On two models of arbitrarily curved three-dimensional thin interphases in elasticity

In boundary value problems involving thin interphases, it is often desirable to have a model of an interphase which makes possible to solve for the fields in the adjacent media without having to solve for the fields in it. This is usually achieved in the literature by replacing the interphase by a geometrical surface with appropriately designed “imperfect interface” conditions on it. In the present study, carried out in the setting of elasticity, another option is explored: the geometry of the interphase is left intact, and conditions are devised for the displacements and tractions pertaining to the media adjacent to the interphase and evaluated at both sides of it such that they will simulate the presence of the interphase. Those conditions do not involve the fields within the interphase, yet they depend on its material properties and on those of the adjacent media as well, and make possible to solve for the fields in the adjacent media without having to solve for the fields in the interphase. The formulation is given in a parallel orthogonal curvilinear coordinate system suitable for the modeling arbitrarily curved three-dimensional interphases of constant thickness. Both types of the above described interphase models are tested in the setting of a coated infinite fiber embedded in a matrix which is subjected to an anti-plane shear loading and an in-plane transverse shear loading at infinity, and their predictions are compared with the exact solutions for the fields in the three-phase configuration consisting of the interphase and its adjacent media. The model in which the interphase geometry is left intact is observed to perform generally better than the one in which the interphase is replaced by an interface.