On Modeling Stress Softening in
Highly Deformable Biomaterials

LUIS DORFMANN
Tufts University


Abstract:
The lecture begins with an overview of experimental results that characterize the elastic behavior of deformable
solids. This is followed by illustrations of how the behavior departs from the purely elastic; we examine stress
softening associated with the Mullins effect, and the different degrees of softening for different materials are
highlighted. The main part of the seminar focuses on recent experimental and theoretical work on the mechanical
properties of muscles in a soft-bodied arthropod under both passive and stimulated conditions. In particular, we
examine the ventral interior lateral muscle of the tobacco hornworm caterpillar, Manduca sexta, and show that its
response is qualitatively similar to the behavior of particle reinforced rubber. Both materials are capable of large
nonlinear elastic deformations, show a hysteretic behavior and display stress softening during the first few cycles
of repeated loading. We summarize the basic equations for transverse isotropic pseudo-elastic materials, first for
general deformations and then for the appropriate uniaxial specialization. Finally, a very brief outline will be given
on the most recent theoretical work concerning the interactions of mechanical and magnetic effects in magneto-
sensitive solids.