Acoustomechanics of semicrystalline polymers

We develop an acoustomechanical theory for semicrystalline polymers and demonstrate that acoustic radiation force is capable of causing giant deformation in these materials. When a polymer layer is subjected to combined tensile mechanical force in plane and acoustic force (sound pressure) through thickness, it becomes initially homogeneously thin but soon inhomogeneous when the two forces reach critical conditions. Critical conditions for such acoustomechanical instability are theoretically determined based on the J(2)-deformation theory. We demonstrate that pull-in instability can be acoustically triggered even if the in-plane mechanical force is fixed. Bifurcation in the critical condition for acoustomechanical instability occurs when the polymer exhibits sufficiently large hardening. The findings of this study enable reliability design of novel acoustic actuated devices. (C) 2016 The Authors. Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics.