Thermo-viscoplasticity of carbon black-reinforced thermoplastic elastomers

Observations are reported on carbon black–filled thermoplastic elastomer (TPE) in uniaxial loading–unloading tensile tests with various strain rates (ranging from $7\times {10}^{-4}$ to $1\times {10}^{-1}{\text{s}}^{-1}$) at temperatures in the interval from 25 to 90 °C. A constitutive model is derived for the viscoplastic response of a TPE composite at three-dimensional deformations with finite strains. The stress–strain relations involve six adjustable parameters that are found by fitting the experimental data. It is shown that the model correctly describes the observations, and its parameters are affected by temperature and strain rate in a physically plausible way.     

Extreme softness of brain matter in simple shear

We show that porcine brain matter can be modelled accurately as a very soft rubber-like material using the Mooney–Rivlin strain energy function, up to strains as high as 60%. This result followed from simple shear experiments performed on small rectangular fresh samples (2.5 cm³ and 1.1 cm³) at quasi-static strain rates. They revealed a linear shear stress–shear strain relationship $(R^2>0.97)$, characteristic of Mooney–Rivlin materials at large strains. We found that porcine brain matter is about 30 times less resistant to shear forces than a silicone gel. We also verified experimentally that brain matter exhibits the positive Poynting effect of non-linear elasticity, and numerically that the stress and strain fields remain mostly homogeneous throughout the thickness of the samples in simple shear.