For the compromise of mechanical properties and product cost, the end-chilled sand casting technique was applied to studying the microstructure evolution of A356 Al alloy with cooling rate and the effect of different ...For the compromise of mechanical properties and product cost, the end-chilled sand casting technique was applied to studying the microstructure evolution of A356 Al alloy with cooling rate and the effect of different as-cast microstructures on the subsequent solution-treatment process. The experimental results show that the secondary dendrite arm spacing (SDAS) of primaryα(Al), the size of eutectic Si and the volume fraction of Al?Si eutectic are reduced with increasing the cooling rate. Eutectic Si, subjected to solution treatment at 540 °C for 1 h followed by water quenching to room temperature, is completely spheroidized at cooling rate of 2.6 K/s; is partially spheroidized atcooling rate of 0.6 K/s; and is only edge-rounded at cooling rates of 0.22 and 0.12 K /s. Whilst the microhardness is also the maximum at cooling rate of 2.6 K/s. It consequently suggests that subjected to modification by high cooling rate, the eutectic Si is more readily modified, thus shortening the necessary solution time at given solution temperature, i.e., reducing the product cost.展开更多
The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated. The results showed that the coarse columnar grains containing a large amount of aci...The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated. The results showed that the coarse columnar grains containing a large amount of acicular α and martensite α′ werepresent in the fusion zone (FZ), some residual α phases and martensite structure were formed in the heat-affected zone (HAZ) onTC4 side, and bulk equiaxed α phase of the HAZ was on TA15 side. An asymmetrical microhardness profile across the dissimilarjoint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM. The orders of yield strengthand ultimate tensile strength were as follows: TC4 BM > TC4/TC4 similar joint > TA15 BM > TA15/TA15 similar joint > TC4/TA15dissimilar joint, and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from1×10?4 s?1 to 1×10?2 s?1. The TC4/TA15 dissimilar joints failed in the TA15 BM, and had characteristics of ductile fracture atdifferent strain rates.展开更多
The superplasticity of Al-6Mg-0.4Mn-0.25Sc-0.12Zr and Al-6Mg-0.4Mn-0.25Er-0.12Zr(mass fraction,%)alloys sheet was investigated,and the effect of Sc and Er was discussed.The results show that the superplastic ductiliti...The superplasticity of Al-6Mg-0.4Mn-0.25Sc-0.12Zr and Al-6Mg-0.4Mn-0.25Er-0.12Zr(mass fraction,%)alloys sheet was investigated,and the effect of Sc and Er was discussed.The results show that the superplastic ductilities of Al-Mg-Mn-Sc-Zr alloy was higher than that of Al-Mg-Mn-Er-Zr alloy at a wide temperature range of 400-540°C and high strain rate range of1.67×10-4-1.67×10-1 s-1.A maximum elongation 673%is obtained at 520°C and 1.67×10-3 s-1 in the Sc-containing alloy;while the Er-containing alloy only gets a maximum elongation 253%at 520°C and 1.67×10-3 s-1.Moreover,the average stress exponent of Sc-containing alloy is about 2.84,which is smaller than that of Er-containing alloy(3.64).Besides,the activation energies of the Sc-containing and Er-containing alloy are 84.8 k J/mol and 87.2 k J/mol,respectively.It is indicated that grain boundary sliding is the dominant mechanism during tensile deformation.According to microstructure examination,the better superplasticity of Sc-containing alloy may be attributed to the presence of Al3_(Sc,Zr)dispersoids,which can inhibit recrystallization and grain growth effectively.展开更多
It has been known that the productivity of artesian wells is strongly dependent on the rheological properties of crude oils. This work targets two deep artesian wells(>5000 m) that are producing heavy crude oil. Th...It has been known that the productivity of artesian wells is strongly dependent on the rheological properties of crude oils. This work targets two deep artesian wells(>5000 m) that are producing heavy crude oil. The impacts of well conditions including temperature, pressure and shear rate, on the crude oil rheology were comprehensively investigated and correlated using several empirical rheological models. The experimental data indicate that this heavy oil is very sensitive to temperature as result of microstructure change caused by hydrogen bonding. The rheological behavior of the heavy oil is also significantly impacted by the imposed pressure, i.e., the viscosity flow activation energy(Eμ) gently increases with the increasing pressure. The viscosity–shear rate data are well fitted to the power law model at low temperature. However, due to the transition of fluid feature at high temperature(Newtonian fluid), the measured viscosity was found to slightly deviate from the fitting data. Combining the evaluated correlations, the viscosity profile of the heavy crude oil in these two deep artesian wells as a function of well depth was predicted using the oilfield producing data.展开更多
