We investigate inertial effects in torsional Kolsky bar tests on
nearly incompressible, soft materials. The results are relevant for
materials with instantaneous elastic shear modulus on the order of
–kPa
and density on the order of water. Examples include brain tissue and many
other soft tissues and tissue surrogates. We have conducted one- and
three-dimensional analyses and simulations to understand the stress and
strain states that exist in these materials in a torsional Kolsky bar test. We
demonstrate that the short loading pulses typically used for high strain-rate (e.g.,
s)
tests do not allow the softer specimens to “ring-up” to uniform stress and strain
states and that consequently the shear stress versus shear strain data reported in the
literature are erroneous. We also show that normal stress components, which are
present even in quasistatic torsion of nonlinear elastic materials, can be amplified in
dynamic torsion tests on soft materials.
Keywords
torsion, Kolsky bar, soft materials, incompressible,
Mooney–Rivlin
