The shear strength of sand-foam mixtures plays a crucial role in ensuring successful earth pressure balance(EPB)shield tunneling.Since the sand-foam mixtures are constantly sheared by the cutterhead and the screw conv...The shear strength of sand-foam mixtures plays a crucial role in ensuring successful earth pressure balance(EPB)shield tunneling.Since the sand-foam mixtures are constantly sheared by the cutterhead and the screw conveyor with varied rotation speeds during tunneling,it is non-trivial to investigate the effect of shear rates on the undrained shear strength of sand-foam mixtures under chamber pressures to extend the understanding on the tunneling process.This study conducted a series of pressurized vane shear tests to investigate the role of shear rates on the peak and residual strengths of sand-foam mixtures at different pore states.Different from the shear-rate characteristics of natural sands or clay,the results showed that the peak strength of sand-foam mixtures under high vertical total stress(σ_(v)≥200 kPa)and low foam injection ratio(FIR30%)decreased with the increase in shear rate.Otherwise,the peak strength was not measurably affected by shear rates.The sand-foam mixtures in the residual state resembled low-viscous fluid with yield stress and the residual strength increased slightly with shear rates.In addition,the peak and residual strengths were approximately linear with vertical effective stress regardless of the total stress and FIR.The peak effective internal friction angle remained almost invariant in a low shear rate(γ′<0.25 s1)but decreased when the shear rate continued increasing.The residual effective internal friction angle was lower than the peak counterpart and insensitive to shear rates.This study unveiled the role of shear rates in the undrained shear strength of sand-foam mixtures with various FIRs and vertical total stresses.The findings can extend the understanding of the rate-dependent shear characteristics of conditioned soils and guide the decision-making of soil conditioning schemes in the EPB shield tunneling practice.展开更多
The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry(PIV)experiments.Not only the average s...The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry(PIV)experiments.Not only the average shear rate in the whole tank but also the local value in the vicinity of impeller increases linearly with impeller speed.Furthermore,the shear coefficient(Ks,imp)at the impeller outlet is linearly related to the impeller flow number(Nq)and decreases with the increase of Nq in general at the constant power consumption per unit volume(Pv).During scale-up based on the constant Pv and geometric similarity,CFD results show that the volume-averaged shear rate(cavg)for RDT decreases faster than that of other impellers with the impeller tip velocity(Utip).The novel multi-blade combined(MBC)impeller with the increased height-to-diameter ratio of the stirred tank is able to more effectively improve the distribution uniformity of shear rate at the same Pv after scale-up.These studies provide a data basis for selecting the impeller types and improving the shear rate environment in the large-scale stirred tank.展开更多
To investigate the effects of rotation speed and shearing time on morphology of semisolid AZ91D alloy,experimental work was undertaken using a twin-screw slurry maker.The results show that increasing the rotation spee...To investigate the effects of rotation speed and shearing time on morphology of semisolid AZ91D alloy,experimental work was undertaken using a twin-screw slurry maker.The results show that increasing the rotation speed and reasonable time can give rise to substantial grain refinement during continuous shearing stage,which can be attributed to the increasing of effective nucleation rate caused by the extremely uniform temperature due to high shear rate and high degree of turbulence.Comparing with low rotation speed at the same thermal condition,the analysis indicates that the microstructures obtained at high rotation speed are homogenous spherical and fine grains instead of dendritic or rosette and exhibits uniform distribution in the eutectic matrix.展开更多
The shear mechanical behavior is regarded as an essential factor affecting the stability of the surrounding rocks in underground engineering.The shear strength and failure mechanisms of layered rock are significantly ...The shear mechanical behavior is regarded as an essential factor affecting the stability of the surrounding rocks in underground engineering.The shear strength and failure mechanisms of layered rock are significantly affected by the foliation angles.Direct shear tests were conducted on cubic slate samples with foliation angles of 0°,30°,45°,60°,and 90°.The effect of foliation angles on failure patterns,acoustic emission(AE)characteristics,and shear strength parameters was analyzed.Based on AE characteristics,the slate failure process could be divided into four stages:quiet period,step-like increasing period,dramatic increasing period,and remission period.A new empirical