A submerged cavitation water jet(SCWJ)is an effective method to recycle solid propellant from obsolete solid engines by the breaking method.Solid propellant's breaking modes and mechanical process under SCWJ impac...A submerged cavitation water jet(SCWJ)is an effective method to recycle solid propellant from obsolete solid engines by the breaking method.Solid propellant's breaking modes and mechanical process under SCWJ impact are unclear.This study aims to understand those impact breaking mechanisms.The hydroxyl-terminated polybutadiene(HTPB)propellant was chosen as the research material,and a self-designed test system was used to conduct impact tests at four different working pressures.The high-speed camera characterized crack propagation,and the DIC method calculated strain change during the impact process.Besides,micro and macro fracture morphologies were characterized by scanning electron microscope(SEM)and computed tomography(CT)scanning.The results reveal that the compressive strain concentration region locates right below the nozzle,and the shear strain region distributes symmetrically with the jet axis,which increases to 4% at first 16th ms,the compressive strain rises to 2% and 6% in the axial and transverse direction,respectively.The two tensile cracks formed first at the compression strain concentrate region,and there generate many shear cracks around the tensile cracks,and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks,forming the tensile-shear cracks and the impact parts eventually fail.The HTPB propellant forms a breaking hole shaped conical after impact 10 s.The mass loss increases by 17 times at maximum,with the working pressure increasing by three times.Meanwhile,the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole.The breaking efficiency is closely affected by working pressures.The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.展开更多
To study the rock breaking method under the free surface induced by disc cutter,the rock breaking simulations were first conducted based on the discrete element method,and the dynamic process of rock breaking under th...To study the rock breaking method under the free surface induced by disc cutter,the rock breaking simulations were first conducted based on the discrete element method,and the dynamic process of rock breaking under the free surface was studied including stressed zone,crush zone,crack initiation and propagation.Then the crack propagation conditions,specific energy,etc.under different free surface distance(S)were also investigated combined with linear cutting experiments.The results show that the rock breaking process under the free surface induced by disc cutter is dominated by tension failure mode.There exists a critical S to promote crack propagation to free surface effectively.And this rock breaking method can improve the rock breaking force and breaking efficiency significantly when proper.展开更多
In order to study rock breaking characteristics of tunnel boring machine(TBM) disc cutter at different rock temperatures,thermodynamic rock breaking mathematical model of TBM disc cutter was established on the basis o...In order to study rock breaking characteristics of tunnel boring machine(TBM) disc cutter at different rock temperatures,thermodynamic rock breaking mathematical model of TBM disc cutter was established on the basis of rock temperature change by using particle flow code theory and the influence law of interaction mechanism between disc cutter and rock was also numerically simulated.Furthermore,by using the linear cutting experiment platform,rock breaking process of TBM disc cutter at different rock temperatures was well verified by the experiments.Finally,rock breaking characteristics of TBM disc cutter were differentiated and analyzed from microscale perspective.The results indicate the follows.1) When rock temperature increases,the mechanical properties of rock such as hardness,and strength,were greatly reduced,simultaneously the microcracks rapidly grow with the cracks number increasing,which leads to rock breaking load decreasing and improves rock breaking efficiency for TBM disc cutter.2) The higher the rock temperature,the lower the rock internal stress.The stress distribution rules coincide with the Buzin Neske stress circle rules: the maximum stress value is below the cutting edge region and then gradually decreases radiant around; stress distribution is symmetrical and the total stress of rock becomes smaller.3) The higher the rock temperature is,the more the numbers of micro,tensile and shear cracks produced are by rock as well as the easier the rock intrusion,along with shear failure mode mainly showing.4) With rock temperature increasing,the resistance intrusive coefficients of rock and intrusion power decrease obviously,so the specific energy consumption that TBM disc cutter achieves leaping broken also decreases subsequently.5) The acoustic emission frequency remarkably increases along with the temperature increasing,which improves the rock breaking efficiency.展开更多