Rocks are heterogeneous from the point of dynamic failure behavior. Both the compressive and microstructure which is of significance to their tensile strength of rock-like materials is regarded different from the stat...Rocks are heterogeneous from the point of dynamic failure behavior. Both the compressive and microstructure which is of significance to their tensile strength of rock-like materials is regarded different from the static strength. The present study adopts smoothed particle hydrodynamics （SPH） which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials. The SPH method is capable of simulating rock fracture, free of the mesh constraint of the traditional FEM and FDM models. A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling. The results show the compressive strength increases with the increase of strain rate as well as the tensile strength, which is important to the engineering design.展开更多
The separate-layer injection in different interlayers and the injection of the same-molecular-weight polymer so- lution in a layer are necessary in the polymer flooding process because of heterogeneous multilayer sand...The separate-layer injection in different interlayers and the injection of the same-molecular-weight polymer so- lution in a layer are necessary in the polymer flooding process because of heterogeneous multilayer sandstone reservoirs in EOR projects. To alleviate the matching problems between the layer permeability and the injected polymer molecular weight, a molecular weight adjusting device with porous medium was designed on the basis of mechanical degradation principle. In terms of four variables （polymer concentration, pore diameter, length of shear component and flow rate ）, the theological behavior of hydrolyzed polyacrylamide （HPAM） solu- tion flowing through the device was investigated in detail. The change of these variables is able to control the shear rate of HPAM solutions through ceramic foam, and achieve the desired degree of shear degradation and the final theological parameters-viscosity loss, viscoelasticity and pressure drop. Therefore, a linear relationship between viscosity loss and shearing rate was established so as to obtain the targeted viscosity easily. Field tests in the Daqing Oil Field showed that the polymer molecular weight could drop 20% to 50%. In a word, the results could guide the industrial application of the novel device and the further study of polymer degradation flowing through the porous medium.展开更多
An experimental investigation of the influence of temperature on the Portevin-Le Chatelier(PLC) effect in Al-Mg alloy is conducted.Under a certain strain rate,the PLC effect is present in the temperature range of 223-...An experimental investigation of the influence of temperature on the Portevin-Le Chatelier(PLC) effect in Al-Mg alloy is conducted.Under a certain strain rate,the PLC effect is present in the temperature range of 223-328 K.The serration amplitude increases monotonically with increasing temperature,whereas the behaviors of the serration period and the critical strain with temperature include a descending branch under corresponding low temperature range and an ascending branch under corresponding high temperature range.The analysis in relation with dynamic strain aging(DSA) indicates that the temperature plays an important role in the PLC effect by dictating the solubility and the diffusibility of solute atoms.Both the concentration and the diffusibility of solute atoms contribute to increasing the serration amplitude.Under the descending branch temperature range,the serration period mainly depends on the preparation phase and the dominant factor of critical strain is the velocity of dislocations.However,under the ascending branch temperature range,the serration period mainly depends on the pinning phase and the dominant factor of critical strain is the applied stress required for unpinning.展开更多
