Recrystallized microstructural evolution of UFG copper prepared by asymmetrical accumulative rolling-bonding process

Copper sheet with grain size of 30-60μm was processed by plastic deformation of asymmetrical accumulative rolling-bonding(AARB)with the strain of 3.2.The effects of annealing temperature and time on microstructural evolution were studied by means of electron backscattered diffraction(EBSD).EBSD grain mapping,recrystallization pole figure and grain boundary misorientation angle distribution graph were constructed,and the characteristics were assessed by microstructure,grain size,grain boundary misorientation and texture.The results show that ultra fine grains(UFG)are obtained after annealing at 250℃ for 30?40 min.When the annealing is controlled at 250℃for 40 min,the recrystallization is finished,a large number of small grains appear and most grain boundaries consist of low-angle boundaries.The character of texture is rolling texture after the recrystallization treatment,but the strength of the texture is faint.While second recrystallization happens,{110}<1ī2>+{112}<11ī> texture component disappears and turns into{122}<212>cube twin texture component.

Investigation of erosion-corrosion behavior of Q235B steel in liquid-solid flows

This work aims to investigate the erosion-corrosion behavior of Q235B steel in liquid-solid two-phase flows.The weight loss rate,surface morphology and electrochemical parameters of Q235B steel at different temperatures(20℃,30℃,40℃)and flow velocities(6 m/s,7 m/s,8 m/s,9 m/s,10 m/s)were studied separately.The results show that the weight loss rate of Q235B steel specimens after erosion-corrosion increases with increasing flow velocity and temperature.For the erosion-corrosion process,the corrosion rates of specimens increase with increasing flow velocity.The results of surface morphology show that the circular pits with clear edges are distributed randomly over specimen surface at low flow velocity,but the pit edge becomes vague at high flow velocity.With temperature increasing,the erosion-corrosion damage became serious as shown by the aggregation of large and small pits on specimen surface.The working mechanism of erosion-corrosion is found to vary with flow velocity and temperature.The relationships among erosion-corrosion components are quantitatively represented and show that synergy dominates the progress of material loss.Corrosion enhances erosion that is a dominant component in the synergy.The inactions of erosion-corrosion can be described by"synergistic"and"additive"behavior.The results show that"additive"effect becomes more significant with increasing flow velocity but decreases with increasing temperature,while"synergistic"effect is not sensitive to flow velocity and temperature.

Numerical Simulations of Liquid-Solid Flows in A Vertical Pipe by MPS-DEM Coupling Method

In the process of deep-sea mining,the liquid-solid flows in the vertical transportation pipeline are very complex.In the present work,an in-house solver MPSDEM-SJTU based on the improved MPS and DEM is developed for the simulation of hydraulic conveying.Firstly,three examples including the multilayer cylinder collapse,the Poiseuille flow and two-phase dam-break are used to validate the precision of the DEM model,the pipe flow model and MPS-DEM coupling model,respectively.Then,the hydraulic conveying with coarse particles in a vertical pipe is simulated.The solid particle distribution is presented and investigated in detail.Finally,the coupling method is successfully applied for the simulation of the liquid-solid flows in a vertical pipe with rotating blades,which shows the stability of the solver under rotating boundary conditions.This fully Lagrangian model is expected to be a new approach for analyzing hydraulic conveying.

On flow characteristics of liquid-solid mixed-phase nanofluid inside nanochannels

The atomic behavior of liquid-solid mixed-phase nanofluid flows inside nanochannels is investigated by a molecular dynamics simulation （MDS）. The results of visual observation and statistic analysis show that when the nanoparticles reach near each other, the strong interatomic force will make them attach together. This aggrega- tion continues until all nanoparticles make a continuous cluster. The effect of altering the external force magnitude causes changes in the agglomeration rate and system enthalpy. The density and velocity profiles are shown for two systems, i.e., argon （Ar）-copper （Cu） nanofluid and simple Ar fluid between two Cu walls. The results show that using nanopar- ticles changes the base fluid particles ordering along the nanochannel and increases the velocity. Moreover, using nanoparticles in simple fluids can increase the slip length and push the near-wall fluid particles into the main flow in the middle of the nanochannel.

