Many engineering components of structures operate at temperatures high enough for creep to be an important design consideration. The paper formulates time-dependent constitutive equations including higher order effects of deformations.

     The steady and oscillatory shear flow behaviors were investigated for the suspension of 8 wt.% microcrystalline cellulose in water. The values of dynamic viscosity higher than those of effective viscosity at 'gama'='omega' are observed in the range of the used frequency and shear rate (0.063-50 s^-1). Modified Akay-Leslie anisotropic liquid model is proposed for quantitative account of the test data.

     The paper is concerned with the investigation of the transient flow regime in the start-up of the Couette simple shear motion of a viscoelastic model with non-monotone flow curve, as a function of Reynolds and Weissenberg numbers. The present paper is particularly focused in establishing a numerical procedure for the problem under investigation, based on the integral expression of the shear stress in viscometric motions, as a function of the deformation history.

     The rheological constitutive equations for dilute suspensions of rigid axisymmetric particles immersed in the Reiner-Rivlin non-Newtonian incompressible isotropic fluid with constant shear and cross viscosities are obtained within the framework of structure-phenomenological approach. The effect of the cross viscosity of dispersion medium is investigated on a steady-state orientation of suspended particles possesing permanent electric dipole moment and on pseudoplastic and elasticoviscous rheological properties of suspensions in stationary simple shear flow in combination with stationary transverse electric field. The accounting of the cross viscosity in the rheological equation of the dispersion medium leads to increasing the apparent suspension viscosity and the first difference of normal stresses compared to the suspension with the Newtonian dispersion medium.

     In the report the basic accent is concentrated on the general approach to the description of reological model of mining rocks, interrelation of their reological properties with stages of crypticy and destruction. Synergetical mechanism of irreversible deformations and their influence on absorb - filtering, durability and temperature characteristics of a mountain file is shown from positions of nonequilibrum thermodynamics. It allows to use reology laws of mining rocks for forecast and study of a nature of geoaccidents.

     The rheological behaviour of setting heterogeneous materials is studied by means of an experimental device. It is based on the propagation of acoustic waves at low frequency (100Hz-1kHz). It enables to follow up material setting, and hardening phases and to quantify by an inverse analysis, the evolution of the complex viscoelastic modulus from the fluid to the solid phase. Different rheological evolutions are presented for various formulations of hydraulic concrete and bituminous mix.

     Capillary rheometric methods (Mooney, twin capillary, rough die, and color marking methods) are presented and application of these techniques to determine wall slip behavior of pastes is discussed, using measurements of aluminum oxide-silicone oil pastes as an example.

     The methods of determination of silicone elastomer KAMAXIL rheological properties and suggestions on it application in checking of quality is presented in the paper.

     The paper describes the application of the helical screw impeller rotating in the draught tube for measurements of rheological properties of suspensions. The system was originally introduced by Kembłowski et al. (1988) for an on-line measurements and process control. Here the possibility of measurement in batch systems is discussed. Also a new model for the flow curve evaluation is presented.

     In this paper a new ultrasonic shear wave apparatus is described. With the apparatus time dependent processes like hydration of hydraulic materials and reaction hardening can be studied. The sensitivity of the instrument to parameters (rheology, composition, water content, fineness, grain size distribution, addition of additives, ageing temperature) influencing these processes is eminent from the results obtained so far, offering several laboratory testing applications. The measurements are continuos, non-destructive and with no shearing applied. It is thus possible to obtain information on the growth of the physical strength of the fragile cement gel in the very early stage of hydration. The earliest usable time is limited by the time needed to prepare the sample and it extends to several days into hardened state. Application examples for cement pastes are presented.

     Experimental time and temperature dependencies of the complex Young's modulus components have been analyzed for isotropic and uniaxially oriented polymers of different chemical structures. In the regions of relaxation transitions, these dependencies have been described by the equations of viscoelasticity. For highly oriented polymers, the relaxation time distribution has been approximated by a rectangular ('box') function. Such an approximation results specific formulae for time and temperature relaxation of the Young's modulus components.

     This paper presents the research of the authors did to determine the current state of two steam pipe-lines after 100 000 hours in function at 500°C and 10MPa. Chemical and metallographic analyses, mechanical tests and creep failure tests have been performed. The results of the creep tests were extrapolated by means of Larson-Miller method. The paper presents graphics of results obtained. The behaviour of the studied materials is interpreted from the residual life assessment.

     Large-scale relaxation properties of multichain models of two- and three-dimensional (2d and 3d, correspondingly) polymer systems with interchain orientational interactions are investigated. The relaxation times of cooperative bending motions increase (in 2d- systems) or, on the contrary, decrease (in 3d- systems) with increasing of the orientational order. The proposed orientational models allow estimating the coefficients of translational diffusion of the macromolecule as the whole in orientational ordered polymer systems. It is shown that the interchain ordering leads to the decreasing of their translational mobility comparatively with that of isolated chain. The theoretical consideration for 3d- systems with the long-range orientational order confirms the interesting effect of the anisotropy of translational mobility of chains relatively the order axis (director), discovered earlier by experimental methods for the systems of LC type. The effective coefficients of translational diffusion of the chain as the whole along the director increases, while its diffusion capacity across this direction decreases with the increasing of interchain ordering.

     A viscosity build-up of various fast curing polyurethane compositions has been investigated under isothermal conditions. A diisocyanate (DI) and a polyol (PO) forming the polyurethane in course of the exothermic reaction were mixed with an original single-screw mixer in the mass ratios from 1:3 to 3:1. The rheokinetic measurements were carried out with a modified cone-plate rheometer in range of shear rates from 0.025 to 6.2 s^-1 at temperatures from 22 to 114^oC. It has found that the maximal rate of viscosity growth is observed for the polyurethanes with the ratio of DI:PO falling in the narrow range between 1:1 and 1.5:1. It is interesting that these curing systems have shown the Newtonian behaviour up to the viscosity value of 105 Pa*s at the shear range of 0.04 to 0.6 s^-1. The obtained curves can be fitted with the equation 'eta'='eta'₀*exp(k*t) on the initial stage of the viscosity rise only. For more precise fitting of the entire rheokinetic curve a modified exponential equation with the parameter k depending on the time t is proposed.

     Although high hydrostatic pressure commonly appears in demanding structural applications and during several manufacturing processes, there is little information available about its effect on material properties. For this reason, the Center for Experimental Mechanics has developed an apparatus that can characterize materials under the combined influence of pressure and temperature. Obtained measurements indicate that materials can be more accurately modeled, if both pressure and temperature are used, rather than temperature alone as it was historically done with the Williams-Landel-Ferry equation.

     The aim of this contribution is to present an additive method enabling a direct determination of axial flowrate for viscous (of power-law model) and viscoplastic (of Robertson-Stiff model) fluids in concentric annuli. This is based on addition of axial flowrates through individual partial concentric annuli forming the actual concentric annulus. The resulting relations for axial flowrate is possible to express in analytical forms without necessity of otherwise complicated derivations. The only numerical calculation consists in a determination of location of a zero shear stress for the original whole concentric annulus.

     When a load is applied to a free surface of cohesive fine powder in a vessel, the powder can spout from a small orifice, which we call the flushing. This phenomenon is explained by using a gas-solid two phase flow modeling in a view of effective stress and Darcy's law, and is verified experimentally and numerically for a case when the powder in a rectangular vessel spouts from a slit by a constant piston load. It is found that near the slit there appears a high-speed region of particle of which velocity is considerably larger than that of free following due to the gravity.

     The analytical method of solving periodic tasks of elasticity theory for layered composites has been suggested in papers (Starushenko et al., 1998). The method based on introduction of special non-smooth argument transformation so-called saw-tooth transformation (t-transformation). The advantage of saw-tooth argument transformation method is connected with possibility of mathematical description in limits of unanimous approach of different nature functions: continuous, piece continuos, with local specialties. Besides its combination with average theory and a lot of scale decomposition method extends opportunities of t-transformation technique application considerably. Solution of elasticity theory for layered composite massive in case of distributed massif forces has been built in paper (Starushenko et al., 1998). In present paper case of general load (acting of periodic distributed and concentrated load in common) is examined.

     A numerical method for solving axisymmetric transient non­Newtonian free surface flows is presented. The methodology employed is an extension of the two­dimensional GENSMAC code, employing a marker­and­cell technique and solving the governing equations using finite differences approximations on a staggered grid. Marker particles are used which provide both the location and the visualization of the free surface. Several simulations demonstrating the differences between Newtonian and non­Newtonian flow are presented.

     The influence of the wall porosity on the pressure distribution of a Shvedov-Bingham fluid flowing in the clearance between two surfaces of revolution is considered. As a result one obtains the formulae expressing the pressure distribution. An example of a squeeze flow between parallel disks is discussed in detail.

     In this study, we have attempted to discuss the effect of phase separation phenomena on the rheological properties of liquid and gel-like locust bean gum (LBG)-gelatin systems.
     Thermodynamic behaviour of such systems indicates the absence of specific interpolymer interaction independently from their state. Liquid-liquid phase separation results in the appearance of a negative deviation of the mixture´s viscosity from the logarithmic additivity law and a shear sensitive behaviour, which are indication of droplets deformation under shear. Viscosity dropped sharply and mechanical spectra were practically the same. Rheological properties of gel-like two-phase systems depend strongly on the relative content of gelatin enriched continuous phase. Phase inversion for both types of systems was accurately detected through the change in rheological behaviour.

    Rheological properties of interface layers determine the emulsion stability against coalescence and effect mechanics and flow of emulsions. The role in emulsion stability of Rehbinder structure-mechanical barrier due to elasticity of interfacial layers formed by fine dispersed solids and liquid droplets, or adsorbed polymers, or multilayers of adsorbed surfactants of any nature is emphasized.
    Emulsions are systems of great importance because of their widespread application. A number of questions of emulsion properties and production was the object of many investigations over a long period of time, of which emulsion stability is the most general.

     Known since a long time but relatively neglected, the venous vasa vasorum form a tiny network to irrigate and drainer the wall. Actually it is re-realized that, just like any tissues, the vein is a living tissue and the vasa vasorum play a key role in the maintenance of its homeostasis. Under the effects of intraluminal pressure, the Young's modulus (E) of the vein following an empirical relationship (Log E)²= - ('alpha' Log(p) + 'beta'), can vary in a very large range (a factor of 100) en even in physiological conditions. In this work, we simulated the deformation of venous vasa vasorum by finite element method. Thus it can be suggested that, at first, a permanent venous hypertension provoquer a local modification of the wallís mechanical properties (decrease of E) to favoriser a large deformation which will lead to a decrease of the irrigation, and secondly, with the decreased irrigation, the wall will loose its elasticity, become rigidified and keep its large deformation. A vicious cycle could be thus created.

