Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for ...Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools.Therefore,it has practical engineering significance to study the rock-breaking mechanism of torsional impact.In this paper,discrete element method(DEM)software(PFC2 D)is used to compare granite breaking under the steady and torsional impacting conditions.Meanwhile,the energy consumption to break rock,microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed.It is found that the average cutting force is smaller in the case of torsional impact cutting(TIC)than that in the case of steady loading.The mechanical specific energy(MSE)and the ratio of brittle energy consumption to total energy are negatively correlated;rock-breaking efficiency is related to the mode of action between the cutting tooth and rock.Furthermore,the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load;the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load,and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.展开更多
By field observation and simulating test in shallow seam longwall mining, the asymmetry breaking of main roof is discovered during the first weighting. Based on simulating model test and theoretical analysis, the mech...By field observation and simulating test in shallow seam longwall mining, the asymmetry breaking of main roof is discovered during the first weighting. Based on simulating model test and theoretical analysis, the mechanism of main roof first breaking is revealed, and the asymmetry breaking parameter is determined at all.展开更多
Under untreated conditions, the germination rate of Viburnum sargentii seeds is very low. By exploring the relationship between the dynamic changes of physicochemical indicators and endogenous hormones and seed germin...Under untreated conditions, the germination rate of Viburnum sargentii seeds is very low. By exploring the relationship between the dynamic changes of physicochemical indicators and endogenous hormones and seed germination during the dormancy and germination of Viburnum sargentii seeds, the mechanism of seed germination of Viburnum sargentii was determined, which provided a theoretical basis for its extensive promotion and development. The contents of soluble sugar and soluble starch were determined by anthrone colorimetry. The soluble protein was determined by Coomassie brilliant blue G-250 staining. The activity of polyphenol oxidase (PPO) was determined by NBT reduction method. The peroxidase (POD) was determined by guaiacol method. And the endogenous hormones ZA, IAA, ABA, GA3 were determined by liquid chromatography. Results show: 1) Under natural conditions, the seeds of Viburnum sargentii are difficult to germinate. 2) Under sand storage for 8 months, the germination rate of untreated seeds was 33%. Puncture and peeling treatment could significantly increase the germination rate, and the germination rate of seeds treated with puncture was 92%, and that treated with peel was 98%. 3) Seed germination was accompanied by the decrease in macromolecular substances such as soluble sugar, soluble starch, and soluble protein. 4) The dynamic changes of hormones during seed germination conform to the hypothesis of “three factors”. 5) The treatment of puncture and peeling increased the content of endogenous hormones promoting germination, decreased the endogenous hormones inhibiting seed germination, and increased the ratio of (IAA + GA + ZR)/ABA or GA/ABA. The seeds of Viburnum sargentii have obvious dormancy characteristics. Under the condition of sand storage, both pricking and peeling treatment can effectively promote the process of breaking dormancy, and the effect of peeling treatment is better.展开更多
The core-disk phenomenon has been observed generally in the drilling process under high-stress conditions.This paper presents the in-situ experimental study of the coring-disking failure mechanism of marble in an unde...The core-disk phenomenon has been observed generally in the drilling process under high-stress conditions.This paper presents the in-situ experimental study of the coring-disking failure mechanism of marble in an underground cavens with 2400 m depth.Based on the disk samples in several boreholes with different diameters,both macro-and micro-morphological characteristics of core-disks’break surface were analysis,using 3D optical scanning and electron microscope scanning.Moreover,the numerical back analysis was also used to simulate the drilling process for demonstrating the development of core disking.The in-situ experiment results showed that the failure types of core disking consisted of tensile break and shear break,i.e.,the shear break usually appears in the edge part of break surface,and tensile break appears in the central part.What’s more,the ration of core-disks thickness to borehole diameter is in a relatively stable range.Numerical back analysis indicated this micro asynchronous break of hard marble is induced by high geostress and unloading drill.展开更多
Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformabl...Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code(3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, infl uence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far fi eld energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.展开更多
When the traditional drill and blast method is applied to rock crushing projects,it has strong vibration,loud noise and dust pollution,so it cannot be used in densely populated areas such as urban public works.We deve...When the traditional drill and blast method is applied to rock crushing projects,it has strong vibration,loud noise and dust pollution,so it cannot be used in densely populated areas such as urban public works.We developed a supercritical CO_(2)true triaxial pneumatic rock-breaking experimental system,and conducted laboratory and field tests of dry ice powder pneumatic rock-breaking.The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed.The fracturing mechanism of dry ice powder pneumatic rock breaking is studied.The research results show that:(1)The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance;(2)The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz.Due to the dispersion effect,the dominant frequency of 10–30 Hz appears abnormally attenuated;(3)The traditional CO_(2)phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology,and the trinitrotoluene(TNT)equivalent of fracturing energy is applicable to the Sadovsky formula;(4)Dry ice powder pneumatic rock breaking is shock wave and highenergy gas acting together to fracture rock,which can be divided into three stages,among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.展开更多