The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by u...The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by using the cutter at three kinds of negative fore angles of 30°, 45° and 60°. The results show that, when the edge of the PDC layer is broken, the layer of tungsten cobalt is broken a little under the angle of 30°, while the layer of tungsten cobalt is broken continuously under the angle of 60°, their maximum depths are about 2 and 7 mm respectively in the two cases. The eccentric distance mainly depends on the negative fore angle of the cutter. When the cutter thrusts into the rock under an attack angle of 60°, the energy of bending waves reaches the maximum since the eccentric distance is the maximum. So the damage of cutter is the most serious. This test result is consistent with the conclusion of theoretical analysis well. The eccentric distance from the axial line of cutter to the point of action between the rock and cutter has great effect on the breakage of the cutter. Thus during the process of cutting, the eccentric distance should be reduced to improve the service life of PDC cutters.展开更多
This study investigates the factors affecting the rock-breaking efficiency of the TBM disc cutter in deep rock excavation,including confining pressure,penetration,cutter spacing,and revolution speed.The finite element...This study investigates the factors affecting the rock-breaking efficiency of the TBM disc cutter in deep rock excavation,including confining pressure,penetration,cutter spacing,and revolution speed.The finite element method is employed to formulate a rock-breaking model of the rotary disc cutters and a numerical simulation is also implemented.The rock breaking effect,rock breaking volume,and rock breaking specific energy consumption under different combinations of the factors are investigated.An orthogonal test of four factors at four levels was constructed.Based on the test results and range analysis in the process of deep rock mass breaking,the order of sensitivity of each influencing factor with respect to the rock breaking specific energy for the disc cutter is cutter spacing>revolution speed>penetration>confining pressure.By constructing a numerical simulation comparison scheme,the orthogonal test results are analyzed and corroborated,and the rock breaking law and rock breaking efficiency under different influencing factors are derived.Finally,the sensitivity of different influencing factors on the rock-breaking efficiency is verified.展开更多
In the field of automobile manufacture, during the aluminum alloy cutting, chip forming and breaking process are very complicated. It is affected by many facto rs. Automatic machining process can not be carried throug...In the field of automobile manufacture, during the aluminum alloy cutting, chip forming and breaking process are very complicated. It is affected by many facto rs. Automatic machining process can not be carried through if the chip enlaces t he workpiece or the tool. So the chip control and breaking are key technology. P CD tool has many traits, such as high cutting efficiency, machining precision an d wearability. It is desired that it be used for machining coloured metals.The p aper present the study of prediction of chip breaking when PCD Tool cutting alum inum alloy with chip breaker. In the process of cutting, the method of chip brea king is up-curl-dominant chip. Therefore, based on the theory of chip breaking with chip breaker, used the cutting condition of chip breaking, this paper dedu ce the chip breaking mathematical model when cutting aluminum alloy, that is to say, the chip breaker parameters(Angle of chip break,chip groove width, bevel a ngle, the normal rake angle of chip groove, tool cutting edge angle)influence th e critical feed rate. The following conclusion can be made from theoretic analys is. The critical feed rate will decrease when the Angle of chip break and bevel angle and the normal rake angle of chip groove and tool cutting edge angle incre ase. The critical feed rate will increase when chip groove width increase. The e xperimental results are well coincided with the theoretic ones, it is proved tha t the predicting system is correct.展开更多
With the increasing short-circuit power of system,it is an effective way to solve the large capacity of short-circuit breaking by using parallel breaking technology which composed by a high coupling splitter reactor a...With the increasing short-circuit power of system,it is an effective way to solve the large capacity of short-circuit breaking by using parallel breaking technology which composed by a high coupling splitter reactor and two parallel breakers in series.According to research the TRV equivalent calculation circuit and initial conditions in equal current mode and limit current mode respectively,the prospective TRV of CB1and CB2have been calculated for rated voltage of 252 kV and rated short-circuit current of85 k A.The results indicate that TRV of CB1and CB2are not affected by high split coupled reactor in equal current interruption mode,and TRV of CB1is under the standard requirement values after first current zero crossing and the TRV of CB2is exceed the standard requirement values after second current zero crossing which is also higher than the ITRV and line-side TRV of SLF in limit current interruption mode.Furthermore,the research conclusions of this paper can provide the theory and reference basis for parallel breaking technology.展开更多
