Periodic perturbation of a flat surface

Suppose that, in its reference configuration, an elastic material has a nominally flat surface that is free of applied traction. If the solid is then stressed, is the flat surface shape stable under perturbations in shape These perturbations are changes in the reference configuration both the material that are achieved by rearrangement of mass, and are not a consequence of deformation of the material. The question is addressed in this section for the case of periodic perturbation of surface shape. Perturbations of very small amplitude are considered first, and this discussion is followed by consideration of higher order effects and substrate stiffness. Cases of nonperiodic surface perturbations are considered in the following section. 

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