High purity and ultrafine DAAF(u-DAAF)is an emerging insensitive charge in initiators.Although there are many ways to obtain u-DAAF,developing a preparation method with stable operation,accurate control,good quality c...High purity and ultrafine DAAF(u-DAAF)is an emerging insensitive charge in initiators.Although there are many ways to obtain u-DAAF,developing a preparation method with stable operation,accurate control,good quality consistency,equipment miniaturization,and minimum manpower is an inevitable requirement to adapt to the current social technology development trend.Here reported is the microfluidic preparation of u-DAAF with tunable particle size by a passive swirling microreactor.Under the guidance of recrystallization growth kinetics and mixing behavior of fluids in the swirling microreactor,the key parameters(liquid flow rate,explosive concentration and crystallization temperature)were screened and optimized through screening experiments.Under the condition that no surfactant is added and only experimental parameters are controlled,the particle size of recrystallized DAAF can be adjusted from 98 nm to 785 nm,and the corresponding specific surface area is 8.45 m^(2)·g^(-1)to 1.33 m^(2)·g^(-1).In addition,the preparation method has good batch stability,high yield(90.8%-92.6%)and high purity(99.0%-99.4%),indicating a high practical application potential.Electric explosion derived flyer initiation tests demonstrate that the u-DAAF shows an initiation sensitivity much lower than that of the raw DAAF,and comparable to that of the refined DAAF by conventional spraying crystallization method.This study provides an efficient method to fabricate u-DAAF with narrow particle size distribution and high reproducibility as well as a theoretical reference for fabrication of other ultrafine explosives.展开更多
Coal and gas outburst is a violent disaster driven by released energy from gas desorption.The initial expansion energy of released gas(IEERG)is a new method to predict coal and gas outburst.In this paper,an instrument...Coal and gas outburst is a violent disaster driven by released energy from gas desorption.The initial expansion energy of released gas(IEERG)is a new method to predict coal and gas outburst.In this paper,an instrument for IEERG measurement was developed.Compared with previous setups,the new one which is equipped with three convergent nozzles and quick-release mechanism gets improved in data acquisition and gas sealing and releasing performance.To comprehensively know the effect of gas pressure,particle size,and nozzle area on IEERG,a series of experiments were carried out with this new setup.The variable control test results indicated that the gas pressure-IEERG curves remain the linear trend and the particle size-IEERG curves maintain the negative exponential trend for nozzle areas at 1.13,2.26,and3.39 mm2,respectively.The increase in nozzle area leads to deceases in value of IEERG and absolute value of slope of fitting curves in each test.In addition,the orthogonal experiment showed that the influence of gas pressure,nozzle area,and particle size on IEERG decreases in turn.Only gas pressure had a marked impact on IEERG.This work offers great importance in improving the accuracy of prediction of coal and gas outburst.展开更多
The kinetics of austenite formation in the surface and center regions of a 40 t forged ingot of a high-strength medium- carbon low-alloy steel was studied using high-resolution dilatometry. The starting microstructure...The kinetics of austenite formation in the surface and center regions of a 40 t forged ingot of a high-strength medium- carbon low-alloy steel was studied using high-resolution dilatometry. The starting microstructures from the surface or center regions had different proportions of bainite and residual austenite as well as different prior austenite grain sizes. Two heating rates representing the actual heating rates in the surface （5℃ s -1） and center regions （0.5℃ s -1） of large size forged blocks were utilized. Dilatometric curves revealed only one transformation step of austenite formation at both heating rates independent of grain size or proportion of phases. Optical microscopy, field emission gun scanning electron microscopy and X-ray diffraction were used to study microstructure evolution and confirm the results obtained by dilatometry. The kinetic parameters for austenite formation were determined from the dilatometry data by Johnson-Mehl- Avrami-Kolmogorov （JMAK） equation. The JMAK coefficients were determined for each condition of the investigated steels. The calculations indicated that the nucleation and growth of austenite in the surface region were accelerated more than 10,000 times due to a significantly smaller average prior austenite grain size, stability of initial retained austenite, and accumulation of coarse carbides at the surface. The results were discussed in the framework of classical nucleation and growth theories using the kinetic parameters for austenite formation.展开更多