A U-Pb-He double-dating method is applied to detrital zircons with core-rim structure from the Ganges River in order to de- termine average short and long-term exhumation rates for the Himalayas. Long-term rates are c...A U-Pb-He double-dating method is applied to detrital zircons with core-rim structure from the Ganges River in order to de- termine average short and long-term exhumation rates for the Himalayas. Long-term rates are calculated from the U/Pb ages of metamorphic rims of the grains that formed during the Himalayan orogeny and their crystallization temperatures, which are calculated from the Ti-in-zircon thermometer. Short-term rates are calculated from （U-Th）/He ages of the grains with appro- priate closure temperatures. The results show that short-term rates for the Himalayas, which range from 0.70 ± 0.09 to 2.67 ± 0.40 km/Myr and average 1.75 ± 0.59 （1δ） km/Myr, are higher and more varied than the long-term rates, which range from 0.84 ±0.16 to 1.85 ± 0.35 km/Myr and average 1.26 ±0.25 （let） km/Myr. The differences between the long-term and short-term rates can be attributed to continuous exhumation of the host rocks in different mechanisms in continental collision orogen. The U/Pb ages of 44.0 ± 3.7 to 18.3 ±0.5 Ma for the zircon rims indicate a protracted episode of -：25 Myr for regional metamorphism of the host rocks at deeper crust, whereas the （U-Th）/He ages of 42.2 ± 1.8 to 1.3 ± 0.2 Ma for the zircon grains represent a protracted period of -40 Myr for exposure of the host rocks to shallower crustal level. In particular, the oldest （U-Th）/He ages of the zircon grains are close to the oldest U/Pb ages for the rims, indicating that some parcels of the rocks that contain zircons were rapidly exhumed from deep to shallow levels in the stage of collisional orogeny. On the other hand, some parcels of the rocks may have been carried upwards by thrust faults in the post-collisional stage. The parcels could be carried upwards by the thrust faults that steepen as they near the surface, or by transient movement faults so that areas of rapid exhu- mation became areas of slow exhumation and visa versa on a time scale of a few Myr in order to maintain the continuous ex- humation. In this regard, the Ganges River must be preferentially sampling areas that are currently undergoing above average rates of uplift.展开更多
基金Project(2011CB610403)support by the National Basic Research Program of ChinaProjects(51134011,51431008)supported by the National Natural Science Foundation of China+1 种基金Project(JC20120223)supported by the Fundamental Research Fund of Northwestern Polytechnical University,ChinaProject(51125002)supported by the National Funds for Distinguished Young Scientists of China
文摘For the compromise of mechanical properties and product cost, the end-chilled sand casting technique was applied to studying the microstructure evolution of A356 Al alloy with cooling rate and the effect of different as-cast microstructures on the subsequent solution-treatment process. The experimental results show that the secondary dendrite arm spacing (SDAS) of primaryα(Al), the size of eutectic Si and the volume fraction of Al?Si eutectic are reduced with increasing the cooling rate. Eutectic Si, subjected to solution treatment at 540 °C for 1 h followed by water quenching to room temperature, is completely spheroidized at cooling rate of 2.6 K/s; is partially spheroidized atcooling rate of 0.6 K/s; and is only edge-rounded at cooling rates of 0.22 and 0.12 K /s. Whilst the microhardness is also the maximum at cooling rate of 2.6 K/s. It consequently suggests that subjected to modification by high cooling rate, the eutectic Si is more readily modified, thus shortening the necessary solution time at given solution temperature, i.e., reducing the product cost.
基金Project(51405392)supported by the National Natural Science Foundation of ChinaProject(20136102120022)supported by the Research Fund for the Doctoral Program of Higher Education of ChinaProject(3102015ZY023)supported by the Fundamental Research Funds for the Central Universities,China
文摘The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated. The results showed that the coarse columnar grains containing a large amount of acicular α and martensite α′ werepresent in the fusion zone (FZ), some residual α phases and martensite structure were formed in the heat-affected zone (HAZ) onTC4 side, and bulk equiaxed α phase of the HAZ was on TA15 side. An asymmetrical microhardness profile across the dissimilarjoint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM. The orders of yield strengthand ultimate tensile strength were as follows: TC4 BM > TC4/TC4 similar joint > TA15 BM > TA15/TA15 similar joint > TC4/TA15dissimilar joint, and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from1×10?4 s?1 to 1×10?2 s?1. The TC4/TA15 dissimilar joints failed in the TA15 BM, and had characteristics of ductile fracture atdifferent strain rates.
