In this study, the large strain dynamic behaviour of brain tissue and silicone gel, a brain substitute material used in mechanical head models, was compared. The non-linear shear strain behaviour was characterised 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 behaviour was nearly strain independent. Silicone gel behaved as a linear viscoelastic solid for all strains tested (up to 50%) and frequencies up to 461 Hertz. As a result, the large strain time dependent behaviour of both materials could be derived for frequencies up to 1000 Hz from small strain oscillatory experiments and application of Time Temperature Superpositioning (TTS). It was concluded that silicone gel material parameters are in the same range as those of brain issue. 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. (A)
Abstract