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1.
Zusammenfassung Es wird eine neue berührungslose optische Dehnungsmeßeinrichtung für biaxiale Langzeit-Zug- bzw. Torsionsversuche vorgestellt. Die Ergebnisse der Versuche an kugel- und kurzglasfasergefülltem Polyamid 6 (PA6) zeigen, daß dieses System genügend genau arbeitet. Das untersuchte Material weist sowohl im Zugversuch als auch im Torsionsversuch nichtlineares Verhalten auf. Bei überlagerten Zug/Torsions-Belastungen verschieben sich die Dehnungen, verglichen mit denen bei gleicher einaxialer Last zu höheren Werten. Durch die Füllstoffzugabe ergeben sich unterschiedliche Verstärkungseffekte. Die faserverstärkten Proben sind erwartungsgemäß eher in Richtung der Rohrachse verstärkt, während das kugelgefüllte System eine höhere Verstärkungswirkung bei Torsionsbelastung erkennen läßt.
A new optical device for strain measurement in long-term tension and torsion tests is presented. The new system has been compared with others and the results of the experiments with glass bead and short, glas-fiber-filled Polyamid 6 show that it works well. With a dead-weight loading machine used it is possible to perform combined tension/torsion creep experiments or simple tension and simple torsion tests. The materials under consideration here exhibit nonlinear behavior in tension as well as in torsion tests. Under combined loading, which is tensile stress with a superimposed torsional stress, or vice versa, the amounts of the strains compared with those of the one-dimensional stress state are increasing. The fillers produce different reinforcement effects. The bead-filled system is stiffer when subjected to a torsional load, which may be explained by different load carrying mechanism in tension and torsion. The glassfiber-filled system is stiffer in axis direction, because the fibers are aligned to a considerable extent by the flow of the melt during molding.
Vortrag gehalten auf der Jahrestagung der Deutschen Rheologischen Gesellschaft, TH Darmstadt, 19.–21. 4. 1989.  相似文献   

2.
In this paper a simplified three-dimensional constitutive equation for viscoelastic rubber-like solids is derived by employing a generalized strain measure and an asymptotic expansion similar to that used by Coleman and Noll (1961) in their derivation of finite linear viscoelasticity (FLV) theory. The first term of the expansion represents exactly the time and strain separability relaxation behavior exhibited by certain soft polymers in the rubbery state and in the transition zone between the glassy and rubbery states. The relaxation spectra of such polymers are said to be deformation independent. Retention of higher order terms of the asymptotic expansion is recommended for treating deformation dependent spectra.Certain assumptions for the solid theory are relaxed in order to obtain a constitutive equation for uncross-linked liquid materials which exhibit large elastic recovery properties.Apart from the strain energyW(I1,I 2), which alternatively characterizes the long-time elastic response of solids or the instantaneous elastic response of elastic liquids, only the linear viscoelastic relaxation modulus is required for the first-order theory. Both types of material functions can be obtained, in theory, from simple laboratory testing procedures. The constitutive equations for solids proposed by Chang, Bloch and Tschoegl (1976) and a special form of K-BKZ theory for elastic liquids are shown to be particular cases of the first-order theory.Previously published experimental data on a cross-linked styrene-butadiene rubber (SBR) and an uncross-linked polyisobutylene (PIB) rubber is used to corroborate the theory.  相似文献   

3.
Linear rheology of viscoelastic emulsions with interfacial tension   总被引:6,自引:17,他引:6  
Emulsions of incompressible viscoelastic materials are considered, in which the addition of an interfacial agent causes the interfacial tension to depend on shear deformation and variation of area. The average complex shear modulus of the medium accounts for the mechanical interactions between inclusions by a self consistent treatment similar to the Lorentz sphere method in electricity. The resulting expression of the average modulus includes as special cases the Kerner formula for incompressible elastic materials and the Oldroyd expression of the complex viscosity of emulsions of Newtonian liquids in time-dependent flow.  相似文献   

