- 2018 Elsevier Ltd Nonuniform and localized deformation in planar single crystals subjected to dynamic tensile loading is investigated using finite element method. An idealized planar double-slip model is used to represent the crystal geometry. A size-dependent higher-order gradient crystal plasticity theory accounting for finite strains is adopted to characterize the material. The problem involves two kinds of length scale effect. One is naturally introduced by the inertial effect. The other is the intrinsic material length scale that is related to plastic strain gradients, which are related to a density of geometrically necessary dislocations. For size-independent conventional crystal plasticity, the deformation mode changes from an imperfection-induced (quasi static-like) mode to an imperfection-ignoring mode at some imposed velocity. When the higher-order gradient theory is used, the behavior is more complex with the variation in deformation mode with imposed velocity not necessarily monotonic due to the interaction between the two length scales (an inertia related length scale and a material length scale) affecting the response.