  Monolayer antimonene has drawn the attention of research communities due to
its promising physical properties. But mechanical properties of antimonene is
still largely unexplored. In this work, we investigate the mechanical
properties and fracture mechanisms of two stable phases of monolayer antimonene
-- the ${\alpha}$ antimonene (${\alpha}$-Sb) and the ${\beta}$ antimonene
(${\beta}$-Sb), through molecular dynamics (MD) simulations. Our simulations
reveal that stronger chiral effect results in a greater anisotropic elastic
behavior in ${\beta}$-antimonene than in ${\alpha}$-antimonene. In this paper
we focus on crack-tip stress distribution using local volume averaged virial
stress definition and derive the fracture toughness from the crack-line stress.
Our calculated crack tip stress distribution ensures the applicability of
linear elastic fracture mechanics (LEFM) for cracked antimonene allotropes with
considerable accuracy up to a pristine structure. We evaluate the effect of
temperature, strain rate, crack-length and point-defect concentration on the
strength and elastic properties. Tensile strength goes through significant
degradation with the increment of temperature, crack length and defect
percentage. Elastic modulus is less susceptible to temperature variation but is
largely affected by the defect concentration. Strain rate induces a power law
relation between strength and fracture strain. Finally, we discuss the fracture
mechanisms in the light of crack propagation and establish the links between
the fracture mechanism and the observed anisotropic properties.