4.
J. Zhu 《Rheologica Acta》1990,29(5):409-415
Analytical solutions are obtained for the free surface cell model of packed beds using a third order fluid. Second order perturbed results indicate a substantial increase in resistance to the flow of a viscoelastic fluid through a packed bed. This predicted increase is in good agreement with experimental findings.  相似文献   

5.
6.
Observations are reported on structures induced in an oscillatorily sheared dispersion of glass spheres in a silicon oil and in a highly viscoelastic fluid (mixture of polyisobutylenes). The shear flow used in these experiments is oscillatory with a frequency 200 Hz) and has displacement amplitudes of the order of magnitude as the sphere diameter (40 µm).The interpretation of the structures observed is based on non-linear effects which, even when small, in comparison to the viscous effects, may lead to the irreversible formation of structures over a long time, i.e. a time much larger than the period of the shear. A comparison between similar experiments performed with two different suspending fluids (silicon oil, in which the spheres line up perpendicular to the velocity direction; polyisobutylene mixture, in which the spheres line up in the velocity direction) confirm our interpretation.  相似文献   

7.
Zusammenfassung Das Schubspannungs- und Verfestigungsverhalten verschieden konzentrierter hochmolekularer Polyisobutenlösungen wird mit Hilfe eines neu konstruierten Hochdruckkapillarviskosimeters bis zu sehr hohen Schergeschwindigkeiten untersucht. Hierbei wird gleichzeitig der Einlaufdruckverlust nach Bagley durch Messungen an Kapillaren mit unterschiedlichenL/R-Verhältnissen ermittelt und, um Informationen über das Einströmverhalten der Lösungen zu erhalten, die Einlaufströmung in die Kapillare sichtbar gemacht. Im Bereich niedriger Schergeschwindigkeiten werden die Lösungen zusätzlich mit verschiedenen Rotationsviskosimetern charakterisiert.Die anhand der durchgeführten Untersuchungen erhaltenen Fließkurven lassen sich für Lösungen mit einem Polymergehalt ab 0,5% PIB-B200 in drei Bereiche einteilen, die mit Hilfe von Strömungssichtbarmachungsuntersuchungen verschiedenen Strömungsphänomenen zugeordnet werden können. Dabei kommt es u. a. zu Verfestigungserscheinungen, die sich in einem sprunghaften Ansteigen des Druckverlustes bemerkbar machen. Durch Messungen an Kapillaren mit einem kegelförmigen Einlauf kann gezeigt werden, daß diese Verfestigungserscheinungen und der damit verbundene Druckanstieg nicht nur auf das Auftreten von Sekundärströmungen im Einlaufbereich der Kapillaren zurückgeführt werden kann, sondern daß hierfür andere Effekte wie etwa die Bildung von Assoziaten aus Makromolekülen verantwortlich gemacht werden können. Auch die starke Viskositätszunahme der Lösungen im Verfestigungsbereich und die Beobachtung der Ausbildung heller Streulichtfelder sprechen für eine Bildung von Polymerassoziaten vor der Kapillare.Des weiteren wird bei den Untersuchungen zur Bagley-Korrektur festgestellt, daß zur korrekten Ermittlung des Einlaufdruckverlustes bei höher konzentrierten Polyisobutenlösungen Kapillaren mit einemL/R-Verhältnis von mindestens 1000 verwendet werden müssen. Es zeigt sich nämlich im Bagley-plot dieser Lösungen, daß die Linien konstanter Schergeschwindigkeit bei kleinerenL/R-Verhältnissen eine auffallende Krümmung im Sinne eines mit zunehmendemL/R-Verhältnis abnehmenden Druckgradienten besitzen, der erst oberhalb eines bestimmtenL/R-Verhältnisses konstant wird.
A new design high-pressure capillary-viscometer is used to study the shear behavior of high-molecular polyisobutene solutions up to very high shear rates. The entry pressure loss from the Bagley-plot is estimated by the measurement in capillaries of different length-to-radius (L/R) ratios. Simultaneously, flow visualization of the entry flow is carried out. At low shear rates the flow behavior of the solutions is characterized by different rotational viscometers.The obtained flow curves for the solutions with polymer concentrations being above 0.5% PIB-B200 can be divided into three regions which can be related to different flow phenomena by means of flow visualization. A sudden increase in pressure loss can be related to a shear thickening behavior. Measurements in capillaries with a conical entry show that this thickening behavior is not only due to secondary flows in the entry region of the capillary, but also due to other effects like the association of macromolecules. The assumption of the formation of molecular associates is also supported by the large increase in the viscosity of the solutions in the thickening region and the observed formation of luminous scattered light areas.Furthermore, the investigations on the Bagley-correction show that for higher concentrated polyisobutene solutions capillaries withL/R ratios of at least 1 000 have to be used for a correct determination of the entry pressure loss. The Bagley-plots of these solutions show that lines of constant shear rate are remarkably curved at lowerL/R ratios. The gradient of the pressure loss decreases with increasingL/R ratio and approaches a constant value at a certainL/R ratio.
Erster Teil einer vom Fachbereich Chemietechnik der Universität Dortmund genehmigten Dissertation.  相似文献   

