The initial micro-cracks affect the evolution characteristics of macroscopic deformation and failure of rock but are often ignored in theoretical calculation,numerical simulation,and mechanical experiments.In this stu...The initial micro-cracks affect the evolution characteristics of macroscopic deformation and failure of rock but are often ignored in theoretical calculation,numerical simulation,and mechanical experiments.In this study,we propose a quantitative analysis model to investigate the effects of initial micro-cracks on the evolution of marble deformation and failure.The relationship between the micro-crack propagation and the marble failure characteristics was comprehensively studied by combining theoretical analysis with a micro-computed tomography(micro-CT)scanning technique.We found that with the increase of confining pressure,the matrix elastic modulus of the marble first increased and then tended to be stable,while the micro-cracks increased exponentially.The sensitivity ranges of the marble sample matrix elastic modulus and micro-cracks to confining pressure were 0–30 MPa and 30–50 MPa,respectively.The porosity and Poisson’s ratio decreased exponentially.The increasing proportion of internal micro-cracks led to an increase in the sample non-uniformity.The samples presented mainly shear failure under triaxial compression,and the failure angle decreased linearly with the increase of confining pressure.The convergence direction of cracks decreased gradually.This quantitative analysis model could accurately portray the relationship between the overall macroscopic deformation and the deviatoric stress of the samples at the compaction and the linear elastic stages,thus deepening the understanding of the stress–strain behavior of rocks.展开更多
The evolution of void nucleation inα-A12O3 irradiated by En ≥ 1 MeV neutrons of 3× 1020 cm-2 and post-annealed from 100°C to 1050°C is studied by a positron annihilation lifetime technique. The void n...The evolution of void nucleation inα-A12O3 irradiated by En ≥ 1 MeV neutrons of 3× 1020 cm-2 and post-annealed from 100°C to 1050°C is studied by a positron annihilation lifetime technique. The void nucleation starts at 500℃. The radius of created voids is 0.31 urn and the number of voids increases with increasing annealing temperature from 550℃ to 750℃. Afterwards, the radius of voids increases rapidly and reaches 1.21nm at 1050℃.展开更多
To investigate the effect of surface-modified nanoparticles(NPs)on the inclusion refinement and microstructure evolution,deoxidized experiment ingots with different amounts of modified NPs were manufactured under diff...To investigate the effect of surface-modified nanoparticles(NPs)on the inclusion refinement and microstructure evolution,deoxidized experiment ingots with different amounts of modified NPs were manufactured under different cooling conditions.Laser scanning confocal microscope(LSCM)was hereby used for in-situ observation of the phase transition and microstructural evolution during heat cycle process.The results revealed that the inclusion size was always smaller under water quenching than under air cooling,and the number of inclusions was greater under water quenching.After NP addition,the nucleant inclusions were identified as MgAl_(2)O_(4)spinel and irregular TiN inclusion from SEM-EDS measurement and equilibrium calculations using Factsage thermodynamic software.The higher cooling rate under water quenching resulted in less polygonal ferrite decrease and the formation of bainite in the steel.The LSCM experiments showed that ferrite side plates(FSP)always formed on the boundary prior to the formation of acicular ferrite(AF)on the intragranular inclusions,and the start transformation temperatures of FSP and AF phases both lowered after NP addition.The higher cooling rate and NP addition contributed to AF formation and increased the degree of interlocking of the AF phase.Finally,the relationship between the characteristics of inclusions and the kinetics of AF was investigated.展开更多
The paper presents a principal formulation of statistical evolution of microcracks, occurring in solids, subjected to external loading. In particular, the concept of ideal microcracks is elaborated, in order to descri...The paper presents a principal formulation of statistical evolution of microcracks, occurring in solids, subjected to external loading. In particular, the concept of ideal microcracks is elaborated, in order to describe the fundamental features of damage resulting from nucleation and extension of microcracks. Relevant average damage functions are also discussed.展开更多
Despite the recent progress on controllable synthesis of alkynyl-protected Au nanoclusters,the effective synthetic means are very limited and the cluster formation process still remains puzzling.Here,we develop a nove...Despite the recent progress on controllable synthesis of alkynyl-protected Au nanoclusters,the effective synthetic means are very limited and the cluster formation process still remains puzzling.Here,we develop a novel synchronous nucleation and passivation strategy to fabricate Au36(PA)24(PA=phenylacetylenyl) nanoclusters with high yield.In Au36(PA)24formation process,Au22(PA)18as key intermediate was identified.Meanwhile,Au22(PA)18can be synthesized under a low amount of reductant,and by employing more reductants,Au22(PA)18can turn into Au36(PA)24eventually.Moreover,the structure evolution from Au22(PA)18to Au36(PA)24is proposed,where four Au13cuboctahedra can yield one Au28kernel.Finally,the ratiocination is verified by the good accordance between the predicted intermediate/product ratio and the experimental value.This study not only offers a novel synthetic strategy,but also sheds light on understanding the structural evolution process of alkynyl-protected Au nanoclusters at atomic level.展开更多
