Rheological Behavior and Process Prediction of Low Viscosity Epoxy Resin for RTM

The rheological behavior of a low epoxy resin system-SR8100/SD8734 for RTM in aviation industry was studied with viscosity experiments. The dual-Arrhenius rheological model and the improved engineering viscosity model were introduced and compared with the experimental data. The results indicated that the viscosity in the earlier stage calculated by dual-Arrhenius model matched the experimental data. As rising to 400 m.Pas, the viscosity calculated by the improved engineering model was closer to the experimental data. The processing windows of the resin system for RTM were determined by combining the two models, which could predict the theological behavior of the resin system in a more credible way. 30-45 ℃ was the optimum processing temperature.

Time-dependent Early-age Behaviors of Concrete under Restrained Condition

To investigate the early-age behaviors of concrete under a restrained condition, a set of apparatus was developed. In this way, the tensile creep and other early-age properties can be investigated in depth. By measuring the modulus of elasticity of concrete, synchronous shrinkage of concrete and steel rings and free shrinkage of concrete, the deformations of concrete ring can be quantified respectively. The experimental results show the tensile stress in concrete is time-dependent, and the stress at cracking is much lower than the tensile strength at that age; the tensile creep plays an important role in relaxing the tensile stress and postponing the cracking of concrete.

THE APPARENT VISCOSITY OF SEMI-SOLID AZ91D ALLOY AT STEADY STATE

The rheological behavior of semi-solid AZ91D at steady state is studied usinga Couette type viscometer in the present paper. The results show that the apparent viscosity ofsemi-solid AZ91D at the steady state increases with the solid fraction increasing, and goes upsharply when the solid fraction reaches a certain value, which is called critical fraction. Inaddition, the apparent viscosity of semi-solid AZ91D at the steady state takes on a distinctdowntrend with the shearing rate increasing, which indicates a strong shear thinning property. Inaddition, the critical solid fraction becomes higher under larger shearing rate, owing to the moreglobular shape of the solid particles. Based on the present experiment results, an empiricalequation is built as that, relating the steady state apparent viscosity of semi-solid AZ91D with thesolid fraction f_s and shearing rate gamma at the same time: eta_(app)=10.74 exp (6.95 f_s)gamma^(-0.86).

ONE-DIMENSIONAL VISCOUS RADIATIVE GAS WITH TEMPERATURE DEPENDENT VISCOSITY

This paper is concerned with the construction of global, large amplitude solu- tions to the Cauchy problem of the one-dimensional compressible Navier-Stokes system for a viscous radiative gas when the viscosity and heat conductivity coefficients depend on both specific volume and absolute temperature. The data are assumed to be without vacuum, mass concentrations, or vanishing temperatures, and the same is shown to be hold for the global solution constructed. The proof is based on some detailed analysis on uniform positive lower and upper bounds of the specific volume and absolute temperature.

Laboratory creep tests for time-dependent properties of a marble in Jinping Ⅱ hydropower station

In order to investigate the time-dependent behaviors of deep hard rocks in the diversion tunnel of Jinping II hydropower station, uniaxial creep tests were carried out by using the triaxial testing machine RC-2000. The axial compressive load was applied step by step and each creep stage was kept for over several days. Test results show that： （1） The lateral deformation of rock specimens is 2-3 times the axial compressive deformation and accelerates drastically before damage, which may be employed as an indicator to predict the excavation-induced instability of rocks. （2） The resultant deformation changes from compression to expansion when the Poisson＇s ratio is larger than 0.5, indicating the starting point of damage. （3） In the step-loading stages, the Poisson＇s ratio approximately remains constant; under constantly imposed load, the Poisson＇s ratio changes with elapsed time, growing continuously before the specimen is damaged. （4） When the applied load reaches a certain threshold value, the rock deteriorates with time, and the strength of rocks approximately has a negative exponent relation with time. （5） The failure modes of the deep marble are different in long- and short-term loading conditions. Under the condition of short-term loading, the specimen presents a mode of tensile failure; while under the condition of long-term loading, the specimen presents a mode of shear failure, followed by tensile failure.

On the micropolar flow in a circular pipe: the effects of the viscosity coefficients

This paper considers the stationary flow of incompressible micropolar fluid through a thin cylindrical pipe governed by the pressure drop between pipe’s ends. Its goal is to investigate the influence of the viscosity coefficients on the effective flow. Depending on the magnitude of viscosity coefficients with respect to the pipe’s thickness, it derives different asymptotic models and discusses their properties.