8.
There is experimental evidence to suggest that even under steady-state conditions the velocity of solid spheres or bubbles moving through viscoelastic fluids can become time dependent. One of the possible explanations offered for interpreting this phenomenon has been the generation of a polymer depleted layer in the line of passage of the particles, which disappears due to the counterbalancing effect of molecular diffusion in the long range. We have done some careful experiments and measured these concentrations to show that no such depletion layers are formed. Alternative explanations of the phenomenon have been examined and the importance of the possible effects of microstructures generated through temporary associations has been emphasised.  相似文献   

9.
A study was carried out of the rheological properties of service weathered bitumens and their properties were compared with road performance. Bitumen from 39 test sites was recovered from the uppermost layer of stone particles covering the road surfacing and tested under dynamic and transient loading. Dynamic testing was carried out under forced sinusoidal loading. Testing under transient loading was mainly with a viscosity test conducted at 45°C, but some creep testing in compression was conducted at 0°C. From the results of dynamic testing, master curves of modulus and loss angle were constructed, spanning over ten decades in loading frequency. The hyperbolic expressions of Dickinson and Witt successfully described the frequency dependence of bitumen modulus and loss angle. The Williams, Landel and Ferry (WLF) equation, with newly derived coefficients, described the temperature dependence of the shift factor (or Newtonian viscosity) for the temperature range –10 to 60°C. Attempts were made to compare the measured transient response with that calculated from dynamic results. The result of the viscosity test conducted at 45°C as an indicator of modulus at low temperatures was assessed. Surfacing distress increased as the bitumen viscosity or modulus increased, however service performance of the bitumens was best correlated with the modulus calculated at conditions representative of traffic stressing and lowest site temperature. The changes in the rheological properties of bitumens induced by weathering is discussed.  相似文献   

10.
11.
A very simple reduction procedure is suggested for the blend viscosities of different polymer pairs. This procedure is based on the comparison of the blend viscosity, normalized either to the matrix or to the disperse phase viscosity, with the viscosities ratio of the initial polymers ( m / d ). We have obtained, for 13 different pairs containing 30% of the second component, the universal linear dependencies, mutual analysis of which allows connection of their special points with the stream morphology. The fibrillous morphology takes place in the range of m / d = 0, 1–5. Simultaneous, the thin skin consisting of the disperse phase polymers is formed. These results confirm the predominant role of the viscosities ratio in fibrillar composite material formation in comparison with the interphase tension phenomena.  相似文献   