The influences of initial grain size(IGS)with 20μm and 50μm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and...The influences of initial grain size(IGS)with 20μm and 50μm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and strain rate range of 0.001–0.1 s^(-1).The effects of critical stress and corresponding critical strain were studied based on the internal and external processing parameters.The critical stress and strain decreased with increasing temperature and decreasing strain rate.The investigation results of the microstructure and true strain–stress diagrams showed that dynamic recovery,dynamic recrystallization(DRX),and twinning mechanisms were caused during the hot deformation of pure copper.Microstructure evolution indicated some DRXed fine-grain took place around grain boundary of hot deformed samples with IGS of 20μm whereas DRXed fine-grain took place in interior grains for samples with larger IGS.The results also showed that grain growth is also dependent on IGS as the grain growth rate for samples with the larger IGS is greater than the smaller IGS.The critical strain rate and the temperature were obtained at 0.01 s^(-1) and 973 K,respectively,for the sudden change in the grain growth rate.Also,twinning highly depended on IGS which almost did not happen in fine grain size while the volume fraction of twinning increased with increasing grain size.展开更多
This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex.A series of idealized experiments are conducted by varying the radius of ...This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex.A series of idealized experiments are conducted by varying the radius of maximum wind(RMW)and shape parameter of the initial vortices.The size–intensity relationship is quantified by the linear regression coefficient of the azimuthally-averaged gale-force wind radius against the maximum wind during the development stage,reflecting the degree of size expansion at the same intensity increment.The regression coefficient increases with increased RMW and decreased,with the RMW being the primary constraint.The effect of lowering on the elevation of the regression coefficient gradually stands out when the initial RMW is large.Enlarging the RMW leads to a secondary circulation with a horizontally elongated structure,which retards the intensification while promoting size expansion,thus substantially enhancing size expansion as the vortex intensifies.Broadening the wind field outside the RMW by reducing results in abounding convection in the outer region,which promotes size expansion.Based on the axisymmetric tangential wind tendency and Sawyer–Eliassen equations,when the RMW is large,the active convection in the outer region can weaken the radial inflow induced by the eyewall heating in the inner region,thus retarding the intensification by reducing the radial imports of vorticity near the RMW.展开更多
Effect of initial grain size (I.G.S.) on static recrystallization softeningin Cr steel (0.77 wt. percent Cr) has been investigated through the use of interrupted hotcompression tests and stress relaxation curves from ...Effect of initial grain size (I.G.S.) on static recrystallization softeningin Cr steel (0.77 wt. percent Cr) has been investigated through the use of interrupted hotcompression tests and stress relaxation curves from Gleeble 1500. Initial grain sizes were variedbetween 20 and 93 microns. Stress strains curves for Cr steel for different initial grain sizes andrecrystallization times have been highlighted. Similar observation was made for metadynamicrecrystallization with shorter retardation times. Statically recrystallized grain size alsoincreased as initial grain size increases. It is found that the values of initial grain size havesignificant effects on the mean flow stress and static recrystallization kinetics as well as thepeak strain values to initiate dynamic recrystallization.展开更多
In this paper the influence of sample initial size on their convective drying at 80°C using convective dryer is determined. Results prove that initial size must be taken into account when drying process was estim...In this paper the influence of sample initial size on their convective drying at 80°C using convective dryer is determined. Results prove that initial size must be taken into account when drying process was estimated. This influence is limited by its form of cut. Comparing cubic form and parallelepiped (slice) one;results seem to show that thickness is the most important parameter governing the transfer phenomena during foodstuff convective drying. Three slices with thickness of 0.5 cm and surface area of 17, 82 and 112 cm2 respectively, dry better than cubic sample with a = 1 cm or a = 2 cm of arrest and having respectively 6 and 24 cm2 of surface area. All things seem to show that initial surface is not only the essential parameter;but also the thickness of the sample must be taken into account. Indeed, all of the samples with equal thickness (0.5 cm) and different exchange surfaces dry at the same time, about 210 min, comparing with cubic form 1 cm of arrest and 6 cm2 of surface and drying time of 230 min. A new parameter noted Dc called characteristic diameter is so considered to bridge the gaps. It is defined to be the diameter of the biggest sphere we can cut into a sample. This parameter is independent of form of the sample, and time increase with characteristic diameter increasing.展开更多
