  A novel 3D micromechanical Finite Element Model (FEM) has been developed to
depict the Poynting effect in bi-phasic Representative volume element (RVE)
with axons embedded in surrounding extra-cellular matrix (ECM) for simulating
the brain white matter response under simple and pure shear. In the proposed 3D
FEM, nonlinear Ogden hyper-elastic material model describes axons and ECM
materials. The modeled bi-phasic RVEs have axons tied to surrounding matrix. In
this proof-of-concept (POC) FEM, three simple shear loading configurations and
a pure shear scenario were simulated. Root mean square deviation (RMSD) were
computed for stress and deformation response plots to depict role of axon-ECM
orientations & loading condition on the Poynting effect. Variations in normal
stresses (S11, S22, or S33) perpendicular to the shear plane emphasized role of
fiber-matrix interactions. At high strains, the stress-strain% plots also
indicated modest strain stiffening effects and bending stresses in purely
sheared axons.