     The aim of this work was to study the morphological behavior and the surface adhesion molecules expression and localization of a human endothelial cell line subjected in vitro to a laminar flow in a parallel plate flow chamber, by a 3-D fluorescence microscopy and cytofluorimetry. At rest, endothelial cells showed an array of microfilament bundles of the actin fibers, and a peripheral distribution of ICAM-1 molecules. After shear stress (1 to 30 dyne/cm², 1 to 24 hours), the stress fibers appeared and were oriented related to the flow direction but also to the shear. The ICAM-1 expression varied according to the shear stress characteristics and their distribution at the cell surface appeared also modified and related to the stress fibers formation.

     The subject of this paper is the modelling and computer - aided strength analysis of a human hip joint endoprosthesis - femoral bone system, taking into account the heterogeneity and rheological properties of bone tissue. The three distinct types of material in the system (cortical bone, trabecular bone and implant) display significant differences in their elastic and rheological properties. The analysis is carried out using the finite element method. Consideration of the rheological properties of bone tissue during analysis makes it possible to observe, under conditions of fixed loads, changes in the fields of stresses, strains and strain energy density in the bone - implant system.

    Atherosclerosis is the major cause of morbidity and mortality in much of the world. Atherogenesis is a complex process and have three stages. The first stage is the fatty streak lesion. The second stage is fibrous plaque. And the final stage is the complex lesion which show evidence of thrombus formation. However thrombus formation is always a result of rheologic disorders too. Rheologic properties are high depended from blood physical-and-chemical conditions including the concentration of serum lipids. The last are main target for free radicals action. Because atherosclerosis is always accompanied by increased free radical activity in blood we supposed that disorders of blood rheology are determined by mainly free radical influence. And those influence can contribute to the development of thrombotic conditions by constant parameters of blood coagulation. So the aim was to study the influence of lipid oxidation to hemorheology as possible risk-factor for the development of thrombotic complications.
    Low density lipoproteins (LDLP) were extracted with use of cold centrifugation from the blood of healthy volunteers. Then the part of them were oxidized to various degrees in a presence of cupric ions (2+). The oxidation degree was determined in test serum via the concentration of malone dialdehyde (later, MDA, nmol per ml of serum). For in vitro experiments non-oxidized or oxidized LDLP added in whole blood from healthy donors. In vitro models with antioxidants were used too. Rheology was analyzed with use of viscosimetry for plasma by shear rate 250 s^-1 and for whole blood by shear rate from 10 to 300 s^-1. Rotational viscosimeter AKR-2 (Russia) was used. By viscosity datas some hemorheologic parameters were calculated. Erythrocytes osmotic resistance was used for the estimation of membrane state in red blood cells. So the osmotic resistance of erythrocytes was as a marker of cell membrane damages.
    And nineteen patients after orthotopic heart transplantation were surveyed during initial stages of atherosclerotic lesion. These patients had the increase of lipids oxidation but had not disorders of blood coagulation and thrombophilic state.
    The values of thrombotic risk were calculated by software "Aggregate State of Blood" (Ver. 2.1; NRCS RAMS, 1995).
    For clear comparison each parameter in normal whole blood was accepted as 100 per cents. Experimental datas had comparative aspect.
    It was established that the degree of lipid oxidation play independent role for the development of hemorheologic disorders. Microrheology (erythrocytes-depended properties) are affected first and already in cases with MDA level in the borderline between normal and pathological values. For oxidized LDLP action the first target is erythrocytes membranes. Further increase of lipids oxidation affects plasma components - fibrinogen and albumin too. In all cases the reduction of blood fluidity has been arised. Pathologic changes appears in blood flow profile too. Just this condition can contribute to the development of thrombophilic state even by normal parameters of blood coagulation.
    Antioxidants protection of erythrocytes membranes allows to counteract to microrheologic disorders with further reduction of blood fluidity and, as consequence, to the development of thrombophilic state. Nevertheless this effect can be shown by low degree of lipids oxidation.
    Results of study contributes to an understanding of pathologic processes by atherosclerosis and by atherothrombosis.

     The external or superficial heat or cold action has a strong influence on blood rheology and systemic and microvessels blood circulation. The tissue blood flow rate intensity is generally accepted to describe by Stolwijk's phenomenological model in the skin and Sekins's model in the muscle. We proposed an own model - a modification of Stolwijk's model, including influence of blood viscosity and vessel wall elasticity on the blood flow rate. A single equivalent vessel presents the arterioles and small arteries. The wall stress and the wall deformation of this vessel have described by Hook and Voigt-Kelvin models. The analytical expression has been obtained, which generalised Stolwijk and Sekins models. The quantitative analysis of the vessel wall elasticity influence on blood flow rate in the equivalent vessel has been performed out with the help of two dimensionless parameters, namely, the so-called "primary reaction" of the vessel at heating or cooling Dr and dimensionless complex p. The parameter 'DELTA''ro' is controlled by temperature. The p-complex is directly proportional to the transmural pressure value (P_inside-P_outside) and inverse proportional to elasticity modulus of the equivalent vessel wall. It has been found that the twofold increase of elasticity modulus decreases the blood flow rate on 30% at 'DELTA''ro' = 0,1 and < 1% at 'DELTA''ro' = 0,6. This means, that the elasticity modulus influence is increased with the stress relaxation of the vessel muscles. The new rheodynamics model of the thermoregulation was applied to the numerical simulation of the human body cooling process. The combined influence of vessel wall elasticity and temperature on blood flow rate and heat transfer for water hypothermia conditions has been considered. The tem-perature dependence of the apparent blood viscosity has been described by Arrenius' model. The results show the strong influence of blood viscosity and vessel wall elasticity alternations on blood flow rate and the heat transfer of man at moderate hypothermia (T_{core > 29-31^oC). In the case water hypothermia at +10^oC it has been shown that twofold increase of initial blood viscosity and wall elasticity modulus reduce the brain temperature on 3^oC.}

