Kim, Jong Hyun (2005-08). Passive machine augmented composite for multifunctional properties. Doctoral Dissertation.
This dissertation studies by experiment and numerical analysis an advanced composite material (Machine Augmented Composite or MAC) for enhancement of the passive damping while maintaining its stiffness. This MAC is composed of a pre-buckled wall structure placed within a viscoelastic matrix. The pre-buckled machine can contain viscous fluids for additional energy dissipation. For the experiments, the MAC was fabricated by using rigid and soft polyurethane as a machine and matrix material respectively. Various viscosity fluids (0.83 ~ 4730 cps) filled the inner-channel of the machine structure. Dynamic properties such as tan ?? and the loss modulus (E") of the composite were measured and compared with those of a homogeneous matrix sample over a frequency range of 0.1 to 100 Hz at room temperature through load-controlled cyclic testing. Measured tan ?? and loss modulus values for the composite were higher than those of the matrix alone in the 1 to 40 Hz range. However the viscous fluid effects on the overall damping properties were small. The performance of a theoretical MAC was explored through numerical analysis. The amount of inner-channel gap closure was calculated for various matrix Poisson??s ratios, for various Young??s modulus ratios between the machine and matrix (Emachine/Ematrix), and for the volume fraction of the machines. The most desirable performance of the composite was obtained when the matrix Poisson??s ratio was 0.49, and there was interaction between the Emachine/Ematrix and the volume fraction of the machines. Also the proper volume fraction range of the machine was predicted to be between 0.15 and 0.2 for the lamina shape MAC. Based upon the analysis, a sandwich structure MAC was fabricated and tested. This composite showed 11 times higher stiffness than the matrix without loosing the matrix damping property. This dissertation shows that the research met these objectives: 1) the MAC concept is effective for passive damping of vibrations, 2) that material combinations studied here had optimal combinations for best performance, and 3) that this is a promising field study for future passive and active materials development.