In this paper, mantle circulation flow, continental drift, earthquake origin and other mechanical principles are examined as they apply to earthquake engineering, seismology and dynamics of fluid saturated porous medi...In this paper, mantle circulation flow, continental drift, earthquake origin and other mechanical principles are examined as they apply to earthquake engineering, seismology and dynamics of fluid saturated porous medium. The relationship of mantle flow to earthquakes is examined and clarified, and a new model, different from Haskell’s, is proposed for the earthquake mechanism. The proposed new model is based on the discovery that two pairs of jump stress and jump velocity will start to act from the fault plane. Records obtained directly from recent earthquakes nearby and right on the fault break show a very large velocity impulse, which verify, indirectly, the new mechanism proposed by the author. Further, at least two physical parameters that characterize the seismic intensity must be specified, because according to the discontinuous (jump) wave theory, at the earthquake source, the stress jump and the velocity jump of particle motion should act simultaneously when a sudden break occurs. The third key parameter is shown to be the break (fracture) propagation speed together with the break plane area. This parameter influences the form of the unloading time function at the source. The maximum seismic stress in and displacement of a building are estimated for two unfavorable combinations of the building and its base ground in terms of their relative rigidity. Finally, it is shown that Biot’s theory of wave propagation in fluid saturated porous media is valid only when fluid flow cannot occur.展开更多
Electrical arc contour cutting(EACC)is a novel high-efficiency material cutting process that applies arc plasma to perform efficient and economical contour cutting of difficult-to-cut materials.Compared to conventiona...Electrical arc contour cutting(EACC)is a novel high-efficiency material cutting process that applies arc plasma to perform efficient and economical contour cutting of difficult-to-cut materials.Compared to conventional electrical arc machining(EAM),this process can remove the allowance of open structures and plates in bulk mode,rather than entirely in the form of debris.Compared with existing contour cutting methods,EACC possesses the advantages of high cutting efficiency and a deep cutting depth.Particularly,a compound arc breaking mechanism(CABM),which integrates hydrodynamic force and mechanical motion,has been applied to control the discharge arc column in EACC,while also strengthening the debris expelling effect in the narrow discharge gap.The CABM implementation conditions were studied,based on arc column distortion images captured by a high-speed camera and simulation results of the flow field and debris distribution.A set of machining experiments was designed and conducted to optimize the performance of the proposed process.Finally,a SiC_(p)/Al metal matrix composite(MMC)space station workpiece was machined to verify the feasibility and efficiency of this process.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51674214)International Cooperation Project of Sichuan Science and Technology Plan(2016HH0008)+1 种基金Youth Science and Technology Innovation Research Team of Sichuan Province(2017TD0014)Applied Basic Research of Sichuan Province(Free Exploration-2019YJ0520)
文摘Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools.Therefore,it has practical engineering significance to study the rock-breaking mechanism of torsional impact.In this paper,discrete element method(DEM)software(PFC2 D)is used to compare granite breaking under the steady and torsional impacting conditions.Meanwhile,the energy consumption to break rock,microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed.It is found that the average cutting force is smaller in the case of torsional impact cutting(TIC)than that in the case of steady loading.The mechanical specific energy(MSE)and the ratio of brittle energy consumption to total energy are negatively correlated;rock-breaking efficiency is related to the mode of action between the cutting tooth and rock.Furthermore,the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load;the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load,and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.
文摘By field observation and simulating test in shallow seam longwall mining, the asymmetry breaking of main roof is discovered during the first weighting. Based on simulating model test and theoretical analysis, the mechanism of main roof first breaking is revealed, and the asymmetry breaking parameter is determined at all.
文摘Under untreated conditions, the germination rate of Viburnum sargentii seeds is very low. By exploring the relationship between the dynamic changes of physicochemical indicators and endogenous hormones and seed germination during the dormancy and germination of Viburnum sargentii seeds, the mechanism of seed germination of Viburnum sargentii was determined, which provided a theoretical basis for its extensive promotion and development. The contents of soluble sugar and soluble starch were determined by anthrone colorimetry. The soluble protein was determined by Coomassie brilliant blue G-250 staining. The activity of polyphenol oxidase (PPO) was determined by NBT reduction method. The peroxidase (POD) was determined by guaiacol method. And the endogenous hormones ZA, IAA, ABA, GA3 were determined by liquid chromatography. Results show: 1) Under natural conditions, the seeds of Viburnum sargentii are difficult to germinate. 2) Under sand storage for 8 months, the germination rate of untreated seeds was 33%. Puncture and peeling treatment could significantly increase the germination rate, and the germination rate of seeds treated with puncture was 92%, and that treated with peel was 98%. 3) Seed germination was accompanied by the decrease in macromolecular substances such as soluble sugar, soluble starch, and soluble protein. 4) The dynamic changes of hormones during seed germination conform to the hypothesis of “three factors”. 5) The treatment of puncture and peeling increased the content of endogenous hormones promoting germination, decreased the endogenous hormones inhibiting seed germination, and increased the ratio of (IAA + GA + ZR)/ABA or GA/ABA. The seeds of Viburnum sargentii have obvious dormancy characteristics. Under the condition of sand storage, both pricking and peeling treatment can effectively promote the process of breaking dormancy, and the effect of peeling treatment is better.