    One fundamental property of living tissues is their ability of adaptation to environment because cells are always exposed to mechanical stresses related to environment or to movement (i.e. external pressure, blood flow pressure related to walking, ...). Today it's generally accepted that these mechanical forces can modify the biological behaviour of cells by affecting their metabolism, secretion of autocrin factors, phenotype, etc ... and that tissus can be remodelled by the mechanical environment.
    The modifications induced by mechanical factors are now considered as determinant to the comprehension of some patho-physiological processes (i.e.: atherosclerosis, thrombosis, arthrosis, inflammation, ...).
    In this work, we are going to demonstrate, through 3 examples of cells (cartilage chondrocyte, osteocyte and vascular endothelial cell), the importance of the mechanical factors in cell behaviour and the need of a better link between physics, mechanics and biology. Although numerous studies on this topics, the mechanisms of transduction from a mechanical signal to physiological responses or gene expression in cells remain unclear. In vitro studies on cultured cells allow us to have a good control of mechanical parameters and thus to understand better the induced modifications.

     Mechanical forces induced by blood flow influence largely endothelial cells' behavior. Also they can modify the expression and distribution of biological receptors, orient cytoskeleton, modify vasoactive factors, etc.. The objective of this study was to determine the deformation of a model endothelial cell exposed to a laminar flow. The cell was supposed to be a two dimensional elastic material. The interaction between the flow and cell deformation was simulated numerically by finite element method. Thus the distributions of mechanical forces on cell surface were obtained. The numerical results showed that the cell deformation depended on imposed flow velocity and that the mechanical stresses on cell surface were not uniform and lower with deformation than without. These numerical results suggest that it'll be interesting to study eventual correlation between the distribution of cell's biological receptors and that of mechanical factors.

     The experimental comparison of the results of different measuring techniques in determination of the rheological parameters of visco - elastic fluids producing of the friction reduction effect in turbulent region of a flow in the tubes, has been carried out. This effect is peculiar to the solutions of high - molecular polymers such as polyethylene oxide (PEO) and polyacryloamide (PAA). The studies were directed on the effect of both the structure deformation and the rheological properties with solution ageing, on the choice of the optimal measure system and on the estimation of the relationship between the results obtained by means of different techniques.

     The present study is concerned with the experimental comparison of the liquid phase properties effect on minimum fluidization velocities for shear thinning fluids and surface active agents solutions. For all studied additives the reduction of pressure drop in the flow through fixed bed has been observed. The mechanical degradation of polymer has been observed. The decrease of the consistency index increases with the aqueous solution concentration.

     In this study, we have investigated clay dispersions as a the rheologic characteristics of four different function NaCl electrolyte concentration. In the presence of NaCl electrolyte in clay / water system; clay mineral particles can aggregate in different ways; association between edge surface of neighboring particles (edge-to-edge,EE); and association between flat oxygen planes of two parallel platelets (face-to-face) association between edge surfaces and a flat oxygen planar surface (edge-to-face, EF). Electrolytes can increase or decrease the stability of the networks. The formation of gel structures with water, can be altered by the addition of NaCl and that, in this process, the type of clay, the type of the electrolyte and the concentration are influental factors.

     Blends of ethylene-vinyl alcohol (EVOH) copolymers with different contents of amorphous copolyamide were studied. Blends films were prepared by various way as melt mixing and cast by dissolving both polymers in a common solvent. The techniques applied on blends films were isothermal and dynamic thermogravimetric (TGA), infrared spectroscopy analysis (FTIR) and dynamic mechanical analysis. The effects on thermal stability and degradation reaction were studied. Weight loss of blends were studied as a function of time under isothermal conditions. Moreover, dynamic TGA tests were used as a qualitative measure of thermal stability by comparing the temperature at which samples degradation begin. Test were performed isothermally at temperatures ranging from 170^oC to 220^oC. Dynamic test were also performed at rates from 10^oC/min at temperatures ranging from 25^oC to 550^oC. Preliminary studies of EVOH copolymer thermal degradation were performed for 215^oC exposure temperature by means of FTIR analysis. Results demonstrated that increasing the content of amorphous polyamide the thermal stability was increased. The dynamic mechanical analysis of blends showed that the polyamide content increases in the blend acts as stiffener of the EVOH copolymer.

     In this paper the analysis of fly ash influence on rheological properties of cement pastes have been carried out. It was pointed that rheological properties of cement pastes containing fly ash from bituminous coal depend mostly on content fly ash in cement and on the quantity of fine fraction in fly ash as well as on the shape of fly ash particle.

    The concentration effect on rheological properties of polychloroprene/piperylene-styrene copolymer blends has been investigated under steady shear Couette flow conditions. Rheological measurements, performed at various temperatures and a variety of copolymer content, show that effect of shear rate is more significant at the high concentrated adhesive systems and at 25-30wt% copolymer content. Such content of copolymer results in an appreciable decrease in adhesive viscosity and affords opportunity to restrict the use of volatile organic solvents in the composition.
    Concentration-temperature analogies were applied. The superposed data were measured at different temperature and various copolymer contents and shifted to the unmodified adhesive data. The influence of the copolymer and temperature on shift factor decreases when adhesive solid content increases.

