  Recently, a new two-dimensional carbon allotrope, named biphenylene network
(BPN) was experimentally realized. The BPN structure is composed of four-,
six-, and eight-membered rings of sp$^2$-hybridized carbon atoms. In this work,
we carried out fully-atomistic reactive (ReaxFF) molecular dynamics simulations
to study the thermomechanical properties and fracture patterns of non-defective
and defective (nanocracks) BPN. Our results show that under uniaxial tensile
loading, BPN is converted into four distinct morphologies before fracture
starts. This conversion process is dependent on the stretching direction. Some
of the formed structures are mainly formed by eight-membered rings, which have
different shapes in each morphology. In one of them, a graphitization process
was observed before the complete fracture. Importantly, in the presence of
nanocracks, no new morphologies are formed. BPN exhibits a distinct fracture
process when contrasted to graphene. After the critical strain threshold, the
graphene transitions from an elastic to a brittle regime, while BPN can exhibit
different inelastic stages. These stages are associated with the appearance of
new morphologies. However, BPN shares some of the exceptional graphene
properties. Its calculated Young's modulus and melting point values are
comparable to the graphene ones, about 1019.4 GPa and 4024K, respectively.
