A phenomenological model for plastic flow behavior of rotating band material with a large temperature range

The plastic flow behavior of the rotating band material is investigated in this paper. The rotating band material is processed from H96 brass alloy, which is hardened to a much higher yield strength compared to the annealed one. The dynamically uniaxial compression behavior of the material is tested using the split Hopkinson pressure bar(SHPB) with temperature and strain rate ranging from 297 to 1073 K and500 to 3000 s^(-1), respectively, and a phenomenological plastic flow stress model is developed to describe the mechanical behavior of the material. The material is found to present noticeable temperature sensitivity and weak strain-rate sensitivity. The construction of the plastic flow stress model has two steps. Firstly, three univariate stress functions, taking plastic strain, plastic strain rate and temperature as independent variable, respectively, are proposed by fixing the other two variables. Then, as the three univariate functions describe the special cases of flow stress behavior under various conditions, the principle of stress compatibility is adopted to obtain the complete flow stress function. The numerical results show that the proposed plastic flow stress model is more suitable for the rotating band material than the existing well-known models.

Flow behavior and microstructure of ZK60 magnesium alloy compressed at high strain rate

Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.

Size dependent flow behaviors of particles in hydrocyclone based on multiphase simulation

To investigate the flow behaviors of different size particles in hydrocyclone,a designed process was numerically simulated by the transient solver,where the quartz particles possessing a size distribution were injected into a 100 mm diameter hydrocyclone with the steady water field and air core inside.A lab experimental work has validated the chosen models in simulation by comparing the classification efficiency results.The simulated process shows that the 25 μm quartz particles,close to the cut size,need much more time than the finer and coarser particles to reach the steady flow rate on the outlets of hydrocyclone.For the particles in the inner swirl,with the quartz size increasing from 5 to 25 μm,the particles take more time to enter the vortex finder.The 25 μm quartz particles move outward in the radial direction when they go up to the vortex finder,which is contrary to the quartz particles of 5 μm and 15 μm as they are closely surrounding the air core.The studies reveal that the flow behaviors of particles inside the hydrocyclone depend on the particle size.

The Effect of Sparger Geometry on Gas Bubble Flow Behaviors Using Electrical Resistance Tomography

By electrical resistance tomography (ERT) the cross sectional profiles of gas hold-up in a φ56mm bubble column are obtained with four designs of gas sparger. The effect of sparger geometry on the bubble distribution is re-vealed by applying a sensitivity conjugated gradients reconstruction method (SCG). Experimental results show that over-all hold-up obtained by ERT is generally in good agreement with those measured with the pressure transducer and the ERT system produces informative evidence that the radial profiles of hold-up is very similar to the sparger design in the lower section of bubble column. Meanwhile, the rise velocity of bubble swarm and the Sauter mean bubble size are evaluated using ERT based on dynamic gas disengagement theory. The experimental results are in good agreement with correlations and conventional estimation obtained using pressure transmitter methods.

Flow Behaviors of Non-spherical Granules in Rectangular Hopper

Flow behaviors of four kinds of granular particles(i.e. sphere,ellipsoid,hexahedron and binary mixture of sphere and hexahedron) in rectangular hoppers were experimentally studied. The effects of granular shape and hopper structure on flow pattern,discharge fraction,mean particle residence time and tracer concentration distribu-tion were tested based on the visual observation and particle tracer technique. The results show that particle shape affects significantly the flow pattern. The flow patterns of sphere,ellipsoid and binary mixture are all parabolic shape,and the flow pattern shows no significant difference with the change of wedge angle. The flowing zone be-comes more sharp-angled with the increasing outlet size. The flow pattern of hexahedron is featured with straight lines. The discharge rates are in increasing order from hexahedron,sphere,binary mixture to ellipsoid. The dis-charge rate also increases with the wedge angle and outlet size. The mean particle residence time becomes shorter when the outlet size increases. The difference of mean particle residence time between the maximum and minimum values decreases as the wedge angle increases. The residence time of hexahedron is the shortest. The tracer concen-tration distribution of hexahedron at any height is more uniform than that of binary mixture. The tracer concentra-tion of sphere in the middle is lower than that near the wall,and the contrary tendency is found for ellipsoid particles.

