Danila A. Prikazchikov

A long-wave model for the surface elastic wave in a coated half-space

The paper deals with the three-dimensional problem in linear isotropic elasticity for a coated half-space. The coating is modelled via the effective boundary conditions on the surface of the substrate initially established on the basis of an ad hoc approach and justified in the paper at a long-wave limit. An explicit model is derived for the surface wave using the perturbation technique, along with the theory of harmonic functions and Radon transform. The model consists of three-dimensional ‘quasi-static’ elliptic equations over the interior subject to the boundary conditions on the surface which involve relations expressing wave potentials through each other as well as a two-dimensional hyperbolic equation singularly perturbed by a pseudo-differential (or integro-differential) operator. The latter equation governs dispersive surface wave propagation, whereas the elliptic equations describe spatial decay of displacements and stresses. As an illustration, the dynamic response is calculated for impulse and moving surface loads. The explicit analytical solutions obtained for these cases may be used for the non-destructive testing of the thickness of the coating and the elastic moduli of the substrate.

Some comments on the dynamic properties of anisotropic and strongly anisotropic pre-stressed elastic solids

The effect of pre-stress on the propagation of small amplitude waves in an incompressible, transversely isotropic elastic solid is discussed in respect of the most general appropriate strain energy function. A simple set of sufficient conditions is noted which ensures that two real wave speeds exist for all directions of propagation. In the case of bi-axial primary deformations, and for propagation within each principal plane of the homogeneous primary deformation, the propagation condition is factorised and conditions which are both necessary and sufficient to ensure the existence of two real wave speeds are established. The paper also includes some graphical illustrations of the associated slowness and wave surfaces and discussion of the strongly anisotropic case, for which the extensional modulus along the preferred fibre direction is much larger than other material parameters.

The near-resonant regimes of a moving load in a three-dimensional problem for a coated elastic half-space

This paper deals with the three-dimensional analysis of the near-resonant regimes of a point load, moving steadily along the surface of a coated elastic half-space. The approach developed relies on a specialized hyperbolic–elliptic formulation for the wave field, established earlier by the authors. Straightforward integral solutions of the two-dimensional perturbed wave equation describing wave propagation along the surface are derived along with their far-field asymptotic expansions obtained using the uniform stationary phase method. Both sub-Rayleigh and super-Rayleigh cases are studied. It is shown that the singularities arising at the contour of the Mach cones typical of the super-Rayleigh case, are smoothed due to the dispersive effect of the coating.

Explicit Models for Surface, Interfacial and Edge Waves

We derive explicit asymptotic formulations for surface, interfacial and edge waves in elastic solids. The effects of mixed boundary conditions and layered structure are incorporated. A hyperbolic-elliptic duality of surface and interfacial waves is emphasized along with a parabolic-elliptic duality of the edge bending wave on a thin elastic plate. The validity of the model for the Rayleigh wave is illustrated by several moving load problems.

On three-dimensional edge waves in semi-infinite isotropic plates subject to mixed face boundary conditions

This paper is concerned with the propagation of three-dimensional waves localized near the edge of a semi-infinite elastic plate subject to mixed face boundary conditions. In the linear isotropic case it is shown that the problem is closely related to that of Rayleigh surface wave propagation along the free surface of the corresponding half-space. The cut-off frequencies of the analyzed edge waves coincide with the natural frequencies of the associated cross-sectional semi-infinite strip. It is also demonstrated that the eigenspectrum of a rectangular rod can be expressed in terms of the considered three-dimensional waves. The results are then generalized to a prestressed isotropic incompressible material. It is noted that the density of the edge wave spectrum is strongly influenced by the prestress. It is illustrated that the areas of negative group velocity may exist for large primary deformation. Long-wave asymptotic expansions in the vicinity of the cut-off frequencies are presented.

Buckling of a spherical shell under external pressure and inward concentrated load: Asymptotic solution

An asymptotic solution is suggested for a thin isotropic spherical shell subject to uniform external pressure and concentrated load. The pressure is the main load and a concentrated lateral load is considered as a perturbation that decreases buckling pressure. First, the post-buckling solution of the shell under uniform pressure is constructed. A known asymptotic result for large deflections is used for this purpose. In addition, an asymptotic approximation for small post-buckling deflections is obtained and matched with the solution for large deflections. The proposed solution is in good agreement with numerical results. An asymptotic formula is then derived, with the load-deflection diagrams analyzed for the case of combined load. Buckling load combinations are calculated as limiting points in the load-deflection diagrams. The sensitivity of the spherical shell to local perturbations under external pressure is analyzed. The suggested asymptotic result is validated by a finite element method using the ANSYS simulation software package.

The edge wave on an elastically supported Kirchhoff plate.

This Letter deals with an analysis of bending edge waves propagating along the free edge of a Kirchhoff plate supported by a Winkler foundation. The presence of a foundation leads to a non-zero cut-off frequency for this wave, along with a local minimum of the associated phase velocity. This minimum phase velocity corresponds to a critical speed of an edge moving load and is analogous to that in the classical 1D moving load problem for an elastically supported beam.

Edge bending wave on a thin elastic plate resting on a Winkler foundation

This paper is concerned with elucidation of the general properties of the bending edge wave in a thin linearly elastic plate that is supported by a Winkler foundation. A homogeneous wave of arbitrary profile is considered, and represented in terms of a single harmonic function. This serves as the basis for derivation of an explicit asymptotic model, containing an elliptic equation governing the decay away from the edge, together with a parabolic equation at the edge, corresponding to beam-like behaviour. The model extracts the contribution of the edge wave from the overall dynamic response of the plate, providing significant simplification for analysis of the localized near-edge wave field.

Adhesive contact problems for a thin elastic layer: Asymptotic analysis and the JKR theory

Contact problems for a thin compressible elastic layer attached to a rigid support are studied. Assuming that the thickness of the layer is much less than the characteristic dimension of the contact area, a direct derivation of asymptotic relations for displacements and stress is presented. The proposed approach is compared with other published approaches. The cases are established when the leading-order approximation to the non-adhesive contact problems is equivalent to contact problem for a Winkler–Fuss elastic foundation. For this elastic foundation, the axisymmetric adhesive contact is studied in the framework of the Johnson–Kendall–Roberts (JKR) theory. The JKR approach has been generalized to the case of the punch shape being described by an arbitrary blunt axisymmetric indenter. Connections of the results obtained to problems of nanoindentation in the case that the indenter shape near the tip has some deviation from its nominal shape are discussed. For indenters whose shape is described by power-law functions, the explicit expressions are derived for the values of the pull-off force and for the corresponding critical contact radius.

On steady-state moving load problems for an elastic half-space

The steady-state regime of a moving load on an elastic half-plane is addressed. It is shown that the solution can be expressed through a single harmonic function, similarly to the known eigensolution for surface Rayleigh wave, thus reducing a vector problem in linear elasticity to a scalar one for the Laplace equation. Examples of steadily moving vertical force and punch are investigated, illustrating the proposed approach.