Deformation Mechanisms of Toughening of Nanocrystalline Materials

We provide a brief review of our recent studiesconcerning the effects of various mechanisms of plasticdeformation of nanocrystalline materials on their fracturetoughness. We consider both conventional deformationmechanisms, such as lattice dislocation slip, and the deformationmechanism pronounced mostly in nanocrystalline solids, such asgrain boundary (GB) sliding and migration. We demonstrate thatwith a decrease in grain size, the effect of conventional latticedislocation slip on fracture toughness enhancement significantlydecreases. At the same time, for nanocrystalline solids withsmallest grain size fracture toughness can be increased due to GBsliding and migration. This implies that a transition from latticedislocation-mediated toughening to GB-deformation-producedtoughening can occur at a critical grain size in nanocrystallinesolids.

Aspects of interface elasticity theory

Interfaces significantly influence the overall material response especially when the area-to-volume ratio is large, for instance in nanocrystalline solids. A well-established and frequently applied framework suitable for modeling interfaces dates back to the pioneering work by Gurtin and Murdoch on surface elasticity theory and its generalization to interface elasticity theory. In this contribution, interface elasticity theory is revisited and different aspects of this theory are carefully examined. Two alternative formulations based on stress vectors and stress tensors are given to unify various existing approaches in this context. Focus is on the hyper-elastic mechanical behavior of such interfaces. Interface elasticity theory at finite deformation is critically reanalyzed and several subtle conclusions are highlighted. Finally, a consistent linearized interface elasticity theory is established. We propose an energetically consistent interface linear elasticity theory together with its appropriate stress measures.