     In the paper an original transformation method has been proposed to describe the laminar flow of non- Newtonian fluid through the pipe of elliptic cross section. The method allows to show that the non- Newtonian fluid flow in the straight conduct of elliptic cross section can be successfully replaced by the analogical Newtonian flow in the tube of circular cross section.

    Processability and rheological behaviour, two key parameters in polymer processing, have been investigated. The first material function generated by data of a capillary rheometer for miscible two component polymer mixtures of PVC and atac-PMMA, shows monotonic shear thinning behaviour, which is enhanced by the temperature increasing. No phase separation occurrs when these blends are subjected to different shear conditions.
    Processability tests performed in a Brabender rheometer, indicated that the presense of PMMA in blends has a significant influence on the fusion characteristics. Fusion time dropps for three times, while plasticating energy decreases for almost 40% (compared to those of pure PVC). Also, the effect of various lubricants has been examined. Some changes have been noticed, but not to such extent as PMMA caused.

     A static, kinematic and dynamic small sample rheometer for the characterisation of electrically controlled functional fluids and supporting methodology to link automatically produced data from it to full scale prototype machine performance, and vice-versa, are outlined. This is done in response to requirements for better and faster testing of ERF/MRS and similar hydraulic power transmission media as they enter the second phase of development, to promote standardisation of terms and methods of application of fluids and to speed up the appraisal period. One scheme which is based on an integration of existing ad hoc techniques is set before this meeting. Its purpose is to attract criticism, suggestions and collaborative networking so as to promote from the outset the best code of rheological practice.

     The paper is an attempt to generalize the results of studies concerned with the "intelligent" fluids. Regularities of variation of mechanical (viscosity, elasticity, plasticity) properties of a class of liquid-disperse suspensions sensitive to an external electric field which are known as electrorheological fluids or "smart" fluids, are analyzed. The designs and operation principles of converters of electric energy to mechanical in power systems, and friction devices and others are described.

     A new scanning electrorheometer is presented, based on a single measurement of liquid height variation with respect to time. The apparatus consisting mainly of a pressure vessel, an ER-channel, and a CCD camera connected with computer is described with the experimental procedure. The present method overcomes one of major drawbacks of the viscometer, the inability to produce yield stress in a low shear rate range. The present results with the rheometer is compared with those of the commercially available rheometer and showed an excellent agreement with them.

    The steady laminar flow of an electrorheological fluid (ERF) through narrow space between two rotating surfaces of revolution is considered. The ERF is modelled as a viscoplastic fluid of Herschel - Bulkley.
    The quasi - linearized equations of flow for axial symmetry in the curvilinear coordinate system x, 'teta', y are used. The obtained solutions to the equations of motion have been illustrated by examples of flow through the clearance of constant thickness between rotating disks and spherical surfaces.

     The description of an algorithm for predicting the relaxation spectra of polysiloxane compositions is presented in this work. In order to generate optimal values 'lambda'_i and G_i to obtain expresion(1), a genetic algorithm and the SVD method were applied.The spectra predicted by these calculations are compared both with the outputs of a professional program, IRIS, and with the experimental results for Polastosil ABM-45.

     The theory of second order nonlinear in time evolution dissipative ordinary differential equations (ODEs) is applied to a mathematical model concerning the oscillatory flow of molten polymers in extrusion capillary rheometer operating at constant pressure drop. Using a special one-parameter function as an example, a procedure for straight-line sector definition is explained. Then an appropriate system characteristic-function in such domain can be chosen. Such characteristic guarantees all solutions corresponding to ODE to be oscillatory with oscillatory time that can be estimated. Oscillatory time as an approximate equivalent of almost half-period of oscillatory flow rate is computed.

Mathematics subject classification: 34 C 10, 34 C 15, 35 Q 35.

     Polyelectrolytes are macromolecules which carry a large quantity of ionizable groups along their chains. By dissolving them in suitable solvents, for example water, these groups dissociate in highly charged macroions and an equivalent quantity of low molecular counter ions. Through the bonding of polymer and electrolyte properties this class of materials obtains its peculiar characteristic behaviour. For the characterization of phenomenological effects of polyelectrolyte solutions, viscometric and conductometric methods will be applied for this paper. There, the viscosity measurements will be carried out using highly dilute polymer concentrations where the intermolecular interactions play a role. The experiments undertaken here were carried out using a commercial, anionic polyacrylamide and xanthan gum with different hydrolysis factors and molecular weights. The reduced viscosity increases strongly with the decrease of polymer concentration for low cp values. It reaches a maximum and then decreases again.

     Rheological properties and thermal behavior of a copolyester (CPE) prepared as high oriented fibers from PET, hydroxybenzoic, terephthalic acids and hydroquinone (40:20:20:20 mol %) in a temperature range of 30-350^oC have been investigated by capillary viscosimetry, WAXS, SAXS and DSC. The copolyester under study can be characterized by an existence of two temperature regions with various shapes of flow curves. Different values of flow activation energies in the low and high temperature regions were determined. This material revealed a prominent dependence of viscosity on a residence time at 240^oC and its absence at higher temperatures. It has been found that the non-crystalline structure of as-spun fibers can be identified as a LC smectic state with non-periodic layers. The crystalline phase (˜8 %) coexists with LC one. A first-order phase transition takes place at 220^oC, related to a presence of block sequences of PET that can be formed during the synthesis. The remaining part represents solid crystalline phase melting at 293^oC. This phase plays role of net junctions that prevent the actual flow of soften CPE. Therefore, in a temperature range 240-250^oC a pure slippage and a superposition of the flow and slippage ( 255-280^oC) take place. Only at T>290^oC a real flow proceeds.

