Paper Number
SG17 

Session
Self-assembled Systems, Gels and Liquid Crystals

Title
From non-linear rheology to the onset of macroscopic failure: An integral constitutive model for biopolymer gels

Presentation Date and Time
February 14, 2017 (Tuesday) 10:50

Track / Room
Track 3 / White Ibis

Authors (Click on name to view author profile)

1. Keshavarz, Bavand (MIT, Mechanical Engineering)
2. Divoux, Thibaut (Centre de Recherche Paul Pascal)
3. Manneville, Sébastien (Ecole Normale Supérieure de Lyon, Laboratoire de Physique)
4. McKinley, Gareth H. (Massachusetts Institute of Technology, Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Bavand Keshavarz¹, Thibaut Divoux², Sébastien Manneville³, and Gareth H. McKinley^1
1Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; ²Centre de Recherche Paul Pascal, Pessac, France; ³Laboratoire de Physique, Ecole Normale Supérieure de Lyon, Lyon, France

Speaker / Presenter 
Keshavarz, Bavand

Text of Abstract
We explore the nonlinear rheology of a class of biopolymer gels (namely acid-induced protein gels), which display a multiscale microstructure that is responsible for their solid-like properties. These soft viscoelastic materials exhibit a generic nonlinear mechanical response characterized by pronounced stress- or strain-stiffening prior to irreversible damage and failure, most often through macroscopic fractures. Using a series of acid-induced casein gels we show that the nonlinear viscoelastic properties of these hydrogels can be described in terms of a “damping function” which describes the gel mechanical response quantitatively up to the onset of macroscopic failure. Using a nonlinear integral constitutive equation built upon the experimentally-measured damping function, in conjunction with a power-law linear viscoelastic response, we derive the form of the stress growth in the gel following the start up of steady shear. We further couple the shear stress response with Bailey’s durability criteria for brittle solids in order to predict the critical values of the stress $\sigma_c$ and strain $\gamma_c$ for failure of the gel, and how they scale with the applied shear rate. This provides a generalized failure criterion for biopolymer gels over a range of different deformation histories. Finally, we apply this framework to fatigue tests and provide qualitative predictions for the fracture parameters associated with these oscillatory tests.