expression of cohesion for layered rock was proposed,which was compared with linear and sinusoidal cohesion expressions based on the results made by this paper and previous experiments.The comparative analysis demonstrated that the new expression has better prediction ability than other expressions.The proposed empirical equation was used for direct shear simulations with the combined finite-discrete element method(FDEM),and it was found to align well with the experimental results.Considering both computational efficiency and accuracy,it was recommended to use a shear rate of 0.01 m/s for FDEM to carry out direct shear simulations.To balance the relationship between the number of elements and the simulation results in the direct shear simulations,the recommended element size is 1 mm.展开更多
This study investigates a 2D gas-solid fast fluidized bed of typical Geldart A particles using highly resolved simulations with two-fluid model.The results show that the solid shear rate has a considerable impact on t...This study investigates a 2D gas-solid fast fluidized bed of typical Geldart A particles using highly resolved simulations with two-fluid model.The results show that the solid shear rate has a considerable impact on the orientation of the meso-scale structures and hence on the filtered drag force.On the basis of the correlation for the filtered drag force established in the literature using the traditional markers(such as filtered solid volume fraction,filtered slip velocity and filter scale),a correction correlated with the solid shear rate in the direction of gravity is proposed for better prediction of the filtered drag force.The corrected model is shown to produce improved results in posterior tests of flows in different fluidization regimes including bubbling,turbulent and fast fluidization.展开更多
We examined the shear rate effect on drag reduction of superhydrophobic surfaces with different slip lengths.For this purpose,turbulent channel flow was considered at the friction Reynolds numbers of Re=180,395,500.By...We examined the shear rate effect on drag reduction of superhydrophobic surfaces with different slip lengths.For this purpose,turbulent channel flow was considered at the friction Reynolds numbers of Re=180,395,500.By using Navier’s slip condition it is shown that increasing shear rate leads to the greater reduction in drag force and also more reduction occurs in larger slip length.Based on the results,more than 25%drag reduction happens at a friction Reynolds number of Re=500 for slip length of 1×10–5m.The simulation results suggest that reduction in drag force occurs because slip condition reduces the Reynolds stresses,also weakens vorticity filed and the near-wall coherent structures,and therefore turbulence production is decreased.展开更多
Background Ilexonin A (IA), purified from the Chinese herbal medicine Maodongqing (Ilex pubescens Hook, et Am) has been commonly used in south China to treat thrombotic disorders. In this study, we aimed to study the ...Background Ilexonin A (IA), purified from the Chinese herbal medicine Maodongqing (Ilex pubescens Hook, et Am) has been commonly used in south China to treat thrombotic disorders. In this study, we aimed to study the inhibiting effects and mechanism of lA on von Willebrand factor (vWF)-dependent high shear-induced platelet aggregation. Methods vWF-dependent high shear (10 800 s-1) induced aggregation of platelets obtained from normal donors in the presence or absence of lA was measured by a modified cone-plate viscometer and shear-induced vWF binding was measured by quantitative flowcytometry with monoclonal antibody known to bind exclusively to the C-terminal domain of vWF (LJ-C3) directly labeled with fluorescein isothiocyanate (FITC). P-selectin surface expression was also measured by a similar method with FITC conjugated anti-P-selectin monoclonal antibody (WGA1).Results Shear-induced platelet aggregation was inhibited by IA in a dose-dependent manner. The extent of aggregation decreased from (78.6±4.6)% in the absence of lA to (36.5±2.1 )% in the presence of lA (3.3 mmol/L) (P＜0.0001, n=9) with a high shear rate of 10800 s-1. vWF binding and P-selectin expression were also inhibited by lA in a dose dependent manner. The number of binding FITC-LJ-C3 molecules increased after exposure of platelet-rich plasma to a high shear rate of 10 800 s-1 for 6 minutes, but this shear-induced increased binding platelet surface vWF molecules and P-selectin expression can be decreased in the presence of IA.Conclusion vWF binding and vWF mediated platelet activation, aggregation occurring under high shear rate were inhibited by IA. lA may be a unique antithrombotic drug inhibiting the vWF-GP Ib α interaction, and may thus facilitate drug design targeting arterial thrombosis.展开更多