Constitutive modeling of flow behavior of precipitation-hardened AA7022-T6 aluminum alloy at elevated temperature

The thermomechanical behavior of precipitation-hardened aluminum alloy AA7022-T6 was studied using isothermal compression at temperatures of 623−773 K and strain rates of 0.01−1 s^−1.The experimental results indicated that dynamic recrystallization(DRX)is a predominant hot deformation mechanism,especially at elevated temperatures and low strain rates.The modified Johnson−Cook(J−C)and the strain compensated Arrhenius-type models were developed to predict the hot flow behavior under different deformation conditions.The correlation coefficients of modified J−C model and the strain compensated Arrhenius-type models were 0.9914 and 0.9972,respectively,their average relative errors(ARE)were 6.074%and 4.465%,respectively,and their root mean square errors(RMSE)were 10.611 and 1.665 MPa,respectively,indicating that the strain compensated Arrhenius-type model can predict the hot flow stress of AA7022-T6 aluminum alloy with an appropriate accuracy.

Flow behavior modeling of IMI834 titanium alloy during hot tensile deformation

A proper constitutive model was developed to predict the hot tensile flow behavior of IMI834 titanium alloy in α+β region. Hot tensile tests were performed at 800–1025 °C and 0.001–0.1 s−1. The constitutive model was developed through an Arrhenius-type equation at strains of 0.08–0.22 to characterize the hot tension behavior. It was found that the activation energies for hot tensile deformation of IMI834 titanium alloy are in the range of 519–557 kJ/mol at different strain values. The accuracy of predicted flow stress curves was evaluated using standard statistical parameters. These curves are appropriately found to be in good agreement with the experimental ones.

Molecular dynamics simulation of water transport through graphene-based nanopores: Flow behavior and structure characteristics

The flow behavior of pressure-driven water infiltration through graphene-based slit nanopores has been studied by molecular simulation.The simulated flow rate is close to the experimental values,which demonstrates the reasonability of simulation results.Water molecules can spontaneously infiltrate into the nanopores,but an external driving force is generally required to pass through the whole pores.The exit of nanopore has a large obstruction on the water effusion.The flow velocity within the graphene nanochannels does not display monotonous dependence upon the pore width,indicating that the flow is related to the microscopic structures of water confined in the nanopores.Extensive structures of confined water are characterized in order to understand the flow behavior.This simulation improves the understanding of graphene-based nanofluidics,which helps in developing a new type of membrane separation technique.

Visualization of flow behavior in ore-segregated packed beds with fine interlayers

Ore particles,especially fine interlayers,commonly segregate in heap stacking,leading to undesirable flow paths and changeable flow velocity fields of packed beds.Computed tomography(CT),COMSOL Multiphysics,and MATLAB were utilized to quantify pore structures and visualize flow behavior inside packed beds with segregated fine interlayers.The formation of fine interlayers was accompanied with the segregation of particles in packed beds.Fine particles reached the upper position of the packed beds during stacking.CT revealed that the average porosity of fine interlayers(24.21%)was significantly lower than that of the heap packed by coarse ores(37.42%),which directly affected the formation of flow paths.Specifically,the potential flow paths in the internal regions of fine interlayers were undeveloped.Fluid flowed and bypassed the fine interlayers and along the sides of the packed beds.Flow velocity also indicated that the flow paths easily gathered in the pore throat where flow velocity(1.8×10^-5 m/s)suddenly increased.Fluid stagnant regions with a flow velocity lower than 0.2×10^-5 m/s appeared in flow paths with a large diameter.

Flow behavior and fracture of Al−Mg−Si alloy at cryogenic temperatures

The tensile and fracture behaviors of AA6061 alloy were investigated in order to provide quantitative data about this alloy at cryogenic temperatures.Specimens of AA6061 alloy were solution heat treated before tensile tests at 298,173 and 77 K and tested at strain rates in the range from 0.1 to 0.0001 s^(−1).The results indicate the suppression of the Portevin−Le Chatelier(PLC)effect and dynamic strain aging(DSA)at 77 K.In contrast,at 298 K,a remarkable serrated flow,characteristic of the PLC effect,is observed.Furthermore,the tensile behavior at 77 K,compared with that observed at 173 and 298 K,shows a simultaneous increase in strength,uniform elongation,modulus of toughness,strain-hardening exponent and strain rate sensitivity,which is related to a decrease in the dynamic recovery rate at low temperature.These responses are reflected on the fracture morphology,since the dimple size decreases at 77 K,while the area covered by dimples increases.Comparisons of the Johnson−Cook model show that a good agreement can be obtained for tests at 173 and 77 K,in which DSA is suppressed.

