| dc.description.abstract | Fiber-reinforced polymer composites (FRPs) are extensively utilized in many industries due to their remarkable mechanical properties, corrosion resistance and light-weight attributes. Notwithstanding, FRP laminates are critically susceptible to delaminations, which are often initiated due to invisible interlaminar cracks. Delaminations in turn weaken the overall strength and stiffness of FRPs, thus degrading their longevity and in-service reliability. Delamination phenomenon, which is one of the most common failure modes in FRP structures, is considered as a matrix dominant failure, because it is governed by matrix’s fracture toughness and the fiber/matrix interface bond strength.
The recent emergence of carbon nano-particles (CNPs), such as carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), have, however, enabled the engineers and scientists to develop a new generation of multi-functional modifiers for FRP composites. As a result, new breeds of FRPs, with remarkable mechanical, electrical and thermal properties have been generated in the recent years. However, the endeavor has not been without significant challenges; indeed, the production cost of CNPs, coupled with the effort (cost) associated with uniform dispersion of CNPs in resins, have been some of the major challenges encountered in the fabrication of CNP nanocomposites.
In the first section of this thesis, therefore, the details of an integrated and systematic investigation into the influence of processing parameters on the multi-functional performances of GNP/epoxy nanocomposites are presented. The obtained results led to the establishment of an optimized method for dispersing GNPs in epoxy resins, as a function of the configuration and geometry of the GNPs. In addition, a design diagram has been developed by which one could design GNP-reinforced composites, for a given application, in an effective manner.
In the second part, the details of efforts expended in studying the fracture and toughening mechanisms of GNP-nanocomposites, and the assessment of their interlaminar fracture toughness (IFT) of FRPs formed by the GNP-reinforced resins, are presented. As another contribution to the field, the performance of a GNP-reinforced epoxy was further enhanced by functionalizing the GNPs with a silane agent. Moreover, to the best of author’s knowledge, for the first time, the fracture mechanics of GNP-reinforced epoxy under pure modes I and II fracture are assessed qualitatively and quantitatively, using the micro-structural analysis technique. Furthermore, in response to the lack of a comprehensive test method for evaluating the mode III IFT of FRPs reinforced by GNPs, a new torsion-based test method has been developed and proposed. It will be shown that the fracture toughnesses of both GNP nanocomposites and mode-I IFT of the FRPs formed by the GNP-reinforced resin were significantly enhanced, while it will be demonstrated that inclusion of GNPs in the resin produced much less enhancement when the nanocomposite become subjected to mode-II and -III fracture in comparison to the mode-I fracture.
Finally, the mechanical response of the developed resilient GNP-reinforced epoxy adhesive is evaluated under various strain rates subject to both tensile and compressive loading schemes. Empirical models were also developed and proposed based on the performed experiments. The models enable one to predict the stiffness of such nanocomposites, under different stain rates, based on the weight content of GNPs | en_US |
