ncku-talk2009-02-26

NCKU Math colloquium

DATE 2009-02-26　16:10-17:00

PLACE 國家理論科學中心 204 室

SPEAKER 王雲哲助理教授（成功大學土木系）

TITLE Viscoelastic Composites with Unbounded Overall Stiffness and Damping

ABSTRACT This work reported here is in collaboration with Professor R. S. Lakes at the University of Wisconsin-Madison. Negative stiffness entails a reversal of the usual directional relationship between force and displacement in deformed objects. Of course an isolated object with negative stiffness is unstable. But incremental negative stiffness can be achieved in some materials. Examples are (1) a column buckled into an S shape, (2) flexible tetrakaidecahedra (models of single cells in foams) deformed in compression under displacement control, and(3) ferroelastic domainsin the vicinity of a phase transition.
Analysis discloses peak damping and large stiffness anomalies are possible in viscoelastic composites with inclusions of negative stiffness. An experimental illustration discloses singular mechanical damping tan delta in a lumped unit cell system containing post-buckled polymeric elastomer tubes. A further experimental illustration of extreme behavior showed composites prepared with a dilute concentration of ferroelastic inclusions (vanadium dioxide or barium titanate) exhibited large peaks in tan delta and anomalies in dynamic modulus.
These results point to thepossibility of achieving extreme behavior in designed composites. We report analysis of extreme thermal expansion and piezoelectric coefficients in thermoelastic and piezoelectric composites. We examine the stability of a lumped system and show that extreme mechanical damping is possible within the regime of stability according to the Routh-Hurwitz method.

NCKU Math colloquium

DATE	2009-02-26　16:10-17:00

PLACE	國家理論科學中心 204 室

SPEAKER	王雲哲助理教授（成功大學土木系）

TITLE	Viscoelastic Composites with Unbounded Overall Stiffness and Damping

ABSTRACT	This work reported here is in collaboration with Professor R. S. Lakes at the University of Wisconsin-Madison. Negative stiffness entails a reversal of the usual directional relationship between force and displacement in deformed objects. Of course an isolated object with negative stiffness is unstable. But incremental negative stiffness can be achieved in some materials. Examples are (1) a column buckled into an S shape, (2) flexible tetrakaidecahedra (models of single cells in foams) deformed in compression under displacement control, and(3) ferroelastic domainsin the vicinity of a phase transition. Analysis discloses peak damping and large stiffness anomalies are possible in viscoelastic composites with inclusions of negative stiffness. An experimental illustration discloses singular mechanical damping tan delta in a lumped unit cell system containing post-buckled polymeric elastomer tubes. A further experimental illustration of extreme behavior showed composites prepared with a dilute concentration of ferroelastic inclusions (vanadium dioxide or barium titanate) exhibited large peaks in tan delta and anomalies in dynamic modulus. These results point to thepossibility of achieving extreme behavior in designed composites. We report analysis of extreme thermal expansion and piezoelectric coefficients in thermoelastic and piezoelectric composites. We examine the stability of a lumped system and show that extreme mechanical damping is possible within the regime of stability according to the Routh-Hurwitz method.