Abstract: Dynamics of a pair of voids located along loading direction under uniaxial tension is investigated using molecular dynamics method.Size effects in void growth and coalescence are studied.It shows that different-sized voids grow and coalesce through dislocation nucleating on void surfaces.In early elastic stage,voids grow along loading direction,then along vertical direction and finally form octahedral-like structures in plastic stage.Critical yield stress increases with decreasing of void size.If radius is large,dislocations nucleate and migrate symmetrically.Voids elongate in loading direction,and evolution process is similar.If radius is small,dislocations nucleate asymmetrically and voids elongate along vertical direction.The process of void growth may be characterized by elastic deformation,independent growth,coalescence and steady growth.Independent growth stage diminishes gradually as void size becomes smaller.

Key words: molecular dynamics, dislocation, void coalescence