Topic
Rheometer
About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.
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TL;DR: The authors' measurements support a universal scaling of both the linear viscoelastic and steady-shear viscometric response, and allow us to extract the elastic shear modulus of semidilute nanotube networks for values near or below the resolution limit of the rheometers used.
Abstract: The rheological properties of non-Brownian carbon nanotube suspensions are measured over a range of nanotube volume fractions spanning the transition from semidilute to concentrated. The polymer-stabilized nanotubes are “sticky” and form a quiescent elastic network with a well-defined shear modulus and yield stress that both depend strongly on nanotube volume fraction with different but related critical exponents. We compare controlled-strain-rate and controlled-stress measurements of yielding in shear flow, and we study the effect of slow periodic stress reversal on yielding and the arrest of flow. Our measurements support a universal scaling of both the linear viscoelastic and steady-shear viscometric response. The former allows us to extract the elastic shear modulus of semidilute nanotube networks for values that are near or below the resolution limit of the rheometers used, while the latter provides a similar extrapolation of the yield stress. A simple scaling argument is used to model the dependence...
143 citations
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TL;DR: In this paper, a technique of yield stress investigation based upon the combined use of two devices (an applied stress rheometer and an instrument for measuring the propagation velocity of small amplitude, torsional shear waves) is described.
Abstract: A technique of yield stress investigation based upon the combined use of two devices (an applied stress rheometer and an instrument for measuring the propagation velocity of small amplitude, torsional shear waves) is described. Investigations into the low shear rate rheological properties of illitic suspensions are reported for shear rates, typically, in the range 10−4— 10−1 s−1 under applied stresses in the range 0.01 — 10 Nm−2 and involving shear strains between 10−1 and 10−4. Results are presented which demonstrate that the technique does not invoke the excessive structural disruption of material associated with applied shear rate based methods (direct and otherwise) and the widely encountered problem of wall slip at the surface of rotational measuring devices is avoided using miniature vane geometries. Results are compared with those obtained using smooth-walled cyclindrical measuring devices in both applied stress and applied shear rate instruments. Yield measurements are considered in relation to the structural properties of the undisturbed material state and shear moduli obtained by studying the propagation of small amplitude (10−5 rad), high frequency (~ 300 Hz) torsional shear waves through the test materials are reported. Experimental techniques and instrument modifications to permit these measurements are described.
142 citations
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TL;DR: In this paper, the authors measured the birefringence following the inception of a steady shearing flow on a series of concentrated polyisoprene solutions and measured the steady-state shear stress in a mechanical rheometer.
Abstract: Experiments measuring the birefringence following the inception of a steady shearing flow were conducted on a series of concentrated polyisoprene solutions. The steady‐state shear stress was also measured in a mechanical rheometer. The data obtained from the two experiments confirmed that the birefringence and stress were linearly related (stress‐optical law) over a range of shear rates that extended far into the non‐Newtonian region. Interesting nonlinear effects were also observed during the transient response at high shear rates. Both the shear stress and the first normal stress pass through maximums before reaching their steady‐state values. A maximum in the normal stress is not predicted by the original Doi‐Edwards model but a modification of their theory which includes chain stretching is in qualitative agreement with our results.
142 citations
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TL;DR: A 2.0 m diameter steel 30° inverted cone-and-plate viscometer/rheometer was designed, constructed, and used to test the behaviour of coarse-grained debris flow materials as mentioned in this paper.
141 citations
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TL;DR: In this article, the authors report a large amount of experimental data on the stress overshoot phenomenon which takes place during start-up shear flows in a simple yield stress fluid, namely a carbopol microgel.
Abstract: We report a large amount of experimental data on the stress overshoot phenomenon which takes place during start-up shear flows in a simple yield stress fluid, namely a carbopol microgel. A combination of classical rheological measurements and ultrasonic velocimetry makes it possible to get physical insights on the transient dynamics of both the stress σ(t) and the velocity field across the gap of a rough cylindrical Couette cell during the start-up of shear under an applied shear rate . (i) At small strains (γ w. Finally, by changing the boundary conditions from rough to smooth, we show that there exists a critical shear rate s fixed by the wall surface roughness below which slip at both walls allows for faster stress relaxation and for stress fluctuations strongly reminiscent of stick-slip. Interestingly, the value of s is observed to coincide with the shear rate below which the flow curve displays a kink attributed to wall slip.
141 citations