Understanding the mechanical properties of coal-rock-bolt(CRB)combinations at high strain rates and the anchoring mechanism of bolts is crucial for ensuring the safety of coal mining operations.However,the dynamic beh...Understanding the mechanical properties of coal-rock-bolt(CRB)combinations at high strain rates and the anchoring mechanism of bolts is crucial for ensuring the safety of coal mining operations.However,the dynamic behaviors of these combinations,especially the mechanism of action of prestressed bolts,still need to be further investigated.This study carried out split Hopkinson pressure bar(SHPB)tests on three sets of coal-rock(CR),CRB,and coal-rock-prestressed bolt(CRPB)combinations with different interface angles(β=15°,30°,45°,and 60°).The dynamic properties of the combinations were analyzed based on the stress-strain curve,energy dissipation,dynamic strength,fractal dimension of cracks,and failure mode of bolts.The test results show that a larger β will affect the stress transfer and anti-sliding ability of CR,resulting in a decrease in CR strength.The anchoring force of the bolt effectively suppresses the slip feature of CRB at the yield stage.As the strain rate increases,CRB shows a more pronounced'sudden increase'in strength,and the bolt significantly enhances its dynamic strength.The prestressed bolts enhance the dynamic strength of CRPB while weaken the effect of β.The fractal dimension of the macrocracks increases with strain rate,with smaller variations in CRB and CRPB,indicating that the bolt reduces the complexity degree of CRB and CRPB.The anchoring force of CRB depends on bolt strength,which reduces the slip along the interface.The anchoring force of CRPB balances the coal-rock slip and suppresses crack formation,resulting in a more cohesive response under dynamic load.展开更多
Corresponding to the continuous dynamic recrystallization mechanism,we proposed a dislocation entanglement model and an energy-based criterion to capture the formation of subgrain boundaries during high strain rate de...Corresponding to the continuous dynamic recrystallization mechanism,we proposed a dislocation entanglement model and an energy-based criterion to capture the formation of subgrain boundaries during high strain rate deformation.A physical relationship between grain refinement and dislocation evolution is established and incorporated into the crystal plasticity constitutive model,where the spatial position of the subgrain boundaries can be determined by the energy minimization path.The developed constitutive model is implemented to simulate the dynamic compression and tension tests of pure copper by the crystal plasticity finite element method.Results show that the developed grain refinement model based on the dislocation entanglement gives good agreement with the experimental data validating its feasibility and rationality.The strengthening effect of grain refinement on the flow stress of metals at high strain rates depends on the competition between the strengthening of grain boundary and the softening of dislocation consumption during grain refinement.Further,a series of dynamic compressions are performed on copper samples with different grain sizes to explore the strengthening effect of grain refinement.The corresponding mechanisms of strengthening are analyzed and their respective contributions are also discussed in detail.The developed model can accurately predict the grain refinement of metals and capture its effect on strain hardening under high strain rate deformation.展开更多
The commercial ZK 60 magnesium alloy with extruded state experienced aging heat treatment(T 6)was dynamically loaded at strain rate of 3000 s−1 by means of the split Hopkinson pressure bar(SHPB)in this paper.Transmiss...The commercial ZK 60 magnesium alloy with extruded state experienced aging heat treatment(T 6)was dynamically loaded at strain rate of 3000 s−1 by means of the split Hopkinson pressure bar(SHPB)in this paper.Transmission electron microscopy(TEM)observations showed that the precipitatedβ′_(1) phases partially dissolved(spheroidized)with blurred interfaces within 160μs at 3000 s^(−1).The average length and diameter of the rod-shapedβ′_(1) phase particles were 48.5 and 9.8 nm after the T 6 heat treatment;while the average diameter of the sphericalβ′_(1) phases changed to 8.8 nm after loading.The deformedβ′_(1) phase generated larger lattice distortion energy than Mg matrix under high strain rate loading.Therefore,the difference of free energy(the driving force of dissolution)between theβ′_(1) phase and the matrix increased,making the instantaneous dissolution of theβ′_(1) phase thermodynamically feasible.The dissolution(spheroidization)of theβ′_(1) phase particles was kinetically promoted because the diffusion rate of the solute Zn atoms was accelerated by combined actions of adiabatic temperature rise,high density of dislocations(vacancies)and high deviatoric stresses during high strain rate loading.The increase in hardness of ZK 60-T 6 alloy could be attributed to solid solution strengthening,dislocation strengthening and second phase particle strengthening.展开更多
