Paper Number
FI20 Keynote My Program
Session
Flow-Induced Instabilities and Non-Newtonian Fluids
Title
The mechanism of incomplete stress relaxation in brittle yield stress fluids
Presentation Date and Time
October 21, 2025 (Tuesday) 10:50
Track / Room
Track 7 / Sweeney Ballroom D
Authors
- Lee, Jiye (University of Illinois Urbana-Champaign)
- Thompson, Gunnar B. (University of Illinois Urbana-Champaign)
- Harley, Brendan A. (University of Illinois Urbana-Champaign)
- Rogers, Simon A. (University of Illinois Urbana-Champaign, Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Jiye Lee, Gunnar B. Thompson, Brendan A. Harley and Simon A. Rogers
Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, Urbana, IL 61801
Speaker / Presenter
Rogers, Simon A.
Keywords
experimental methods; additve manufacturing; advanced manufacturing; applied rheology; biomaterials; colloids; emulsions; foams; gels; geoscience; industrial applications; networks; non-Newtonian fluids; particualte systems; selft-assemblies; suspensions
Text of Abstract
When the flow of yield stress fluids is stopped, the stress relaxes over some timescale but is eventually arrested, leading to finite residual stresses that are important in additive manufacturing, geological flows, foods, and consumer products. We study this phenomenon from the perspective of recovery rheology, where stress relaxation is seen to be an exchange between recoverable and unrecoverable deformation under conditions of fixed total strain. We combine traditional and recovery rheology experiments with predictions of the KDR model with brittility, which describes the rheology of yield stress fluids in a continuum manner with a rate-dependent relaxation time. In this model, plastic deformation is enhanced by rapid acquisition of recoverable strain scaled by a factor called the brittility, which allows for a sufficient exchange of recoverable strain for unrecoverable strain. The rate that the materials responds to, which we call the effective shear rate, can therefore be different from the total applied shear rate. It is this difference that allows for relaxation to take place, as the effective shear rate is small but finite even when the total shear rate is zero. The rate-dependence of the relaxation time allows for the construction of a relaxation master curve using shift factors that relate the initial shear rate to a reference shear rate. The results of our study have implications for numerous applications as well as understanding phenomena such as memory formation and retrieval and thixotropy.