Modeling of transverse welds formation during liquid-solid extrusion directly following vacuum infiltration of magnesium matrix composite

Liquid-solid extrusion directly following vacuum infiltration(LSEVI)is an infiltration-extrusion integrated forming technique,and transverse weld between upper residual magnesium alloy and magnesium matrix composites is a common internal defect,which can severely reduce the yield of composite products.To improve current understanding on the mechanism of transverse welding phenomenon,a thermo-mechanical numerical model of LSEVI for magnesium matrix composites was developed.The formation of transverse weld during extrusion was visualized using finite element simulation method,and the formation mechanism was discussed from the aspect of velocity field using a point tracking technique.The simulation results were verified by the experimental results in term of weld shape.

Interfacial Microstructure of Al-Sn-Pb Alloy/Steel During Liquid-Solid Bonding Rolling

Studies were conducted on the interfacial microstructure of a steel/liquid aluminium and its evolution during the bonding rolling process. The effects of wetting time and deformation on the diffusion layer and on the bonding strength were examined. By means of electron microscopy and electron probe analysis, it was found that the diffusion layer is mainly composed of FeAI3. For a steel temperature of 250℃ and an aluminium temperature of 850 ~C, the diffusion layer was formed within 3 s, and the shear strength of the samples increased after 8 to 14 s. Although the interface was not damaged, it was deformed notably. For an aluminium temperature of 750℃ and a wetting time of 11 to 17 s, the shear strength of the interface remained high, but the interface was obviously broken during rolling, leading to reduced bonding strength.

Coupling of discrete-element method and smoothed particle hydrodynamics for liquid-solid flows

Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. This paper presents a computational method combining these two methods for solid-liquid medium. The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method. The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.

LIQUID-SOLID COUPLED SYSTEM OF MICROPUMP

This paper employs the integral-averaged method of thickness to approximate the periodical flows in a piezoelectric micropump, with a shallow water equation including nonlinearity and viscous damp presented to characterize the flows in micropump. The finite element method is used to obtain a matrix equation of fluid pressure. The fluid pressure equation is combined with the vibration equation of a silicon diaphragm to construct a liquid-solid coupled equation for reflecting the interaction between solid diaphragm and fluid motion in a micropump. Numerical results of a mode analysis of the coupled system indicate that the natural frequencies of the coupled system are much lower than those of the non-coupled system. The influence of additional mass and viscous damp of fluid on the natural frequencies of the coupled system is more significant as the pump thickness is small. It is found that the vibration shape functions of silicon diaphragm of the coupled system are almost the same as those of the non-coupled system. This paper also gives the first-order amplitude-frequency relationship of the silicon diaphragm, which is necessary for the flow-rate-frequency analysis of a micropump.

FORCES AND MOMENTS OF THE LIQUID FINITE AMPLITUDE SLOSHING IN A LIQUID-SOLID COUPLED SYSTEM

Nonlinear coupling dynamics between a spring-mass system and a finite amplitude sloshing system with liquid in a cylindrical tank is investigated. Based on a group of nonlinear coupling equations of six degrees of freedoms, analytical formulae of forces and moments of the liquid large amplitude sloshing were obtained. Nonlinearity of the forces and moments of the sloshing was induced by integrating on final configuration of liquid sloshing and the nonlinear terms in the liquid pressure formula. The symmetry between the formula of Ox and Oy direction proves that the derivation is correct. According to the coupled mechanism, the formulae are available in other liquid-solid coupled systems. Simulations and corresponding experimental results arecompared. It is shown that the forces and moments formulae by integrating on the final sloshing configuration are more reasonable. The omitted high-dimensional modal bases and high-order nonlinear terms and the complexity of sloshing damping are main sources of errors.

