When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
Carbon-Nanotube-Reinforced-Polymer-Composite (CNRPC) materials have generated widespread interest over the last several years in practical engineering applications, such as aeronautical and aerospace engineering structures. However, studies still need to be carried out to characterize their mechanical properties, especially the dynamic properties, and the effects of defects on the mechanical properties. Experimental investigations intended for this purpose have limitations and, in most cases, reliable cost-effective experimental work could not be carried out. Computational modelling and simulation encompassing multiscale material behavior provide an alternate approach in this regard to characterize the material behavior. A probabilistic approach serves as a suitable approach to characterize the effects of material and structural defects. The present thesis reports the development of a computational framework of the Representative Volume Element (RVE) of a CNRPC material model to determine its static and dynamic responses, and also for the evaluation of its static and dynamic reliabilities based on a probabilistic characterization approach. A 3D multiscale finite element model of the RVE of the nanocomposite material consisting of a polymer matrix, a Single-Walled-Carbon-Nanotube (SWCN) and an interface region has been constructed for this purpose. The multiscale modeling is performed in terms of using different theories and corresponding strain energies to model the individual parts of the RVE of the CNRPC material. The macroscale continuum mechanics is used for the polymer matrix, the mesoscale mechanics is used for the interface region, and the nanoscale-level atomistic mechanics is used for the SWCN. The polymer matrix is modeled using the Mooney-Rivlin strain energy function to calculate its non-linear response, while the interface region is modeled via the van der Waals links. The SWCN is first modeled as a space frame structure by using the Morse potential, and then as a thin shell based on a suitable shell theory. For this purpose, the suitability and the accuracy of popular shell theories for use in the multiscale model of the RVE are assessed.