12.
Suspensions consisting of particles of colloidal dimensions have been reported to form connected structures. When attractive forces act between particles in suspension they may flocculate and, depending on particle concentration, shear history and other parameters, flocs may build-up in a three-dimensional network which spans the suspension sample. In this paper a floc network model is introduced to interpret the elastic behavior of flocculated suspensions at small deformations. Elastic percolation concepts are used to explain the variation of the elastic modulus with concentration. Data taken from the suspension rheology literature, and new results with suspensions of magnetic -Fe2O3 and non-magnetic -Fe2O3 particles in mineral oil are interpreted with the model proposed.Non-zero elastic modulus appeared at threshold particle concentrations of about 0.7 vol.% and 0.4 vol.% of the magnetic and non-magnetic suspensions, respectively. The difference is attributed to the denser flocs formed by magnetic suspensions. The volume fraction of particles in the flocs was estimated from the threshold particle concentration by transforming this concentration into a critical volume concentration of flocs, and identifying this critical concentration with the theoretical percolation threshold of three-dimensional networks of different coordination numbers. The results obtained indicate that the flocs are low-density structures, in agreement with cryo-scanning electron micrographs. Above the critical concentration the dynamic elastic modulus G was found to follow a scaling law of the type G ( f - f c ) f , where f is the volume fraction of flocs in suspension, and f c is its threshold value. For magnetic suspensions the exponent f was found to rise from a low value of about 1.0 to a value of 2.26 as particle concentration was increased. For the non-magnetic a similar change in f was observed; f changed from 0.95 to 3.6. Two other flocculated suspension systems taken from the literature showed a similar change in exponent. This suggests the possibility of a change in the mechanism of stress transport in the suspension as concentration increases, i.e., from a floc-floc bond-bending force mechanism to a rigidity percolation mechanism.  相似文献   

13.
We show that Extended Irreversible Thermodynamics (EIT) may be regarded as a unifying thermodynamic scheme which generates a variety of non-linear viscoelastic equations of state. In particular, we show how the so-called eight-constants Oldroyd model, with all its invariant properties, may be derived from the postulates of EIT. It is also shown that the structure of the thermodynamic based rheological equations of state is in complete agreement with that of the representation theorems formulation of constitutive relationships originally proposed by Rivlin and Ericksen. We discuss how more complex rheological models can be derived from higher order approximations of the theory. Finally, the connections between our approach and other related works are briefly discussed.  相似文献   

14.
Theoretical force-time relationships were derived for squeezing flow of a Newtonian liquid between lubricated rigid and elastic plates. It is shown how the elastic number, representing the ratio between the elastic plate's rigidity and the specimen's viscosity, affects the force-time curve and under what circumstances the fluid specimen's thickness becomes a significant factor. Potential implications of the analysis in oral sensory evaluations of viscous foods are also considered.  相似文献   

15.
Two series of oscillatory flow tests were carried out on two concentrated polysaccharide systems (hydroxyethyl guar gum and scleroglucan) in order to evaluate the possibilities offered by large-deformation techniques for the discrimination between different classes of macromolecular systems (i.e., entanglement networks and weak gels). Frequently and strain sweeps, as well as combined steady and oscillatory shear tests were performed to analyze the influence of strain amplitude and of the superposed parallel shear rate on the dynamic properties of these materials.  相似文献   

16.
Predictions are made for the elongational-flow transient rheological properties of the dilute-solution internal viscosity (IV) model developed earlier by Bazua and Williams. Specifically, the elongational viscosity growth function e + (t) is presented for abrupt changes in the elongational strain rate . For calculating e +, a novel treatment of the initial rotation of chain submolecules is required; such rotation occurs in response to the macroscopic step change of at t = 0. Representative are results presented for N = 100 (N = number of submolecules) and = 1000 f and 10000 f (where is the IV coefficient and f is the bead friction coefficient), using h * = 0 (as in the original Rouse model) for the hydrodynamic interaction. The major role of IV is to cause the following changes relative to the Rouse model: 1) abrupt stress jump at t = 0 for e +; 2) general time-retardance of response. There is no qualitative change from the Rouse-model prediction of unbounded il growth when exceeds a critical value ( ), and calculations of submolecule strains at various show that the unbounded- e behavior arises from unlimited submolecule strains when . However, the time-retardance could delay such growth beyond the timescale of most experiments and spinning processes, so that the instability might not be detected. Finally, e + (t) and e ( ) in the limit are presented for N = 1 and compared with exact predictions for the analogous rigid-rod molecule; close agreement lends support for the new physical approximation introduced for solving the transient dynamics for any N.  相似文献   

