  The mechanical response of graphene nano-ribbon under tensile loading has
been investigated using atomistic simulation. Lattice symmetry dependence of
elastic properties are found, which fits prediction from Cauchy-Born rule well.
Concurrent brittle and ductile behaviors are observed in the failure process at
elastic limit, which dominates at low and high temperature respectively. In
addition, the free edges of finite width ribbon help to activate bond-flip
events and initialize ductile behavior.
