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Yield Stress (yield + stress)
Kinds of Yield Stress Selected AbstractsFactors Determining Yield Stress and Overrun of Whey Protein FoamsJOURNAL OF FOOD SCIENCE, Issue 5 2002P.J. Luck ABSTRACT: Foams were formed by whipping whey protein solutions (15% w/v protein) containing NaCl, CaCl2, lactose, or glycine. Foam overrun and yield stress were determined. Foams made from whey protein ingredients have greater overrun and yield stress if the concentration of ,-lactoglobulin is high relative to a-lactalbumin. The presence of 0.4 M CaCl2 in the foaming solution increases overrun and yield stress for ,-lactoglobulin and a-lactalbumin. The high yield stress of ,-lactoglobulin and a-lactalbumin foams made from solutions containing CaCl2 suggests that CaCl2 is altering rheological properties of the interfacial protein film and/or contributing to protein aggregation or network formation in the lamellae. [source] Polar-Molecule-Dominated Electrorheological Fluids Featuring High Yield StressesADVANCED MATERIALS, Issue 45 2009Rong Shen Abstract Recent works on the development of various electrorheological (ER) fluids composed of TiO2, SrTiO, and CaTiO particles coated with CO/HO polar groups are summarized, in which an extremely large yield stress up to 200,kPa is measured and the dynamical yield stress reaches 117,kPa at a shear rate of 775,s,1. Moreover, unlike that of traditional dielectric ER fluids, the yield stress displays a linear dependence on electric field strength. Experimental results reveal that it is the polar molecules adsorbed onto the dielectric particles that play the decisive role: the polar-molecule-dominated ER effect arises from the alignment of polar molecules by the enhanced local electric field in the gap between neighboring particles. The pretreatment of electrodes and the contrivance of new measuring procedures, which are desirable for the characterization and practical implementation of this material, are also discussed. The successful synthesis of these fluids has made many of the long since conceived applications of the ER effect available. [source] TEXTURAL CHARACTERIZATION OF SOY-BASED YOGURT BY THE VANE METHODJOURNAL OF TEXTURE STUDIES, Issue 2 2002IGOR V. KOVALENKO ABSTRACT The vane method was applied to evaluate failure characteristics of soy-based yogurts prepared from five soybean varieties at Brix values of 6, 8, and 10°. Yield stress, yield strain, and water-holding capacity were compared. Yield stress values ranging from 133 to 420 Pa at 2.5% protein and 498 to 1171 Pa at 4.0% protein were dependent on soybean variety and increased with increasing protein concentration. The average yield strain of samples was not affected by protein or variety. Compared to commercial dairy yogurt, soy yogurt had 132 to 445% higher yield stress at similar protein content, and was less deformable based on yield strain measurements. Water-holding capacity of soy yogurts was variety dependent, although this dependence was less pronounced at higher protein concentrations. The vane method may be effectively used as a rapid and inexpensive technique for detecting textural differences of soy-based yogurts. [source] Yield stress and rheological characterization of the low shear zone of an epoxy molding compound for encapsulation of semiconductor devicesPOLYMER ENGINEERING & SCIENCE, Issue 4 2008Masaki Yoshii In encapsulation molding of IC packages, the melt flow inside the cavity is generally controlled in a low shear to prevent wire sweep, and other molding defects. Therefore, it is important to evaluate the rheological properties of epoxy molding compounds (EMC) in a low shear zone including determining the yield stress. In this study, a newly specialized Parallel-Plate Plastometer for EMCs was built up. Using this plastometer, the yield stress and its temperature dependence were clarified, and the rheological properties in the low shear zone were evaluated. As a result, the rheological properties in a low shear zone of 0.1,10 s,1 were characterized using the Herschel,Bulkley viscosity model which introduced the yield stress, the Castro,Macosko equation as a dependency model of cure, and the WLF equation as a dependency model for temperature. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Derivation of Recovery Kinetics From Stress Relaxation Tests,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Sheila Bhaumik The recovery behavior of a commercial aluminum alloy 3103 was investigated by the means of two alternative experimental methods: stress relaxation (SR) and double tension tests (DT). In case of SR, the stress,time evolution after deformation was recorded, and for DT the yield stress after several recovery times were measured. The DT tests were further sub-divided into tests with and without external load during recovery. The results revealed that the recovery kinetics is clearly accelerated by the external stress during the SR. However, the difference between the DT and SR stresses is much larger. It is caused by continued dislocation glide after the deformation, which causes continued plastic elongation of the specimens. This is demonstrated quantitatively by appropriate evaluation models for both experiments. In contrast to DT, the SR evaluation accounts for the elastic SR due to plastic elongation, but the recovery parameters are the same ones as for DT. This makes it possible to replace DT by SR experiments, which are materially less laborious. [source] Physical and Numerical Simulation of Cold Rolling of an AlFeSi Alloy in Consideration of Static Recovery,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Christoph Heering The influence of static recovery on the yield stress of AA8079 was investigated in lab-scale cold rolling experiments. The yield stress of AA8079 in the cold rolling process is affected by static recovery, but the softening caused by static recovery is completely compensated in the subsequent cold rolling pass. Thus, the effect of static recovery on the yield stress of the final product is of minor importance. For the TPM, the kinetics of static recovery of the AlFeSi alloy AA8079 were determined for different temperatures and strain rates. The measured softening kinetics were then implemented in the physically based flow stress model 3IVM+. This flow stress model was extended with an empirical approach for static recovery to enable the through-process modeling of cold-rolled aluminum in consideration of static recovery. Future work will focus on physically based modeling of static recovery without using empirical approaches. [source] Thermo-mechanical methods for improving fatigue performance of wrought magnesium alloysFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2010M. SHAHZAD ABSTRACT Wrought magnesium alloys AZ80 and ZK60 were extruded at 300 °C with extrusion ratios of ER = 12 and 44. Resulting microstructures, crystallographic textures and mechanical properties were investigated. Extruding led to profound reduction in grain size, which drastically improved yield stress, tensile elongation and HCF performance. Strength differentials in ZK60 after extruding at ER = 12 were more pronounced than after extruding at ER = 44, whereas no such effect of ER was observed in AZ80. Swaging after extruding further increased yield stress and endurance limit, while strength differential increased and ductility was lowered. [source] Fatigue crack initiation life estimation in a steel welded joint by the use of a two-scale damage modelFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2009N. LAUTROU ABSTRACT This work deals with the fatigue behaviour of S355NL steel welded joints classically used in naval structures. The approach suggested here, in order to estimate the fatigue crack initiation life, can be split into two stages. First, stabilized stress,strain cycles are obtained in all points of the welded joint by a finite element analysis, taking constant or variable amplitude loadings into account. This calculation takes account of: base metal elastic,plastic behaviour, variable yield stress based on hardness measurements in various zones of the weld, local geometry at the weld toe and residual stresses if any. Second, if a fast elastic shakedown occurs, a two-scale damage model based on Lemaitre et al.'s work is used as a post-processor in order to estimate the fatigue crack initiation life. Material parameters for this model were identified from two Wöhler curves established for base metal. As a validation, four-point bending fatigue tests were carried out on welded specimens supplied by ,DCNS company'. Two load ratios were considered: 0.1 and 0.3. Residual stress measurements by X-ray diffraction completed this analysis. Comparisons between experimental and calculated fatigue lives are promising for the considered loadings. An exploitation of this method is planned for another welding process. [source] Low-cycle fatigue of 1Cr,18Ni,9Ti stainless steel and related weld metal under axial, torsional and 90° out-of-phase loadingFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2004X. CHEN ABSTRACT The fatigue behaviour of base metal and weld joints of 1Cr,18Ni,9Ti stainless steel has been studied under uniaxial, torsional and 90° out-of-phase loading. A significant degree of additional hardening is found for both base metal and weld metal under 90° out-of-phase loading. Both base metal and weld metal have the same cyclic stable stress,strain relationship under torsional cyclic loading and 90° out-of-phase cyclic loading. Base metal exhibits higher