Effects of grain boundary on the sources of size effects
  The present work investigates the role of grain boundary (GB) on the sources of size effects. Up to now, several studies have been conducted to address the role of GBs in size effects from the atomistic point of view. However, a study which addresses the role of GB on different governing mechanisms of size effects as the sample length scale varies has not been presented yet. The results show that the main role of GB at larger length scale is to change the pattern of dislocation structure in a way that the dislocations are piled up near the GB which increases the hardness. 
George Z. Voyiadjis, Mohammadreza Yaghoobi
cond-mat.mtrl-sci