Rheologic behaviors of A356 aluminum alloy billet produced by semisolid continuous casting process

The experiments for rheologic behaviors of semisolid continuous casting billets of A356 alloy in semisolid state had been carried out with a multifunctional rheometer. The results show that the deformation rate increases with loading time, the maximum strain reaches to 120％ (which is one time larger than that of traditional mold casting billet) and the strain can be rapidly eliminated to 10％ after unloading. Moreover, there is a critic stress for billet deformation even in semisolid state, which is named as critic shear stress. This stress increases with the decreasing of heating time. The theologic behaviors can be expressed by five elements mechanical model (H_2- [N_1|H_2]-[N_2|S]) and can be modified with the increasing of heating time.

Rheological Behavior of Aqueous Solutions of Cationic Guar in Presence of Oppositely Charged Surfactant

The cationic guar （CG） is synthesized and the rheological behavior of aqueous solutions of CG in the presence of sodium dodecyl sulfate （SDS） is studied in detail. The steady viscosity measurements show that the zero shear viscosity enhancement can be almost 3 orders of magnitude as the concentration of SDS increases from 0 to 0.043%. The gel-like formation is observed as the concentration of SDS is greater than 0.016%. The oscillatory rheological measurements of CG solutions in the presence of SDS show that the crossover modulus is almost independent of the concentration of SDS whereas the apparent relaxation time increases swiftly upon increasing the concentration of SDS. The experimental results indicate that the strength rather than the number of the cross-links is greatly affected by SDS molecules. The mechanism concerning the effect of SDS upon the rheology of CG solutions can be coined by the two-stage model. Before the formation of cross-links at the critical concentration, the electrostatic interaction between SDS and cationic site of CG chains plays a key role and the SDS molecules bind to CG chains through the electrostatic interaction. After the formation of cross-links at the concentration greater than the critical concentration, the cooperative hydrophobic interaction become dominant and SDS molecules bind to the cross-links through the hydrophobic interaction. The theological behavior of aqueous solutions of CG in the presence of SDS is chiefly determined by the micelle-like cross-links between CG chains. In fact, the flow activation energy of CG solution, obtained from the temperature dependence of the apparent relaxation time, falls in the range of transferring a hydrophobic tail of SDS from the micelle to an aqueous environment.

Rheological behavior of ZnO suspension with thermosensitive poly(N-isopropylacrylamide) for colloidal processing of ceramics

Novel colloidal processing using thermosensitive poly（N-isopropylacrylamide） （PNIPAM） as a coagulating agent has beendeveloped to prepare complex-shaped ceramic components. In this work, the properties of PNIPAM aqueous solutions and therheological behavior of ZnO suspensions with PNIPAM were investigated. The results show that the PNIPAM solutions exhibitobvious thermosensitivity and its transition temperature is around 32℃. When the temperature is above 40℃ （Tc, the criticaltransition temperature of thermosensitive suspension）, the 50% ZnO （volume fraction） suspension with 8 mg/mL PNIPAM has asharp increase in viscosity and reaches up to 11.49 Pa·s at 50℃, displaying strong elasticity. The main reasons are the increase ofeffective volume fraction attributed to precipitation of PNIPAM segments and the flocculation between ZnO powder particles. Inaddition, the maximum solid loading （volume fraction） at 20 ℃ is higher than that at 40℃, which proves that the phase transition ofPNIPAM can induce the flocculation of suspension.

Effect of Potassium Oleate on Rheological Behavior of Cationic Guar in Aqueous Solution with Varying Temperatures

The rheology of the cationic guar （CG） solution was measured and the effects of potassium oleate （KOA） upon the rheological properties of CG solution were studied. The steady shear viscosity measurement has shown that the viscosity of CG solution increased dramatically in the presence of KOA. The viscosity enhancement of KOA upon CG solution can be approximate three orders in magnitude. The gel-like formation of CG solution is observed at the high concentration of KOA. The excess addition of KOA results in the phase separation of CG solution. The oscillatory rheological measurement has shown that the crossover modulus Gc （corresponding to either storage modulus G＇ or loss modulus G＇＇ at the frequency wc where G＇ equals G＇＇） for CG solution, decreases with the increasing the concentration of KOA in solution. On the other hand, the apparent relaxation time 7-app （=1/wc） increases with increasing the concentration of KOA in solution. Our experimental results suggest that for surfaetant such as KOA which has a stronger tendency to form micelles in solution, the cooperative hydrophobic interaction of polymer bound to surfactants is less necessary to the formation of aggregates in solution, especially at the high concentration of surfactants. In fact, with the increase of the concentration of KOA, the number of the aggregates which associate polymer together decreases whereas the intensity of these aggregates increases. The effect of temperature upon the aggregation is also significant. With the increase of temperature, the number of the aggregates increases whereas the intensity of these aggregates decreases, probably because the ionization of KOA increases at high temperature.

