Wednesday  |  Carnegie III  |  09:40 AM–10:00 AM

#13360, Nonlinear Viscoelasticity for Polyampholyte Hydrogels

Most constitutive models for viscoelastic solid adopt linear viscoelastic assumption, where the relaxation function is independent of stress and strain history and depends only on time. However, molecular physics tells us that bond breaking and healing kinetics should be affected by stress or strain. For a nonlinear viscoelastic solid, we expect that its bond will break faster at the place where the stress/strain is higher. As a result, the stress at those places will drops faster. Based on those theoretical analysis, we expect to see that the strain field near the crack tip will change during the relaxation test. In this work, we first observe this phenomenon directly by doing relaxation tests for polyampholyte hydrogels (PA gels). Digital image correlation (DIC) is used for tracking the deformation of PA gel samples. Uniaxial tension tests are conducted for rectangular, precut and bell-like samples. The nonlinear viscoelastic behavior of PA gels is almost the same as the prediction of our PA nonlinear viscoelastic constitutive model. We further study the coupled behaviors of nonlinear viscoelasticity and hyperelasticity. It turns out that hyperelasticity will suppress nonlinear viscoelasticity at some points and lead to an opposite behavior, which can be explained almost perfectly by our PA constitutive model with chemical crosslinkers as well.

Jikun Wang   Cornell University
Bangguo Zuo   Cornell University
Chung-Yuen Hui   Cornell University
Alan Zehnder   Cornell University