  Dislocations govern the properties of any crystals. Yet, how dislocation of
pentagonheptagon (5|7) in grain boundaries (GBs) affects the mechanical
properties of two-dimensional MoS2 crystals remains poorly known. Using
atomistic simulations and continuum disclination dipole model, we show that,
depending on the tilt angle and 5|7 dislocation arrangement, MoS2 GB strength
can be enhanced or reduced with tilt angle. For zigzag-tilt GBs primarily
composed of Mo5|7+S5|7 dislocations, GB strength monotonically increases as the
square of tilt angle. For armchair-tilt GBs with Mo5|7 or S5|7 dislocations,
however, the trend of GB strength breaks down as 5|7 dislocations are
non-evenly spaced. Moreover, mechanical failure initiates at the bond shared by
5|7 rings, in contrast to graphene where failure occurs at the bond shared by
6|7 rings. This work provides new insights into mechanical design of synthetic
transition metal dichalcogenide crystals via dislocation engineering.