System-size effect on the friction at liquid-solid interfaces

The friction at the liquid-solid interfaces is widely involved in various phenomena ranging from nanometer to micrometer scales. By the molecular dynamic(MD)simulation, the friction properties of liquid-solid interfaces at the molecular level are calculated via the Green-Kubo relation. It is found that the system size will influence the value of the friction coefficient, especially for the solid surfaces with the larger polar charge. The value of the friction coefficient decreases with the increase in the system size and converges at large system sizes. The large polar charge will lead to a significant friction coefficient. However, the diffusion of water molecules on this surface is almost a constant, indicating that the diffusion coefficient seems to be independent of the system size and polar charge. This work provides insights for the selection of the system size in modeling the frictional properties of hydrophobic/hydrophilic surfaces.

Numerical Simulation of Liquid-Solid Coupling in Multi-Angle Fractures in Pressure-Sensitive Reservoirs

This study clarifies the seepage characteristics of complex fractured pressure-sensitive reservoirs,and addresses a common technological problem,that is the alteration of the permeability degree of the reservoir bed(known to be responsible for changes in the direction and velocity of fluid flows between wells).On the basis of a new pressuresensitive equation that considers the fracture directional pressure-sensitive effect,an oil-gas-water three-phase seepage mathematical model is introduced,which can be applied to pressure-sensitive,full-tensor permeability,ultralow-permeability reservoirs with fracture-induced anisotropy.Accordingly,numerical simulations are conducted to explore the seepage laws for ultralow-permeability reservoirs.The results show that element patterns have the highest recovery percentage under a fracture angle of 45°.Accounting for the pressure-sensitive effect produces a decrease in the recovery percentage.Several patterns are considered:inverted five-seven-and nine-spot patterns and a cross-row well pattern.Finally,two strategies are introduced to counteract the rotation of the direction of the principal permeability due to the fracture directional pressure-sensitive effect.

Immediate-release Mechanism of Dehydrotrametenolic Acid and Dehydroeburicoic Acid in Poriae Cutis Total Triterpenoids Tablets Based on Liquid-solid Compact Technique

[Objectives]To study the immediate-release mechanism of dehydrotrametenolic acid and dehydroeburicoic acid in Poriae Cutis total triterpenoids tablets by liquid-solid compacts technique.[Methods] Taking dehydrotrametenolic acid and dehydroeburicoic acid as indicators,differences in dissolution were compared between liquid-solid compressed tablets and crude drug of total triterpenoids in Poriae Cutis;crude drug,powder of liquid-solid compressed tablets and excipients of liquid-solid compressed tablets were characterized by differential scanning calorimetry( DSC).[Results]Liquid-solid compact technique could significantly improve dissolution rate of dehydrotrametenolic acid and dehydroeburicoic acid. The total dissolution rate of dehydrotrametenolic acid and dehydroeburicoic acid in Poriae Cutis total triterpenoids tablets was 92%,t50( time for 50% total dissolution rate) and t_D( time for 63. 2% total dissolution rate) were 11. 18 min and 22. 71 min; the total dissolution rate of dehydrotrametenolic acid and dehydroeburicoic acid in crude drug of total triterpenoids was 29%,and t50 and t_D were231. 06 min and 359. 23 min. DSC showed that there was no mutual interaction between excipients and total triterpenoids in Poriae Cutis; on the DSC curve for powder of liquid-solid compressed tablets,the absorption peak vanished completely,indicating that the drug exists in the amorphous form in the liquid-solid powder.[Conclusions] Liquid-solid compact technique can increase the dissolution rate of total triterpenoids in Poriae Cutis and allow rapid release of poorly water soluble drugs.