cyclic stress than weld metal under uniaxial loading, and Young's modulus and yield stress of weld metal are smaller than those of base metal. Weld metal exhibited lower fatigue resistance than base metal under uniaxial and torsional loading, but no significant difference was found between the two materials under 90° out-of-phase loading. A large scatter of fatigue life is observed for weld metal, perhaps because of heterogeneity of the microstructure. The Wang,Brown (WB) damage parameter and the Fatemi,Socie (FS) damage parameter, both based on the shear critical plane approach, were evaluated relative to the fatigue data obtained. [source] Fatigue crack closure analysis of bridged cracks representing composite repairsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2000C. H. Wang This article presents an analytical and numerical study of the fatigue crack-closure behaviour of a bridged crack representing a crack that has been repaired by a composite patch. It is shown that, provided that the plate stress beneath the patch is less than 40% of the material's yield stress, the crack-closure stress of a patched crack is approximately equal to that of an unbridged crack under small-scale yielding, depending only on the stress ratio. Furthermore, it is shown that the transient crack-closure behaviour of a patched crack subjected to variable amplitude loading can be determined by analysing an unpatched crack subjected to the same stress intensity factor history. Based on these findings, it is proposed that the fatigue crack closure of a patched crack can be determined by analysing an unpatched centre crack subjected to an adjusted stress, for which an explicit expression is given. Predictions based on the proposed method are shown to correlate very well with experimental results obtained under two aircraft loading spectra. [source] Approximation methods for reliability-based design optimization problemsGAMM - MITTEILUNGEN, Issue 2 2007Irfan Kaymaz Abstract Deterministic optimum designs are obtained without considering of uncertainties related to the problem parameters such as material parameters (yield stress, allowable stresses, moment capacities, etc.), external loadings, manufacturing errors, tolerances, cost functions, which could lead to unreliable designs, therefore several methods have been developed to treat uncertainties in engineering analysis and, more recently, to carry out design optimization with the additional requirement of reliability, which referred to as reliability-based design optimization. In this paper, two most common approaches for reliability-based design optimization are reviewed, one of which is reliability-index based approach and the other performancemeasure approach. Although both approaches can be used to evaluate the probabilistic constraint, their use can be prohibitive when the associated function evaluation required by the probabilistic constraint is expensive, especially for real engineering problems. Therefore, an adaptive response surface method is proposed by which the probabilistic constraint is replaced with a simple polynomial function, thus the computational time can be reduced significantly as presented in the example given in this paper. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The influence of grout and bentonite slurry on the process of TBM tunnelling.GEOMECHANICS AND TUNNELLING, Issue 3 2009Der Einfluss von Ringspaltmörtel und Bentonitsuspension auf den TBM-Vortrieb Abstract The bentonite and grout flow around a TBM is elaborated, as well as grout flow along the lining. The calculated grout flow along the lining is compared with the results of measurements. Measurement data for the flow around the TBM are not available. Both the bentonite and the grout are modelled as a Bingham liquid and it will be shown that, due to the relatively low flow velocities, the yield stress is the governing parameter. The results of the calculations show that both the flow around the TBM and the flow around the lining may significantly influence loading on the TBM, the soil, and the lining. The bentonite and grout flow around the TBM may result in a lower volume loss than calculated when assuming that the soil follows the tapered TBM. The grout flow and especially grout consolidation lead to lower pressures around the lining if the tunnel is constructed in sandy soil. Der Bentonit- und Mörtelfluss um eine TBM und der Mörtelfluss entlang der Auskleidung werden diskutiert. Der berechnete Mörtelfluss entlang der Auskleidung wird mit Messdaten verglichen. Für die Strömungen um eine TBM existieren keine Messdaten. Sowohl der Bentonit als auch der Mörtel werden als Bingham Flüssigkeit modelliert, und es wird gezeigt, dass wegen der relativ niedrigen Strömungsgeschwindigkeiten die Fließspannung