     A two-dimentional hydrodynamic model of a rheokinetic fluid during filling a thin and long mold packed with reinforcement materials are proposed. A core layer of the mold is a porous and rather thick spacer mat. The location of other denser and thinner reinforcement materials into the mold was symmetrical with respect to the spacer mat. During mold filling the fluid easily flows along the core spacer mat and simultaneously impregnates the peripheral reinforcement mats. The model allows to simulate the flow front propagation of the fluid and pressure rise inside the mold during filling. In order to verify the model an original glass mold has been designed and built. The experimental results for the flow front propagation of the fluid were compared with the model predictions and a good coincidence between them has been obtained. For correct comparison of the experimental pressure profiles with the calculated data, the pressure losses in the mold gate must be taken into consideration. These losses can essentially exceed the pressure level into the mold.

     With the ultimate aim of improving mixer geometry by using a mathematical model for rubber mixing, this Paper concentrates on the dispersive mixing process of filler disagglomeration. Specially designed elongational flow experiments were used to achieve dispersive mixing under conditions of known stress and strain rate history. It was found that the disagglomeration process is satisfactorily described by a first order differential equation with the rate constant proportional to the power density experienced by the compound during mixing. The kinetic model was implemented in original finite element software to obtain a 2-dimensional simulation of mixing in a twin rotor internal mixer. It was concluded that the 2-dimensional simulation would be useful for relating cross-sectional rotor geometry to efficiency of filler disagglomeration, and hence dispersive mixing.

     In this laboratory work, several types of clays have been considered as additives to the bentonite and sepiolite mixtures that are used as drilling mud-making colloids for high temperature stability. To develop suitable mud composition resistant to high temperature, several experiments were conducted on sepiolite samples of different compositions taken from Eskişehir region of Turkey. Mud compositions were obtained with different combination of sepiolite clay and other materials. Rheologic and filtration properties of these compositions were determined under room conditions. Additives with high temperature stability were added to these muds and they were aged at different temperatures. Afterwards, the changes in their rheological behavior and filtration properties were observed when the mud was exposed to high temperature. Finally, three prototypes of mud were developed and their properties were reported.

     Aqueous dispersion of polyurethane (PU) ionomers, latex interpenetrating polymer networks (LIPN), and latex ABCP based on PU ionomer dispersion have been prepared and tested for the improved properties of the dispersion cast films.

     Dynamic, torsion mechanical studies of two polysiloxane based compositions, Polastosil ABM45 and R-P, in wide frequency (0.2 - 100 Hz) and temperature (-140 - 0^oC) ranges and for linear range of strain amplitude ('gamma' = 0.2 %) are presented. The observed G'- minima, near -90^oC, magnitudes of which are a decreasing function of frequency proved to be the manifestation of some reversible kinetic transition to a more ordered, crystalline structure .The enthalpy of activation for that transition was estimated to be of the order of 19 kJ/mole. On the basis of DSC measurements the average number of links between polymer chains formed during the crystalization was found to be within the range of 120 - 600, depending on the preliminary cooling rate.

     The influence of fillers on rheological properties and structural-rheological states of polymer-monomer systems as models of polymerization filling has been studied. The structure of such systems is created not only due to the interaction polymer-polymer, polymer-filler but the contacts between the filler particles.

     The lyophobization of a filler surface relative to a polymer-monomer medium and the introduction in a copolymr of units poorly solvatable with a solvent enhance the interaction of macromolecules with the filler, and thereby increase the structure formation of high-filled systems. The structure formation of systems was estimated by rheological methods.

    The dependence of the viscosity of adhesives, such as polyurethane and polychlororpene, on polyvinyl acetate (PVAc) content has been studied. This PVAc with high T_g and good dimensional stability was obtained as waste in process of polyvinyl acetate emulsion production. Low content of PVAc (2-3wt%) significantly increases the adhesives viscosity. The changes in the viscosity are accompanied by the changes in morphology and in the adhesion and cohesion properties.
    It is shown that PVAc is active polymer-modifier towards polyurethane adhesive, but inert towards polychloroprene.

     The thixotropic properties of the bentonite dispersions were analysed by the use of an approach derived from a Moore-Cheng model in which a single structure parameter 'lambda' varies within the range 0=<'lambda'<1. 'lambda'=0 corresponds to the complete break-down of structure at high shear rates, and 'lambda'=1 to the equilibrium gel structure at rest. In our method the Casson model (which was found to fit adequately the flow curves) was modified to incorporate the effect of changes in the structure parameter 'lambda'. This model was able to describe adequately the time-dependent behaviour of clay dispersions. Creep flow tests give indications about the elastic properties of the material. It was found that the viscoelastic behaviour of the bentonite dispersions could be represented by the generalised Kelvin-Voigt mechanical.

    Semi-solid metal alloys, as used in the modern forming process Thixoforming, consist of a special microstructure of spherical grains suspended in the liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration.
    The material under investigation is a tin-lead alloy (Sn-15%Pb), that is initially cooled down from the liquid state to the semi-solid range under constant shearing and then kept under isothermal conditions. Rheological experiments such as step-changes of shear rate and shear stress ramps were performed for different fractions of solid. The alloy exhibits a yield stress and highly thixotropic flow behavior. A model is presented which can predict the thixotropic behaviour in addition to the phase segregation owing to inclusion of the solid fraction with proper balance equations. The model equations are employed into FEM software and a characteristic flow case is simulated and validated by experiments.

