated.Thus,the effects of joint orientation and joint space on rock fragmentation by double disc cutter are highlighted in this study.During the test,jointed concrete specimens are adopted to simulate jointed rock mass.Improved RYL-600rock shear rheological instrument was employed during the indentation process under disc cutters,and acoustic emission location system was used to analyze the rock damage and physical deterioration.The results show that there are four failure modes and three modes of crack initiation and propagation in jointed rock mass.It is concluded that the existing joint planes have obviously restrained the crack initiation and propagation during the rock fragmentation process.The results also indicate that samples are damaged most seriously when joint orientation equals60°,which is proved to be the optimum joint orientation in TBM penetration.
基金Project(50465002) supported by the National Natural Science Foundation of China
文摘In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.