der bestimmende Parameter ist. Die Ergebnisse der Berechnungen zeigen, dass sowohl die Strömung um die TBM als auch entlang der Auskleidung einen bedeutenden Einfluss auf die Belastung der TBM, des Bodens und der Auskleidung haben. Der Bentonit- und Mörtelfluss um die TBM kann einen niedrigeren Volumenverlust zur Folge haben als berechnet, wenn man annimmt, dass der Boden der konisch zulaufenden TBM folgt. Der Mörtelfluss und besonders die Mörtelverfestigung führen zu einem niedrigeren Druck auf die Auskleidung wenn der Tunnel in sandigem Boden errichtet wird. [source] Polar-Molecule-Dominated Electrorheological Fluids Featuring High Yield StressesADVANCED MATERIALS, Issue 45 2009Rong Shen Abstract Recent works on the development of various electrorheological (ER) fluids composed of TiO2, SrTiO, and CaTiO particles coated with CO/HO polar groups are summarized, in which an extremely large yield stress up to 200,kPa is measured and the dynamical yield stress reaches 117,kPa at a shear rate of 775,s,1. Moreover, unlike that of traditional dielectric ER fluids, the yield stress displays a linear dependence on electric field strength. Experimental results reveal that it is the polar molecules adsorbed onto the dielectric particles that play the decisive role: the polar-molecule-dominated ER effect arises from the alignment of polar molecules by the enhanced local electric field in the gap between neighboring particles. The pretreatment of electrodes and the contrivance of new measuring procedures, which are desirable for the characterization and practical implementation of this material, are also discussed. The successful synthesis of these fluids has made many of the long since conceived applications of the ER effect available. [source] Length-Dependent Mechanics of Carbon-Nanotube NetworksADVANCED MATERIALS, Issue 8 2009Sameer S. Rahatekar The microstructure and deformation mechanics of carbon-nantotube networks are measured, and demonstrate a crossover from strain-induced deformation, dominated by aggregates of short rigid nanorods, to deformation dominated by individual long semi-flexible nanotubes. Our results suggest that short nanotubes provide the same network attributes as long ones at modestly higher concentrations, but with a significantly lower network yield stress, which implies better processability. [source] A density-dependent elastoplastic hydro-mechanical model for unsaturated compacted soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2007D. A. Sun Abstract This paper presents a three-dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled-suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water-retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water-retention behaviour is studied using data obtained from controlled-suction wetting,drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress,strain-strength behaviour and the effect of void ratio on the water-retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three-dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka,Nakai criterion. Model predictions of the stress,strain and water-retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd. [source] Three-dimensional analysis of single pile response to lateral soil movementsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2002J. L. Pan Abstract Three-dimensional finite element analysis was carried out to investigate the behaviour of single piles subjected to lateral soil movements and to determine the ultimate soil pressures acting along the pile shaft. The finite element analysis program ABAQUS was used for the analysis and run on a SUN Workstation. The von Mises constitutive model was employed to model the non-linear stress,strain soil behaviour. The pile was assumed to have linear elastic behaviour. This was considered to be a reasonable approximation, as the maximum stress developed in the pile did not exceed the yield stress of the concrete pile. The length of the pile is 15 m, the width of the square pile is 1 m. The three-dimensional finite element mesh used in the analysis was optimized taking into account the computing capacity limitations of the Sun Workstation. The computed ultimate soil pressures agreed well with those from the literature. The shapes of the soil pressure versus soil movement curves and the soil pressure versus the relative soil,pile displacement curves as well as the magnitude of the relative soil,pile displacement to mobilize the ultimate soil pressures were in reasonable agreement with those reported by other researchers. Copyright © 2002 John Wiley & Sons, Ltd. [source] Thermal and mechanical numerical modelling of electric discharge machining processINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008Nizar Ben Salah Abstract In electric discharge