  Pentahexoctite (PH) is a pure sp$^2$ hybridized planar carbon allotrope whose
structure consists of a symmetric combination of pentagons, hexagons, and
octagons. The proposed PH structure was shown to be an intrinsically metallic
material exhibiting good mechanical and thermal stability. PH nanotubes (PHNTs)
have also been proposed, and their properties were obtained from first
principles calculations. Here, we carried out fully-atomistic simulations,
combining reactive (ReaxFF) molecular dynamics (MD) and density functional
theory (DFT) methods, to study the PHNTs elastic properties and fracture
patterns. We have investigated the mechanical properties behavior as a function
of the tube diameter and temperature regimes. Our results showed that the
PHNTs, when subjected to large tensile strains, undergo abrupt structural
transitions exhibiting brittle fracture patterns without a plastic regime.
