Elastodynamics of radially inhomogeneous spherically anisotropic elastic materials in the Stroh formalism

A method for solving elastodynamic problems in radially inhomogeneous elastic materials with spherical anisotropy is presented, i.e. materials having c(ijkl) = c(ijkl) (r) in a spherical coordinate system {r, theta, phi}. The time-harmonic displacement field u(r, theta, phi) is expanded in a separation of variables form with dependence on theta, phi described by vector spherical harmonics with r-dependent amplitudes. It is proved that such separation of variables solution is generally possible only if the spherical anisotropy is restricted to transverse isotropy (TI) with the principal axis in the radial direction, in which case the amplitudes are determined by a first-order ordinary differential system. Restricted forms of the displacement field, such as u(r, theta), admit this type of separation of variables solution for certain lower material symmetries. These results extend the Stroh formalism of elastodynamics in rectangular and cylindrical systems to spherical coordinates.