Surface:

If it's a free surface, the dislocation can penetrate through the surface easily, but, if it's a coating or oxide layer, it will be hard for dislocation to glid out of the surface

Grain boundary:

In discrete dislocation dynamic simulation, some authors take grain boundary as a impenetrable, such as a rigide wall, But in other papers, grain boundary was thought to be a penetrable wall.

 So,Is there somthing or simillar property for us to derive.

As our body, we birth, grow up and dead? Wil the dislocation souce be the same process, if it’s so, what’s the detail process.

(1):the birth of dislocation source

When dislocation meet the grain boundary. The grain boundary present obstacles to dislocation motion. A usual point is that the dislocation will pile up against the grain boundary(But from the expriments , it seldomly see this phenomenon.). Macroscopic yielding occours when the adjacent grain can deform plastically Which maybe effected by the emission of dislocation from the grain boundary, or in another way , the pileup dislocation can produce a stress concentration which can active the dislocation source in the adjacent grain. As we knowe ,in polycrystalline, the material will express a Hall-Petch relationship between the yielding stress and the grain dimension. There are many models to explain the H-P relationship,such as pile-up dislocations, average fress distance....

    Interpersonal
communication is a very important part of our life. With communication
we become closer, we learn more from each other.

   
Graduate students as a special ,elite and academic group, also gives
the interpersonal communication with a new connotation. It will have a
very big impact on our future life and career development. Therefore, I
have prepared here to talk about some points on communication of
graduate students .