     Rheological properties of MCC hydro- and alcogels have been studied. MCC gels were obtained by way of dispersing in water, ethyl alcohol and propyl alcohol media the wood pulp destructed to the levelling-off degree of polymerization (LODP) of cellulose by a method developed by us. At a sufficiently high cellulose concentration which was dependent on the liquid medium, MCC gels with rheological properties typical for liquid crystalline polymers (flow curves with three characteristic regions, viscosity concentrations curves with a local maximum, etc.) were obtained. These properties are more pronounced for hydrogels. MCC hydrogels are characterized also by a higher liquid phase retention volume (~ 380%), which is an important characteristic of a stable gel. For MCC alcogels, it makes up 40-65%. Inferior properties of MCC alcogels are connected with the chemical structure of alcohol molecules which, as compared to water molecules, are less favourable for bonds formation among cellulose microcrystallites and the liquid medium.

    Several polysaccharides exhibit weak gel properties when dissolved in aqueous phases and, hence, they can be profitably used to prepare aqueous matrices suitable to host disperse phases and to improve the stability and workability of the dispersions. Such an application is particularly interesting in the ceramic field, where high concentration levels of the disperse phase must be reached.
    In the present paper the rheological properties of concentrated dispersions of ceramic powders (alumina and calcium carbonate) in aqueous polysaccharide matrices (welan and rhamsan) are examined under flow conditions as well as in the linear viscoelastic regime. The comparison with the corresponding properties of aqueous suspensions and polysaccharide matrices highlights the beneficial effects of the polymer addition. The results obtained can be considered paradigmatic of the advantages deriving from the usage of such polymers for the rheological and stability properties of many other disperse systems.

     The rheological properties (yield stress, storage modulus) of a series of high internal phase ratio oil-in-water emulsions were investigated using a controlled-stress rheometer. The volume fraction of the dispersed phase ranged from 0.7124 to 0.8961. The yield stress for any given emulsion was determined from three different experiments: steady shear, oscillatory shear, and creep/recovery experiments. The yield stress values obtained from different experiments show good agreement with each other. Both yield stress and storage modulus of the emulsions increase with the increase in the dispersed phase concentration. The Princen and Kiss equations are used to interpret the yield stress and storage modulus data of this study.

     The steady shear and oscillatory shear data of concentrated emulsions obtained from measuring geometries of different design and size were analyzed and compared. The measuring geometries used were: smooth cone-and-plate geometries with cone angles of 1o and 4o, and serrated parallel plate geometry. A controlled stress rheometer was used to collect the data. In the high shear stress range, the steady shear data obtained from the three measuring geometries (for the same emulsion) show good agreement with each other. However, in the low shear stress range, the data obtained from the smooth cone-and-plate geometries exhibit a strong slippage effect. The oscillatory data are also significantly influenced by slip effects. The stress sweep experiments exhibit a linear viscoelastic region (LVE) covering a wide range of shear stress when a serrated plate geometry is used. The smooth cone and plate geometries, on the other hand, either fail to identify the LVE region or exhibit a much smaller LVE region covering a small range of shear stress.

     The rheological properties (flow curves and viscoelastic behavior) of injection moulding suspension prepared from nanosized plasma processed AlN powder and paraffin wax were investigated in the broad region of shear rates (0.07-1350 s^-1). Two viscosity platoaux are observed on the flow curves and the values of two yield stresses are obtained. The linear viscoelastic region is not reached at the lowest deformation amplitude (0.66 %). Higher values of dynamic viscosity than those of effective viscosity at 'gamma'='omega' are observed in all the range of the used frequency and shear rate (0.1-80 s^-1). The rebuilding of destroyed particle packing structure during ultrasound or shear treatment is observed. It results in the dependence of rheologic properties on the pretreatment history of suspensions.

     The aim of the present work is to evaluate the effectiveness of some commercial dispersing agents employed for maximizing the solid loading of kaolin suspensions. Two commercial deflocculants were used: a sodium polyacrylate (Reotan L) and a sodium benzenedisulfonate (Tiron). Kaolin aqueous suspensions were prepared at various solid contents (40 to 55 wt%). Rheological tests were carried out at 25^oC by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. All the suspensions prepared without deflocculant show a rheological behaviour of the shearthinning type. The slurries prepared with Tiron present the same flow behaviour as the plain suspensions, whereas the addition of Reotan L brings about a shearthickening behaviour above a critical deflocculant concentration. The application of oscillatory techniques permitted to evaluate more accurately the efficiency of the dispersing agents. The sodium polyacrylate proved to be more effective than the benzenedisulfonate as dispersant for kaolin slurries.

     The rheological behaviour of calcium carbonate/kaolin aqueous suspensions has been studied. The mixes were prepared with a vane stirrer at various solid volume fractions (0.32 to 0.43). The tests were carried out at 25^oC by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. Flow curves were determined by varying the shear rate from 0 to 1000 s^-1 at constant shear acceleration. All systems show shearthinning flow behaviour. Some rheological models which correlate relative viscosity with shear rate and solid volume fraction were taken into consideration with the purpose of selecting one model suitable for describing the shear-dependent behaviour of calcite/kaolin suspensions. The Eilers-Robinson equation written in a modified form was checked at any solid volume fraction. An excellent fitting of the experimental data was also performed with the Quemada equation.