machining (EDM), the heat gradients caused by the electric discharge create a non-uniform local thermal expansion on the level of the surface layers of machined materials from where genesis of thermal stresses takes place. These thermal stresses, if exceeding yield stress, can remain and become residual after the cooling of the part. The modelling of these phenomena, during the heating by the electric discharge and the cooling by the dielectric liquid, requires a heat transfer model, the material behaviour identification, a thermo-mechanical model for the thermal and the residual stress models. This paper presents numerical results concerning the temperature distribution, the thermal and residual stresses of a stable steel material (AISI316L) machined by EDM. Comparison of numerical results with experimental data and numerical results from the literature shows good agreement and is hence quite satisfactory. Copyright © 2008 John Wiley & Sons, Ltd. [source] Using Rheology to Achieve Co-Extrusion of Cement-Based Materials with Graded Cellular StructuresINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Yunbo Chen Co-extrusion involves simultaneous extrusion of multiple layers and can be used to produce functionally graded materials whose layers have different properties. Rheological control is vital for successful co-extrusion. During extrusion, flow in the barrel and die land in a ram extruder should be plug-like, while the paste should be sheared and uniformly elongated in the die entry region. In the barrel of the extruder, the paste flow velocity field was inferred by direct observation of the paste left in the barrel, and evidence for plug flow in the barrel was seen only at low-extrudate velocities. In the die land, the Benbow nonlinear model was employed to assess the paste flow behavior, and plug flow was achieved only when the shear stress applied to the paste by the die land wall was smaller than its yield stress. For co-extrusion, a simple method using thin-walled tubes was found to be effective to prepare layered feedrods. Functionally graded cellular structures of cement-based materials were successfully co-extruded by using a low-extrudate velocity when the paste had decreasing shear viscosity from inner to outer layers. [source] Rheological behaviour and colour changes of ginger paste during storageINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2004Jasim Ahmed Summary Ginger paste was prepared from fresh ginger by addition of 8% common salt and citric acid. The paste was thermally processed and packed in glass, polyethyleneterephthalate or high-density-polyethylene containers and stored at 5 ± 1 and 25 ± 1 °C for 120 days. The rheological characteristics of the paste were studied by using a computer controlled rotational viscometer over the temperature range of 20,80 °C. Samples were subjected to a programmed shear rate, increasing linearly from 0 to 200 s,1 in 3 min, followed by a steady shear at 200 s,1 for 3 min and finally decreasing linearly from 200 to 0 s,1 in 3 min. Ginger paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel,Bulkley model. The yield stress decreased exponentially with process temperature and ranged between 3.86 and 27.82 Pa. The flow behaviour index (n) varied between 0.66 and 0.82 over the temperature range. Both consistency index and apparent viscosity decreased with increase in temperature and the process activation energies were found to be in the range of 16.7 to 21.9 kJ mol,1. The effect of temperature was significant (P < 0.05) on the Hunter colour combination value of the paste during storage; however it was not affected by type of packaging material (P > 0.05). It is recommended that ginger paste is stored at 5 ± 1 °C in polyethyleneterephthalate or glass containers. [source] Effect of polymerization method on structure and properties of cationic polyacrylamideJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Yinghua Shen Abstract Acrylamide and 2-(methacryloyloxy)ethyltrimethylammonium chloride (AM/MADQUAT) copolymers were synthesized by solution and inverse microemulsion polymerization using (NH4)2S2O8/NaHSO3 as redox initiator at the same feed mole ratio, and their microstructure, such as sequence distribution and composition distribution, was calculated from monomer reactivity ratios of different polymerization methods. The results show that charge distribution is more uniform for copolymer prepared in inverse microemulsion than that in solution, and copolymer composition distribution is close to unity, and maintains approximately at the feed ratio. Furthermore, the influence of the two structures of cationic polyacrylamides on kaolinite floc size and effective floc density, reduction of Zeta potential and floc compressive yield stress had been investigated