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Pressure and shear responses in brain injury models
Technical Paper
2001-06-0197
Sector:
Language:
English
Abstract
Finite element (FE) models of the brain are regularly used to
investigate brain injury mechanisms. Validation of these models
against cadaver impacts is usually restricted to intracranial
pressure data. However, the low shear modulus of neural tissue
means that injurious strains result from shear deformations. We
show that brain injury models that are validated for pressure alone
can give a wide range of shear responses to the same impact.
Holbourn's arguments on the harmlessness of pressure are
extended by introducing separate wave equations for pressure and
shear, derived from the Helmholtz vector decomposition. Two
idealized models of traumatic brain injury are used to show that
there is no one-to-one relation between pressure and shear in head
impacts lasting a few milliseconds. The first is an analytical
model of wave propagation in the brain under the action of local
skull bending. The second is a strain-validated FE representation
of the coronal plane of the human head under rotational
acceleration.
As there is no one-to-one relation between dilatation and
distortion in typical head impacts, it is not acceptable to
validate FE models for pressure and then use them to predict
injury.