     The aim of the present work is to study the flow behaviour of calcium carbonate suspensions in order to determine the effectiveness of some commercial dispersing agents. Three commercial deflocculants were used: a sodium polyphosphate, a sodium salt of benzenedisulfonic acid, and a sodium polyacrylate. Calcium carbonate aqueous suspensions were prepared at various solid volume fractions (0.31 to 0.46). Rheological tests were carried out at 25^oC by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. All the suspensions prepared without deflocculant show a rheological behaviour of the shearthinning type; good correlations between relative viscosity and shear rate data were found by applying the Quemada model. The application of both static and oscillatory techniques permitted to evaluate the efficiency of dispersing agents. The sodium polyacrylate proved to be the most effective deflocculant for calcium carbonate slurries; the highest efficiency of sodium polyacrylate can be explained on the basis of its polymeric nature.

     The paper presents the viscous non-linear behaviour determining high dissipation energy related to high order harmonics when subjected to a harmonic excitation.

     The paper presents the rheological modelling of fresh concrete subjected to vibrations during the compacting process. The compacting efficiency can be estimated by means of the vibration transmissibility from the vibrating tool to the fresh concrete mass. Also the experimental results are presented.

     The traditional approach to the statement of problems for the flow of Bingham media does not conespond to the model adopted for such media. We analyse this mismatch and suggest statements of problems of the flow of Bingham media and the methods for solving these problems that remove the inconsistency. The essence of this approach is that we treat the core of the flow as a plastic body and use Hencky s equations in the entire domain of the flow of the medium, i.e., both in the shear flow domain and in the core of the flow. The applicability of the approach proposed to the solution of problems associated with the analysis of flows of Bingham media is demonstrated by solving classical example problems. The new approach was applied to the analyses of processes in food technology in which Bingham media are used.

     Some time the plastic yield of roughness has a conducting role in shaping actual area of contact. Emerging of plastic deformation as a rule is accompanied by a creep. Thus, geometric and rheology characteristics of a surface has essential influence on contact rigidity and distribution of contact stress. The approach of the analysis of influence of roughness rheology on contact rigidity is developed. The analytical expression for determination of greatest contact displacement is obtained. The analysis may considerably facilitate application of the theoretical results in practice.

    Shape memory alloys, SMAs, have been in use as actuators in many mechanical processes for some time. The alloys are "trained" to return to a given shape when an actuation temperature is reached. These alloys can be incorporated into clothing systems to give, on actuation, an increased air gap between the clothing layers and hence greater insulation.
    The air gap is one of the determining factors for insulation but to have this increased prior to exposure to intense heat, i.e. a bulky garment, would subject the wearer to heat stress. Currently, Nickel Titanium alloy has been investigated as an SMA. A flat spring shape with a transition temperature of ~45oC has shown good potential in this rôle. Initial testing on the Cone Calorimeter has demonstrated a significant increase of protection at a heat flux of 15 kW/m2, a level that the UK Fire Service regards as life threatening. The clothing layers separate when the SMA spring is actuated and this in turn greatly reduces the temperature experienced at skin level, resulting in an increase of 40 seconds before the onset of second-degree skin burn. The results obtained demonstrate the potential for utilising SMAs in clothing for protection against flame and heat.
    The springs can be incorporated in bellows-style pocket panels. The pleats allow for the expansion of the air gap while the attachment of the spring holds the fabric layers together prior to actuation.
    Potential applications are for the fire service, drivers in enclosed vehicles, e.g. tank crew, racing drivers, and any other personnel who may be accidentally exposed to intense heat.

     Paper presents the experimental tests results and description of creep longitudinal and transverse strain of plywood under tension. The Leaderman's - Rozovski's method known as tensor polynomial (TP) and proposed by first of authors modified tensor polynomial (MTP) are used in description of creep strain. Correctness of the proposed mathematical models has been confirmed using graphical and statistical verification.

     Shape memory behavior of segmented polyurethanes and their ionomers has been determined in terms of various structural parameters including soft segment type and content, hard segment type and content, ionomer content, and extent of phase separation.

     In this paper, the measurement results of rheological behaviour of the surfactant solutions have been presented. The influence of pipe diameter and non-Newtonian behaviour index of the surfactant solutions on drag reduction phenomena were investigated. The results are presented in various, dimensionless co-ordinate systems. The influence of the Reynolds number definition on the shape and the position of the friction factor curve has been emphasised. The phenomena of drag reductions caused by high molecular polymers and surfactants have been compared.

    Orbitz is a non-carbonated soft drink, within which flavoured gel spheres (orbs) are suspended. It comes in five different flavours and colours; in the current experiments, we have concentrated on orange, red, white and yellow orbitz, particularly the first two. Interestingly, in what must have been a rogue batch of red Orbitz, the orbs readily settled.
    In the present communication, we address two related questions. First, why do the orbs generally remain in suspension? Is it the matched densities of the orbs and the surrounding liquid or is it the distinctive rheology of the liquid? We show that, although both may be involved, rheology is certainly the dominant influence.
    Secondly, why did the orbs settle readily in the rogue red sample? We again show that (imperfect) rheology is responsible for the malfunction.

     Damping effect of macromolecular additives on cavitation in the pipe constriction is studied. The numerical analysis of a single cavitation bubble as well as the results of experimental investigation of the cavitation cloud are presented.

     Flow properties of soft cheese type Fromage frais were obtained using standard coaxial cylinder system and resulting from measurements torque on the shaft of the rotating 4-blade vane immersed in the fluid tested. The rheological characterisation was performed as a function of temperature varied from 10 to 65^oC. The 'static' yield stress of the material tested was also determined by so-called 'vane method'. The shear stress - shear rate data were approximated using power-law, Casson and Herschel-Bulkley models. Further discussion was performed with respect to temperature effect on the rheological parameters by matching the Arrhenius type equations.