Research

Summary

My research interests lie broadly in the field of nonlinear rheology. Past research projects have ranged from experimental studies of shear-banding fluids to development of nonlinear constitutive models. A few examples are given below:

Flow Visualization of Material Instabilities

Non-Newtonian fluids often exhibit material instabilities, e.g. shear banding. Flow vizualization tools can be used to study and understand these instabilities, and gain insight into microstructural evolution during shearing/deformation.
(a) RheoPIV device for measuring flow instabilities in a cone-plate rheometer. (b-c) Shear banded flows in the 1-2 plane under steady and oscillatory shear for a wormlike micellar solution (CPyCl) (d) Birefringent images in the 1-3 plane of a model crude oil undergoing shear (image taken using a Linkam shear cell)

Large Amplitude Oscillatory Shear

Large Amplitude Oscillatory Shear (LAOS) is a useful tool for characterizing nonlinear rheology of soft materials. We have utilized stress controlled techniques (LAOStress) to probe the response of yield stress fluids.
(a) Pipkin space plot of a Carbopol microgel undergoing LAOStress. An analytical framework is applied in order to obtain the unique material "fingerprint" in (b)

Constitutive Modeling of Yield Stress Fluids

Yield stress fluids exhibit a transition from solid-like to liquid-like behavior above a critical stress (the yield stress). This behavior can be modeled using a strain decomposition and hardening mechanisms from plasticity. Thixotropy also often arises in these materials, requiring more sophisticated constitutive models
(a) Fit of the kinematic hardening (KH) model (red) to the response of the Carbopol microgel to LAOStress (blue). (b) Shear rejuvenation and aging causing thixotropic behavior in a model crude oil (c) Implementing isotropic hardening into the KH model gives thixotropic behavior, with different static and dynamic yield stresses