Effects of pin geometry on the material flow behavior of friction stir spot welded 2A12 aluminum alloy

A three-dimensional finite volume model was established by the ANSYS FLUENT software to simulate the material flow behavior during the friction stir spot welding （FSSW） process. Effects of the full-threaded pin and the reverse-threaded pin on the material flow behavior were mainly discussed. Results showed that the biggest material flow velocity appeared at the outer edge of the tool shoulder. The velocity value became smaller with the increase of the distance away from the tool surface. In general, material flows downwards along the pin thread when the full-threaded pin is used. Meanwhile, both the materials of the upper and the lower plates flow towards the lap interface along the pin thread when the reverse-threaded pin is used. The numerical simulation results were investigated by experiment, in which 2A12 aluminum alloy was used as the research object. The effective sheet thickness （EST） and stir zone （SZ） width of the joint by the reverse-threaded pin were much bigger than those by the full-threaded pin. Accordingly, cross tension failure load of the joint by the reverse-threaded pin is 23% bigger than the joint by the full-threaded pin.

The flow behavior in as-extruded AZ31 magnesium alloy under impact loading

As-extruded AZ31 magnesium alloy samples were compressed at ambient temperature and strain rates of 1000-3000 s^(−1).The fracture surfaces of cracked samples,the evolution of microstructures and macrotextures were detected.The received flow curves exhibit an abnormal behavior at strain rates above 1500 s^(−1).A strain constitutive model based on strain equivalent principle was applied to analyze the flow curves of the damaged samples.The results indicate that the abnormal flow behaviors of the fractured samples are related to the increasing area of crack surfaces,and kinetic energy during dynamic crack nucleation and propagation.The initiation of the micro-crack also causes obvious flow softening in the cracked samples.The shapes of flow stresses of the intact samples are affected by twinning.©2018 Published by Elsevier B.V.on behalf of Chongqing University.

Material flow behavior and microstructural evolution during refill friction stir spot welding of alclad 2A12-T4 aluminum alloy

In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of alclad 2A12-T4 aluminum alloy during refill friction stir spot welding.There are two material flow components, i.e., the inward-or outward-directed spiral flow on the horizontal plane and the upward-or downward-directed flow on the vertical plane.In the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower layer.In the refill stage, this is process reversed.As such, there is no obvious vertical plasticized metal flow between adjacent layers.Welding leads to the coarsening of S(Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir zone.Continuous dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.

The Flow Behavior of Poly(m-Phenyleneisophthalamide) Concentrated Solution

By means of HAAKE RS105L cone and plate rheometer the concentrated solution, including viscous flow activation energy, non-Newtonian index, structural viscosity index and relaxation time of the PMIA solution were studied. The effect of concentration and temperature of the solution and molecular weight of the polymer on its non-Newtonian behavior was investigated. The results showed that PMIA concentrated solution prepared via low temperature condensation was of non-Newtonian fluid. With the decrease of temperature, increase of solution concentration and PMIA molecular weight, the deviation of the solution from Newtonian behavior decreased. The molecular weight of the polymer and the concentration of the solution affected the non- Newtonian behavior mete intensively.

Hydrate agglomeration modeling and pipeline hydrate slurry flow behavior simulation

Dynamic modeling and numerical simulation of hydrate slurry flow behavior are of great importance to offshore hydrate management.For this purpose, a dynamic model of hydrate agglomeration was proposed in this paper.Based on population balance equation, the frame of the dynamic model was established first, which took both hydrate agglomeration and hydrate breakage into consideration.Then, the calculating methods of four key parameters involved in the dynamic model were given according to hydrate agglomeration dynamics.The four key parameters are collision frequency, agglomeration efficiency, breakage frequency and the size distribution of sub particles resulting from particle breakage.After the whole dynamic model was built, it was combined with several traditional solid–liquid flow models and then together solved by the CFD software FLUENT 14.5.Finally, using this method, the influences of flow rate and hydrate volume fraction on hydrate particle size distribution, hydrate volume concentration distribution and pipeline pressure drop were simulated and analyzed.

Flow behavior of Ti-46.2Al-2.5V-1.0Cr-0.3Ni alloy in secondary hot deformation

The flow behavior of already forged Ti-46.2Al-2.5V-1.0Cr-0.3Ni alloy was investigated by the isothermal compression experiments. The direction of secondary hot deformation was taken to be vertical to the former forging axis. And the deformation activation energy was calculated. Specimens have three kinds of starting microstructures, i.e. as-forged, relief annealed and duplex. The true strain—stress curves show that the duplex microstructure has the lowest flow resistance, better steady-state flow behavior compared with other two microstructures. It is found that obtaining duplex microstructure makes the work hardening rate and the strain rate sensitivity increase. The duplex microstructure alloy has the lowest value.

