The M Waves Emitted by an Expanding Phase Boundary Create a “Lacuna”

The M waves introduced by Burridge and Willis (1969, “The Self-Similar Problem of the Expanding Crack in an Anisotropic Solid,” Math. Proc. Cambridge Philos. Soc., 66(2), pp. 443–468) are emitted by the surface of a self-similarly expanding elliptical crack, and they give Rayleigh waves at the corresponding crack speed. In the analysis for the self-similarly expanding spherical inclusion with phase change (dynamic Eshelby problem), the M waves are related to the waves obtained on the basis of the dynamic Green’s function containing the contribution from the latest wavelets emitted by the expanding boundary of phase discontinuity, and they satisfy the Hadamard jump conditions for compatibility and linear momentum across the moving phase boundary of discontinuity. In the interior of the expanding inclusion, they create a “lacuna” with zero particle velocity by canceling the effect of the P and S. It is shown that the “lacuna” and Eshelby properties are also valid for a Newtonian fluid undergoing phase change in a self-similarly expanding ellipsoidal region of a fluid with different viscosity.

Properties of the self-similarly expanding Eshelby inclusions and application to the dynamic “Hill Jump Conditions”

For a self-similarly subsonically dynamically expanding Eshelby inclusion, we show by an analytic argument (based on the analyticity of the coefficients of the ensuing elliptic system and the Cauchy–Kowalevska theorem) that the particle velocity vanishes in the whole interior domain of the expanding inclusion. Since the acceleration term is thus zero in the interior domain in the Navier equations of elastodynamics, this reduces to an Eshelby problem. The classical Hill jump conditions across the interface of a region with transformation strain are expanded here to dynamics when the interface is moving with inertia satisfying the Hadamard jump conditions. The validity of the Eshelby property and the determination of the constrained strain from the dynamic Eshelby tensor in the interior domain allow one to fully determine from the Hill jump conditions the stress across the moving phase boundary of a self-similarly expanding ellipsoidal Eshelby inhomogeneous inclusion. The driving force can then be obtained. Self-similar motion grasps the early response of the system.

The dynamic generalization of the Eshelby inclusion problem and its static limit

The dynamic generalization of the celebrated Eshelby inclusion with transformation strain is the (subsonically) self-similarly expanding ellipsoidal inclusion starting from the zero dimension. The solution of the governing system of partial differential equations was obtained recently by Ni & Markenscoff (In press. J. Mech. Phys. Solids ( doi:10.1016/j.jmps.2016.02.025 )) on the basis of the Radon transformation, while here an alternative method is presented. In the self-similarly expanding motion, the Eshelby property of constant constrained strain is valid in the interior domain of the expanding ellipsoid where the particle velocity vanishes (lacuna). The dynamic Eshelby tensor is obtained in integral form. From it, the static Eshelby tensor is obtained by a limiting procedure, as the axes' expansion velocities tend to zero and time to infinity, while their product is equal to the length of the static axis. This makes the Eshelby problem the limit of its dynamic generalization.