Place: International Conference on the Strength of Materials, Dresden, Germany
The mechanical strength of interfaces determines the fracture and deformation behavior of nanostructured materials. In nanocomposites or nanocrystals hetero-interfaces or grain boundaries may serve as easy crack paths, due to weakened atomic bonds. Furthermore in these nanostructured materials interfacial sliding may provide a further deformation mechanism adding to the conventional plastic deformation carried by lattice dislocations. The interesting length scale effects caused by interfacial sliding in a metallic nanocomposite material are studied by large-scale atomistic simulations. To describe materials with coarser microstructures, it is necessary to develop a multiscale scheme, in which the mechanical properties of interfaces under shear and tension are calculated by electronic structure methods within the density functional theory. This is necessary, because the interfacial behavior is dominated by atomic bonds. Furthermore, this method allows us to study the influence of impurities at interfaces. From the resulting tensile force-displacement curves physical parameters like the work of separation, the maximum stress and the displacement across the interface are derived. For the case of shearing generalized gamma-surfaces for the interface are calculated. These parameters are used to validate cohesive zone models that describe the mechanical behavior of interfaces directly on the continuum scale. Hence methods like crystal plasticity or dislocation dynamics can be applied to deal with plastic deformation in the neighborhood of the interfaces. An application of this multiscale model on the deformation of nanocrystalline and ultra-fine grained metals is presented.