基金Project(2014M552149) supported by the China Postdoctoral Science FoundationProject(CX2016B041) supported by the Hunan Provincial Innovation Foundation For Postgraduate,ChinaProject(CSUZC201614) supported by the Open-End Fund for the Valuable and Precision Instruments of Central South University,China
文摘The superplasticity of Al-6Mg-0.4Mn-0.25Sc-0.12Zr and Al-6Mg-0.4Mn-0.25Er-0.12Zr(mass fraction,%)alloys sheet was investigated,and the effect of Sc and Er was discussed.The results show that the superplastic ductilities of Al-Mg-Mn-Sc-Zr alloy was higher than that of Al-Mg-Mn-Er-Zr alloy at a wide temperature range of 400-540°C and high strain rate range of1.67×10-4-1.67×10-1 s-1.A maximum elongation 673%is obtained at 520°C and 1.67×10-3 s-1 in the Sc-containing alloy;while the Er-containing alloy only gets a maximum elongation 253%at 520°C and 1.67×10-3 s-1.Moreover,the average stress exponent of Sc-containing alloy is about 2.84,which is smaller than that of Er-containing alloy(3.64).Besides,the activation energies of the Sc-containing and Er-containing alloy are 84.8 k J/mol and 87.2 k J/mol,respectively.It is indicated that grain boundary sliding is the dominant mechanism during tensile deformation.According to microstructure examination,the better superplasticity of Sc-containing alloy may be attributed to the presence of Al3_(Sc,Zr)dispersoids,which can inhibit recrystallization and grain growth effectively.
基金Supported by the National Key Science&Technology Projects during 13th Five-Year Plan(2016ZX05053-003)Young Scholars Development fund of SWPU(201499010121)
文摘It has been known that the productivity of artesian wells is strongly dependent on the rheological properties of crude oils. This work targets two deep artesian wells(>5000 m) that are producing heavy crude oil. The impacts of well conditions including temperature, pressure and shear rate, on the crude oil rheology were comprehensively investigated and correlated using several empirical rheological models. The experimental data indicate that this heavy oil is very sensitive to temperature as result of microstructure change caused by hydrogen bonding. The rheological behavior of the heavy oil is also significantly impacted by the imposed pressure, i.e., the viscosity flow activation energy(Eμ) gently increases with the increasing pressure. The viscosity–shear rate data are well fitted to the power law model at low temperature. However, due to the transition of fluid feature at high temperature(Newtonian fluid), the measured viscosity was found to slightly deviate from the fitting data. Combining the evaluated correlations, the viscosity profile of the heavy crude oil in these two deep artesian wells as a function of well depth was predicted using the oilfield producing data.
文摘Rocks are heterogeneous from the point of dynamic failure behavior. Both the compressive and microstructure which is of significance to their tensile strength of rock-like materials is regarded different from the static strength. The present study adopts smoothed particle hydrodynamics （SPH） which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials. The SPH method is capable of simulating rock fracture, free of the mesh constraint of the traditional FEM and FDM models. A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling. The results show the compressive strength increases with the increase of strain rate as well as the tensile strength, which is important to the engineering design.
