  Cyclic loading on granular packings and amorphous media exhibits a transition
from reversible elastic behavior to irreversible plasticity. The present study
compares the irreversibility transition and microscopic details of colloidal
polycrystals under oscillatory tensile-compressive and shear strain. Under both
modes, the systems exhibit a reversible to irreversible transition. However,
the strain amplitude at which the transition is observed is larger in the shear
strain than in the tensile-compressive mode. The threshold strain amplitude is
confirmed by analyzing the dynamical properties, such as mobility and atomic
strain (von-Mises shear strain and the volumetric strain). The structural
changes are quantified using a hexatic order parameter. Under both modes of
deformation, dislocations and grain boundaries in polycrystals disappear, and
monocrystals are formed. We also recognize the dislocation motion through
grains. The key difference is that strain accumulates diagonally in oscillatory
tensile-compressive deformation, whereas, in shear deformation, strain
accumulation is along the $x$ or $y$ axis.
