Apparent Negative Stiffness Induced by Constriction

Lateral constriction (transverse elastic constraint) of elastic rod controls its apparent (longitudinal) stiffness and can even make it negative. (The total energy of system rod + constriction device remains positive.) The apparent stiffness depends upon moduli of the rod material and the constriction modulus relating lateral normal stress and strain components. Apparent negative stiffness can arrest wave propagation along the rod. This opens a way to design hybrid materials consisting of a stiff matrix and parallel lubricated elastic rods. The matrix is constricting the rods making them exhibit negative stiffness and thus ensuring elevated sound or vibration isolation of the hybrid. A mechanism of controlling the constriction modulus by lateral compression is proposed.