GH4169 at 650℃ in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crac...GH4169 at 650℃ in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crack initiation life accounted for more percentages of the total fatigue life for the alloy with smaller grain size. The fatigue life generally increased with increasing crack initiation life. The small crack transited to long crack when its length reached 10 times the grain size.展开更多
Tangential separator is widely used in industries as vital demulsification and dewatering separation devices but leads to high breakage rate of droplets.To address this,the swirl separator with progressive process was...Tangential separator is widely used in industries as vital demulsification and dewatering separation devices but leads to high breakage rate of droplets.To address this,the swirl separator with progressive process was developed by exploiting operational merits of swirl element to minimize the breakage rate of droplet.The initial droplet size distribution has an influence on the droplet size distribution within the flow field.Accordingly,the droplet size distribution was analyzed numerically and verified through experimental measurements.The evolution of the droplet size distribution from the numerical simulation was then investigated.Based on these,the mechanism of droplet coalescence and breakup were examined.The results show that the initial equilibrium droplet size distribution is d_(50)=85–90μm at V=5 m/s.Simultaneously,the turbulent dissipation rate is lower than the other initial droplet size distributions.Moreover,the numerical model can reasonably be utilized to the investigation.When the initial droplet size distribution is above d_(50)=90μm,the effect of droplet breakup is dominated.The rate of droplet breakup increases,and the coalescence rate decreases with the draining time of liquid film for coalescence increasing,which is unconducive to improve the separation efficiency.Conversely,if the initial droplet size distribution is below d_(50)=85μm,the swirl element promotes the droplet coalescence.The separation efficiency has an improvement.Additionally,the swirl element enhances the turbulent dissipation rate within the flow field.展开更多
After finishing 102 replicate constant amplitude crack initiation and growth tests on Ly12-CZ aluminum alloy plate, a statistical investigation of the fatigue crack initiation and growth process is conducted in this p...After finishing 102 replicate constant amplitude crack initiation and growth tests on Ly12-CZ aluminum alloy plate, a statistical investigation of the fatigue crack initiation and growth process is conducted in this paper. According to the post-mortem fractographic examination by scanning electron microscopy (SEM), some qualitative observations of the spacial correlation among fatigue striations are developed to reveal the statistical nature of material intrinsic inhomogeneity during the crack growth process. From the test data, an engineering division between crack initiation and growth is defined as the upper limit of small crack. The distributions of crack initiation life N-i, growth life N, and the statistical characteristics of crack growth rate da/dN are also investigated. It is hoped that the work will provide a solid test basis for the study of probabilistic fatigue, probabilistic fracture mechanics, fatigue reliability and its engineering applications.展开更多
基金the National Natural Science Foundation of China (Grant No.22105184)Research Fund of SWUST for PhD (Grant No.22zx7175)+1 种基金Sichuan Science and Technology Program (Grant No.2019ZDZX0013)Institute of Chemical Materials Program (Grant No.SXK-2022-03)for financial support。
文摘High purity and ultrafine DAAF(u-DAAF)is an emerging insensitive charge in initiators.Although there are many ways to obtain u-DAAF,developing a preparation method with stable operation,accurate control,good quality consistency,equipment miniaturization,and minimum manpower is an inevitable requirement to adapt to the current social technology development trend.Here reported is the microfluidic preparation of u-DAAF with tunable particle size by a passive swirling microreactor.Under the guidance of recrystallization growth kinetics and mixing behavior of fluids in the swirling microreactor,the key parameters(liquid flow rate,explosive concentration and crystallization temperature)were screened and optimized through screening experiments.Under the condition that no surfactant is added and only experimental parameters are controlled,the particle size of recrystallized DAAF can be adjusted from 98 nm to 785 nm,and the corresponding specific surface area is 8.45 m^(2)·g^(-1)to 1.33 m^(2)·g^(-1).In addition,the preparation method has good batch stability,high yield(90.8%-92.6%)and high purity(99.0%-99.4%),indicating a high practical application potential.Electric explosion derived flyer initiation tests demonstrate that the u-DAAF shows an initiation sensitivity much lower than that of the raw DAAF,and comparable to that of the refined DAAF by conventional spraying crystallization method.This study provides an efficient method to fabricate u-DAAF with narrow particle size distribution and high reproducibility as well as a theoretical reference for fabrication of other ultrafine explosives.