DYNAMIC RHEOLOGICAL BEHAVIOR OF POLYPROPYLENE FILLED WITH ULTRA-FINE POWDERED RUBBER PARTICLES

Dynamic rheological characteristics of polypropylene (PP) filled with ultra-fine full-vulcanized powdered rubber (UFPR) composed of styrene-butadiene copolymer were studied through dynamic rheological measurements on an Advanced Rheometric Expansion System (ARES). A specific viscoelastic phenomenon, i.e. 'the second plateau', appeared at low frequencies, and exhibits a certain dependence on the amount of rubber particles and the dispersion state in the matrix. This phenomenon is attributed to the formation of aggregation structure of rubber particles. The analyses of Cole-Cole diagrams of the dynamic viscoelastic functions suggest that the heterogeneity of the composites is enhanced on increasing both particle content and temperature.

Effects of fractal surface on rheological behavior and combustion kinetics of modified brown coal water slurries

The paper reports the effects of surface fractal structures on the rheological behavior and combustion kinetics of raw brown coal and three modified coal water slurries （CWSs）. The results show that the fractal structures and physicochemical properties of samples are dependent on various modification processes. The apparent viscosities of the coal water slurries increase with increasing surface fractal dimensions （D）, especially with decreasing shear rates. Fur- thermore, it has been proved that the ignition temperatures and apparent activation energies of modified CWSs are lower than that of raw coal water slurry. Compared with the traditional qualitative analysis of the effect of pore structures on CWSs properties, D can more efficiently indicate the quantificational effect of pore structures on the rheological behavior and combustion kinetics of CWSs.

Rheological Behavior of Semi-Solid AZ91D Alloy

The rheological behavior and microstructure of semi-solid AZ91D was studied using a Couette type viscometer. The results show that the apparent viscosity of semi-solid AZ91D increases with the cooling rate increasing when it is continuously cooled and mechanically stirred and the empiric relation of the apparent viscosity with the cooling rate and solid fraction at shearing rate 93.7 s-1 is expressed as η=[0.66-0.63e(-ε/3.01)]e(fa/0.14), and with the shearing rate and solid fraction at cooling rate 4℃/min is shown as η=0.55e(fa/0.11-γ/87.59), as well as the cooling rate and shearing rate have an important effect on the microstructure of the semi-solid AZ91D alloy slurry, and decreasing the cooling rate and increasing the shearing rate are favorable to the nondendritic evolution of the primary grains.

Rheological Behavior for Mica-filled Polypropylene Composite Melts

The study on rheological properties of a series of mica-filled polypropylene ( PP ) composites was carried out. The influence of surface-treatment of mica particles on dynamic rheological behavior of the composites were dealt with. The viscosity ( h ) and dynamic modulus ( G ) of the composite melts were higher than those of PP matrix, especially those for systems treated with silane, which was attributed to the interfacial adhesion enhancement. However, surface-treatment of mica by titanate resulted in lower h and G, as compared with the treatment by silane. The reason for this is believed to be the formation of the mono-molecular layer on the mica surface.

Rheological behavior of Shengli coal-solvent slurry at low-temperatures and atmospheric pressure

We report the results from systematic studies of Shengli lignite coal-solvent slurries. Solvent type, temperature, coal to solvent ratio, particle granularity, shear rate and shear time were investigated. The viscosity of the solvents is time independent. However, the slurries are thixotropic. A change from pseudo-plastic to Newtonian behavior occurs as the temperature, or as the solvent to coal ratio, increases. The solvent used in the slurry affects the point at which the rheology changes from pseudo-plastic to Newtonian. The REC slurry changes at 1:1.2 coal to solvent ratio and at 40 °C. The HAR slurry changes at a 1:1.5 ratio and at 60 °C. The rheology of the slurries is pseudo-plastic at low shear rates but Newtonian at high shear rates.