Thermochemical Heat Storage Performance in the Gas/Liquid-Solid Reactions of SrCl2 with NH3

Thermochemical heat storage is a promising technology for improving energy efficiency through the utilization of low-grade waste heat. The formation of a SrCl2 ammine complex was selected as the reaction system for the purpose of this study. Discharge characteristics were evaluated in a packed bed reactor for both the gas-solid reaction and the liquid-solid reaction. The average power of the gas-solid reaction was influenced by the pressure of the supplied ammonia gas, with greater powers being recorded at higher ammonia pressure. For the liquid-solid reaction, the obtained average power was comparable to that obtained for the gas-solid reaction at 0.2 MPa. Moreover, the lower heat transfer resistance in the reactor was observed, which was likely caused by the presence of liquid ammonia in the system. Finally, the short-term durability of the liquid-solid reaction system was demonstrated over 10 stable charge/discharge cycles.

Premature deposition of lithium polysulfide in lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries have attracted extensive attention due to ultrahigh theoretical energy density of 2600 Wh kg^(-1).Liquid-solid deposition from dissolved lithium polysulfides(LiPSs)to solid lithium sulfide(Li_(2)S)largely determines the actual battery performances.Herein,a premature liquidsolid deposition process of LiPSs is revealed at higher thermodynamic potential than Li_(2)S deposition in Li-S batteries.The premature solid deposit exhibits higher chemical state and hemispherical morphology in comparison with Li_(2)S,and the premature deposition process is slower in kinetics and higher in deposition dimension.Accordingly,a supersaturation deposition mechanism is proposed to rationalize the above findings based on thermodynamic simulation.This work demonstrates a unique premature liquid-solid deposition process of Li-S batteries.

A NOVEL APPROACH TO RHEOLOGICAL CHARACTERIZATION FOR THE GELATION IN POLYMER CRYSTALLIZATION

The isothermal crystallizations of three kinds of commercial isotactic polypropylene have been studied by DSC and rheometric experiments,in a range of temperatures where the rate of crystallization is moderate.As the crystallization proceeds,volume contraction induces tensile force upon the parallel plates.The tensile force relaxed quickly in liquid states, but after a critical amount of the relative crystallinity,it starts to accumulate in the static test,that is,with the motionless parallel plates.A new method to determine the liquid-solid transition by the static tensile force is proposed and compared with two dynamic methods of detecting liquid-solid transition,that is,the power-law modulus theory and the yield modulus model.The tensile force method predicted considerably earlier transition than the dynamic methods,and the corresponding DSC data indicate relative crystallinity of larger than 0.2 at the transition times.The limitation of dynamic methods and other possible errors have been analyzed.While the dynamic methods are suitable for slow crystallization,the tensile force method is more appropriate for the crystallization of moderate rates.Moreover,it has the advantage of almost not disturbing the crystallizing materials before the transition.

Numerical Simulation for Arc Windshields of Aircrafts Subjected to Bird Impact

A finite element model including full-scale circular arc windshield glass and the relative parts of the military plane is established in this paper. The model is analyzed by using an explicit element code LS-DYNA3D for analyzing the nonlinear dynamic response of structures. The data in aspects of displacement, strain, stress and contact force in the process of deformation are obtained. The deformation and failure mechanism of circular arc windshield glass are discussed. The possible location at which failure may take place is given. The valuable data are provided for designing,researching and producing new windshields with high crashworthiness.

Experimental determination of solubilities and＇supersolubilities of 2,2＇,4,4＇,6,6＇-hexanitrostilbene in different organic solvents

The laser monitor technique was used to determine solubilities and supersolubilities of HNS in N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, N-methyl-2-pyrrolidone and 1,4-butyrolactone. The experimental solubility values were correlated with λh equation, modified Apelblat equation and NRTL model. Furthermore, the dissolution enthalpy, dissolution entropy and the Gibbs energy of HNS were calculated by the experimental data. The results show that the solubilities of HNS in the above solvents increase with the increasing temperature. Besides, at the same temperature, the order of solubility is N-methyl-2-pyrrolidone > dimethyl sulfoxide > N,N-dimethylformamide > 1,4-butyrolactone > acetonitrile. The temperature dependence of predicted solubility is in agreement with the experimental data.

