Effects of instrument and fluid inertia in oscillatory shear in rotational rheometers

Läuger, Jörg; Stettin, H.

doi:10.1122/1.4944512

Cited by 47 publications

(35 citation statements)

References 18 publications

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“…For the intermediate case, the non-homogeneous deformation profile needs to be accounted for Läuger and Stettin (2016), which given the fact that in rheological measurements, fluid properties are unknown and requires an iterative solver. Schrag (1977) provided expressions for correcting the measured viscoelastic properties in case of a shear wave travelling between two walls.…”

Section: Shear Wave Propagationmentioning

confidence: 99%

Bulk rheometry at high frequencies: a review of experimental approaches

et al. 2019

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High-frequency rheology is a form of mechanical spectroscopy which provides access to fast dynamics in soft materials and hence can give valuable information about the local scale microstructure. It is particularly useful for systems where timetemperature superposition cannot be used, when there is a need to extend the frequency range beyond what is possible with conventional rotational devices. This review gives an overview of different approaches to high-frequency bulk rheometry, i.e. mechanical rheometers that can operate at acoustic (20 Hz-20 kHz) or ultrasound (> 20 kHz) frequencies. As with all rheometers, precise control and know-how of the kinematic conditions are of prime importance. The inherent effects of shear wave propagation that occur in oscillatory measurements will hence be addressed first, identifying the gap and surface loading limits. Different high-frequency techniques are then classified based on their mode of operation. They are reviewed critically, contrasting ease of operation with the dynamic frequency range obtained. A comparative overview of the different types of techniques in terms of their operating window aims to provide a practical guide for selecting the right approach for a given problem. The review ends with a more forward looking discussion of selected material classes for which the use of high-frequency rheometry has proven particularly valuable or holds promise for bringing physical insights.

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Section: Shear Wave Propagationmentioning

confidence: 99%

Bulk rheometry at high frequencies: a review of experimental approaches

et al. 2019

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“…External stress, σ E , is applied through the system boundaries. In a rheometer, this is the 'geometry', which has far higher mass than the suspension for a typical gap height, h, between the boundaries [26], Fig. 1(e).…”

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confidence: 99%

Competing Timescales Lead to Oscillations in Shear-Thickening Suspensions

et al. 2019

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Competing time scales generate novelty. Here, we show that a coupling between the time scales imposed by instrument inertia and the formation of inter-particle frictional contacts in shear-thickening suspensions leads to highly asymmetric shear-rate oscillations. Experiments tuning the presence of oscillations by varying the two time-scales support our model. The observed oscillations give access to a shear-jamming portion of the flow curve that is forbidden in conventional rheometry. Moreover, the oscillation frequency allows us to quantify an intrinsic relaxation time for particle contacts. The coupling of fast contact network dynamics to a slower system variable should be generic to many other areas of dense suspension flow, with instrument inertia providing a paradigmatic example.

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“…The right-hand side of Eq. 10 In rheological measurements, there are always concerns about misleading observations sourced from inertia [42]. At a finite Reynolds number for a rather large channel width, there is a nonuniform time-dependent velocity distribution across the channel.…”

Section: Oscillatory Shear Rheometrymentioning

confidence: 99%

“…Therefore, one cannot completely prevent inertia from affecting the measured viscoelastic properties of fluids [40]. Inertia leads to a non-uniform velocity gradient and consequently alters the stress response [41] which was revealed to further reduce the apparent elasticity of a viscoelastic fluid [42]. For MR fluids in the pre-yield state, inertial effects are negligible due to the imposed restriction on the movement of solid particles, however, inertia can play a significant role in the post-yield state.…”

Section: Introductionmentioning

confidence: 99%

Direct numerical simulation of magnetic particles suspended in a Newtonian fluid exhibiting finite inertia under SAOS

Hashemi

Manzari

Fatehi

2018

Journal of Non-Newtonian Fluid Mechanics

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A direct numerical simulation approach is utilized to understand the oscillatory shear rheology of a confined suspension of magnetic chains formed by paramagnetic circular cylinders under the influence of an external magnetic field. The common assumption of gap-spanning chains made in the literature is relaxed in this work, so that a fully suspended (periodic) array of magnetic chains is formed. In this sense, the effective rheological parameters are only influenced through a layer of fluid adjacent to the walls. All tests are conducted at very low but finite particle Reynolds numbers, and typical inertial effects are discussed. The main aim of the present study is to investigate the apparent viscoelasticity of the system as a function of the external magnetic field and frequency of the input strain. This work concentrates on cases with large blockage ratio in order to have pronounced viscoelastic behaviours.

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Effects of instrument and fluid inertia in oscillatory shear in rotational rheometers

Cited by 47 publications

References 18 publications

Bulk rheometry at high frequencies: a review of experimental approaches

Bulk rheometry at high frequencies: a review of experimental approaches

Competing Timescales Lead to Oscillations in Shear-Thickening Suspensions

Direct numerical simulation of magnetic particles suspended in a Newtonian fluid exhibiting finite inertia under SAOS

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