Rheological Behavior of Bauxite-Based SiC-Containing Castables

Low cement (LC) and ultra low cement (ULC) bauxite SiC castables are important and high performance monolithic refractories and they have been widely used in iron making and incinerator linings. In this work, rheological behavior of LC and ULC bauxite based SiC containing castables has been studied, including the effects of SiC content and cement content on rheological properties of the castables. The results show that with an increase of SiC and cement content, rheological properties of the castables deteriorate. On the other hand, moderate amounts of SiC (4%～8%) and of calcium aluminate cement (2%～4%) have very slight influence on rheological properties, (i.e. when the castables are sheared their torque and yield torque only slightly increase with the shearing speed). The rheological characteristics of the castables follow Bingham fluid and always show shear thinning behavior.

Effects of milling and active surfactants on rheological behavior of powder injection molding feedstock

The effects of milling and active surfactants on the rheological behavior of powder injection molding feedstock were discussed. The feedstock consists of traditional compositional 90W 7Ni 3Fe powder mixture and a wax based polymer binder. Before mixing feedstock, the powder mixture was milled for different times in a QM 1 high energy ball mill. The viscosity of the feedstock was examined in a capillary rheometer. The rheological behavior was evaluated from viscosity data. The results show that the feedstock belongs to a pseudoplastic fluid, milling decreases viscosity of the feedstock and the sensitivity of viscosity to shear strain rate. The flowability, rheology and powder loading of this feedstock are improved by milling. Active surfactants such as stearic acid (SA) and di n octyl o phthalate (DOP) have great influences on the rheological properties of the feedstock. DOP improves the flowability and rheological stability of the feedstock further. [

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.

Rheological behavior and constitutive equations of heterogeneous titanium-bearing molten slag

Experimental studies on the rheological properties of a Ca O–Si O2–Al2O3–Mg O–Ti O2–(Ti C) blast furnace(BF) slag system were conducted using a high-temperature rheometer to reveal the non-Newtonian behavior of heterogeneous titanium-bearing molten slag. By measuring the relationships among the viscosity, the shear stress and the shear rate of molten slags with different Ti C contents at different temperatures, the rheological constitutive equations were established along with the rheological parameters; in addition, the non-Newtonian fluid types of the molten slags were determined. The results indicated that, with increasing Ti C content, the viscosity of the molten slag tended to increase. If the Ti C content was less than 2wt%, the molten slag exhibited the Newtonian fluid behavior when the temperature was higher than the critical viscosity temperature of the molten slag. In contrast, the molten slag exhibited the non-Newtonian pseudoplastic fluid characteristic and the shear thinning behavior when the temperature was less than the critical viscosity temperature. However, if the Ti C content exceeded 4wt%, the molten slag produced the yield stress and exhibited the Bingham and plastic pseudoplastic fluid behaviors when the temperature was higher and lower than the critical viscosity temperature, respectively. When the Ti C content increased further, the yield stress of the molten slag increased and the shear thinning phenomenon became more obvious.

Rheological Behaviors and Processing Windows of Low Viscosity Epoxy Resin for VIMP

The chemorheological behaviors of a low viscosity epoxy resin system （Huntsman 1564/3486） for vacuum infusion moulding process （VIMP） were studied with viscosity experiments.The dual-Arrhenius rheological model and the engineering viscosity model were established and compared with the experimental data.The result showed that the viscosity in the earlier stage calculated by dual-Arrhenius model were smaller than the experimental data,while the data calculated by the engineering model were larger.Combining the two models together can predict the rheological behaviors of the resin system in a more credible manner.The processing windows of the resin system for VIMP were determined based on the two models.The optimum processing temperature is 30-45 ℃.

Rheological Behavior for Polymer Melts and Concentrated Solutions——Part Ⅶ: A Quantitative Verification for the Molecular Theory of Non-linear Viscoelasticity with Entanglement Constraints in Polymer Melts

Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between. eta((gamma) over dot), psi (10)((gamma) over dot) and shear rate ((gamma) over dot), and topologically constrained dimension number n ' and a were derived. Linear viscoelastic parameters (eta (0) and G(N)(0)) and topologically constrained dimension number (n ' a and <(<upsilon>)over bar>) as a function of the primary molecular weight (M-n), molecular weight between entanglements (M-C) and the entanglement sites sequence distribution in polymer chain were determined. A new method for determination of viscoelastic parameters (eta (0), psi (10), G(N)(0) and J(e)(0)), topologically constrained dimension number (n ', a and v) and molecular weight (M-n, M-c and M-e) from the shear flow measurements was proposed. It was used to determine those parameters and structures of HDPE, making a good agreement between these values and those obtained by other methods. The agreement affords a quantitative verification for the molecular theory of nonlinear viscoelasticity with constrained entanglement in polymer melts.

