Local Micromorphic Non-affine Anisotropy with Applications to Biological Tissue
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There has been increasing experimental evidence of non-affine elastic deformation mechanisms in biological soft tissues. These observations call for novel constitutive models which are able to describe the dominant underlying micro-structural kinematic aspects, in particular relative motion characteristics of fibrous constituents and the implication to oriented material behaviour. This contribution proposes a flexible and modular continuum framework based on a micromorphic continuum encompassing bulk and fibre phases, respectively. In addition to the displacement field, it features so-called director fields which can independently deform and intrinsically carry orientational information. Accordingly, the fibrous constituents can be naturally associated with the micromorphic directors and their non-affine motion within the bulk material can be efficiently captured. Furthermore, constitutive relations can be formulated based on kinematic quantities specifically linked to the material response of the bulk continuum, the fibres and their mutual interactions. Associated stress quantities are naturally derived from a micromorphic variational principle featuring dedicated governing equations for displacement field and a tangent map describing the deformation of the director fields which are treated as tangent vectors. This aspect of the framework is crucial for the truly non-affine kinematics description within the elastic deformation regime. In contrast to conventional micromorphic approaches, any non-local higher-order material behaviour is excluded, thus significantly reducing the number of material parameters to a range typically found in related classical approaches. In the context of biological soft tissue modelling, the applicability of the formulation is studied for tension-inflation experiments of carotid arteries [1].