Dynamic simulation of the effect of time-dependent variation of pH on response variable of the tailing thickener of coal washing plant

Dynamic simulation approach can be used for understanding the nonlinear behavior in mineral processing circuits. In this study, the gel point, the main parameters of batch flux density function and the main parameters of effective solid stress were determined at different conditions (pH, flocculant dosage and particle size). Therefore, the main parameters of phenome no logical model of sedimentation and thickening were determined as a functio n of particle size, pH and flocculant dosages using the result of experimental tests and Curve expert professional software. Then, the dynamic simulation was carried out for the industrial thickener of coal washing plant and the time-dependent variation of response variables was investigated by time-dependent variation of pH of input feed to thickener using the obtained equations. It was observed that it is possible to predict the thickener behavior as a function of time for time dependent variation of pH of input feed to the thickener of coal washing plant using obtained equations that it was not possible using phenomenological model of thickener alone.

基于分子动力学方法的致密砂岩储层CO_(2)驱油研究进展

随着致密砂岩储层CO_(2)-EOR项目的不断增加,亟需对CO_(2)与致密砂岩储层流体在孔隙介质中的相互作用机理进行研究,但室内实验难以观察到CO_(2)与流体在孔隙通道中的动态过程,而分子动力学模拟则可以弥补传统实验和数值方法的不足。为此,围绕该方法在CO_(2)-EOR研究中的2大重点——界面行为与受限空间运移行为,对包括萃取、溶胀、降黏、降低界面张力、最小混相压力、润湿性等6个方面界面行为的相关研究成果进行了系统梳理,结合前人对CO_(2)与致密砂岩储层流体在受限空间中运移行为的研究成果,提出了分子动力学在致密砂岩储层CO_(2)-EOR研究中的关键科学问题。研究结果表明:①分子动力学能够很好地将CO_(2)萃取原油中—轻烃组分的过程进行可视化,建议根据原油实际组分构成分析CO_(2)的萃取能力,从而弄清CO_(2)萃取原油中各组分的优先顺序及效率;②有关CO_(2)分子对原油溶胀降黏作用的研究,大多数成果中的原油组分体系较为单一,建议根据实际储层的原油组分,系统探讨高温高压条件下CO_(2)的溶胀降黏作用;③对于CO_(2)与油水两相之间界面张力的研究更多是在体相中进行展开,而在纳米受限空间界面行为的研究还有待完善;④有关地层水在孔隙壁面的润湿性研究,对不同因素之间的协同效应影响润湿性的机理尚不明确。结论认为,随着量子力学研究的不断深入以及计算性能的日益强大,该方法可以在更大尺度上进行复杂体系的计算,以其为基础的油藏、页岩油气藏CO_(2)-EOR机理等研究将会取得较大的突破。

Rheological behaviors of coal slime produced by filter-pressing

It is an effective way to use coal slime as fuel for circulating fluidized bed boilers, which will not only solve its pollution to the environment, but also turn waste to treasure. In order to provide basic technical information for transportation of coal slime from the coal preparation plant to the boiler, this paper experimentally studied the rheological behaviors of coal slime produced by filter-pressing. By using a rotational viscometer, the influences of water content, temperature, and shear time on the rheological behaviors of coal slime were investigated. Experimental results show that the coal slime will behave like Bingham plastics with low water content and like Bingham pseudo-plastics with 37.5% water content,while like pseudo-plastics with 40% water content. This indicates that the water content of coal slime must be controlled in consideration of both transportation resistance and combustion efficiency. Study results also show that, the apparent viscosity of coal slime at 5℃ is about 1.5–1.7 times of that at 40℃ for water contents 32%–37.5%, while the influence of temperature can be neglected when the water content is 40%. With increasing of water content, the influences of shear time on the apparent viscosity of coal slime becomes less. When the water content is more than 30%, the effect of shear time is negligible. It indicates that water content has the most important influence on the rheological behaviors of coal slime. There must be an optimal water content in considering conveying resistance and combustion efficiency. The environmental temperature must also be considered in coal slime transportation.