The shape of underground chambers in deep mining varies due to their geological environment and intended use,which results in different failure modes under the influence of mining activities.However,the effect of cham...The shape of underground chambers in deep mining varies due to their geological environment and intended use,which results in different failure modes under the influence of mining activities.However,the effect of chamber shape on the mechanism of structural integrity under dynamic load is still unclear.In this paper,granite samples with circular(C),rectangular(R),long ellipse(EL),and short ellipse(ES)holes were prepared.The dynamic mechanical response and cracking mechanism of granite were systematically analyzed using the split Hopkinson pressure bar(SHPB)test system and the hybrid finite and discrete element method(HFDEM).The results indicate that the dynamic strengths of granite with EL and ES represent the maximum and minimum values within the range of close strain rates,respectively.When EL granite is subjected to dynamic load,the axial stress concentration(in the load direction)is weak,and the transverse stress shows relative dispersion,which is the primary reason for its highest dynamic strength.The failure of granite with various holes primarily involves a tensile-shear mixed fracture,with relatively few pure typeⅡcracks.The chamber’s transverse span is the primary factor influencing the distribution range of the fracture area.展开更多
Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dyna...Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.展开更多
Superplasticity of AZ 31 magnesium matrix composites reinforced with 10 vol% SiC（2 μm） particulate i s investigated at temperature range from 365℃ to 565℃ and strain rate from 2.0 8×10<sup>-3</sup&g...Superplasticity of AZ 31 magnesium matrix composites reinforced with 10 vol% SiC（2 μm） particulate i s investigated at temperature range from 365℃ to 565℃ and strain rate from 2.0 8×10<sup>-3</sup> to 5.21×10<sup>-1</sup> s<sup>-1</sup>. The maximum total elongation of 228 % is obtained at a strain rate of 2.08×10<sup>-1</sup> s<sup>-1</sup>. The strain rate se nsitivity exponent （m） higher than 0.3, is observed when the strain rate is high er than 10<sup>-1</sup> s<sup>-1</sup> at 525℃. Increasing the test temperature to 540℃, the maximum total elongation exceeding 195% is achieved at a higher strain rate of 5.21×10<sup>-1</sup> s<sup>-1</sup> than that at 525℃. SiC in AZ31/SiCp composite ca n fine the matrix grain size. Filament is observed on the fracture surface of th e specimens showing superplasticity.展开更多
The aim of this study is to investigate the dynamic stress-strain relation for the hybrid composite （nylon ＋carbon）. Three groups of specimens are used with different number of carbon layers. The specimens were sub...The aim of this study is to investigate the dynamic stress-strain relation for the hybrid composite （nylon ＋carbon）. Three groups of specimens are used with different number of carbon layers. The specimens were subjected to high velocity impact with different strain rates. SHPB （split Hopkinson pressure bar） is used in this investigation. The results show that, the stress-strain relation various with the strain rate. The maximum stress and strain are proportion directly with the strain rate. Also, the results revealed that, as the number of carbon layer increased, the maximum strain decreased.展开更多
The dynamic tensile properties and microstructural evolution of an extruded EW75 magnesium alloy deformed at ambient temperature and different high strain rates(from 1000 to 3000 s^(-1))along extrusion direction(ED)we...The dynamic tensile properties and microstructural evolution of an extruded EW75 magnesium alloy deformed at ambient temperature and different high strain rates(from 1000 to 3000 s^(-1))along extrusion direction(ED)were investigated by Split Hopkinson Tension Bar(SHTB).The corresponding deformation mechanisms,texture evolution and microstructure changes were analyzed by optical microscope(OM),electron backscatter diffraction(EBSD)and transmission electron microscope(TEM).The results show that the extruded EW75 magnesium alloy along ED exhibits a conventional positive strain rate sensitivity that the dynamic flow stresses increase with in creasing strain rate.Texture measurements show that after dynamic tension,the initial weak texture of extruded EW75 magnesium alloy tansforms to a relatively strong<10-10>//ED texture with increasing strain rates.The microstructural analysis demonstrates that dislocation motion are main deformatin mode to accommodate dynamic tensile deformation at high strain rates.In addition,the interactions of dislocation-dislocation and dislocation-second phase lead to the in crease of flow stress and strain hardening with increasing strain rate.展开更多
