The Large Shear Strain Dynamic Behavior of In-Vitro Porcine Brain Tissue and a Silicone Gel Model Material 2000-01-SC17

The large strain dynamic behavior of brain tissue and silicone gel, a brain substitute material used in mechanical head models, was compared. The non-linear shear strain behavior was characterized using stress relaxation experiments. Brain tissue showed significant shear softening for strains above 1% (approximately 30% softening for shear strains up to 20%) while the time relaxation behavior was nearly strain independent. Silicone gel behaved as a linear viscoelastic solid for all strains tested (up to 50%) and frequencies up to 461 Hz. As a result, the large strain time dependent behavior of both materials could be derived for frequencies up to 1000 Hz from small strain oscillatory experiments and application of Time Temperature Superpositioning. It was concluded that silicone gel material parameters are in the same range as those of brain tissue. Nevertheless the brain tissue response will not be captured exactly due to increased viscous damping at high frequencies and the absence of shear softening in the silicone gel. For trend studies and benchmarking of numerical models the gel can be a good model material.