Soil-rock mixtures(S-RMs) are widely distributed in the nature. The mesoscopic deformation and failure mechanisms as well as the macro-mechanical behaviors of the S-RMs depend largely upon the rate of deformation, wat...Soil-rock mixtures(S-RMs) are widely distributed in the nature. The mesoscopic deformation and failure mechanisms as well as the macro-mechanical behaviors of the S-RMs depend largely upon the rate of deformation, water content and particle sizes. In this research, a series of large-scale direct shear tests with different water contents and different grain-size distributions were conducted to study the influence of the aforementioned factors on the mechanical properties of the S-RMs. Due to the effect of the rock blocks' breakage in the S-RMs, the relationship between the shear strength and the vertical stress of S-RM follows a power law instead of a linear one. It is found that there exists a threshold value for the vertical stress during the shearing process,below which the soil strength is mainly determined by the inter-locking of particles and the re-arrangement of meso-structure,and otherwise large-sized rock blocks are gradually broken into smaller fragments, resulting in a decrease in the soil strength.The shear rate can also significantly influence the degree of particle breakage and the meso-structural rearrangement of the SRMs, namely, under low shear rate, the particles of the samples are fully broken resulting in enhanced macro-strength. As a result, the lower the shear rate, the higher the macroscopic strength. So under unsaturated conditions, the water content will affect the strength of the S-RMs by reducing the strength of rock blocks. As the water content increases, the soil strength decreases gradually, and assumes a moderate value when the water content reaches 8%. At the same water content, the soil strength increases with the sizes of large rock blocks. For the occlusion, breakage and structure re-arrangement of the oversized rock blocks inside S-RM, which have a huge influence on the mechanical characteristics of the samples.展开更多
1 INTRODUCTIONThe suspensions employed in ceramic processing arehighly concentrated.These suspensions are normallyknown as slip or slurry in materials science and engi-neering.It is of great interest that concentrated...1 INTRODUCTIONThe suspensions employed in ceramic processing arehighly concentrated.These suspensions are normallyknown as slip or slurry in materials science and engi-neering.It is of great interest that concentrated sus-pension exhibit many of the phenomena of very dilutecolloidal suspensions.This is probably because boththe suspension systems have charged particles,so thatthe principles of colloid chemistry can be applied forthem.展开更多
The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopo...The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopotential theory Solitary waves were generated in the sample under mechanical loading. Their interaction with the vacancy complexes was shown to be able to initiate hot spot in that local region of the complexes. Some parameters of the hot spot as well as solitary waves were calculated. The initiation of the hot spot is accompanied with sufficient local structural relaxation.展开更多
The temperature distribution under shearwith a high strain rate and the cooling rateof the shear bands of Al, Cu and 0.06C steelhave been calculated using a computer. The resultsshow that the temperature of shear band...The temperature distribution under shearwith a high strain rate and the cooling rateof the shear bands of Al, Cu and 0.06C steelhave been calculated using a computer. The resultsshow that the temperature of shear band increaseswith the increase of the average strain rate(_o). When _o is in the range 8×10~5 to 10~6 1/s,the structure of the adiabatic shear band ina 0.06C steel is martensite but it becomesmetallic glass if _o=10~6 1/s. As to A1 andCu, the structure of the adiabatic shear bandscan also be of metallic glass if _o is greaterthan 1.8×10~6 and 5.5×10~7 1/s respectively.It explains that Cu tends most difficultly toform adiabatic shear band, while 0.06C steelmost readily among the three metals.展开更多
This study proposes an alternative approach to the investigation of high flow hydrogeological fractures within the basement in the Dabakala region of north-central Côte d’Ivoire. The used approach consists o...This study proposes an alternative approach to the investigation of high flow hydrogeological fractures within the basement in the Dabakala region of north-central Côte d’Ivoire. The used approach consists of exploring the subsurface by measuring electrical resistivity contrasts along the main shear direction within crystallophyllian rocks. Electrical resistivity profiling and vertical electrical sounding techniques, coupled with boreholes monitoring, have identified fractured aquifers whose best flow rates are around 96 and 116 m<sup>3</sup>/h. These aquifers mostly hosted in granodiorite have an average strength of 10 meters and are located at depth of around 100 meters. They are associated with open fractures created by tangential shear stresses that have affected the Dabakala volcano-sedimentary trench formations. The search for fractured aquifers along the main shear direction offers great perspective for obtaining high flow rates.展开更多
Following the parameterization of sheared entrainment obtained in the companion paper,Liu et al.(2016),the present study aims to further investigate the characteristics of entrainment,and develop a simple model for pr...Following the parameterization of sheared entrainment obtained in the companion paper,Liu et al.(2016),the present study aims to further investigate the characteristics of entrainment,and develop a simple model for predicting the growth rate of a well-developed and sheared CBL.The relative stratification,defined as the ratio of the stratification in the free atmosphere to that in the entrainment zone,is found to be a function of entrainment flux ratio(Ae).This leads to a simple expression of the entrainment rate,in which Aeneeds to be parameterized.According to the results in Liu et al.(2016),Ae can be simply expressed as the ratio of the convective velocity scale in the sheared CBL to that in the shear-free CBL.The parameterization of the convective velocity scale in the sheared CBL is obtained by analytically solving the bulk model with several assumptions and approximations.Results indicate that the entrainment process is influenced by the dynamic effect,the interaction between mean shear and environmental stratification,and one other term that includes the Coriolis effect.These three parameterizations constitute a simple model for predicting the growth rate of a well-developed and sheared CBL.This model is validated by outputs of LESs,and the results show that it performs satisfactorily.Compared with bulk models,this model does not need to solve a set of equations for the CBL.It is more convenient to apply in numerical models.展开更多
Strain-rate frequency superposition(SRFS) is often employed to probe the low-frequency behavior of soft solids under oscillatory shear in anticipated linear response. However, physical interpretation of an apparently ...Strain-rate frequency superposition(SRFS) is often employed to probe the low-frequency behavior of soft solids under oscillatory shear in anticipated linear response. However, physical interpretation of an apparently well-overlapped master curve generated by SRFS has to combine with nonlinear analysis techniques such as Fourier transform rheology and stress decomposition method. The benefit of SRFS is discarded when some inconsistencies of the shifted master curves with the canonical linear response are observed. In this work, instead of evaluating the SRFS in full master curves, two criteria were proposed to decompose the original SRFS data and to delete the bad experimental data. Application to Carabopol suspensions indicates that good master curves could be constructed based upon the modified data and the high-frequency deviations often observed in original SRFS master curves are eliminated. The modified SRFS data also enable a better quantitative description and the evaluation of the apparent structural relaxation time by the two-mode fractional Maxwell model.展开更多
基金the National Outstanding Youth Science Fund Project of the National Natural Science Foundation of China(Grant No.52022112)the Hunan Provincial Innovation Foundation for Postgraduate of China(Grant No.2020zzts152)are acknowledged.
文摘The shear strength of sand-foam mixtures plays a crucial role in ensuring successful earth pressure balance(EPB)shield tunneling.Since the sand-foam mixtures are constantly sheared by the cutterhead and the screw conveyor with varied rotation speeds during tunneling,it is non-trivial to investigate the effect of shear rates on the undrained shear strength of sand-foam mixtures under chamber pressures to extend the understanding on the tunneling process.This study conducted a series of pressurized vane shear tests to investigate the role of shear rates on the peak and residual strengths of sand-foam mixtures at different pore states.Different from the shear-rate characteristics of natural sands or clay,the results showed that the peak strength of sand-foam mixtures under high vertical total stress(σ_(v)≥200 kPa)and low foam injection ratio(FIR30%)decreased with the increase in shear rate.Otherwise,the peak strength was not measurably affected by shear rates.The sand-foam mixtures in the residual state resembled low-viscous fluid with yield stress and the residual strength increased slightly with shear rates.In addition,the peak and residual strengths were approximately linear with vertical effective stress regardless of the total stress and FIR.The peak effective internal friction angle remained almost invariant in a low shear rate(γ′<0.25 s1)but decreased when the shear rate continued increasing.The residual effective internal friction angle was lower than the peak counterpart and insensitive to shear rates.This study unveiled the role of shear rates in the undrained shear strength of sand-foam mixtures with various FIRs and vertical total stresses.The findings can extend the understanding of the rate-dependent shear characteristics of conditioned soils and guide the decision-making of soil conditioning schemes in the EPB shield tunneling practice.