I_(1)stacking faults(SFs)in Mg alloys are regarded as the nucleation sites of<c+a>dislocations that are critical for these alloys to achieve high ductility.Previously it was proposed that the formation of I_(1)S...I_(1)stacking faults(SFs)in Mg alloys are regarded as the nucleation sites of<c+a>dislocations that are critical for these alloys to achieve high ductility.Previously it was proposed that the formation of I_(1)SFs requires the accumulations of a large number of vacancies,which are difficult to achieve at low temperatures.In this study,molecular dynamics(MD)and molecular statics(MS)simulations based on empirical interatomic potentials were applied to investigate the deformation defect evolutions from the symmetric tilt grain boundaries(GBs)in Mg and Mg-Y alloys under external loading along<c>-axis.The results show the planar faults(PFs)on Pyramidal I planes first appear due to the nucleation and glide of(1/2 c+p)partial dislocations from GBs,where p=1/3(1010).These partial dislocations with pyramidal PFs interact with other defects,including pyramidal PFs themselves,GBs,and ppartial dislocations,generating a large amount of I_(1)SFs.Detailed analyses show the nucleation and growth of I_(1)SFs are achieved by atomic shuffle events and deformation defect reactions without the requirements of vacancy diffusion.Our simulations also suggest the Y clusters at GBs can reduce the critical stress for the formation of pyramidal PFs and I_(1)SFs,which provide a possible reason for the experimental observations that Y promotes the<c+a>dislocation activities.展开更多
Micron-sized internal cracks were introduced into rounded bars of pure iron by low cycle fatigue,and the cracks had irregular penny-shaped morphology with the critical diameter of about 30μm and the thickness of 0.5...Micron-sized internal cracks were introduced into rounded bars of pure iron by low cycle fatigue,and the cracks had irregular penny-shaped morphology with the critical diameter of about 30μm and the thickness of 0.5～1.5μm.The initi- ation and propagation of the cracks were investigated quantitatively as well as their location and geometry.After vacuum annealing of the samples fatigued,the mor- phology in a two-dimensional longitudinal section of cracks within grains had evolved from initially elliptical one into arrays of spherical voids controlled by surface diffu- sion.Furthermore,a typical morphology for a broken crack with a center spherical void surrounded by outer doughnut-like cavities was observed along a perpendicu- lar section of the specimen.Subsequently the spherical voids shrink and diminish gradually dominated by bulk diffusion.A physical model to heal an internal micro- crack was proposed,in particular for the various healing stages controlled by the related dominant diffusion mechanism and their dependencies upon the morphology and geometry of an original micro-crack in materials.展开更多
The ideal micro-cracks are treated with the number-density function; the characteristics of their evolution are investigated; a deterministic model is applied to the discussion of their extension. It is discowred that...The ideal micro-cracks are treated with the number-density function; the characteristics of their evolution are investigated; a deterministic model is applied to the discussion of their extension. It is discowred that under certain conditions saturation may occur in the number-density. The main features of the statistical formulationare illustrated by several examples and compared with those observed in experiments.展开更多
Experiments on sonic transmission show that a slabstone can directly transmit part of the energy of a wave excited by knocking or by a transducer into the air. The other part of the wave energy can generate the normal...Experiments on sonic transmission show that a slabstone can directly transmit part of the energy of a wave excited by knocking or by a transducer into the air. The other part of the wave energy can generate the normal mode of vibration on the slabstone and excite measurable acoustic signals in the air. The dominant frequency is related to the size of the slabstone. These results indicate that the acoustic emission (AE) in rock also displays similar behavior if the source is shallow. It is demonstrated that with the nucleation and propagation of cracks, the dominant frequency of the radiated wave will be lower. When the frequency becomes very low, the wave can be transmitted through the rock into the air and be received by a microphone. According to the theory of similarity of size, there will be low-frequency waves before strong earthquakes because of nucleation of cracks, which can be received by special low-frequency transducers or infrasonic detectors. Before earthquakes, the mechanism of precursors could be very complicated. They might be produced by plastic creep or attributed to liquids but not brittle fracture in most cases. So the periods of the produced waves will be longer. This perhaps accounts for the lack of foreshocks before many strong earthquakes.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12272119 and U1965101).