The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinso...The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinson pressure bar(SHPB)was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4,0.8,and 1.2 MPa.And the failure modes were determined by macro and micro analysis.CPB with different cement-to-tailings ratios,solid mass concentrations,and curing ages was prepared to conduct the SHPB test.The results showed that increasing the cement content,tailings content,and curing age can improve the dynamic compressive strength and elastic modulus.Under an impact load,a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading.And the dynamic compressive strength of CPB has an exponential correlation with the strain rate.The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading.The local damage was enhanced,and fine cracks were formed in the interior of the CPB.This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.展开更多
The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^...The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding（GBS）,and the dislocation creep mechanism is considered as the main accommodation mechanism.展开更多
The Al−Mg alloy with high Mg addition(Al−9.2Mg−0.8Mn−0.2Zr-0.15Ti,in wt.%)was subjected to different passes(1,2 and 4)of high strain rate rolling(HSRR),with the total thickness reduction of 72%,the rolling temperature...The Al−Mg alloy with high Mg addition(Al−9.2Mg−0.8Mn−0.2Zr-0.15Ti,in wt.%)was subjected to different passes(1,2 and 4)of high strain rate rolling(HSRR),with the total thickness reduction of 72%,the rolling temperature of 400℃and strain rate of 8.6 s^(−1).The microstructure evolution was studied by optical microscope(OM),scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and transmission electron microscope(TEM).The alloy that undergoes 2 passes of HSRR exhibits an obvious bimodal grain structure,in which the average grain sizes of the fine dynamic recrystallization(DRX)grains and the coarse non-DRX regions are 6.4 and 47.7mm,respectively.The high strength((507±9)MPa)and the large ductility((24.9±1.3)%)are obtained in the alloy containing the bimodal grain distribution.The discontinuous dynamic recrystallization(DDRX)mechanism is the prominent grain refinement mechanism in the alloy subjected to 2 passes of HSRR.展开更多
For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical prope...For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.展开更多
Tensile mechanical properties of 1.6Si-1.58Mn-0.195C TRIP (transformation-induced plasticity) steels under high strain rate and effects of DP (dual-phase) treatments were studied and compared to the quasi-static tensi...Tensile mechanical properties of 1.6Si-1.58Mn-0.195C TRIP (transformation-induced plasticity) steels under high strain rate and effects of DP (dual-phase) treatments were studied and compared to the quasi-static tensile behavior. The results show that the increasing of strain rate leads to increasing in their strengths and decreasing in the uniform elongation remarkably. Because the stable retained austenite in TRIP steel can transform to martensite during tensile testing and the material exhibits excellent characteristic of transformation induced plasticity, the plastic deformation behavior is evidently improved and the combination of strength and elongation is superior to that of dual-phase steel, although its strength is smaller than that of DP steel. However, DP treated steel shown lower elongation under dynamic tension in spite of higher strength. A model was proposed to explain the excellent elongation rate of TRIP steel compared with DP steel on the basis of SEM analysis and the strength of the components in microstructure.展开更多
How the wave propagation analysis plays a key role in the studies of dynamic response of materials at high strain rates is analyzed. For the wave propagation technique, the followings are important: the loading and un...How the wave propagation analysis plays a key role in the studies of dynamic response of materials at high strain rates is analyzed. For the wave propagation technique, the followings are important: the loading and unloading constitutive relation presumed, the positions of the sensors embedded, the interactions between loading waves and unloading waves. For the split Hopkinson pressure bar (SHPB) technique, the assumption of one-dimensional stress wave propagation and the assumption of stress uniformity along the specimen should be satisfied. When the larger diameter bars are employed, the wave dispersion effects should be considered, including the high frequency oscillations, non-uniform stress distribution across the bar section, increase of rise time, and amplitude attenuation. The stress uniformity along the specimen is influenced by the reflection times in specimen, the wave impedance ratio of the specimen and the bar, and the waveform.展开更多
Static recrystallization of a high strain rate compressed Mg-1 Zn(wt.%)alloy was investigated using electron backscattered diffraction(EBSD).A novel 53°1010 structure was observed in the as-deformed alloy,which s...Static recrystallization of a high strain rate compressed Mg-1 Zn(wt.%)alloy was investigated using electron backscattered diffraction(EBSD).A novel 53°1010 structure was observed in the as-deformed alloy,which showed a{1012}-{1012}double twin relationship with the matrix.When the as-deformed alloy was annealed at 200°C,the{1011}compression twins and{1011}-{1012}double twins showed a higher priority to recrystallize.In addition,the coarse{1012}tension twins and their inner double twins were preferentially to recrystallize,while the lenticular tension twins had little impact on the recrystallization.Therefore,obtaining more compression twins or coarse twins instead of lenticular tension twins can be an effective approach to manipulate recrystallization process in deformed Mg alloys.展开更多