基金supported by the National Key Scientific Instruments and Equipment Development Projects of China(No.51427804)the National Science Foundation of Shandong Province(No.ZR2017MEE023)。
文摘Coal and gas outburst is a violent disaster driven by released energy from gas desorption.The initial expansion energy of released gas(IEERG)is a new method to predict coal and gas outburst.In this paper,an instrument for IEERG measurement was developed.Compared with previous setups,the new one which is equipped with three convergent nozzles and quick-release mechanism gets improved in data acquisition and gas sealing and releasing performance.To comprehensively know the effect of gas pressure,particle size,and nozzle area on IEERG,a series of experiments were carried out with this new setup.The variable control test results indicated that the gas pressure-IEERG curves remain the linear trend and the particle size-IEERG curves maintain the negative exponential trend for nozzle areas at 1.13,2.26,and3.39 mm2,respectively.The increase in nozzle area leads to deceases in value of IEERG and absolute value of slope of fitting curves in each test.In addition,the orthogonal experiment showed that the influence of gas pressure,nozzle area,and particle size on IEERG decreases in turn.Only gas pressure had a marked impact on IEERG.This work offers great importance in improving the accuracy of prediction of coal and gas outburst.
文摘The kinetics of austenite formation in the surface and center regions of a 40 t forged ingot of a high-strength medium- carbon low-alloy steel was studied using high-resolution dilatometry. The starting microstructures from the surface or center regions had different proportions of bainite and residual austenite as well as different prior austenite grain sizes. Two heating rates representing the actual heating rates in the surface （5℃ s -1） and center regions （0.5℃ s -1） of large size forged blocks were utilized. Dilatometric curves revealed only one transformation step of austenite formation at both heating rates independent of grain size or proportion of phases. Optical microscopy, field emission gun scanning electron microscopy and X-ray diffraction were used to study microstructure evolution and confirm the results obtained by dilatometry. The kinetic parameters for austenite formation were determined from the dilatometry data by Johnson-Mehl- Avrami-Kolmogorov （JMAK） equation. The JMAK coefficients were determined for each condition of the investigated steels. The calculations indicated that the nucleation and growth of austenite in the surface region were accelerated more than 10,000 times due to a significantly smaller average prior austenite grain size, stability of initial retained austenite, and accumulation of coarse carbides at the surface. The results were discussed in the framework of classical nucleation and growth theories using the kinetic parameters for austenite formation.