at pH 7. The results show that the kaolinite floc size and effective floc density are strongly dependent upon copolymer microstructure, with greater floc size and lower effective floc density being observed for copolymer prepared in inverse microemulsion than for that in solution. Copolymer microstructure has a marked effect on the Zeta potential, whose reduction in the magnitude was much greater in the presence of copolymer prepared in inverse microemulsion than that in solution. Greater compressive yield stress was achieved for the strong flocs produced by copolymer prepared in inverse microemulsion than for the weak flocs produced by that in solution. The difference in flocs compressive yield stress may be attributed to flocs structure. Therefore, in this article, a correlation between the cationic polyacrylamide structure and flocculation property for kaolinite suspension was established. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effect of cavitation on the plastic deformation and failure of isotactic polypropyleneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Bing Na Abstract To clarify the effect of cavitation, which is mostly induced by crystalline phase, on the plastic deformation and failure of isotactic polypropylene, solid-state annealing at 160°C for 1.5 h is adopted to change the crystalline phase only while the amorphous phase keeps nearly intact. With aid of a special video setup, the relation of true stress and strain as well as the evolution of volume strain with axial strain has been derived. Enhancing crystalline phase due to annealing increases the yield stress and volume strain simultaneously. Moreover, the strain corresponding to steep increasing of volume strain is comparable with that related to yield, indicating that cavitation at early stage is accompanied with process of yield. With knowledge of toughness derived from impact tensile stretching and essential work of fracture (EWF), respectively, the relationship between cavitation and toughness has been correlated to some degree. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] FLOW PROPERTIES AND TUBE FRICTION FACTOR OF MILK CREAM: INFLUENCE OF TEMPERATURE AND FAT CONTENTJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2010RODRIGO DIAZ FLAUZINO ABSTRACT The rheological behavior of milk cream was studied for different fat contents (0.10 to 0.31) and for a wide temperature range (2 and 87C) using a rotational rheometer. Newtonian behavior was observed, except for fat content between 0.20 and 0.31 and temperature between 2 and 33C, where viscoplastic behavior was remarkable. The rheological parameters (Newtonian viscosity, plastic viscosity and yield stress) and density were well correlated to temperature and fat content. Tube friction factor during flow of cream was experimentally obtained at various flow rates, temperatures and tube diameters (86 , Re , 2.3 × 104, 38 , ReB , 8.8 × 103, 1.1 × 103 , He , 6.7 × 103). The proposed correlations for density and rheological parameters were applied for the prediction of friction factor for laminar and turbulent flow of cream using well-known equations for Newtonian and viscoplastic flow. The good agreement between experimental and predicted values confirms the reliability of the proposed correlations for describing the flow behavior of cream. PRACTICAL APPLICATIONS This paper presents correlations for the calculation of density and rheological parameters (Newtonian viscosity, Bingham plastic viscosity and yield stress) of milk cream as functions of temperature (2,87C) and fat content (0.10,0.31). Because of the large temperature range, the proposed correlations are useful for process design and optimization in dairy processing. An example of practical application is presented in the text, where the correlations were applied for the prediction of friction factor for laminar and turbulent tube flow of cream using well-known equations for Newtonian and viscoplastic flow, which are summarized in the text. The comparison with experimental data obtained at various flow rates, temperatures and tube diameters showed a good agreement, which confirms the reliability of the proposed correlations. [source] RHEOLOGICAL PROPERTIES OF CRYSTALLIZED HONEY PREPARED BY A NEW TYPE OF NUCLEIJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2009YUE-WEN CHEN ABSTRACT Good spreadability is a highly desirable quality for crystallized honey used in product applications. In this study, we processed Taiwanese liquid litchi honey into crystallized honey by adding a new nuclei material, namely 0.1% (w/w) glucose powder, instead of the traditional 5,10% (w/w) natural nuclei. Rheological properties of the resulting product were determined during heating and cooling utilizing small amplitude oscillatory shear