Path of a solid inclusion embedded in a soft matrix subject to finger palpation

Abstract

A solid inclusion is embedded in a soft matrix supported by a rigid substrate. To simulate finger palpation, a spherical indenter exerts a vertical load on the matrix surface, followed by a lateral motion. A deep inclusion first rises close to the surface, dives under the indenter, and emerges from the leeside of the traversing indenter. The inclusion trajectory is essentially symmetric about the axis where the inclusion lies. A shallow inclusion is first pushed sideways, but an instability causes it to jump spontaneously to the rear following an asymmetric path. Such instability is a specific feature in hyperelastic materials.