We report the first-ever complete measurement of MAOStress material functions, which reveal that stress can be more fundamental than strain or strain rate for understanding linearity limits as a function of Deborah number. The material used is a canonical viscoelastic liquid with a single dominant relaxation time: polyvinyl alcohol (PVA) polymer solution cross-linked with tetrahydroborate (Borax) solution. We outline experimental limit lines and their dependence on geometry and test conditions. These MAOStress measurements enable us to observe the frequency dependence of the weakly nonlinear deviation as a function of stress amplitude. The observed features of MAOStress material functions are distinctly simpler than MAOStrain, where the frequency dependence is much more dramatic. The strain-stiffening transient network model was used to derive a model-informed normalization of the nonlinear material functions that accounts for their scaling with linear material properties. Moreover, we compare the frequency dependence of the critical stress, strain, and strain-rate for the linearity limit, which are rigorously computed from the MAOStress and MAOStrain material functions. While critical strain and strain-rate change by orders of magnitude throughout the Deborah number range, critical stress changes by a factor of about 2, showing that stress is a more fundamental measure of nonlinearity strength. This work extends the experimental accessibility of the weakly nonlinear regime to stress-controlled instruments and deformations, which reveal material physics beyond linear viscoelasticity but at conditions that are accessible to theory and detailed simulation.
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September 2024
Research Article|
August 28 2024
Stress-controlled medium-amplitude oscillatory shear (MAOStress) of PVA–Borax
Nabil Ramlawi
;
Nabil Ramlawi
1
Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign
, Urbana, Illinois 61801
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Mohammad Tanver Hossain
;
Mohammad Tanver Hossain
1
Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign
, Urbana, Illinois 61801
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Abhishek Shetty
;
Abhishek Shetty
2
Rheology Division, Anton Paar USA
, 10215 Timber Ridge Dr, Ashland, Virginia 23005
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Randy H. Ewoldt
Randy H. Ewoldt
a)
1
Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign
, Urbana, Illinois 618013
Materials Research Laboratory, University of Illinois Urbana-Champaign
, Urbana, Illinois 61801a)Author to whom correspondence should be addressed; electronic mail: ewoldt@illinois.edu
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a)Author to whom correspondence should be addressed; electronic mail: ewoldt@illinois.edu
J. Rheol. 68, 741–763 (2024)
Article history
Received:
February 26 2024
Accepted:
June 21 2024
Citation
Nabil Ramlawi, Mohammad Tanver Hossain, Abhishek Shetty, Randy H. Ewoldt; Stress-controlled medium-amplitude oscillatory shear (MAOStress) of PVA–Borax. J. Rheol. 1 September 2024; 68 (5): 741–763. https://doi.org/10.1122/8.0000843
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