Microstructure of fly ash cenosphere/AZ91D composite during solution treatment at 380-420℃

The fly ash cenosphere/AZ91D (FAC/AZ91D) composites containing 5 wt.% and 100 μm in size of fly-ash cenosphere particles were fabricated by means of the compcasting method.The microstructures of the as-cast samples and the effect of the solution treatment at 380℃,400℃,and 420℃ for 16 h on the microstructures of the samples were investigated by using of OM,SEM,XRD and EDS.The results showed that the cenospheres distributed homogeneously in the Mg alloy,and were almost filled with Mg alloy.The main interfacial phase between the cenospheres and AZ91D Mg alloy was identified as MgAl2O4 according to XRD,EDS and thermodynamic analysis.Mg2Si particles tended to be spheroidized via the solution treatment and the β phase (Mg17Al12) dissolved completely at 400℃.

Pressure Drop of Liquid–Solid Two-Phase Flow in the Vertical Tube Bundle of a Cold-Model Circulating Fluidized Bed Evaporator

A cold-model vertical multi-tube circulating fluidized bed evaporator was designed and built to conduct a visualization study on the pressure drop of a liquid–solid two-phase flow and the corresponding particle distribution.Water and polyformaldehyde particle(POM)were used as the liquid and solid phases,respectively.The effects of operating parameters such as the amount of added particles,circulating flow rate,and particle size were systematically investigated.The results showed that the addition of the particles increased the pressure drop in the vertical tube bundle.The maximum pressure drop ratios were 18.65%,21.15%,18.00%,and 21.15%within the experimental range of the amount of added particles for POM1,POM2,POM3,and POM4,respectively.The pressure drop ratio basically decreased with the increase in the circulating flow rate but fluctuated with the increase in the amount of added particles and particle size.The difference in pressure drop ratio decreased with the increase in the circulating flow rate.As the amount of added particles increased,the difference in pressure drop ratio fluctuated at low circulating flow rate but basically decreased at high circulating flow rate.The pressure drop in the vertical tube bundle accounted for about 70%of the overall pressure drop in the up-flow heating chamber and was the main component of the overall pressure within the experimental range.Three-dimensional phase diagrams were established to display the variation ranges of the pressure drop and pressure drop ratio in the vertical tube bundle corresponding to the operating parameters.The research results can provide some reference for the application of the fluidized bed heat transfer technology in the industry.

Influence of Particles on the Loading Capacity and the Temperature Rise of Water Film in Ultra-high Speed Hybrid Bearing

Ultra-high speed machining technology enables high efficiency, high precision and high integrity of machined surface. Previous researches of hybrid bearing rarely consider influences of solid particles in lubricant and ultra-high speed of hybrid bearing, which cannot be ignored under the high speed and micro-space conditions of ultra-high speed water-lubricated hybrid bearing. Considering the impact of solid particles in lubricant, turbulence and temperature viscosity effects of lubricant, the influences of particles on pressure distribution, loading capacity and the temperature rise of the lubricant film with four-step-cavity ultra-high speed water-lubricated hybrid bearing are presented in the paper. The results show that loading capacity of the hybrid bearing can be affected by changing the viscosity of the lubricant, and large particles can improve the bearing loading capacity higher. The impact of water film temperature rise produced by solid particles in lubricant is related with particle diameter and minimum film thickness. Compared with the soft particles, hard particles cause the more increasing of water film temperature rise and loading capacity. When the speed of hybrid bearing increases, the impact of solid particles on hybrid bearing becomes increasingly apparent, especially for ultra-high speed water-lubricated hybrid bearing. This research presents influences of solid particles on the loading capacity and the temperature rise of water film in ultra-high speed hybrid bearings, the research conclusions provide a new method to evaluate the influence of solid particles in lubricant of ultra-high speed water-lubricated hybrid bearing, which is important to performance calculation of ultra-high speed hybrid bearings, design of filtration system, and safe operation of ultra-high speed hybrid bearings.