Fatigue and Fracture Behavior of Graphene-based Nanomaterials

Mechanical durability is an important factor for a reliable design and commercialization of nanostructured products, where the components are susceptible to mechanical failure induced by static and cyclic loads. Known as "wonder material" graphene has demonstrated a great potential to be used in multifunctional nanostructures and nanodevices. However, after more than a decade of research, studies have reported the mechanical performance of graphene-based nanomaterials is far from the initial hype. The key issues are that graphene suffers from an intrinsically brittle behavior and an interfacially weak interaction in contact with adjacent constituents. The present thesis studies both issues under static and cyclic loads. Initially, atomistic simulations were performed to understand the underlying mechanisms and required kinetic conditions for the fatigue failure of graphene. While the failure was a thermally activated process, an extreme defect sensitivity was captured for graphene in which the fatigue life was completely dominated by the first covalent bond dissociation. Considering the inevitability of defects, such a drawback stressed a need for modifying the lattice structure of graphene such as by using chemical functionalization. Using extensive atomistic simulations coupled with AFM-based nanoindentation tests, we systematically studied the fatigue behavior of graphene oxide and presented the tailoring of functional groups as a tool to tune the intrinsic fatigue resistance and lifetime of graphene. It was demonstrated how a controlled chemical functionalization of graphene oxide can indeed enhance the defect tolerance and maximize the fatigue lifetime of graphene, up to five-fold at a low degree of functionalization (5\%) with higher content of epoxy groups. Using a similar approach, the possibility of tailoring functional groups was evaluated on enhancing the interfacial properties of graphene/polymer nanocomposites. From an atomistic insight, an enhanced load transfer was observed at the interface of functionalized graphene/polymer owing to the creation of mechanical entanglements and hydrogen-bond networks. We also reported that by a selective degree of functionalization (approximately 10\%), a superior fracture resistance can be achieved for the graphene-based polymer nanocomposites. This was attributed to a transition in the failure mode from interfacial slippage (for graphene/polymer) to an interfacial crack arresting (for graphene oxide/polymer).

Department dc:contributor.department

Mechanical and Industrial Engineering

Year dc:date.issued

2022

Author dc:creator

• Najafi, Farzin

Advisors dc:contributor.advisor

• Singh, Chandra Veer CV
• Sain, Mohini M

Handle dc:identifier.uri

http://hdl.handle.net/1807/127041

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/127041