Stress-localization induced toughening in CNT–silica nanocomposites

(Top) The average atomic stress field and the physical states of the Carbon Nanotube (CNT) at the same cohesive strength for (a) a CNT of small diameter showing debonding at the interface and (b) a CNT of larger diameter showing failure of the nanotube in Molecular Dynamics (MD) simulation.

(Middle) (a) The average stress field at the onset of debonding of the nanotube from the silica matrix for low cohesive strength. (b) The average stress field at the fracture state of the nanotube for high cohesive strength in MD simulation.

(Bottom) Finite Element Method (FEM) simulations yield similar results compared to MD simulations.

Distinctive patterns in stress localization are dependent on interfacial interactions. (a) Virial stress distribution at the onset of nanotube delamination for low cohesive strength. (b) Virial stress distribution at the onset of nanotube fracture for high cohesive strength. 

During debonding, the tensile stress at the left and right edges is significantly lower, as illustrated in (a). Conversely, in the fracture scenario, the nanotube undergoes higher stress due to its stronger interaction with the matrix, as depicted in (b).

For lower cohesive strength between the silica matrix and carbon nanotube, the carbon nanotube debonds from the matrix in carbon nanotube-reinforced amorphous silica when the crack propagates at the CNT. The behavior of the amorphous silica matrix is modeled using the Reactive Force Field (ReaxFF) potential, while the behavior of the carbon nanotubes is modeled with the Adaptive Intermolecular Reactive Empirical Bond Order potential (AIREBO). The interaction between CNT and silica is represented by an empirical potential derived from density functional theory (DFT) and expressed in the Lennard–Jones form. These simulations are conducted using the LAMMPS molecular dynamics simulation package. 

For high cohesive strength between the silica matrix and carbon nanotube (CNT), the nanotube fails in carbon nanotube-reinforced amorphous silica when the crack propagates through the CNT. The behavior of the amorphous silica matrix is modeled using the Reactive Force Field (ReaxFF) potential, and the behavior of the carbon nanotubes is modeled with the Adaptive Intermolecular Reactive Empirical Bond Order potential (AIREBO). The interaction between the CNT and silica is represented by an empirical potential derived from density functional theory (DFT) and expressed in the Lennard–Jones form. These simulations are conducted using the LAMMPS molecular dynamics simulation package.