Electrically Tunable Composites by Making Positive Use of Instabilities
Charles Wojnar (Caltech), Dennis Kochmann (Califonia Institute of Techn.)
Instability in Solids and Structures
Mon 2:40 - 4:00
Barus-Holley 190
Phase instabilities in materials give rise to incrementally non-positive-definite elastic moduli (or “negative stiffness”). Recent stability analysis of composites containing negative-stiffness inclusions has shown such composites are indeed stable so long as the surrounding matrix material is sufficiently stiff and thick. Scientists have been able to manufacture composites with extreme viscoelastic moduli (i.e. extremely high stiffness and damping capacity) by making positive use of instabilities arising during temperature-induced phase transformations in ferroelectric inclusions. We will explain the experimental results by a stability analysis that reveals how stable extreme properties of composites can arise due to a resonant-like behavior of the composite. With a theoretical understanding of how negative-stiffness can lead to extreme effective properties of composites, we seek to construct novel composites whose viscoelastic properties can be tuned by external electric fields (instead of temperature), which trigger domain-switching instabilities in ferroelectric inclusions. To characterize electrically tunable composites, we will outline an experimental apparatus being fabricated that adds to current Broadband Viscoelastic Spectroscopy methods the capability to apply electric fields to specimens via surface electrodes.