  As most materials available in macroscopic quantities, graphene appears in a
polycrystalline form and thus contains grain boundaries. In the present work,
the effect of uniaxial strain on the electronic transport properties through
graphene grain boundaries is investigated using atomistic simulations. A
systematic picture of the transport properties with respect to the strain and
the lattice symmetry of graphene domains on both sides of the boundary is
provided. In particular, it is shown that the strain engineering can be used to
open a finite transport gap in all graphene systems where two domains exhibit
different orientations. This gap value is found to depend on the strain
magnitude, on the strain direction and on the lattice symmetry of graphene
domains. By choosing appropriately the strain direction, a large transport gap
of a few hundred meV can be achieved when applying a small strain of only a few
percents. For a specific class of graphene grain boundary systems, the strain
engineering can also be used to reduce the scattering on defects and hence to
significantly enhance the conductance. With a large strain-induced gap, these
graphene heterostructures are proposed to be possible candidates for highly
sensitive strain sensors, flexible transistors and p-n junctions with a strong
non-linear I-V characteristics.
