A novel dislocation dynamics framework is developed to simulate dislocation evolutions in thin film heterostructures at nanoscale. It is based on 3-D dislocation motion together with its physical background by adding the solid viscous effect. As the numerical simulation results demonstrate, this new model completely solves a long-standing paradoxical phenomenon with which the simulation results were dependent on dislocation-segment lengths in the classical discrete dislocation dynamics theory. The proposed model is applied to simulate the effect of dislocations on the mechanical performance of thin films. The interactions among the dislocation loop, free surface and interface are rigorously computed by decomposing this complicated problem into two relatively simple sub-problems. This model is allowed to determine the critical thickness of thin films for a surface loop to nucleate and to simulate how a surface loop evolves into two threading dislocations. Furthermore, the relationship between the film thickness and yield strength is constructed and compared with the conventional Hall-Petch relation.

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