Effect of erbium on microstructure and thermal compressing flow behavior of Mg-6Zn-0.5Zr alloy

A series of thermal compressing tests of Mg-6Zn-0.5Zr and Mg-6Zn-0.5Zr-1Er alloys were performed on a Gleeble-1500D thermal simulator. The microstructures of thermal compressed Mg-6Zn-0.5Zr and Mg-6Zn-0.5Zr-lEr alloys were determined by optical microscopy, transmission electron microscopy and X-ray diffractometry. The results show that Mg-6Zn-0.5Zr alloy mainly consists of a-Mg and MgZn2 phase, while Mg-6Zn-0.5Zr-1Er alloy comprises a-Mg phase, coarse Mg3Zn4Er2 eutectic, rod-liked Mg3Zn4Er2 precipitated phase, fine I phase particle (Mg3Zn6Er, icosahedral quasicrystal structure). The peak flow stress becomes larger with increasing strain rate and erbium addition at the same temperature, and gets smaller with increasing deformation temperature at the same strain rate. The deformation activation energy increases with increasing temperature, strain rate and erbium addition. In addition, it is observed that the growth of dynamic recrystallization (DRX) grains of Mg-6Zn-0.5Zr-1Er alloy was markedly suppressed due to the pinning effect of fine I phase and Mg3Zn4Er2 phase during thermal compression.

Axial segregation characteristics and size-induced flow behavior of particles in a novel rotary drum with curved sidewalls

Particle mixing and segregation are common phenomena in rotary drums,which are challenging to be controlled and driven artificially in powder technology.In this work,the discrete element method(DEM)was applied to construct the novel rotary drum composed of different shaped curved sidewalls.By varying the operation parameters of particle and sidewall shapes as well as the length-to-diameter(L/D)ratio of drums,the axial mixing and segregation processes of binary size-induced particles were investigated.The results show that the axial flow velocity of the particle mixtures is noticeably weakened once the particle angularity increases,making the non-spherical particles to mix better in rotary drums compared to the spherical particles.Besides,in the short drums with size-induced spherical particles,the axial segregation characteristics are significantly enhanced by the convex sidewalls while suppressed by the concave sidewalls.However,for size-induced non-spherical particles,the axial segregation structure can be present in rotary drums with plane and concave sidewalls while not in drums with convex sidewalls.Moreover,the axial segregation band structure of spherical particles eventually increases proportionally with the increased drum L/D ratios.In contrast,the non-spherical particles cannot form obvious multi-proportional segregation bands.

Micro-macro Unified Analysis of Flow Behavior of Particle-reinforced Metal Matrix Composites

This article presents a micro-macro unified model for predicting the deformation of metal matrix composites （MMCs）. A macro-scale model is developed to obtain the proper boundary conditions for the micro-scale model, which is used to assess the microstructural deformation of materials. The usage of the submodel technique in the analysis makes it possible to shed light on the stress and strain field at the microlevel. This is helpful to investigate the linkage between the microscopic and the macroscopic flow behavior of the composites. An iterative procedure is also proposed to find out the optimum parameters. The results show that the convergence can be attained after three iterations in computation. In order to demonstrate the reliability of mi- cro-macro unified model, results based on the continuum composite model are also investigated using the stress-strain relation of composite obtained from the iterations. By comparing the proposed unified model to the continuum composite model, it is clear that the former exhibits large plastic deformation in the case of little macroscopic deformation, and the stresses and strains obtained from the submodel are higher than those from the macroscopic deformation.

Effect of static bed height in the upper fluidized bed on flow behavior in the lower riser section of a coupled reactor

To study olefin reduction by using an auxiliary reactor for FCC naphtha upgrading, a large-scale cold model of a riser-bed coupled to an upper fluidized bed was established. The effect of static bed height in the upper fluidized bed on narticle flow behavior in the lower riser was investigated experimentally. A restriction index of solids holdup was used to evaluate quantitatively the restrictive effect of the upper fluidized bed. Experimental results show that, under the restrictive effect of the upper fluidized bed, the riser could be divided into three regions in the longitudinal direction： accelerating, fully developed and restriction. The axial distribution of solids holdup in the riser is characterized by large solids holdup in the top and bottom sections and small solids holdup in the middle section. Overall solids holdup increased with increasing static bed height in the upper fluidized bed, while particle velocity decreased. Such restrictive effect of the upper fluidized bed could extend from the middle and top sections to the whole riser volume when riser outlet resistance is increased, which increases with increasing static bed height in the upper fluidized bed. The upper bed exerts the strongest restriction on the area close to the riser outlet.