基金Supported by the Program for Yangtse River Scholars and Innovative Research Terms in Universities(IRT0936)the National Basic Research Program of China(2009CB219905+2 种基金2009CB219907)the Daqing Oilfield Co.Ltd
文摘The separate-layer injection in different interlayers and the injection of the same-molecular-weight polymer so- lution in a layer are necessary in the polymer flooding process because of heterogeneous multilayer sandstone reservoirs in EOR projects. To alleviate the matching problems between the layer permeability and the injected polymer molecular weight, a molecular weight adjusting device with porous medium was designed on the basis of mechanical degradation principle. In terms of four variables （polymer concentration, pore diameter, length of shear component and flow rate ）, the theological behavior of hydrolyzed polyacrylamide （HPAM） solu- tion flowing through the device was investigated in detail. The change of these variables is able to control the shear rate of HPAM solutions through ceramic foam, and achieve the desired degree of shear degradation and the final theological parameters-viscosity loss, viscoelasticity and pressure drop. Therefore, a linear relationship between viscosity loss and shearing rate was established so as to obtain the targeted viscosity easily. Field tests in the Daqing Oil Field showed that the polymer molecular weight could drop 20% to 50%. In a word, the results could guide the industrial application of the novel device and the further study of polymer degradation flowing through the porous medium.
基金supported by the National Natural Science Foundation of China (Grant Nos 10732080 and 10872189)
文摘An experimental investigation of the influence of temperature on the Portevin-Le Chatelier(PLC) effect in Al-Mg alloy is conducted.Under a certain strain rate,the PLC effect is present in the temperature range of 223-328 K.The serration amplitude increases monotonically with increasing temperature,whereas the behaviors of the serration period and the critical strain with temperature include a descending branch under corresponding low temperature range and an ascending branch under corresponding high temperature range.The analysis in relation with dynamic strain aging(DSA) indicates that the temperature plays an important role in the PLC effect by dictating the solubility and the diffusibility of solute atoms.Both the concentration and the diffusibility of solute atoms contribute to increasing the serration amplitude.Under the descending branch temperature range,the serration period mainly depends on the preparation phase and the dominant factor of critical strain is the velocity of dislocations.However,under the ascending branch temperature range,the serration period mainly depends on the pinning phase and the dominant factor of critical strain is the applied stress required for unpinning.
基金supported by the Australian Research Council Discovery Project(Grant No.DP 0556923)the Chinese Academy of Sciences Distinguished ProfessorshipGuangzhou Institute of Geochemistry,Chinese Academy of Sciences(Grant No.Y234041001)
文摘A U-Pb-He double-dating method is applied to detrital zircons with core-rim structure from the Ganges River in order to de- termine average short and long-term exhumation rates for the Himalayas. Long-term rates are calculated from the U/Pb ages of metamorphic rims of the grains that formed during the Himalayan orogeny and their crystallization temperatures, which are calculated from the Ti-in-zircon thermometer. Short-term rates are calculated from （U-Th）/He ages of the grains with appro- priate closure temperatures. The results show that short-term rates for the Himalayas, which range from 0.70 ± 0.09 to 2.67 ± 0.40 km/Myr and average 1.75 ± 0.59 （1δ） km/Myr, are higher and more varied than the long-term rates, which range from 0.84 ±0.16 to 1.85 ± 0.35 km/Myr and average 1.26 ±0.25 （let） km/Myr. The differences between the long-term and short-term rates can be attributed to continuous exhumation of the host rocks in different mechanisms in continental collision orogen. The U/Pb ages of 44.0 ± 3.7 to 18.3 ±0.5 Ma for the zircon rims indicate a protracted episode of -：25 Myr for regional metamorphism of the host rocks at deeper crust, whereas the （U-Th）/He ages of 42.2 ± 1.8 to 1.3 ± 0.2 Ma for the zircon grains represent a protracted period of -40 Myr for exposure of the host rocks to shallower crustal level. In particular, the oldest （U-Th）/He ages of the zircon grains are close to the oldest U/Pb ages for the rims, indicating that some parcels of the rocks that contain zircons were rapidly exhumed from deep to shallow levels in the stage of collisional orogeny. On the other hand, some parcels of the rocks may have been carried upwards by thrust faults in the post-collisional stage. The parcels could be carried upwards by the thrust faults that steepen as they near the surface, or by transient movement faults so that areas of rapid exhu- mation became areas of slow exhumation and visa versa on a time scale of a few Myr in order to maintain the continuous ex- humation. In this regard, the Ganges River must be preferentially sampling areas that are currently undergoing above average rates of uplift.
