Cha, Gene (2013-12). Passive Apaptive Damping for High Stiffness-low Mass Materials Incorporating Negative Stiffness Elements. Doctoral Dissertation.
High stiffness / low mass materials or structures reduce structure weight in transportation, but show little inherent damping. A new composite material that exhibits high stiffness and high damping might reduce issues with vibration in mechanical systems and structures. The material comprises three constituents: negative springs, positive springs, and damping elements. These components help achieve high stiffness with passive adaptive response over a frequency range. When applying sinusoidal loads on the material, the positive/negative spring interface oscillates, but body is relatively steady. This material needs a damping element to dissipate the vibrational energy at the interface. This research proposes new damping elements with novel properties starting with the fluid pumping element from the Synthetic Multifunctional Materials program. The low-hydraulic-radius hourglass (LHG) machine modified from Hawkins' original design provides high stiffness with a high damping ability. The LHG machine pumps a fluid and dissipates energy by viscous dissipation and mass transfer. This pumping creates a hysteresis effect that indicates the energy dissipation. Stacking LHG layers using Newtonian fluids in the LHG channel or a single layer using non-Newtonian fluids can produce passive adaptive damping through a frequency range. Shear thinning fluids placed in the LHG machine's channel provide adaptive performance by changing their dynamic viscosity. Experiments show passive adaptive damping up to tan ? one with a shear thinning fluid from 0.1 to 10 Hz. Computational fluid-solid interaction studies suggest a theoretical shear thinning fluid that produces high passive adaptive damping.