基金National Key Research and Development Program (2020YFA0906800)the National Natural Science Foundation of China (21808221, 91934301, 21961160745)+2 种基金External Cooperation Program of BIC, Chinese Academy of Sciences (122111KYSB20190032)the Key Research Program of Nanjing IPE Institute of Green Manufacturing Industry (No. E0010719)Innovation Academy for Green Manufacture, Chinese Academy of Sciences (IAGM2020C06)
文摘The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry(PIV)experiments.Not only the average shear rate in the whole tank but also the local value in the vicinity of impeller increases linearly with impeller speed.Furthermore,the shear coefficient(Ks,imp)at the impeller outlet is linearly related to the impeller flow number(Nq)and decreases with the increase of Nq in general at the constant power consumption per unit volume(Pv).During scale-up based on the constant Pv and geometric similarity,CFD results show that the volume-averaged shear rate(cavg)for RDT decreases faster than that of other impellers with the impeller tip velocity(Utip).The novel multi-blade combined(MBC)impeller with the increased height-to-diameter ratio of the stirred tank is able to more effectively improve the distribution uniformity of shear rate at the same Pv after scale-up.These studies provide a data basis for selecting the impeller types and improving the shear rate environment in the large-scale stirred tank.
基金Project (2009DFB50210) supported by the International Cooperation in Technical Research and Development Program of ChinaProject (2009AA03Z534) supported by the National High-Tech Research and Development Program of ChinaProject (2006CB605203) supported by the National Basic Research Program of China
文摘To investigate the effects of rotation speed and shearing time on morphology of semisolid AZ91D alloy,experimental work was undertaken using a twin-screw slurry maker.The results show that increasing the rotation speed and reasonable time can give rise to substantial grain refinement during continuous shearing stage,which can be attributed to the increasing of effective nucleation rate caused by the extremely uniform temperature due to high shear rate and high degree of turbulence.Comparing with low rotation speed at the same thermal condition,the analysis indicates that the microstructures obtained at high rotation speed are homogenous spherical and fine grains instead of dendritic or rosette and exhibits uniform distribution in the eutectic matrix.
基金support from the Natural Science Foundation of China(Grant Nos.41941018,U21A20153,42177140).
文摘The shear mechanical behavior is regarded as an essential factor affecting the stability of the surrounding rocks in underground engineering.The shear strength and failure mechanisms of layered rock are significantly affected by the foliation angles.Direct shear tests were conducted on cubic slate samples with foliation angles of 0°,30°,45°,60°,and 90°.The effect of foliation angles on failure patterns,acoustic emission(AE)characteristics,and shear strength parameters was analyzed.Based on AE characteristics,the slate failure process could be divided into four stages:quiet period,step-like increasing period,dramatic increasing period,and remission period.A new empirical expression of cohesion for layered rock was proposed,which was compared with linear and sinusoidal cohesion expressions based on the results made by this paper and previous experiments.The comparative analysis demonstrated that the new expression has better prediction ability than other expressions.The proposed empirical equation was used for direct shear simulations with the combined finite-discrete element method(FDEM),and it was found to align well with the experimental results.Considering both computational efficiency and accuracy,it was recommended to use a shear rate of 0.01 m/s for FDEM to carry out direct shear simulations.To balance the relationship between the number of elements and the simulation results in the direct shear simulations,the recommended element size is 1 mm.
基金supported by the HPC Platform at Xi'an Jiaotong University and National Natural Science Foundation of China(grant number 21978228).
文摘This study investigates a 2D gas-solid fast fluidized bed of typical Geldart A particles using highly resolved simulations with two-fluid model.The results show that the solid shear rate has a considerable impact on the orientation of the meso-scale structures and hence on the filtered drag force.On the basis of the correlation for the filtered drag force established in the literature using the traditional markers(such as filtered solid volume fraction,filtered slip velocity and filter scale),a correction correlated with the solid shear rate in the direction of gravity is proposed for better prediction of the filtered drag force.The corrected model is shown to produce improved results in posterior tests of flows in different fluidization regimes including bubbling,turbulent and fast fluidization.
