Identification of linear viscoelastic constitutive models

Accelerations induce in the brain mechanical stresses that may explain the loss of consciousness feared by fighter pilots. In this study, the brain is modelled as a multi-domain structure and a finite element method is used t o identify the constitutive law parameters of each domain and then to analy se the stress level in the brain. The loading and observed strain rates ind uced by hypergravity seem to indicate a quasi-static behaviour of the brain structure. A general procedure has been developed to characterise the beha viour of a structure including several domains. Each of them is assumed to be isotropic and homogeneous with a linear viscoelastic behaviour. These co nstitutive laws were identified using only the displacements of several nod es on the envelope discarding the displacements between domains at the inte raction surfaces. These interfaces may be buried inside the structure and n ot connected with the external surface. Two validation examples are propose d to show the reliability and effectiveness of the method. (C) 2000 Elsevie r Science Ltd. All rights reserved.