Damage and plastic deformation accumulation in fretting fatigue occurs within a depth of a few crystallographic grains. Therefore, more accurate assumptions concerning length scale, damage volume, and the material model are needed to establish a more solid physical foundation necessary for next generation fretting fatigue damage prediction. Major thrusts include: (1) development and implementat...

We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-...

Strong size effects have been experimentally observed when microstructural features approach the geometric dimensions of the sample. In this work experimental investigations and discrete dislocation analyses of plastic deformation in metallic thin films have been performed. Columnar grains representative of the film microstructure are here considered. Simulations are based on the assumptions th...

Two-phase bimetal composites contain both grain boundaries and bi-phase interfaces between dissimilar crystals. In this work, we use a crystal plasticity finite element framework to explore the effects of grain boundary interactions on the plastic stability of bi-phase interfaces. We show that neighboring grain interactions do not significantly alter interface plastic stability during plane str...

Gallium nitride light emitting diodes were deposited on a sapphire substrate that was pre-patterned with an ordered two-dimensional structure. The size and arrangement of the substrate surface pattern was designed to increase the diffraction and extraction of light from the device as well as define the grain size and thus dislocation density of the GaN crystal. A close-packing of self-assembled...

Grain-boundary relaxation in nanocrystalline Fe was studied by high-resolution transmission electron microscopy HREM , and its effect on plasticity was characterized by nanoindentation. Samples with grain size of 9.8 nm were synthesized by mechanical attrition and subsequently annealed at low temperatures 80 and 100 °C without affecting the grain size. While the hardness is not significantly af...

A framework for investigating plasticity phenomena and their dependence on the underlying physical and size-dependent mechanisms is developed. The framework is based on crystal plasticity and three-dimensional discrete dislocation dynamics analyses. Particularly, the mesoscale model couples continuum crystal plasticity framework with a set of spatio-temporal evolution equations for dislocation ...

Acoustic emission experiments were performed on polycrystalline and single crystal 99.990/0 aluminium while undergoing tensile deformation. It was found that acoustic emission counts as a function of grain size showed a maximum value at a particular grain size. Furthermore, the slip area associated with this particular grain size corresponded to the threshold level of detectability of single di...

Four principal factors contribute to grain-boundary strengthening: (a) the grain boundaries act as barriers to plastic flow; (b) the grain boundaries act as dislocation sources; (c) elastic anisotropy causes additional stresses in grain-boundary surroundings; (d) multislip is activated in the grain-boundary regions, whereas grain interiors are initially dominated by single slip, if properly ori...