Anisotropic tensile mechanics of vertically aligned carbon nanotube reinforced silicon carbide ceramic nanocomposites

Vertically aligned carbon nanotubes (VACNTs)/silicon carbide (SiC) nanocomposites (VSNs) present remarkably anisotropic mechanical properties originated from their intrinsic heterogeneous microstructures. However, the studies related to tensile mechanical behaviors and failure mechanisms of VSNs are still suspended so far. In this work, the tensile mechanical properties of VSNs were investigated by an in-situ transmission electron microscopy (TEM) tensile test combined with classic molecular dynamics (MD) simulation. The testing results show that the fracture strength and Young's modulus of VSNs along CNT-axis (∥ direction) are higher than those perpendicular to CNT-axis (⊥ direction). In addition, the fracture surface along ∥ direction is uneven whereas it is flat along ⊥ direction. The MD simulation reveals that the stronger behavior along ∥ direction is mainly benefited by the excellent tensile mechanical properties of CNTs, however, the relatively weak van der Waals interaction between CNTs and SiC matrix dominates the tensile performances of VSNs along ⊥ direction. Finally, the remarkable mechanical anisotropy of VSNs is explained by pulling-out and peeling-off failures of CNTs based on MD simulation. This work provides experimental and theoretical insights into the dominant mechanisms of mechanical anisotropy in typical VACNT/ceramic nanocomposites.