Place: Materials Modelling Lab Seminar, Oxford University, Oxford, UK
The mechanical strength of interfaces determines the fracture and deformation behavior of nanostructured materials. In nanocomposites or nanocrystals heterointerfaces 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 plastic deformation carried by lattice dislocations. This is demonstrated on the example of a metallic nanocomposite material. To generalize these results, a multiscale model is presented in which the mechanical properties of interfaces under shear and tension are calculated by electronic structure methods within the density functional theory. From the resulting tensile force-displacement curves physical parameters like the work of separation, maximum stress and displacement across the interface are derived. For the case of shearing a generalized gamma-surfaces are calculated. These parameters are used to validate cohesive zone models that describe the mechanical behavior of interfaces directly on the continuum scale. An application of the model to describe the deformation of nanocrystalline and ulta-fine grained metals is presented.