Peculiarities of the rheological behavior and structure formation of aluminum under deformation at near-solidus temperatures

This paper deals with a peculiar rheological behavior of aluminum at near-solidus temperatures. It has been experimentally estab- lished that there is an inverse strain rate dependence of strain resistance at temperatures ranging between 560 and 640℃ and strain rates ranging from 0.06 to 1.2 s-1. Electron backscatter diffraction analysis has shown that at temperatures ranging between 540 and 640℃ and strain rates ranging from 0.06 to 0.1 s-1, the main process of softening is dynamic polygonization, resulting in in situ recrystallization. At higher strain rates, ranging between 0.8 and 1.2 s-1, and temperatures ranging between 560 and 640℃, the recovery is dynamic. This unusual behavior of the mechanism of softening and the presence of the inverse strain rate dependence of strain resistance can be explained by blocking the motion of free dislocations by foreign atoms, which occurs at strain rates ranging between 0.06 and 0.1 s-1 This process results in dislocation pile-up, thereby causing in sire recrystallization. At strain rates exceeding 0.16 s-1, there is no intensive blocking of dislocations, leading to a direct strain rate dependence of strain resistance.

Rheological Behavior of the Melts for Polyethylene-based Montmorillonite Nanocomposites

The viscoelastic properties of melts of nanocomposites with partially exfoliated structures, which were composed of low-density polyethylene （LDPE）, ethylene vinyl acetate copolymer （EVA）, and montmofillonite and modified by cetyltrimethyl ammonium bromide and octadecyltrimethyl ammonium bromide, were studied. The results obtained through measurements of the dynamic storage modulus G′, the dynamic loss modulus G″, and the transiem stress relaxation modulus G（t） of the composites, reveal that the viscoelastic properties of the composites strongly depend on the amount of montmorillonite that is exfoliated into the composites. With the increase in montmoriUonite content, the composites show an obvious property of pseudo solid-like materials within the region of lower frequencies （ω）. The montmorillonite layers are aligned along the stress direction, and the dependence of dynamic modulus on ω, appears quite different for the composites before and after being exposed to a large amplitude oscillatory shears.

RHEOLOGICAL BEHAVIOR OF POLYPHENYLENE SULFIDE/POLYAMIDE-66 BLENDS

Blends of polyphenylene sulfide (PPS) containing trace amounts of branching and/or cross-linking in chain and Polyamide-66 (PA-66) have been prepared by melt blending. The rheological behavior of PPS/PA-66 blends has been studied by means of capillary rheometer, and compared with PPS. The effects of shear rate, shear stress and temperature on the how of PPS/PA-66 blends and PPS are discussed. The non-Newtonian indexes and the activation energies of viscous how are obtained. The results show that the apparent viscosity of PPS/PA-66 blends is not sensitive to shear rate and stress, but decreases with the elevation of temperature. On the contrary, the apparent viscosity of the PPS decreases obviously with the increasing of shear rate and shear stress, but it is increased by the elevation of temperature.

Electrospinning and Rheological Behavior of Poly(vinyl alcohol)/Collagen Blended Solutions

Poly（vinyl alcohol）/collagen （PVA/COL） micro-nanofibers were successfully prepared by electrospinning process. Water, green, and non-toxic was used as the solvent. The electrospun mats consisted of micro-nanoscale fibers with mean diameter ranging from approximately 363 nm to 179 nm. It was observed that the mean diameters of PVA/COL electrospun fibers decreased with increasing collagen content. The effects of PVA/COL blending ratio on the rheological behavior of PVA/COL blended solutions were investigated by rotate rheometer. It was found that PVA/COL blended solutions behaved as Non-Newtonian fluids. With increasing collagen content, the Non-Newtonian index （n） of PVA/COL blended solutions decreased. Meanwhile, a linear relationship was found between the Non-Newtonian index （n） and the mean diameters of the PVA/COL micro- nanofibers. The chemical structures of PVA/COL electrospun fibers were also characterized by FTIR.

STUDIES ON APPARENT KINETICS AND RHEOLOGICAL BEHAVIOR OF EPOXY/ACRYLATE IPNS AS VACUUM PRESSURE IMPREGNATION RESINS

The apparent kinetics and cure behavior of novel interpenetrating polymer networks(IPNs) based on cycloaliphatic epoxy resin(CER) and tri-functional acrylate have been investigated by means of differential scanning calorimetry(DSC) and Fourier transform infrared spectroscopy(FT-IR).The results of DSC measurements show that the curing reaction of the TMPTMA component is much earlier than that of the CER component,which can lead to the formation of the IPNs.In contrast to neat anhydride-CER system,the anhydri...