to assess spreadability. As the product was heated, it exhibited decreased consistency and improved fluidity (evidenced by decreasing storage modulus [G,] and loss modulus [G,] values) and three distinct regions within the G,curve ("softening,""crystalline plateau" and "melting"). As the product was cooled from 55 to 0C, moduli were lower than those obtained during heating, and the product did not exhibit the three G,curve regions across the temperature range. Therefore, we observed incomplete reversible crystallization and rheological properties during temperature migration. Flow properties of crystallized honey in the 0,25C temperature range could be successfully predicted using the Herschel,Bulkley model (R2 > 0.97). However, the product approached Newtonian flow behavior as temperatures neared the upper end of this range. Higher viscosity and lower yield stress were observed at temperatures below 15C. The crystallized honey developed for this study exhibited shear-thinning properties desirable in honey products intended to be spread. PRACTICAL APPLICATIONS Crystallized honey is traditionally prepared by introducing 5,10% natural nuclei into liquid honey. Our lab developed a new method that replaces the natural nuclei with glucose powder, which, at 0.1% (w/w), produces a good quality creamed honey that, in commercial production, offers the potential for significant production cost advantages. As crystallized honey is used in commercial/consumer applications as a spread, its dynamic rheology is of both academic and industrial interest. In this study, we discuss the physical properties of the crystallized honey developed using glucose powder to help better identify the factors and variables involved in honey spreadability and thus facilitate the development of better honey products with more desirable spreadability profiles. This study also provides a rheological properties and spreadability database for crystallized honey that reflects the range of temperature changes that can be expected to occur during normal product storage and use. [source] RHEOLOGICAL PROPERTIES OF NONCOHESIVE APPLE DISPERSION WITH HELICAL AND VANE IMPELLERS: EFFECT OF CONCENTRATION AND PARTICLE SIZEJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2000DENIS CANTÚ-LOZANO ABSTRACT The proportionality constant, ks, between shear rate, ,, and agitation velocity, N, for a helical ribbon-screw (HRS) agitator was 17.8. Using the HRS agitator, values of consistency index K and the flow behavior index n of 14 apple pulp suspensions at seven different solids concentrations and two average particle diameters 0.71 mm and 1.21 mm were determined; in addition, values of the Casson viscosity ,c and yield stress ,OC were also calculated. The magnitudes of K increased and of n decreased with increase in pulp concentration. Experimental values of the vane yield stress, ,O,, measured with a six-blade vane increased with increase in pulp content. The values of ,OC obtained using the Casson model were close to the experimental values ,O,. The effect of particle size on the relative viscosity, ,r, was correlated with Peclet number. [source] FLOW PROPERTIES OF MALT CONCENTRATE-SWEETENED CONDENSED MILK MIXTURESJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2000S. TEJINDER ABSTRACT The rheological characteristics of various malt extract concentrate-sweetened condensed milk mixtures in the ratios of 50:50, 60:40, 70:30 and 80:20 (w/w) were studied at 30 to 80C, using a coaxial viscometer. The magnitudes of flow behavior index varied from 0.42,0.93. Experimental temperatures and concentrations of sweetened condensed milk considerably affected pseudoplasticity, consistency index and yield stress values of the mixtures. At 60 to 80C, the 60:40, 70:30 and 80:20 mixtures showed spectacularly higher flow behavior index values than those of the 50:50. The yield stress values increased with increasing temperature. The increases were considerably high in the 50:50 mixtures. The hulless barley malt concentrate-sweetened condensed milk mixtures, however, were mildly non-Newtonian and showed decreases in the values for yield stress with increasing temperatures. The activation energy values for flow behavior index and yield stress were negative in magnitudes, whereas those of consistency index were positive, which ranged from 1.6 to 15.0 Kcal/g mole. [source] FLOW AND VISCOELASTIC PROPERTIES OF PRESSURIZED AVOCADO PUREEJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 3-4 2005G. TABILO-MUNIZAGA ABSTRACT The flow and viscoelastic properties of pressurized avocado puree were evaluated. Avocado puree with pH adjusted to 4.1 was treated with ultra high pressure (UHP) at 517, 600 or 676 MPa at 21C. Each pressure was applied in oscillation mode, three pulses of 6 min each. Flow