Particle impact damping is measured for a cantilevered beam vibrating freely in the horizontal plane. Several particle configurations are investigated beginning with a single particle and progressing to multiple layers of particles. The effects of clearance between the particles and enclosure, initial displacement of the primary system, repeatability of damping, and damping efficiency per unit mass added are evaluated for each particle configuration. The investigation shows that the particle configuration significantly affects damping. Configurations with the fewest particles per cavity demonstrate higher damping efficiency per unit mass. Generally, for configurations with a definable clearance between the particles and enclosure, damping is shown to be a function of the clearance and initial system displacement. For configurations with multiple layers of particles, for which horizontal clearance between the particles and enclosure has no meaning, a new dimensionless parameter which captures the geometry of the particle arrangement is proposed.

In this study the energy dissipation performance of machine augmented composite (MAC) materials is investigated. MAC materials are formed by inserting simple machines into a matrix material. In this work the machines take the form of fluid filled tubes, and the tube cross-sectional geometry induces fluid flow when it is deformed in its plane. This flow dissipates mechanical energy, and thus provides the composite material with attractive damping properties. The objective of this study is to gain insight into the geometry, the material property combinations, and the boundary conditions that are effective in producing high damping MAC materials. Particular attention is given to tube geometry and to dimensionless parameters that govern the energy dissipation efficiency of a MAC lamina. An important dimensionless parameter is the ratio of solid elastic moduli to the product of the driving frequency and the fluid dynamic viscosity. This is a measure of the ratio of elastic forces in the solid material to the viscous forces in the fluid material that makes up a MAC lamina. Governing equations and simulation methods are discussed. Simplified equations are derived to predict the pressure generated when a tube/matrix cell is squeezed with zero pressure end conditions. Transient, three dimensional finite element models are also used to predict the performance of the damping MAC materials with zero pressure at the ends of the tubes. For the geometry and material properties considered, the highest energy dissipation efficiency predicted by these models is approximately 0.8 out of a maximum of 1.0.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 77-80).

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Young S. Shin, Ilbae Ham. Includes bibliographical references (p. 49). Also available online.

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