文摘The initial micro-cracks affect the evolution characteristics of macroscopic deformation and failure of rock but are often ignored in theoretical calculation,numerical simulation,and mechanical experiments.In this study,we propose a quantitative analysis model to investigate the effects of initial micro-cracks on the evolution of marble deformation and failure.The relationship between the micro-crack propagation and the marble failure characteristics was comprehensively studied by combining theoretical analysis with a micro-computed tomography(micro-CT)scanning technique.We found that with the increase of confining pressure,the matrix elastic modulus of the marble first increased and then tended to be stable,while the micro-cracks increased exponentially.The sensitivity ranges of the marble sample matrix elastic modulus and micro-cracks to confining pressure were 0–30 MPa and 30–50 MPa,respectively.The porosity and Poisson’s ratio decreased exponentially.The increasing proportion of internal micro-cracks led to an increase in the sample non-uniformity.The samples presented mainly shear failure under triaxial compression,and the failure angle decreased linearly with the increase of confining pressure.The convergence direction of cracks decreased gradually.This quantitative analysis model could accurately portray the relationship between the overall macroscopic deformation and the deviatoric stress of the samples at the compaction and the linear elastic stages,thus deepening the understanding of the stress–strain behavior of rocks.
基金the National Natural Science Foundation (No.19835050) and Nuclear industryScience Foundation (No.H7196BOll6)
文摘The evolution of void nucleation inα-A12O3 irradiated by En ≥ 1 MeV neutrons of 3× 1020 cm-2 and post-annealed from 100°C to 1050°C is studied by a positron annihilation lifetime technique. The void nucleation starts at 500℃. The radius of created voids is 0.31 urn and the number of voids increases with increasing annealing temperature from 550℃ to 750℃. Afterwards, the radius of voids increases rapidly and reaches 1.21nm at 1050℃.
基金The Chinese Scholarship Council(CSC)financially supported by the National Natural Science Foundation of China(Nos.51874024 and 51734003)the Fundamental Research Funds for the Central Universities(No.FRF-TP-18–009C1)
文摘To investigate the effect of surface-modified nanoparticles(NPs)on the inclusion refinement and microstructure evolution,deoxidized experiment ingots with different amounts of modified NPs were manufactured under different cooling conditions.Laser scanning confocal microscope(LSCM)was hereby used for in-situ observation of the phase transition and microstructural evolution during heat cycle process.The results revealed that the inclusion size was always smaller under water quenching than under air cooling,and the number of inclusions was greater under water quenching.After NP addition,the nucleant inclusions were identified as MgAl_(2)O_(4)spinel and irregular TiN inclusion from SEM-EDS measurement and equilibrium calculations using Factsage thermodynamic software.The higher cooling rate under water quenching resulted in less polygonal ferrite decrease and the formation of bainite in the steel.The LSCM experiments showed that ferrite side plates(FSP)always formed on the boundary prior to the formation of acicular ferrite(AF)on the intragranular inclusions,and the start transformation temperatures of FSP and AF phases both lowered after NP addition.The higher cooling rate and NP addition contributed to AF formation and increased the degree of interlocking of the AF phase.Finally,the relationship between the characteristics of inclusions and the kinetics of AF was investigated.
基金The project partially supported by National Natural Science Foundation of China.
文摘The paper presents a principal formulation of statistical evolution of microcracks, occurring in solids, subjected to external loading. In particular, the concept of ideal microcracks is elaborated, in order to describe the fundamental features of damage resulting from nucleation and extension of microcracks. Relevant average damage functions are also discussed.
基金This work was supported by Guangdong Natural Science Funds for Distinguished Young Scholars(2015A030306006)Guangzhou Science and Technology Plan Projects(201804010323)+1 种基金the fundamental funds for central universities(SCUT,2018ZD022)the National Natural Science Foundation of China(21971070).
文摘Despite the recent progress on controllable synthesis of alkynyl-protected Au nanoclusters,the effective synthetic means are very limited and the cluster formation process still remains puzzling.Here,we develop a novel synchronous nucleation and passivation strategy to fabricate Au36(PA)24(PA=phenylacetylenyl) nanoclusters with high yield.In Au36(PA)24formation process,Au22(PA)18as key intermediate was identified.Meanwhile,Au22(PA)18can be synthesized under a low amount of reductant,and by employing more reductants,Au22(PA)18can turn into Au36(PA)24eventually.Moreover,the structure evolution from Au22(PA)18to Au36(PA)24is proposed,where four Au13cuboctahedra can yield one Au28kernel.Finally,the ratiocination is verified by the good accordance between the predicted intermediate/product ratio and the experimental value.This study not only offers a novel synthetic strategy,but also sheds light on understanding the structural evolution process of alkynyl-protected Au nanoclusters at atomic level.
基金supported by the U.S.Department of Energy,Office of Basic Energy Sciences,Division of Materials Sciences and Engineering under Award DE-SC0008637 as part of the Center for PRedictive Integrated Structural Materials Science(PRISMS Center)at University of Michigan。
文摘I_(1)stacking faults(SFs)in Mg alloys are regarded as the nucleation sites of<c+a>dislocations that are critical for these alloys to achieve high ductility.Previously it was proposed that the formation of I_(1)SFs requires the accumulations of a large number of vacancies,which are difficult to achieve at low temperatures.In this study,molecular dynamics(MD)and molecular statics(MS)simulations based on empirical interatomic potentials were applied to investigate the deformation defect evolutions from the symmetric tilt grain boundaries(GBs)in Mg and Mg-Y alloys under external loading along<c>-axis.The results show the planar faults(PFs)on Pyramidal I planes first appear due to the nucleation and glide of(1/2 c+p)partial dislocations from GBs,where p=1/3(1010).These partial dislocations with pyramidal PFs interact with other defects,including pyramidal PFs themselves,GBs,and ppartial dislocations,generating a large amount of I_(1)SFs.Detailed analyses show the nucleation and growth of I_(1)SFs are achieved by atomic shuffle events and deformation defect reactions without the requirements of vacancy diffusion.Our simulations also suggest the Y clusters at GBs can reduce the critical stress for the formation of pyramidal PFs and I_(1)SFs,which provide a possible reason for the experimental observations that Y promotes the<c+a>dislocation activities.
基金The project supported by the National Outstanding Young Investigator Grant of China (59925104)the National Natural Science Foundation of China (59889101)
文摘Micron-sized internal cracks were introduced into rounded bars of pure iron by low cycle fatigue,and the cracks had irregular penny-shaped morphology with the critical diameter of about 30μm and the thickness of 0.5～1.5μm.The initi- ation and propagation of the cracks were investigated quantitatively as well as their location and geometry.After vacuum annealing of the samples fatigued,the mor- phology in a two-dimensional longitudinal section of cracks within grains had evolved from initially elliptical one into arrays of spherical voids controlled by surface diffu- sion.Furthermore,a typical morphology for a broken crack with a center spherical void surrounded by outer doughnut-like cavities was observed along a perpendicu- lar section of the specimen.Subsequently the spherical voids shrink and diminish gradually dominated by bulk diffusion.A physical model to heal an internal micro- crack was proposed,in particular for the various healing stages controlled by the related dominant diffusion mechanism and their dependencies upon the morphology and geometry of an original micro-crack in materials.
基金Project partly supported by the National Natural Science Foundation of China.
文摘The ideal micro-cracks are treated with the number-density function; the characteristics of their evolution are investigated; a deterministic model is applied to the discussion of their extension. It is discowred that under certain conditions saturation may occur in the number-density. The main features of the statistical formulationare illustrated by several examples and compared with those observed in experiments.
文摘Experiments on sonic transmission show that a slabstone can directly transmit part of the energy of a wave excited by knocking or by a transducer into the air. The other part of the wave energy can generate the normal mode of vibration on the slabstone and excite measurable acoustic signals in the air. The dominant frequency is related to the size of the slabstone. These results indicate that the acoustic emission (AE) in rock also displays similar behavior if the source is shallow. It is demonstrated that with the nucleation and propagation of cracks, the dominant frequency of the radiated wave will be lower. When the frequency becomes very low, the wave can be transmitted through the rock into the air and be received by a microphone. According to the theory of similarity of size, there will be low-frequency waves before strong earthquakes because of nucleation of cracks, which can be received by special low-frequency transducers or infrasonic detectors. Before earthquakes, the mechanism of precursors could be very complicated. They might be produced by plastic creep or attributed to liquids but not brittle fracture in most cases. So the periods of the produced waves will be longer. This perhaps accounts for the lack of foreshocks before many strong earthquakes.