In this paper,the superplastic characteristics of the beta-SiC whisker reinforced 2024aluminum composite, fabricated by squeeze casting and hot-rolling after extrusion were investigated. The compsite had a fine grain ...In this paper,the superplastic characteristics of the beta-SiC whisker reinforced 2024aluminum composite, fabricated by squeeze casting and hot-rolling after extrusion were investigated. The compsite had a fine grain size of about 2μm, and exhibited a strain rate sensitivity of about 0.35 and a maximum elongation of 350% at an initial strain rate of 1.1×10-1s-1 at 803K. In addition, the superplastic deformation mechanisme of the composite were also examined.展开更多
Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high...Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization展开更多
The dynamic compressive deformation of frozen soil was investigated by conducting the split-Hopkinson pressure bar(SHPB)experiments at three temperatures and different high strain rates,and the dynamic stress–strain ...The dynamic compressive deformation of frozen soil was investigated by conducting the split-Hopkinson pressure bar(SHPB)experiments at three temperatures and different high strain rates,and the dynamic stress–strain responses and failure modes of the frozen soil were analyzed.The experimental results demonstrate that the frozen soil exhibits evident dependence on the strain rate and temperature under the dynamic loading condition.The dynamic compressive stress–strain curve of the frozen soil was divided into three parts:the linear,nonlinear rising,and strain softening parts.The nonlinear rising and strain softening parts were both caused by the damage attributed to the debonding between the ice particles and soil matrix,from which a rate-dependent damage evolution equation was obtained.Moreover,a damage-coupled dynamic viscoelastic constitutive model of frozen soil at high strain rate was derived.A comparison between the theoretically predicted results and the experimental ones showed that the developed dynamic viscoelastic model could well describe the dynamic mechanical behavior of frozen soil at high strain rate.展开更多
The true stress-sWain relationships of Ti-5A1-2Sn-2Zr-4Mo-4Cr（TC17） alloy with a wide range of strain rates were investigated by tmiaxial quasi-static and dynamic compression tests, respectively. Quasi- static compr...The true stress-sWain relationships of Ti-5A1-2Sn-2Zr-4Mo-4Cr（TC17） alloy with a wide range of strain rates were investigated by tmiaxial quasi-static and dynamic compression tests, respectively. Quasi- static compression tests were carried out with Instron 8874 test machine, while dynamic compression tests were performed with the split Hopkinson pressure bar （SHPB） which was installed with heating device and synchro- assembly system. The dynamic mechanical behaviors tests of TC17 were carded out from room temperature to 800 ℃ at intervals of 200 ℃ and at high sWain rates （5 500-1 9200 s-l）. The stress-strain curves considering temperature-sWain rate coupling actions were obtained. The Johnson-Cook constitutive model was developed through data fitting of the stress-sWain curves. The material constants in the developed constitutive model can be determined using isothermal and adiabatic stress-strain curves at different strain rates. The Johnson-Cook constitutive model provided satisfied prediction of the plastic flow stress for TC17 alloy.展开更多
Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse directi...Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse direction(TD)and normal direction(ND))were carried out at strain rates of 1000,2000 and 4000 s-1,respectively.From the microscopic point of view,the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope(SEM),metallographic microscope and electron backscatter diffraction(EBSD).The results showed that there was obvious asymmetry between tension and compression,especially that the yield strength of the material in tension was higher than that in compression.The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate.At the same strain rate,the changing trend of the flow stress was distinct under different orientations of tension and compression,which was related to the stress direction of the grains.According to EBSD grain orientation analysis and raw material texture pole figure analysis,it was found that the larger the difference in the degree of grain refinement during tension and compression,the larger the macro-flow stress difference.展开更多
基金Financial support from the National Natural Science Foundation of China(Grant No.52374119)the Province Education Department of Liaoning(Grant No.LJ212410146068)the opening fund of State Key Laboratory of Performance Monitoring and Protecting of Rail Transit Infrastructure,East China Jiaotong University(Grant No.HJGZ2023103).