curves were obtained for each treatment, and hysteresis areas were also evaluated. The corrected flow curves were fitted using the Herschel-Bulkley model, and flow index (n), consistency index (k), and yield stress (,0) were reported. The storage (G,) and loss (G,) moduli of avocado puree were obtained through oscillatory testing. The results showed that the Herschel-Bulkley model fitted the curves with correlation coefficients ranging from 0.85 to 0.97; however, good correlation was not observed after 20/s of shear rate. Pressurized avocado puree exhibited pseudoplastic characteristics and time dependency. The flow index values were <1 for all pressure treatments. The magnitudes of elastic modulus (G,) and complex viscosity increased with increased intensity of UHP treatments. [source] Factors Determining Yield Stress and Overrun of Whey Protein FoamsJOURNAL OF FOOD SCIENCE, Issue 5 2002P.J. Luck ABSTRACT: Foams were formed by whipping whey protein solutions (15% w/v protein) containing NaCl, CaCl2, lactose, or glycine. Foam overrun and yield stress were determined. Foams made from whey protein ingredients have greater overrun and yield stress if the concentration of ,-lactoglobulin is high relative to a-lactalbumin. The presence of 0.4 M CaCl2 in the foaming solution increases overrun and yield stress for ,-lactoglobulin and a-lactalbumin. The high yield stress of ,-lactoglobulin and a-lactalbumin foams made from solutions containing CaCl2 suggests that CaCl2 is altering rheological properties of the interfacial protein film and/or contributing to protein aggregation or network formation in the lamellae. [source] Flow Characterization of Peach Products During ExtrusionJOURNAL OF FOOD SCIENCE, Issue 3 2000H. Akdogan ABSTRACT: Suitability of Bingham, Herschel-Bulkley, Casson, and Mizrahi-Berk models, to characterize the flow behavior of peach products during extrusion was investigated. The Casson equation sufficiently described the flow of peach extrudates within the 49 to 125 s -1 shear rate range. As concentration increased, yield stress and consistency coefficients increased. A rheological model was proposed to describe the viscosity of peach extrudates. The model incorporates the effect of shear rate by the Casson equation and the effect of concentration by a linear expression. The model provided good fit to the experimental data for peach extrudates reconstituted from drum-dried peach purees. [source] One-dimensional model of vacuum filtration of compressible flocculated suspensionsAICHE JOURNAL, Issue 10 2010Anthony D. Stickland Abstract This work details the one-dimensional modeling of the different processes that may occur during the vacuum filtration of compressible flocculated suspensions. Depending on the operating conditions of the applied pressure and the initial solids concentration relative to the material properties of the compressive yield stress and the effective capillary pressure at the air,liquid interface, the dewatering process undergoes a combination of cake formation, consolidation, and/or desaturation. Mathematical models for these processes based on the compressional rheology approach are presented and appropriate solution methods outlined. Results using customary material properties are given for different operating conditions to illustrate the three dewatering processes. This approach lays the theoretical basis for further work understanding two- and three-dimensional effects during desaturation, such as cracking and wall detachment. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Drying-induced birefringence of polyimide optical filmsAICHE JOURNAL, Issue 3 2010Po-Ju Chen Abstract Drying-induced birefringence of polyimide film was investigated. The polyimide solutions were coated and dried on two different types of substrates and then removed for optical measurements. The operating window, which was a region for stable and uniform film formation, was determined experimentally. The out-of-plane birefringence (OPBR) was found to increase with decreasing dry film thickness, and the increase became more significant for films less than 10 ,m thick. The experimental OPBR results were compared with the predictions of two theoretical models. The results agreed reasonably well with the one-dimensional model of Lei et al. (J Appl Polym Sci. 2001;81:1000-1013). On the other hand, a simple viscoelastic model, which is an extension of the elastic model of Croll (J Appl Polym Sci. 1979;23:847-858), could provide clear physical insight, but its applicability was somewhat limited. The effects of several variables such as elasticity number, solidification concentration, yield stress, and mass transfer rate on OPBR were examined. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] | |||||||||||||||||||||||||||||||