文摘The influences of initial grain size(IGS)with 20μm and 50μm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and strain rate range of 0.001–0.1 s^(-1).The effects of critical stress and corresponding critical strain were studied based on the internal and external processing parameters.The critical stress and strain decreased with increasing temperature and decreasing strain rate.The investigation results of the microstructure and true strain–stress diagrams showed that dynamic recovery,dynamic recrystallization(DRX),and twinning mechanisms were caused during the hot deformation of pure copper.Microstructure evolution indicated some DRXed fine-grain took place around grain boundary of hot deformed samples with IGS of 20μm whereas DRXed fine-grain took place in interior grains for samples with larger IGS.The results also showed that grain growth is also dependent on IGS as the grain growth rate for samples with the larger IGS is greater than the smaller IGS.The critical strain rate and the temperature were obtained at 0.01 s^(-1) and 973 K,respectively,for the sudden change in the grain growth rate.Also,twinning highly depended on IGS which almost did not happen in fine grain size while the volume fraction of twinning increased with increasing grain size.
基金This study is supported by the National Natural Science Foundation of China(Grant Nos.42175073 and 41975071).
文摘This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex.A series of idealized experiments are conducted by varying the radius of maximum wind(RMW)and shape parameter of the initial vortices.The size–intensity relationship is quantified by the linear regression coefficient of the azimuthally-averaged gale-force wind radius against the maximum wind during the development stage,reflecting the degree of size expansion at the same intensity increment.The regression coefficient increases with increased RMW and decreased,with the RMW being the primary constraint.The effect of lowering on the elevation of the regression coefficient gradually stands out when the initial RMW is large.Enlarging the RMW leads to a secondary circulation with a horizontally elongated structure,which retards the intensification while promoting size expansion,thus substantially enhancing size expansion as the vortex intensifies.Broadening the wind field outside the RMW by reducing results in abounding convection in the outer region,which promotes size expansion.Based on the axisymmetric tangential wind tendency and Sawyer–Eliassen equations,when the RMW is large,the active convection in the outer region can weaken the radial inflow induced by the eyewall heating in the inner region,thus retarding the intensification by reducing the radial imports of vorticity near the RMW.
文摘Effect of initial grain size (I.G.S.) on static recrystallization softeningin Cr steel (0.77 wt. percent Cr) has been investigated through the use of interrupted hotcompression tests and stress relaxation curves from Gleeble 1500. Initial grain sizes were variedbetween 20 and 93 microns. Stress strains curves for Cr steel for different initial grain sizes andrecrystallization times have been highlighted. Similar observation was made for metadynamicrecrystallization with shorter retardation times. Statically recrystallized grain size alsoincreased as initial grain size increases. It is found that the values of initial grain size havesignificant effects on the mean flow stress and static recrystallization kinetics as well as thepeak strain values to initiate dynamic recrystallization.
文摘In this paper the influence of sample initial size on their convective drying at 80°C using convective dryer is determined. Results prove that initial size must be taken into account when drying process was estimated. This influence is limited by its form of cut. Comparing cubic form and parallelepiped (slice) one;results seem to show that thickness is the most important parameter governing the transfer phenomena during foodstuff convective drying. Three slices with thickness of 0.5 cm and surface area of 17, 82 and 112 cm2 respectively, dry better than cubic sample with a = 1 cm or a = 2 cm of arrest and having respectively 6 and 24 cm2 of surface area. All things seem to show that initial surface is not only the essential parameter;but also the thickness of the sample must be taken into account. Indeed, all of the samples with equal thickness (0.5 cm) and different exchange surfaces dry at the same time, about 210 min, comparing with cubic form 1 cm of arrest and 6 cm2 of surface and drying time of 230 min. A new parameter noted Dc called characteristic diameter is so considered to bridge the gaps. It is defined to be the diameter of the biggest sphere we can cut into a sample. This parameter is independent of form of the sample, and time increase with characteristic diameter increasing.
基金ffinancially supported by the National Natural Science Foundations of China (Nos. 51725503, 51605164 and 51575183)the 111 project+3 种基金support by Shanghai Technology Innovation Program of SHEITC (No. CXY-2015-001)Fok Ying Tung Education Foundationsupport by Shanghai Sailing Program (No. 16YF1402300)Shanghai Chenguang Program (No. 16CG34).