文摘Understanding the mechanical properties of coal-rock-bolt(CRB)combinations at high strain rates and the anchoring mechanism of bolts is crucial for ensuring the safety of coal mining operations.However,the dynamic behaviors of these combinations,especially the mechanism of action of prestressed bolts,still need to be further investigated.This study carried out split Hopkinson pressure bar(SHPB)tests on three sets of coal-rock(CR),CRB,and coal-rock-prestressed bolt(CRPB)combinations with different interface angles(β=15°,30°,45°,and 60°).The dynamic properties of the combinations were analyzed based on the stress-strain curve,energy dissipation,dynamic strength,fractal dimension of cracks,and failure mode of bolts.The test results show that a larger β will affect the stress transfer and anti-sliding ability of CR,resulting in a decrease in CR strength.The anchoring force of the bolt effectively suppresses the slip feature of CRB at the yield stage.As the strain rate increases,CRB shows a more pronounced'sudden increase'in strength,and the bolt significantly enhances its dynamic strength.The prestressed bolts enhance the dynamic strength of CRPB while weaken the effect of β.The fractal dimension of the macrocracks increases with strain rate,with smaller variations in CRB and CRPB,indicating that the bolt reduces the complexity degree of CRB and CRPB.The anchoring force of CRB depends on bolt strength,which reduces the slip along the interface.The anchoring force of CRPB balances the coal-rock slip and suppresses crack formation,resulting in a more cohesive response under dynamic load.
基金the National Science Foundation of China(Grant No.12172144)the Fundamental Research Funds for Central Universities(Grant No.2016YXMS097)。
文摘Corresponding to the continuous dynamic recrystallization mechanism,we proposed a dislocation entanglement model and an energy-based criterion to capture the formation of subgrain boundaries during high strain rate deformation.A physical relationship between grain refinement and dislocation evolution is established and incorporated into the crystal plasticity constitutive model,where the spatial position of the subgrain boundaries can be determined by the energy minimization path.The developed constitutive model is implemented to simulate the dynamic compression and tension tests of pure copper by the crystal plasticity finite element method.Results show that the developed grain refinement model based on the dislocation entanglement gives good agreement with the experimental data validating its feasibility and rationality.The strengthening effect of grain refinement on the flow stress of metals at high strain rates depends on the competition between the strengthening of grain boundary and the softening of dislocation consumption during grain refinement.Further,a series of dynamic compressions are performed on copper samples with different grain sizes to explore the strengthening effect of grain refinement.The corresponding mechanisms of strengthening are analyzed and their respective contributions are also discussed in detail.The developed model can accurately predict the grain refinement of metals and capture its effect on strain hardening under high strain rate deformation.
基金Projects(51871243,51574290)supported by the National Natural Science Foundation of ChinaProject(ASSIKFJJ202304001)supported by the Open Fund of the National Key Laboratory of Strength and Structural Integrity,China+3 种基金Project(HT-CSNS-DG-CD-0092/2021)supported by the Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology,ChinaProject(2022KF-08)supported by the Hubei Longzhong Laboratory,ChinaProject(22kfgk06)supported by the Shock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province,ChinaProject(PBSKL2022C01)supported by the State Key Laboratory of Precision Blasting and Hubei Key Laboratory of Blasting Engineering,China。
文摘The commercial ZK 60 magnesium alloy with extruded state experienced aging heat treatment(T 6)was dynamically loaded at strain rate of 3000 s−1 by means of the split Hopkinson pressure bar(SHPB)in this paper.Transmission electron microscopy(TEM)observations showed that the precipitatedβ′_(1) phases partially dissolved(spheroidized)with blurred interfaces within 160μs at 3000 s^(−1).The average length and diameter of the rod-shapedβ′_(1) phase particles were 48.5 and 9.8 nm after the T 6 heat treatment;while the average diameter of the sphericalβ′_(1) phases changed to 8.8 nm after loading.The deformedβ′_(1) phase generated larger lattice distortion energy than Mg matrix under high strain rate loading.Therefore,the difference of free energy(the driving force of dissolution)between theβ′_(1) phase and the matrix increased,making the instantaneous dissolution of theβ′_(1) phase thermodynamically feasible.The dissolution(spheroidization)of theβ′_(1) phase particles was kinetically promoted because the diffusion rate of the solute Zn atoms was accelerated by combined actions of adiabatic temperature rise,high density of dislocations(vacancies)and high deviatoric stresses during high strain rate loading.The increase in hardness of ZK 60-T 6 alloy could be attributed to solid solution strengthening,dislocation strengthening and second phase particle strengthening.