基金supported by the Program for National Defense Science and Technology Foundation Strengtheningthe Youth Foundation of Rocket Force University of Engineering(Grant No.2021QN-B014)。
文摘A submerged cavitation water jet(SCWJ)is an effective method to recycle solid propellant from obsolete solid engines by the breaking method.Solid propellant's breaking modes and mechanical process under SCWJ impact are unclear.This study aims to understand those impact breaking mechanisms.The hydroxyl-terminated polybutadiene(HTPB)propellant was chosen as the research material,and a self-designed test system was used to conduct impact tests at four different working pressures.The high-speed camera characterized crack propagation,and the DIC method calculated strain change during the impact process.Besides,micro and macro fracture morphologies were characterized by scanning electron microscope(SEM)and computed tomography(CT)scanning.The results reveal that the compressive strain concentration region locates right below the nozzle,and the shear strain region distributes symmetrically with the jet axis,which increases to 4% at first 16th ms,the compressive strain rises to 2% and 6% in the axial and transverse direction,respectively.The two tensile cracks formed first at the compression strain concentrate region,and there generate many shear cracks around the tensile cracks,and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks,forming the tensile-shear cracks and the impact parts eventually fail.The HTPB propellant forms a breaking hole shaped conical after impact 10 s.The mass loss increases by 17 times at maximum,with the working pressure increasing by three times.Meanwhile,the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole.The breaking efficiency is closely affected by working pressures.The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.
基金Project(2013CB035401)supported by the National Basic Research Program of ChinaProject(2012AA041803)supported by the National High-Technology Research and Development Program of China+2 种基金Project(51475478)supported by the National Natural Science Foundation of ChinaProject(2015GK1029)supported by the Science and Technology Project of Strategic Emerging Industry in Hunan Province,ChinaProject(CX2017B048)supported by the Hunan Provincial Innovation Foundation For Postgraduate,China
文摘To study the rock breaking method under the free surface induced by disc cutter,the rock breaking simulations were first conducted based on the discrete element method,and the dynamic process of rock breaking under the free surface was studied including stressed zone,crush zone,crack initiation and propagation.Then the crack propagation conditions,specific energy,etc.under different free surface distance(S)were also investigated combined with linear cutting experiments.The results show that the rock breaking process under the free surface induced by disc cutter is dominated by tension failure mode.There exists a critical S to promote crack propagation to free surface effectively.And this rock breaking method can improve the rock breaking force and breaking efficiency significantly when proper.
基金Projects(51274252,51074180)supported by the National Natural Science Foundation of ChinaProject(2013CB035401)supported by the National Basic Research Program of China+1 种基金Projects(2012AA0418012012AA041803)supported by the High-Tech Research and Development Program of China
文摘In order to study rock breaking characteristics of tunnel boring machine(TBM) disc cutter at different rock temperatures,thermodynamic rock breaking mathematical model of TBM disc cutter was established on the basis of rock temperature change by using particle flow code theory and the influence law of interaction mechanism between disc cutter and rock was also numerically simulated.Furthermore,by using the linear cutting experiment platform,rock breaking process of TBM disc cutter at different rock temperatures was well verified by the experiments.Finally,rock breaking characteristics of TBM disc cutter were differentiated and analyzed from microscale perspective.The results indicate the follows.1) When rock temperature increases,the mechanical properties of rock such as hardness,and strength,were greatly reduced,simultaneously the microcracks rapidly grow with the cracks number increasing,which leads to rock breaking load decreasing and improves rock breaking efficiency for TBM disc cutter.2) The higher the rock temperature,the lower the rock internal stress.The stress distribution rules coincide with the Buzin Neske stress circle rules: the maximum stress value is below the cutting edge region and then gradually decreases radiant around; stress distribution is symmetrical and the total stress of rock becomes smaller.3) The higher the rock temperature is,the more the numbers of micro,tensile and shear cracks produced are by rock as well as the easier the rock intrusion,along with shear failure mode mainly showing.4) With rock temperature increasing,the resistance intrusive coefficients of rock and intrusion power decrease obviously,so the specific energy consumption that TBM disc cutter achieves leaping broken also decreases subsequently.5) The acoustic emission frequency remarkably increases along with the temperature increasing,which improves the rock breaking efficiency.
