Differences between stress and strain control in the non-linear behavior of complex fluids

Läuger, Jörg; Stettin, H.

doi:10.1007/s00397-010-0450-0

Cited by 113 publications

(62 citation statements)

References 20 publications

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“…While the ARG2 can control the strain on the sample through the use of a feedback loop, for some very non-linear fluids (e.g. yield stress fluids) controlled stress instruments may fail to impose a perfectly sinusoidal deformation, resulting in higher harmonic contributions to the periodic deformation (Läuger and Stettin, 2010). For all of the present LAOS experiments, the power spectrum of the raw displacement signal from the ARG2 rheometer γ(t) was analyzed to determine the relative magnitude of the next highest harmonic contribution to the strain field.…”

Section: Micellar Fluid -Cpyclmentioning

confidence: 99%

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

et al. 2012

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We explore the behavior of a wormlike micellar solution under both steady and large amplitude oscillatory shear (LAOS) in a cone-plate geometry through simultaneous bulk rheometry and localized velocimetric measurements. First, particle image velocimetry is used to show that the shear banded profiles observed in steady shear are in qualitative agreement with previous results for flow in the cone-plate geometry. Then under LAOS, we observe the onset of shear-banded flow in the fluid as it is progressively deformed into the non-linear regime -this onset closely coincides with the appearance of higher harmonics in the periodic stress signal measured by the rheometer. These harmonics are quantified using the higher order elastic and viscous Chebyshev coefficients e n and v n , which are shown to grow as the banding behavior becomes more pronounced. The high resolution of the velocimetric imaging system enables spatiotemporal variations in the structure of the banded flow to be observed in great detail. Specifically, we observe that at large strain amplitudes (γ 0 ≥ 1) the fluid exhibits a 3-banded velocity profile with a high shear rate band located in-between two lower shear rate bands adjacent to each wall. This band persists over the full cycle of the oscillation, resulting in no phase lag being observed between the appearance of the band and the driving strain amplitude. In addition to the kinematic measurements of shear banding, the methods used to prevent wall slip and edge irregularities are discussed in detail, and these methods are shown to have a measurable effect on the stability boundaries of the shear banded flow.

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Section: Micellar Fluid -Cpyclmentioning

confidence: 99%

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

et al. 2012

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“…27 This includes the minimum-stress elastic compliance J M and the large-stress elastic compliance J L (see Fig. 1) which can be calculated from Lissajous-Bowditch curves of strain versus stress.…”

Section: Analysis Of Laostress Waveformsmentioning

confidence: 99%

“…LAOStress has been previously used to characterise the nonlinear rheology of polymer solutions and gels. 26,27 In the present study, we investigate the suitability of LAOStress for studying the nonlinear behaviour of fibrin clots up to the point of macroscopic fracture. Furthermore, we combine alternating LAOStress and linear viscoelastic measurements in order to study reversible and irreversible changes in fibrin clot microstructure as a consequence of different levels of stress.…”

Section: Introductionmentioning

confidence: 99%

The application of large amplitude oscillatory stress in a study of fully formed fibrin clots

et al. 2017

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The suitability of controlled stress large amplitude oscillatory shear (LAOStress) for the characterisation of the nonlinear viscoelastic properties of fully formed fibrin clots is investigated. Capturing the rich nonlinear viscoelastic behaviour of the fibrin network is important for understanding the structural behaviour of clots formed in blood vessels which are exposed to a wide range of shear stresses. We report, for the first time, that artefacts due to ringing exist in both the sample stress and strain waveforms of a LAOStress measurement which will lead to errors in the calculation of nonlinear viscoelastic properties. The process of smoothing the waveforms eliminates these artefacts whilst retaining essential rheological information. Furthermore, we demonstrate the potential of LAOStress for characterising the nonlinear viscoelastic properties of fibrin clots in response to incremental increases of applied stress up to the point of fracture. Alternating LAOStress and small amplitude oscillatory shear measurements provide detailed information of reversible and irreversible structural changes of the fibrin clot as a consequence of elevated levels of stress. We relate these findings to previous studies involving large scale deformations of fibrin clots. The LAOStress technique may provide useful information to help understand why some blood clots formed in vessels are stable (such as in deep vein thrombosis) and others break off (leading to a life threatening pulmonary embolism).

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“…For the study on thixotropic viscosity, step-loading is widely used which include (1) step shear stress and (2) step shear rate conditions. In a rheometer, shear rate is imposed by setting the rotational speeds of the measuring system [34] . So imposed shear rate condition can be analyzed as the imposed velocity condition.…”

Section: Problem Descriptionmentioning

confidence: 99%

Transient stage comparison of Couette flow under step shear stress and step velocity boundary conditions

Chen

Liu

Zhang

et al. 2016

International Communications in Heat and Mass Transfer

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Couette flow has been widely used in many industrial and research processes, such as viscosity measurement. For the study on thixotropic viscosity, step-loading, which includes (1) step shear stress and (2) step velocity conditions, is widely used. Transient stages of Couette flow under both step wall shear stress and step wall velocity conditions were investigated. The relative coefficient of viscosity was proposed to reflect the transient process. Relative coefficients of viscosity, dimensionless velocities and dimensionless development times were derived and calculated numerically. This article quantifies the relative coefficients of viscosity as functions of dimensionless time and step ratios when the boundary is subjected to step changes. As expected, in the absence of step changes, the expressions reduce to being functions of dimensionless time.When step wall shear stresses are imposed, the relative coefficients of viscosity changes from the values of the step ratios to their steady-state value of 1. but With step-increasing wall velocities, the relative coefficients of viscosity decrease from positive infinity to 1. The relative coefficients of viscosity increase from negative infinity to 1 under the step-decreasing wall velocity condition.During the very initial stage, the relative coefficients of viscosity under step wall velocity conditions is further from 1 than the one under step wall shear stress conditions but the former reaches 1 faster. Dimensionless development times grow with the step ratio under the step-rising conditions and approaches the constant value of 1.785 under the step wall shear stress condition, and 0.537 under the step wall velocity condition respectively. The development times under the imposed step wall shear stress conditions are always larger than the same under the imposed step wall velocity conditions.

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Differences between stress and strain control in the non-linear behavior of complex fluids

Cited by 113 publications

References 20 publications

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

The application of large amplitude oscillatory stress in a study of fully formed fibrin clots

Transient stage comparison of Couette flow under step shear stress and step velocity boundary conditions

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