基金Project(52409128)supported by the National Natural Science Foundation of ChinaProject(SDGZK2425)supported by the Opening Fund of State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering,China。
文摘The shape of underground chambers in deep mining varies due to their geological environment and intended use,which results in different failure modes under the influence of mining activities.However,the effect of chamber shape on the mechanism of structural integrity under dynamic load is still unclear.In this paper,granite samples with circular(C),rectangular(R),long ellipse(EL),and short ellipse(ES)holes were prepared.The dynamic mechanical response and cracking mechanism of granite were systematically analyzed using the split Hopkinson pressure bar(SHPB)test system and the hybrid finite and discrete element method(HFDEM).The results indicate that the dynamic strengths of granite with EL and ES represent the maximum and minimum values within the range of close strain rates,respectively.When EL granite is subjected to dynamic load,the axial stress concentration(in the load direction)is weak,and the transverse stress shows relative dispersion,which is the primary reason for its highest dynamic strength.The failure of granite with various holes primarily involves a tensile-shear mixed fracture,with relatively few pure typeⅡcracks.The chamber’s transverse span is the primary factor influencing the distribution range of the fracture area.
基金Project (14JJ6047) supported by the Natural Science Foundation of Hunan Province,ChinaProject (51274092) supported by the National Natural Science Foundation of ChinaProject (20120161110040) supported by the Doctoral Program of Higher Education ofChina
文摘Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.
文摘Superplasticity of AZ 31 magnesium matrix composites reinforced with 10 vol% SiC（2 μm） particulate i s investigated at temperature range from 365℃ to 565℃ and strain rate from 2.0 8×10<sup>-3</sup> to 5.21×10<sup>-1</sup> s<sup>-1</sup>. The maximum total elongation of 228 % is obtained at a strain rate of 2.08×10<sup>-1</sup> s<sup>-1</sup>. The strain rate se nsitivity exponent （m） higher than 0.3, is observed when the strain rate is high er than 10<sup>-1</sup> s<sup>-1</sup> at 525℃. Increasing the test temperature to 540℃, the maximum total elongation exceeding 195% is achieved at a higher strain rate of 5.21×10<sup>-1</sup> s<sup>-1</sup> than that at 525℃. SiC in AZ31/SiCp composite ca n fine the matrix grain size. Filament is observed on the fracture surface of th e specimens showing superplasticity.
文摘The aim of this study is to investigate the dynamic stress-strain relation for the hybrid composite （nylon ＋carbon）. Three groups of specimens are used with different number of carbon layers. The specimens were subjected to high velocity impact with different strain rates. SHPB （split Hopkinson pressure bar） is used in this investigation. The results show that, the stress-strain relation various with the strain rate. The maximum stress and strain are proportion directly with the strain rate. Also, the results revealed that, as the number of carbon layer increased, the maximum strain decreased.
基金The authors would like to thank Professor Kui Zhang,Beijing General Research Institute for Nonferrous Metal,for providing EW75 magnesium alloy for this work and acknowledge the funding from the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.17KJD430006)Scientific and Technological Innovation Team Foundation of Wuxi Institute of Technology(No.30593118001)Scientific Research Project of Wuxi Institute of Technology(No.ZK201901).The help of EBSD experiment provided by Yukyung Shin from Helmholtz-Zentrum Geesthacht is gratefully acknowledged.
文摘The dynamic tensile properties and microstructural evolution of an extruded EW75 magnesium alloy deformed at ambient temperature and different high strain rates(from 1000 to 3000 s^(-1))along extrusion direction(ED)were investigated by Split Hopkinson Tension Bar(SHTB).The corresponding deformation mechanisms,texture evolution and microstructure changes were analyzed by optical microscope(OM),electron backscatter diffraction(EBSD)and transmission electron microscope(TEM).The results show that the extruded EW75 magnesium alloy along ED exhibits a conventional positive strain rate sensitivity that the dynamic flow stresses increase with in creasing strain rate.Texture measurements show that after dynamic tension,the initial weak texture of extruded EW75 magnesium alloy tansforms to a relatively strong<10-10>//ED texture with increasing strain rates.The microstructural analysis demonstrates that dislocation motion are main deformatin mode to accommodate dynamic tensile deformation at high strain rates.In addition,the interactions of dislocation-dislocation and dislocation-second phase lead to the in crease of flow stress and strain hardening with increasing strain rate.