Curing Behavior of Epoxy Asphalt

The curing process of epoxy asphalt was analyzed by Fourier transform infrared （FT-IR） spectroscopy. Effect of curing temperature on viscosity of epoxy asphalt, and changes of mechanical properties with curing time were investigated. The evolution of concentration of epoxy band was followed as a function of the applied curing process.The experimental results indicate that the curing reaction rate of epoxy asphalt is invariable before 70 min at 120 ℃, and it decreases when curing time exceeds 70 min. The viscosity of epoxy asphalt increases slowly with curing time at initial curing stage. But it increases quickly after initial curing stage and the initial curing time decreases as the curing temperature increases, The tensile strength increases slowly at incipient curing stage and increases rapidly when curing time is form 20 min to 70 min. The elongation at break shows a decrease with curing time, but it exceeds 200% after cured.

THE LARGE TIME BEHAVIOR OF SPECTRAL APPROXIMATION FOR A CLASS OF PSEUDOPARABOLIC VISCOUS DIFFUSION EQUATION

The asymptotic behavior of the solutions to a class of pseudoparabolic viscous diffusion equation with periodic initial condition is studied by using the spectral method. The semidiscrete Fourier approximate solution of the problem is constructed and the error estimation between spectral approximate solution and exact solution on large time is also obtained. The existence of the approximate attractor AN and the upper semicontinuity d（AN,A） → 0 are proved.

Rheological behavior of semi-solid Mg_2Si/AM60 magnesium matrix composites at steady state

The microstructure and rheological behavior of semi-solid Mg2Si/AM60 magnesium matrix composite at steady state were investigated.The results show that the primary α-Mg phases are knapped by mechanical stirring and the Chinese script type reinforced Mg2Si phases exist in liquid phase and grain boundary.The analysis of apparent viscosity indicates that the apparent viscosity of semi-solid Mg2Si/AM60 magnesium matrix composite at steady state increases with increasing the volume fraction of Mg2Si and solid fraction of primary α-Mg,but decreases with increasing the shearing rate and shearing time,and the apparent viscosity keeps stable when shearing time reaches 300 s.

New insights into the flotation responses of brucite and serpentine for different conditioning times: Surface dissolution behavior

The inadvertent dissolution of gangue minerals is frequently detrimental to the flotation of valuable minerals.We investigated the effect of conditioning time on the separation of brucite and serpentine by flotation.By analyzing the Mg2+concentration,relative element content,and pulp viscosity,we studied the effect of mineral dissolution on brucite flotation.The results of artificially mixed mineral flotation tests(with-10μm serpentine)showed that by extending the conditioning time from 60 to 360 s,a large amount of Mg2+on the mineral surface gradually dissolved into the pulp,resulting in a decreased brucite recovery(from 83.83%to 76.79%)and an increased recovery of serpentine from 52.12%to 64.03%.To analyze the agglomeration behavior of brucite and serpentine,we used scanning electron microscopy,which clearly showed the different adhesion behaviors of different conditioning times.Lastly,the total interaction energy,as determined based on the extended DLVO(Derjaguin-Landau-Verwey-Overbeek)theory,also supports the conclusion that the gravitational force between brucite and serpentine increases significantly with increased conditioning time.

Time-dependent surrounding soil pressure and mechanical response of tunnel lining induced by surrounding soil viscosity

A numerical simulation method of shield tunnel excavation is developed to capture the time-dependent deformation behaviour of surrounding soil. The simulation method consists of four parts:(i) an elastic-plastic-viscous constitutive model that can not only reasonably describe the viscous deformation behaviour of soil, but also appropriately calculate the plastic deformation under typical stress paths of excavation;(ii) simulation of main factors related to shield tunnel excavation, including the shield machine, face pressure, lining, grout behavior, and contacts between multiple media;(iii) a simulation procedure for excavation to reflect the process of shield tunnel excavation and achieve reasonable stress and strain fields at the end of the construction stage;(iv) a creep process that is used to investigate the long-term mechanical behaviours of the surrounding soil and tunnel lining. Taking the CK570H tunnel project in Taipei as the background, a numerical simulation is conducted by adopting the developed simulation method. Based on the simulation results, the radial and circumferential stresses acting on the lining, which are induced by the surrounding soil viscosity, are analysed. The rule of the mechanical response of lining, including its deformation, bending moment, and axial force, with time is revealed. On this basis, the long-term safety of the lining is evaluated.

