Mechanical Properties of Fiber-reinforced Composites
Fiber-reinforced composites (FRC) have been widely considered as a future material in engineering applications due to their superior mechanical properties over traditional materials. However, most of these “advantages” are poorly quantified and have conflicting results especially with a less traditional reinforcement such as graphene or Boron Nitride (BN):
For instance, composite studies on the reinforcement of hBN, graphene, and their 1D counterparts –boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) –in brittle ceramic matrices are conflicting, with toughening mechanisms ranging from nanotube pullout suggesting interfacial failure to matrix cracking indicative of strongly-bonded interfaces.
Interfacial strength is only one of the many unknown mechanical properties that have hindered a true explosion in the usage of FRC. As a result, we seek to utilize computational models with well-calibrated models from the experiment’s results to have a better understanding of the mechanical properties of FRC.
CURRENT WORK: We are now working on quantifying the pull-out force of a CNT in the matrix. Following from this knowledge, with the help of machine learning, we hope to be able to develop an RVE model representing this property which would greatly help bridge the gaps between nano and continuum scale:
MOST RECENT WORK:
We report the sliding adhesion of hexagonal boron nitride (hBN) and graphene on silica using single nanotube pullout force measurements and potential energy landscape calculations by density functional theory (DFT). In contrast to isotropic sliding of graphene on silica, the sliding of hBN on silica exhibits strong directional dependence with unusually high energy barriers formed by the stacking of unterminated Si or O atoms on N atoms.
We report the stepwise untwisting of nanometer-sized bilayer graphene flakes at elevated temperatures, each step corresponding to a potential energy barrier formed by changes to the commensurability between the moiré superlattice and flake size with twist angle. The number of locally stable energy states and their barrier energies scale with the flake size, allowing twisted graphene flakes of several tens of nanometers to remain thermally stable even at chemical vapor deposition temperatures.
We report the interfacial shear strength of graphene on pure and oxidized Ti and Al metal surfaces using density functional theory calculations. Our results show significant changes to the graphene-metal bonding properties in the presence of an oxide phase. These oxidation effects can be modulated to some extent by the presence of vacancy or Stone Wales defects which increases the binding interactions of weaker graphene-metal interfaces. These dramatic changes to the interfacial properties by surface-oxidation explain the results of recent carbon nanotube pull-out experiments from Al and Ti metal-matrix-nanocomposites.