17.
Aqueous solutions of cationic surfactant systems with strongly binding counterions show the striking phenomenon of shear induced phase transitions. At low shear rates or angular frequencies, the solutions exhibit Newtonian flow. At high rates of shear, however, the rheological properties change dramatically. Above a well defined threshold value of the velocity gradient, a supermolecular structure can be formed from micellar aggregates. This shear induced structure (SIS) behaves like a gel and exhibits strong flow birefringence. The formation of the shear induced structure is very complicated and depends on the specific conditions of the surfactant system. In this paper we discuss new results which have been obtained from rheological measurements and from flow birefringence data. We examine the stability of the shear induced state as a function of temperature, surfactant concentration and salt concentration and we analyse the effect of solubilisation of alcohols and hydrocarbons. The results are interpreted in terms of a kinetic model which accounts for the observed behavior.Dedicated to the 60. birthday of Prof. H. Harnisch, Hoechst AGPartly presented at the 2nd Conference of European Rheologists, Prague, June 17–20, 1986  相似文献   

18.
T. S. Ng 《Rheologica Acta》1987,26(5):453-459
Zusammenfassung Mit Hilfe eines einfachen Dehnrheometers wurden Dehnfließversuche mit thermoplastischen Kautschukblends (Ibuflex-SEH und Santoprene) durchgeführt. Die auf diese Weise erhaltenen Dehnviskositätsdaten wurden mit den von kautschukmodifizierten Thermoplasten (PVC, PE und PS) verglichen. Nach der Anlaufphase zeigt Ibuflex-SEH ein stationäres Fließverhalten, während die Dehnviskosität von Santoprene als Funktion der Zeit monoton ansteigt, ohne einen stationären Zustand zu erreichen. Die Ursachen des Unterschieds im Fließverhalten der untersuchten Polymermaterialien wurden diskutiert.
Extensional flow experiments were carried out on a simple extensional rheometer with the thermoplastic elastomer blends: Ibuflex-SEH and Santoprene. The extensional viscosity data obtained were comparable with those of elastomer modified PVC, PE and PS. After the transient stage Ibuflex-SEH shows a steady-state flow behaviour, whereas the extensional viscosity of Santoprene as a function of time increases monotonically without reaching a stationary state. The causes for these differences were discussed.
Erweiterte Fassung eines Vortrags anläßlich der Jahrestagung der Deutschen Rheologischen Gesellschaft vom 13.–15. Mai 1985 in Berlin  相似文献   

19.
Results are reported for the dynamic moduli,G andG, measured mechanically, and the dynamic third normal stress difference, measured optically, of a series bidisperse linear polymer melts under oscillatory shear. Nearly monodisperse hydrogenated polyisoprenes of molecular weights 53000 and 370000 were used to prepare blends with a volume fraction of long polymer, L, of 0.10, 0.20, 0.30, 0.50, and 0.75. The results demonstrate the applicability of birefringence measurements to solve the longstanding problem of measuring the third normal stress difference in oscillatory flow. The relationship between the third normal stress difference and the shear stress observed for these entangled polymer melts is in agreement with a widely predicted constitutive relationship: the relationship between the first normal stress difference and the shear stress is that of a simple fluid, and the second normal stress difference is proportional to the first. These results demonstrate the potential use of 1,3-birefringence to measure the third normal stress difference in oscillatory flow. Further, the general constitutive equation supported by the present results may be used to determine the dynamic moduli from the measured third normal stress difference in small amplitude oscillatory shear. Directions for future research, including the use of birefringence measurements to determineN 2/N 1 in oscillatory shear, are described.  相似文献   

20.
A two-point laser-Doppler anemometer is used to determine velocity gradients. Measuring additionally the pressure drop in channel flow allows one to use this instrument as a viscometer. This is demonstrated by measuring two polymer solutions as well as water. Besides the velocity gradient, the system also furnishes the velocity as well as velocity fluctuations. For surfactant solutions the sudden increase in these fluctuations go hand-in-hand with the sudden shear thickening reported. This behavior thus seems to be caused by a change in type of flow field (structural turbulence) rather than a change in the rheology of the surfactant solutions.This paper is dedicated to Professor Hanswalter Giesekus on the occasion of his retirement as Editor of Rheologica Acta.  相似文献   

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