Peter B. Winter
Postdoctoral Fellow
Chemical & Biological Engineering
2145 Sheridan Road (Room E136)
Evanston, IL 60208, US
Large amplitude oscillatory shear of pseudoplastic and elastoviscoplastic materials
Rheologica Acta 49, 191-212 (2010)
Abstract
We explore the utility of strain-controlled
large amplitude oscillatory shear (LAOS) deformation
for identifying and characterizing apparent yield stress
responses in elastoviscoplastic materials. Our approach
emphasizes the visual representation of the LAOS
stress response within the framework of Lissajous
curves with strain, strain rate, and stress as the coordinate
axes, in conjunction with quantitative analysis of
the corresponding limit cycle behavior. This approach
enables us to explore how the material properties
characterizing the yielding response depend on both
strain amplitude and frequency of deformation. Canonical
constitutive models (including the purely viscous
Carreau model and the elastic Bingham model) are
used to illustrate the characteristic features of pseudoplastic
and elastoplastic material responses under large
amplitude oscillatory shear. A new parameter, the perfect
plastic dissipation ratio, is introduced for uniquely
identifying plastic behavior. Experimental results are
presented for two complex fluids, a pseudoplastic
shear-thinning xanthan gum solution and an elastoviscoplastic
invert-emulsion drilling fluid. The LAOS test
protocols and the associated material measures provide a rheological fingerprint of the yielding behavior of a
complex fluid that can be compactly represented within
the domain of a Pipkin diagram defined by the amplitude
and timescale of deformation.