基金supported by the National Key R&D Program of China(No.2017YFC0602902)the National Natural Scienceof China(Nos.41807259 and 51874350)+2 种基金the Fundamental Research Funds for the Central Universities of Central South University(No.2016zztx096)The support provided by the China Scholarship Council(CSC)during the visit of the first author toécole Polytechnique de Montréal(Student ID:201706370039)the materials supply by Fan Kou lead-zinc mine of Shenzhen Zhongjin Lingnan Non-ferrous metal Company Limited。
文摘The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinson pressure bar(SHPB)was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4,0.8,and 1.2 MPa.And the failure modes were determined by macro and micro analysis.CPB with different cement-to-tailings ratios,solid mass concentrations,and curing ages was prepared to conduct the SHPB test.The results showed that increasing the cement content,tailings content,and curing age can improve the dynamic compressive strength and elastic modulus.Under an impact load,a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading.And the dynamic compressive strength of CPB has an exponential correlation with the strain rate.The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading.The local damage was enhanced,and fine cracks were formed in the interior of the CPB.This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.
基金supported by the National Natural Science Foundation of China(No.50674067).
文摘The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding（GBS）,and the dislocation creep mechanism is considered as the main accommodation mechanism.
文摘The Al−Mg alloy with high Mg addition(Al−9.2Mg−0.8Mn−0.2Zr-0.15Ti,in wt.%)was subjected to different passes(1,2 and 4)of high strain rate rolling(HSRR),with the total thickness reduction of 72%,the rolling temperature of 400℃and strain rate of 8.6 s^(−1).The microstructure evolution was studied by optical microscope(OM),scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and transmission electron microscope(TEM).The alloy that undergoes 2 passes of HSRR exhibits an obvious bimodal grain structure,in which the average grain sizes of the fine dynamic recrystallization(DRX)grains and the coarse non-DRX regions are 6.4 and 47.7mm,respectively.The high strength((507±9)MPa)and the large ductility((24.9±1.3)%)are obtained in the alloy containing the bimodal grain distribution.The discontinuous dynamic recrystallization(DDRX)mechanism is the prominent grain refinement mechanism in the alloy subjected to 2 passes of HSRR.
基金The authors would like to acknowledge the financial support from the National Key Basic Research Program(973 Program),Project(2013CB632205).
文摘For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.
基金the financial supports of Shanghai Development Foun-dation of Auto Industry and the National Natural Science Foundation of China (No. 50171038).
文摘Tensile mechanical properties of 1.6Si-1.58Mn-0.195C TRIP (transformation-induced plasticity) steels under high strain rate and effects of DP (dual-phase) treatments were studied and compared to the quasi-static tensile behavior. The results show that the increasing of strain rate leads to increasing in their strengths and decreasing in the uniform elongation remarkably. Because the stable retained austenite in TRIP steel can transform to martensite during tensile testing and the material exhibits excellent characteristic of transformation induced plasticity, the plastic deformation behavior is evidently improved and the combination of strength and elongation is superior to that of dual-phase steel, although its strength is smaller than that of DP steel. However, DP treated steel shown lower elongation under dynamic tension in spite of higher strength. A model was proposed to explain the excellent elongation rate of TRIP steel compared with DP steel on the basis of SEM analysis and the strength of the components in microstructure.
文摘How the wave propagation analysis plays a key role in the studies of dynamic response of materials at high strain rates is analyzed. For the wave propagation technique, the followings are important: the loading and unloading constitutive relation presumed, the positions of the sensors embedded, the interactions between loading waves and unloading waves. For the split Hopkinson pressure bar (SHPB) technique, the assumption of one-dimensional stress wave propagation and the assumption of stress uniformity along the specimen should be satisfied. When the larger diameter bars are employed, the wave dispersion effects should be considered, including the high frequency oscillations, non-uniform stress distribution across the bar section, increase of rise time, and amplitude attenuation. The stress uniformity along the specimen is influenced by the reflection times in specimen, the wave impedance ratio of the specimen and the bar, and the waveform.
