Modeling of surface effects in crystalline materials within the framework of gradient crystal plasticity

A finite-deformation gradient crystal plasticity theory is developed, which takes into ac- count the interaction between dislocations and surfaces. The model captures both ener- getic and dissipative effects for surfaces penetrable by dislocations. By taking advantage of the principle of virtual power, the surface microscopic boundary equations are obtained naturally. Surface equations govern surface yielding and hardening. A thin film under shear deformation serves as a benchmark problem for validation of the proposed model. It is found that both energetic and dissipative surface effects significantly affect the plastic be- havior