Shear-thinning behavior of the CaO–SiO2–CaF2–Si3N4 system mold flux and its practical application

Satisfying the mold-flux performance requirements for high-speed continuous casting necessitates the development of a new non-Newtonian-fluid mold flux with shear-thinning behavior, i.e., a mold flux whose viscosity is relatively high under lower shear rates and relatively low under higher shear rates. In this work, a mold flux that exhibits shear-thinning behavior was developed by adding different amounts of Si_3N_4 to the CaO–SiO_2–CaF_2 mold flux. The shear-thinning behavior was investigated using a rotational viscometer. In addition, the microstructure of the newly prepared slags was studied by high-temperature Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that the mechanism of shear-thinning was attributable to a temporary viscosity loss caused by the one-way shear stress, whereas the corresponding magnitude of shear-thinning was closely related to the degree of polymerization(DP). Finally, the non-Newtonian fluid mold flux was used for laboratory casting tests, which revealed that the mold flux could reduce slag entrapment and positively affect the continuous casting optimization.

Rheological behavior of novel polyamide 6/silica nanocomposites containing epoxy resins

A novel polyamide 6/silica nanocomposite containing epoxy resins(EPA6N) was prepared via in situ polymerization using tetraethoxysilane(TEOS) as the precursor of silica.The dynamic rheological properties of pure PA6 and EPA6N at temperatures of 225 and 235 ℃ were investigated.The results of transmission electron microscopy(TEM) and atomic force microscopy(AFM) indicate that the silica particles are well dispersed in the polyamide 6 matrix on about 30 nm in diameter,which demonstrates that this method can effectively avoid agglomeration of the inorganic particles.The rheological results suggest that pure PA6 shows Newtonian behavior.However,the novel EPA6N exhibits a solid-like rheological behavior,which is due to the small size,large surface of silica particles and the stronger polyamide 6-silica chemical bond formed through the reactions of epoxy resins with end groups of PA6 molecular chains.The EPA6N also exhibits higher melt viscosity,storage modulus and loss modulus than those of pure PA6.

Thixotropic behavior of semi-solid AZ91D magnesium alloy

The thixotropic behavior of semi-solid AZ91D slurry was studied through a Couette type viscometer. The results show that the apparent viscosity of semi-solid AZ91D magnesium alloy slurry increases after being isothermally held, but the apparent viscosity quickly falls down to a steady state value after being stirred again and it takes on a sharp shear-thinning behavior. With the same shearing rate and the rest time increasing, the steady apparent viscosity increases because of the agglomeration of the solid particles, and the time required for the slurry to reach the steady state also becomes longer. If the solid fraction increases, it takes longer time for the slurry to reach the steady apparent viscosity with the same shearing rate and the same rest time. If the solid fraction and the rest time are the same, but the shearing rate rises, it takes shorter time for the slurry to reach the steady apparent viscosity and the final steady apparent viscosity also decreases.

Influences of Polycarboxylate Superplasticizers on Rheological Behavior of Low-cement Castables

Influences of different superplasticizers （ STP. KSJSTO and LMS-P） on rheological behavior of low-cement castables and the mechanisms were analyzed. The shear stress and viscosity under different shear rates of matrix slurry were determined using a NXS-I IA rotary viscometer. Effects of different admixtures on the rheological properties of slurry was analyzed theoretically. Sodium tripolyphosphate and poly＇carboxylate superplasticizers KS-JSTO and LMS-P） can improve the fluidity and initial setting time. With STP. the slurry is plastic flow. With KS-JS70 or LMS-P increasing, the slurrv changes from plastic.flow, pseudoplastic flow to dilatant flow successively. Th, e optimum dosages of STP. KS-JSTO and LMS-P are 0. 15%. 0. 25% and 0. 40%, respectively. KS-JS70 and LMS-P can significantly reduce the slurry viscosity and shear stress to improve the workability of construction. Both shear stress and viscosity shall be taken into account for on-site construction.

STUDY ON VISCOELASTIC BEHAVIOR OF PAPER COATING

The flow behavior of paper coating is critical to the coating operation. In this work, the influence of the added agents on the flow behavior and the viscoelastic behavior is investigated using rheometer in steady and dynamic oscillatory modes.

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

By means of HAAKE RS105L cone and plate rheometer the flow behavior of poly(m-phenyleneisophthalamide)(PMIA) 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 more intensively.