Multiscale investigations on structural properties and mechanical applications of carbon nanotube sheets.

摘要

The recent emergence of new nano-materials and nanostructures brings up the development of nanotube sheets or the so-called buckypapers for a variety of meaningful applications in actuating and mechanical properties alterations for structural and electromechanical systems. However, the technology of fabrication as well as the understanding of nanomechanics behaviors for nanotube sheets is still in its infancy. This motivates the present research aimed at investigating the mechanical strength properties and potential applications of buckypapers by using finite element methods, atomic scale modeling and simulation, and experimental tests.; In the first part of the research, experiment-purpose buckypapers have been fabricated in house to investigate their contributions to the strengths of other macrostructures to which they are integrated. Toward this end, a finite element procedure has been developed for three-dimensional modeling of multilayered nanostructures having embedded buckypapers and the resulted natural frequencies increment due to the high stiffness of buckypapers are agreeably verified by experimental tests. In addition, the experimental testing results further imply that buckypapers have superior damping properties indicated by the clear reductions of the power spectral density readings affected by the buckypaper dampers. This first time investigated and verified profound damping characteristics of buckypapers may be useful for vibration suppression, acoustic noise reduction, and structural enhancement for materials and structures where add-on weight is a concern such as sports equipments and airframes. This theoretical and experimental finding of buckypapers' superior damping property is deemed to be the first major contribution of the dissertation research.; To delve into the mechanical properties of carbon nanotubes and buckypapers, in the second part of the dissertation, the atomic scale models of carbon nanotubes and buckypapers are created for the investigation. Along this line, novel simulation models for single and multilayer buckypapers were built which enabled us to understand the bending stiffness and other mechanical properties of buckypapers through an atomic scaled analysis against the existing empirical methods. This new approach of analyzing and observing buckypaper's properties is the second contribution of this dissertation.; The results from the simulation gave a reasonably expected Young's moduli for single wall carbon nanotubes comparing to those found in the literature; for single layer and multilayer buckypapers model, higher Young's moduli values obtained in the simulations than previous done experimental testings which are considered mainly due to the exclusion of such factors as particles impurity, uneven thickness, imperfect alignments, etc. Therefore, these higher values may represent the optimal goal of Young's moduli for buckypapers which could be achieved ultimately when their fabrication techniques are continuously improved in the future.