基金Projects(U1965205,51779251,41672314)supported by the National Natural Science Foundation of China。
文摘The core-disk phenomenon has been observed generally in the drilling process under high-stress conditions.This paper presents the in-situ experimental study of the coring-disking failure mechanism of marble in an underground cavens with 2400 m depth.Based on the disk samples in several boreholes with different diameters,both macro-and micro-morphological characteristics of core-disks’break surface were analysis,using 3D optical scanning and electron microscope scanning.Moreover,the numerical back analysis was also used to simulate the drilling process for demonstrating the development of core disking.The in-situ experiment results showed that the failure types of core disking consisted of tensile break and shear break,i.e.,the shear break usually appears in the edge part of break surface,and tensile break appears in the central part.What’s more,the ration of core-disks thickness to borehole diameter is in a relatively stable range.Numerical back analysis indicated this micro asynchronous break of hard marble is induced by high geostress and unloading drill.
基金National Natural Science Foundation of China under Grant No.90510017
文摘Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code(3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, infl uence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far fi eld energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.
基金supported by the State Key Laboratory Open Fund(No.HKLBEF202004)the Natural Science Foundation of Jiangsu Province(No.BK20201313)+2 种基金the Key Program of National Natural Science Foundation of China(No.51934007)the Major Scientific and Technological Innovation Program in Shandong Province(No.2019JZZY020505)the National Key Research and Development Program of China(No.2022YFC3004700)。
文摘When the traditional drill and blast method is applied to rock crushing projects,it has strong vibration,loud noise and dust pollution,so it cannot be used in densely populated areas such as urban public works.We developed a supercritical CO_(2)true triaxial pneumatic rock-breaking experimental system,and conducted laboratory and field tests of dry ice powder pneumatic rock-breaking.The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed.The fracturing mechanism of dry ice powder pneumatic rock breaking is studied.The research results show that:(1)The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance;(2)The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz.Due to the dispersion effect,the dominant frequency of 10–30 Hz appears abnormally attenuated;(3)The traditional CO_(2)phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology,and the trinitrotoluene(TNT)equivalent of fracturing energy is applicable to the Sadovsky formula;(4)Dry ice powder pneumatic rock breaking is shock wave and highenergy gas acting together to fracture rock,which can be divided into three stages,among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.
文摘In this paper, mantle circulation flow, continental drift, earthquake origin and other mechanical principles are examined as they apply to earthquake engineering, seismology and dynamics of fluid saturated porous medium. The relationship of mantle flow to earthquakes is examined and clarified, and a new model, different from Haskell’s, is proposed for the earthquake mechanism. The proposed new model is based on the discovery that two pairs of jump stress and jump velocity will start to act from the fault plane. Records obtained directly from recent earthquakes nearby and right on the fault break show a very large velocity impulse, which verify, indirectly, the new mechanism proposed by the author. Further, at least two physical parameters that characterize the seismic intensity must be specified, because according to the discontinuous (jump) wave theory, at the earthquake source, the stress jump and the velocity jump of particle motion should act simultaneously when a sudden break occurs. The third key parameter is shown to be the break (fracture) propagation speed together with the break plane area. This parameter influences the form of the unloading time function at the source. The maximum seismic stress in and displacement of a building are estimated for two unfavorable combinations of the building and its base ground in terms of their relative rigidity. Finally, it is shown that Biot’s theory of wave propagation in fluid saturated porous media is valid only when fluid flow cannot occur.
基金The authors acknowledge the National Science Foundation of China(Grants Nos.51235007 and 51575351)the State Key Laboratory of Mechanical System and Vibration of China(Grant No.MSV201305)for their financial support of this research.
文摘Electrical arc contour cutting(EACC)is a novel high-efficiency material cutting process that applies arc plasma to perform efficient and economical contour cutting of difficult-to-cut materials.Compared to conventional electrical arc machining(EAM),this process can remove the allowance of open structures and plates in bulk mode,rather than entirely in the form of debris.Compared with existing contour cutting methods,EACC possesses the advantages of high cutting efficiency and a deep cutting depth.Particularly,a compound arc breaking mechanism(CABM),which integrates hydrodynamic force and mechanical motion,has been applied to control the discharge arc column in EACC,while also strengthening the debris expelling effect in the narrow discharge gap.The CABM implementation conditions were studied,based on arc column distortion images captured by a high-speed camera and simulation results of the flow field and debris distribution.A set of machining experiments was designed and conducted to optimize the performance of the proposed process.Finally,a SiC_(p)/Al metal matrix composite(MMC)space station workpiece was machined to verify the feasibility and efficiency of this process.