文摘GH4169 at 650℃ in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crack initiation life accounted for more percentages of the total fatigue life for the alloy with smaller grain size. The fatigue life generally increased with increasing crack initiation life. The small crack transited to long crack when its length reached 10 times the grain size.
基金supported by grants from the National Natural Science Foundation of China(grant No.22178036)CSTC projects(grant Nos.CSTB2023NSCQ-MSX0791,CSTB2023NSCQ-LZX0096)projects of science and technology research program of Chongqing Education Commission of China(grant Nos.KJQN202100817,KJZD-M202200801,KJZD-M202300802 and CXQT21023).
文摘Tangential separator is widely used in industries as vital demulsification and dewatering separation devices but leads to high breakage rate of droplets.To address this,the swirl separator with progressive process was developed by exploiting operational merits of swirl element to minimize the breakage rate of droplet.The initial droplet size distribution has an influence on the droplet size distribution within the flow field.Accordingly,the droplet size distribution was analyzed numerically and verified through experimental measurements.The evolution of the droplet size distribution from the numerical simulation was then investigated.Based on these,the mechanism of droplet coalescence and breakup were examined.The results show that the initial equilibrium droplet size distribution is d_(50)=85–90μm at V=5 m/s.Simultaneously,the turbulent dissipation rate is lower than the other initial droplet size distributions.Moreover,the numerical model can reasonably be utilized to the investigation.When the initial droplet size distribution is above d_(50)=90μm,the effect of droplet breakup is dominated.The rate of droplet breakup increases,and the coalescence rate decreases with the draining time of liquid film for coalescence increasing,which is unconducive to improve the separation efficiency.Conversely,if the initial droplet size distribution is below d_(50)=85μm,the swirl element promotes the droplet coalescence.The separation efficiency has an improvement.Additionally,the swirl element enhances the turbulent dissipation rate within the flow field.
基金The project is supported by the Aeronautic Science Foundation,China
文摘After finishing 102 replicate constant amplitude crack initiation and growth tests on Ly12-CZ aluminum alloy plate, a statistical investigation of the fatigue crack initiation and growth process is conducted in this paper. According to the post-mortem fractographic examination by scanning electron microscopy (SEM), some qualitative observations of the spacial correlation among fatigue striations are developed to reveal the statistical nature of material intrinsic inhomogeneity during the crack growth process. From the test data, an engineering division between crack initiation and growth is defined as the upper limit of small crack. The distributions of crack initiation life N-i, growth life N, and the statistical characteristics of crack growth rate da/dN are also investigated. It is hoped that the work will provide a solid test basis for the study of probabilistic fatigue, probabilistic fracture mechanics, fatigue reliability and its engineering applications.
文摘大量研究表明,粗粒材料的强度和变形特性受初始颗粒级配(grain size distribution,简称GSD)影响显著。然而,当前关于考虑颗粒初始GSD影响的粗粒材料本构模型的研究尚不多见。通过引入能够反映颗粒破碎难易程度的初始级配指标?,将材料初始GSD和终极GSD相联系,系统地探究并阐明了?对粗粒材料峰值抗剪强度qp和峰值应变εap以及e-p平面临界状态线(critical state line,简称CSL)位置的影响机制。针对?对qp和εap影响的研究表明,随着?增加,qp降低;而εap则随着?的增加而增加。结合上述结论,以沈珠江提出的驼峰型二次曲线模型为基础,建立了考虑初始级配和围压影响的切线杨氏模量;针对?对CSL位置影响的研究显示,随着?减小,CSL向下移动的同时还会沿逆时针方向旋转。基于此结论,以临界状态土力学为框架,通过引入状态参数,建立了考虑初始级配和围压影响与状态相关的切线泊松比。对一种粗粒材料而言,该模型只用一套模型参数,且模型预测结果与试验结果较为吻合。