基金financially supported by National Natural Science Foundation of China(No.51701121,No.51825101)Shanghai Sailing Program(17YF1408800)+2 种基金Science and Technology Commission of Shanghai Municipality(No.18511109302)Qinghai Provincial Science and Technology Key Program(No.2018-GX-A1)Startup Fund for Youngman Research at SJTU(No.18X100040022)
文摘Static recrystallization of a high strain rate compressed Mg-1 Zn(wt.%)alloy was investigated using electron backscattered diffraction(EBSD).A novel 53°1010 structure was observed in the as-deformed alloy,which showed a{1012}-{1012}double twin relationship with the matrix.When the as-deformed alloy was annealed at 200°C,the{1011}compression twins and{1011}-{1012}double twins showed a higher priority to recrystallize.In addition,the coarse{1012}tension twins and their inner double twins were preferentially to recrystallize,while the lenticular tension twins had little impact on the recrystallization.Therefore,obtaining more compression twins or coarse twins instead of lenticular tension twins can be an effective approach to manipulate recrystallization process in deformed Mg alloys.
文摘In this paper,the superplastic characteristics of the beta-SiC whisker reinforced 2024aluminum composite, fabricated by squeeze casting and hot-rolling after extrusion were investigated. The compsite had a fine grain size of about 2μm, and exhibited a strain rate sensitivity of about 0.35 and a maximum elongation of 350% at an initial strain rate of 1.1×10-1s-1 at 803K. In addition, the superplastic deformation mechanisme of the composite were also examined.
文摘Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization
基金the National Natural Science Foundation of China[grant numbers 11672253 and 11972028]the Opening Foundation of the State Key Laboratory of Frozen Soil Engineering[grant number SKLFSE201918].
文摘The dynamic compressive deformation of frozen soil was investigated by conducting the split-Hopkinson pressure bar(SHPB)experiments at three temperatures and different high strain rates,and the dynamic stress–strain responses and failure modes of the frozen soil were analyzed.The experimental results demonstrate that the frozen soil exhibits evident dependence on the strain rate and temperature under the dynamic loading condition.The dynamic compressive stress–strain curve of the frozen soil was divided into three parts:the linear,nonlinear rising,and strain softening parts.The nonlinear rising and strain softening parts were both caused by the damage attributed to the debonding between the ice particles and soil matrix,from which a rate-dependent damage evolution equation was obtained.Moreover,a damage-coupled dynamic viscoelastic constitutive model of frozen soil at high strain rate was derived.A comparison between the theoretically predicted results and the experimental ones showed that the developed dynamic viscoelastic model could well describe the dynamic mechanical behavior of frozen soil at high strain rate.
基金Funded by the National Basic Research Program of China(No.2009CB724401)the Major Science and Technology Program of High-end CNC Machine Tools and Basic Manufacturing Equipment(No.2012ZX04003-041)
文摘The true stress-sWain relationships of Ti-5A1-2Sn-2Zr-4Mo-4Cr（TC17） alloy with a wide range of strain rates were investigated by tmiaxial quasi-static and dynamic compression tests, respectively. Quasi- static compression tests were carried out with Instron 8874 test machine, while dynamic compression tests were performed with the split Hopkinson pressure bar （SHPB） which was installed with heating device and synchro- assembly system. The dynamic mechanical behaviors tests of TC17 were carded out from room temperature to 800 ℃ at intervals of 200 ℃ and at high sWain rates （5 500-1 9200 s-l）. The stress-strain curves considering temperature-sWain rate coupling actions were obtained. The Johnson-Cook constitutive model was developed through data fitting of the stress-sWain curves. The material constants in the developed constitutive model can be determined using isothermal and adiabatic stress-strain curves at different strain rates. The Johnson-Cook constitutive model provided satisfied prediction of the plastic flow stress for TC17 alloy.
基金supported by the Natural Science Foundation of China(No.51675230)the Major Innovation Projects in Shandong Province (No. 2019JZZY010451)。
文摘Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse direction(TD)and normal direction(ND))were carried out at strain rates of 1000,2000 and 4000 s-1,respectively.From the microscopic point of view,the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope(SEM),metallographic microscope and electron backscatter diffraction(EBSD).The results showed that there was obvious asymmetry between tension and compression,especially that the yield strength of the material in tension was higher than that in compression.The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate.At the same strain rate,the changing trend of the flow stress was distinct under different orientations of tension and compression,which was related to the stress direction of the grains.According to EBSD grain orientation analysis and raw material texture pole figure analysis,it was found that the larger the difference in the degree of grain refinement during tension and compression,the larger the macro-flow stress difference.