基金Project(06JJ20094) supported by the Natural Science Foundation of Hunan Province, China
文摘The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by using the cutter at three kinds of negative fore angles of 30°, 45° and 60°. The results show that, when the edge of the PDC layer is broken, the layer of tungsten cobalt is broken a little under the angle of 30°, while the layer of tungsten cobalt is broken continuously under the angle of 60°, their maximum depths are about 2 and 7 mm respectively in the two cases. The eccentric distance mainly depends on the negative fore angle of the cutter. When the cutter thrusts into the rock under an attack angle of 60°, the energy of bending waves reaches the maximum since the eccentric distance is the maximum. So the damage of cutter is the most serious. This test result is consistent with the conclusion of theoretical analysis well. The eccentric distance from the axial line of cutter to the point of action between the rock and cutter has great effect on the breakage of the cutter. Thus during the process of cutting, the eccentric distance should be reduced to improve the service life of PDC cutters.
基金Project(51979156)supported by the National Natural Science Foundation of ChinaProject(tsqn202103087)supported by the Young Taishan Scholars,ChinaProject(2019KJG015)supported by the Youth Innovation Technology Project of Higher School in Shandong Province,China。
文摘This study investigates the factors affecting the rock-breaking efficiency of the TBM disc cutter in deep rock excavation,including confining pressure,penetration,cutter spacing,and revolution speed.The finite element method is employed to formulate a rock-breaking model of the rotary disc cutters and a numerical simulation is also implemented.The rock breaking effect,rock breaking volume,and rock breaking specific energy consumption under different combinations of the factors are investigated.An orthogonal test of four factors at four levels was constructed.Based on the test results and range analysis in the process of deep rock mass breaking,the order of sensitivity of each influencing factor with respect to the rock breaking specific energy for the disc cutter is cutter spacing>revolution speed>penetration>confining pressure.By constructing a numerical simulation comparison scheme,the orthogonal test results are analyzed and corroborated,and the rock breaking law and rock breaking efficiency under different influencing factors are derived.Finally,the sensitivity of different influencing factors on the rock-breaking efficiency is verified.
文摘In the field of automobile manufacture, during the aluminum alloy cutting, chip forming and breaking process are very complicated. It is affected by many facto rs. Automatic machining process can not be carried through if the chip enlaces t he workpiece or the tool. So the chip control and breaking are key technology. P CD tool has many traits, such as high cutting efficiency, machining precision an d wearability. It is desired that it be used for machining coloured metals.The p aper present the study of prediction of chip breaking when PCD Tool cutting alum inum alloy with chip breaker. In the process of cutting, the method of chip brea king is up-curl-dominant chip. Therefore, based on the theory of chip breaking with chip breaker, used the cutting condition of chip breaking, this paper dedu ce the chip breaking mathematical model when cutting aluminum alloy, that is to say, the chip breaker parameters(Angle of chip break,chip groove width, bevel a ngle, the normal rake angle of chip groove, tool cutting edge angle)influence th e critical feed rate. The following conclusion can be made from theoretic analys is. The critical feed rate will decrease when the Angle of chip break and bevel angle and the normal rake angle of chip groove and tool cutting edge angle incre ase. The critical feed rate will increase when chip groove width increase. The e xperimental results are well coincided with the theoretic ones, it is proved tha t the predicting system is correct.
文摘With the increasing short-circuit power of system,it is an effective way to solve the large capacity of short-circuit breaking by using parallel breaking technology which composed by a high coupling splitter reactor and two parallel breakers in series.According to research the TRV equivalent calculation circuit and initial conditions in equal current mode and limit current mode respectively,the prospective TRV of CB1and CB2have been calculated for rated voltage of 252 kV and rated short-circuit current of85 k A.The results indicate that TRV of CB1and CB2are not affected by high split coupled reactor in equal current interruption mode,and TRV of CB1is under the standard requirement values after first current zero crossing and the TRV of CB2is exceed the standard requirement values after second current zero crossing which is also higher than the ITRV and line-side TRV of SLF in limit current interruption mode.Furthermore,the research conclusions of this paper can provide the theory and reference basis for parallel breaking technology.
