Author/Authors :
Hosseini-Farid, M Department of Mechanical Engineering - North Dakota State University - Fargo, USA , Rezaei, A Department of Physiology and Biomedical Engineering - Mayo Clinic - Rochester, USA , Eslaminejad, A Department of Mechanical Engineering - North Dakota State University - Fargo, USA , Ramzanpour, M Department of Mechanical Engineering - North Dakota State University - Fargo, USA , Ziejewski, M Department of Mechanical Engineering - North Dakota State University - Fargo, USA , Karami, G Department of Mechanical Engineering - North Dakota State University - Fargo, USA
Abstract :
Human brain and brainstem tissues have viscoelastic characteristics and
their behaviors are functions of strains as well as strain rates. Determination of the
equilibrium and instantaneous stresses happening at low and high strain rates provides
insights into a better understanding of the behavior of such tissues. In this manuscript,
we present the results of a series of stress relaxation tests at 6 dierent values of strains
conducted on porcine brainstem tissue samples to indirectly measure the equilibrium and
instantaneous stresses. The equilibrium stresses at low strain rates were measured from
long-term responses to the stress relaxation test. The instantaneous stresses at high strain
rates were determined using Quasi-Linear Viscoelasticity (QLV) theory at 6 strains. The
results showed that the instantaneous stresses were much larger (almost 11 times) than
the equilibrium stresses across all the strains. It was concluded that the instantaneous
response could reasonably be estimated from the long-term response, which could easily
be measured in an experimental manner. The experimental results also showed that the
reduced relaxation moduli, estimated by the QLV theory, varied for the 6 strains tested.
Keywords :
Quasi-linear viscoelasticity theory , Brain response , Brainstem tissue , Stress relaxation test , Instantaneous response , Long-term stress