文摘We examined the shear rate effect on drag reduction of superhydrophobic surfaces with different slip lengths.For this purpose,turbulent channel flow was considered at the friction Reynolds numbers of Re=180,395,500.By using Navier’s slip condition it is shown that increasing shear rate leads to the greater reduction in drag force and also more reduction occurs in larger slip length.Based on the results,more than 25%drag reduction happens at a friction Reynolds number of Re=500 for slip length of 1×10–5m.The simulation results suggest that reduction in drag force occurs because slip condition reduces the Reynolds stresses,also weakens vorticity filed and the near-wall coherent structures,and therefore turbulence production is decreased.
基金This work was supported by grants from the Japanese Society for the Promotion of Science (No. JSPS-RFTF97100201) by the Hong Kong Baptist University Faculty Research Grant (No. HKBU/FRG/01-02/11-27).
文摘Background Ilexonin A (IA), purified from the Chinese herbal medicine Maodongqing (Ilex pubescens Hook, et Am) has been commonly used in south China to treat thrombotic disorders. In this study, we aimed to study the inhibiting effects and mechanism of lA on von Willebrand factor (vWF)-dependent high shear-induced platelet aggregation. Methods vWF-dependent high shear (10 800 s-1) induced aggregation of platelets obtained from normal donors in the presence or absence of lA was measured by a modified cone-plate viscometer and shear-induced vWF binding was measured by quantitative flowcytometry with monoclonal antibody known to bind exclusively to the C-terminal domain of vWF (LJ-C3) directly labeled with fluorescein isothiocyanate (FITC). P-selectin surface expression was also measured by a similar method with FITC conjugated anti-P-selectin monoclonal antibody (WGA1).Results Shear-induced platelet aggregation was inhibited by IA in a dose-dependent manner. The extent of aggregation decreased from (78.6±4.6)% in the absence of lA to (36.5±2.1 )% in the presence of lA (3.3 mmol/L) (P＜0.0001, n=9) with a high shear rate of 10800 s-1. vWF binding and P-selectin expression were also inhibited by lA in a dose dependent manner. The number of binding FITC-LJ-C3 molecules increased after exposure of platelet-rich plasma to a high shear rate of 10 800 s-1 for 6 minutes, but this shear-induced increased binding platelet surface vWF molecules and P-selectin expression can be decreased in the presence of IA.Conclusion vWF binding and vWF mediated platelet activation, aggregation occurring under high shear rate were inhibited by IA. lA may be a unique antithrombotic drug inhibiting the vWF-GP Ib α interaction, and may thus facilitate drug design targeting arterial thrombosis.
基金supported by the National Natural Science Foundation of China(Grant Nos.51479095,41372316,and 41572295)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2015272)
文摘Soil-rock mixtures(S-RMs) are widely distributed in the nature. The mesoscopic deformation and failure mechanisms as well as the macro-mechanical behaviors of the S-RMs depend largely upon the rate of deformation, water content and particle sizes. In this research, a series of large-scale direct shear tests with different water contents and different grain-size distributions were conducted to study the influence of the aforementioned factors on the mechanical properties of the S-RMs. Due to the effect of the rock blocks' breakage in the S-RMs, the relationship between the shear strength and the vertical stress of S-RM follows a power law instead of a linear one. It is found that there exists a threshold value for the vertical stress during the shearing process,below which the soil strength is mainly determined by the inter-locking of particles and the re-arrangement of meso-structure,and otherwise large-sized rock blocks are gradually broken into smaller fragments, resulting in a decrease in the soil strength.The shear rate can also significantly influence the degree of particle breakage and the meso-structural rearrangement of the SRMs, namely, under low shear rate, the particles of the samples are fully broken resulting in enhanced macro-strength. As a result, the lower the shear rate, the higher the macroscopic strength. So under unsaturated conditions, the water content will affect the strength of the S-RMs by reducing the strength of rock blocks. As the water content increases, the soil strength decreases gradually, and assumes a moderate value when the water content reaches 8%. At the same water content, the soil strength increases with the sizes of large rock blocks. For the occlusion, breakage and structure re-arrangement of the oversized rock blocks inside S-RM, which have a huge influence on the mechanical characteristics of the samples.
基金Partly supported by Scientific Research Foundation for Returned Overseas Scholars from State Education Committee of China
文摘1 INTRODUCTIONThe suspensions employed in ceramic processing arehighly concentrated.These suspensions are normallyknown as slip or slurry in materials science and engi-neering.It is of great interest that concentrated sus-pension exhibit many of the phenomena of very dilutecolloidal suspensions.This is probably because boththe suspension systems have charged particles,so thatthe principles of colloid chemistry can be applied forthem.
文摘The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopotential theory Solitary waves were generated in the sample under mechanical loading. Their interaction with the vacancy complexes was shown to be able to initiate hot spot in that local region of the complexes. Some parameters of the hot spot as well as solitary waves were calculated. The initiation of the hot spot is accompanied with sufficient local structural relaxation.
文摘The temperature distribution under shearwith a high strain rate and the cooling rateof the shear bands of Al, Cu and 0.06C steelhave been calculated using a computer. The resultsshow that the temperature of shear band increaseswith the increase of the average strain rate(_o). When _o is in the range 8×10~5 to 10~6 1/s,the structure of the adiabatic shear band ina 0.06C steel is martensite but it becomesmetallic glass if _o=10~6 1/s. As to A1 andCu, the structure of the adiabatic shear bandscan also be of metallic glass if _o is greaterthan 1.8×10~6 and 5.5×10~7 1/s respectively.It explains that Cu tends most difficultly toform adiabatic shear band, while 0.06C steelmost readily among the three metals.
文摘This study proposes an alternative approach to the investigation of high flow hydrogeological fractures within the basement in the Dabakala region of north-central Côte d’Ivoire. The used approach consists of exploring the subsurface by measuring electrical resistivity contrasts along the main shear direction within crystallophyllian rocks. Electrical resistivity profiling and vertical electrical sounding techniques, coupled with boreholes monitoring, have identified fractured aquifers whose best flow rates are around 96 and 116 m<sup>3</sup>/h. These aquifers mostly hosted in granodiorite have an average strength of 10 meters and are located at depth of around 100 meters. They are associated with open fractures created by tangential shear stresses that have affected the Dabakala volcano-sedimentary trench formations. The search for fractured aquifers along the main shear direction offers great perspective for obtaining high flow rates.
基金sponsored by the National Natural Science Foundation of China(Grant No.40975004)the State Key Basic Program(973)(Grant No.2013CB430100)
文摘Following the parameterization of sheared entrainment obtained in the companion paper,Liu et al.(2016),the present study aims to further investigate the characteristics of entrainment,and develop a simple model for predicting the growth rate of a well-developed and sheared CBL.The relative stratification,defined as the ratio of the stratification in the free atmosphere to that in the entrainment zone,is found to be a function of entrainment flux ratio(Ae).This leads to a simple expression of the entrainment rate,in which Aeneeds to be parameterized.According to the results in Liu et al.(2016),Ae can be simply expressed as the ratio of the convective velocity scale in the sheared CBL to that in the shear-free CBL.The parameterization of the convective velocity scale in the sheared CBL is obtained by analytically solving the bulk model with several assumptions and approximations.Results indicate that the entrainment process is influenced by the dynamic effect,the interaction between mean shear and environmental stratification,and one other term that includes the Coriolis effect.These three parameterizations constitute a simple model for predicting the growth rate of a well-developed and sheared CBL.This model is validated by outputs of LESs,and the results show that it performs satisfactorily.Compared with bulk models,this model does not need to solve a set of equations for the CBL.It is more convenient to apply in numerical models.
基金Project(11372263)supported by the National Natural Science Foundation of China
文摘Strain-rate frequency superposition(SRFS) is often employed to probe the low-frequency behavior of soft solids under oscillatory shear in anticipated linear response. However, physical interpretation of an apparently well-overlapped master curve generated by SRFS has to combine with nonlinear analysis techniques such as Fourier transform rheology and stress decomposition method. The benefit of SRFS is discarded when some inconsistencies of the shifted master curves with the canonical linear response are observed. In this work, instead of evaluating the SRFS in full master curves, two criteria were proposed to decompose the original SRFS data and to delete the bad experimental data. Application to Carabopol suspensions indicates that good master curves could be constructed based upon the modified data and the high-frequency deviations often observed in original SRFS master curves are eliminated. The modified SRFS data also enable a better quantitative description and the evaluation of the apparent structural relaxation time by the two-mode fractional Maxwell model.
