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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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This report applies models and experiments to answer key questions about the way materials deform; specifics regarding phase field dislocations dynamics; as well as high temperature rolling experiments.
Irradiation-created defects diffuse and agglomerate presenting obstacles for the dislocation motion (both glide and climb). This effect leads to hardening and loss of toughness, which might drive the system to failure.
This was a collaborative effort between Lawrence Livermore National Security, LLC as manager and operator of Lawrence Livermore National Laboratory (LLNL) and The Johns Hopkins University to develop a discrete defect dynamics method to predict the behavior of Magnesium polycrystalline alloys undergoing dynamic deformation though coupled slip and twinning building off of the ParaDiS dislocation dynamics code with finite element coupling.
Figures in this slide show the drag coefficient from phonon wind for edge and screw dislocations in aluminum and copper as a function of velocity and temperature. Velocity βt is given in units of transverse sound speed at room T.
This project combined modeling and experimentation across micro-meso-macro length scales to investigate the role of long-range internal stresses associated with obstacles and dislocation populations, in the deformation response of cubic metals. In addition to unique insights into the physical behavior of metals, advances were also made in modeling techniques and tools at the meso and atomistic level, and new characterization methods were developed and disseminated to the scientific community. Twenty eight journal papers, two dissertations and three theses have served as vehicles to share the gained scientific knowledge, and two open-source software packages have been developed, maintained and distributed. Additional publications are in progress.
GBs have been subject of intense study for several years, including the effects of microstructure on mechanical response. Until recently these have been primarily focused on a limited number of idealized GB structures (i.e, the minimum energy structure). We are specifically focusing on changes in local GB structure and the effect this has on dislocation-grain boundary interactions. This will help us to better understand both (more) realistic and general GB structures.
DFT-optimized structures of dislocations with a solute at different sites. The dataset include the VASP input files (except POTCAR) and output files OSZICAR and OUTCAR. There are also text files containing the DFT-computed interaction energies. The README file contains expressions that can be used to compute the interaction energies and chemical misfit energies using the volumetric size misfit for any solute species in Mg.
DFT-optimized structures of dislocations with a solute at different sites. The dataset include the VASP input files (except POTCAR) and output files OSZICAR and OUTCAR. There are also text files containing the DFT-computed interaction energies. The README file contains expressions that can be used to compute the interaction energies and chemical misfit energies using the volumetric size misfit for any solute species in Mg.
DFT-optimized structures of dislocations with a solute at different sites. The dataset include the VASP input files (except POTCAR) and output files OSZICAR and OUTCAR. There are also text files containing the DFT-computed interaction energies. The README file contains expressions that can be used to compute the interaction energies and chemical misfit energies using the volumetric size misfit for any solute species in Mg.
We fabricated optically pumped and electrically injected ultraviolet (UV) lasers on reduced-threading-dislocation-density (reduced-TDD) AlGaN templates. The overgrowth of sub-micron-wide mesas in the Al 0.32 Ga 0.68 N templates enabled a tenfold reduction in TDD, to (2–3) × 10 8 cm –2 . Optical pumping of AlGaN hetero-structures grown on the reduced-TDD templates yielded a low lasing threshold of 34 kW/cm 2 at 346 nm. Room-temperature pulsed operation of laser diodes at 353 nm was demonstrated, with a threshold of 22.5 kA/cm 2 . Furthermore, reduced-TDD templates have been developed across the entire range of AlGaN compositions, presenting a promising approach for extending laser diodes into the deep UV.
Dislocation relaxation of silver and copper and asymmetry of Bordoni internal friction peak of metals
Dislocations in shear deformed molybdenum crystals examined by transmission electron microscopy
Elastic-plastic shear cracks propagation in two phase composite materials using dislocation model, determining critical fracture strength
Dopant effect on dislocation mobility in elastically loaded silicon crystal using internal friction and modulus defect measurements
Double ended dislocation pileups and elastic cracks at bimaterial interface under screw, edge and shear modes
Single crystal W and W alloys dislocation structures as function of strain, temperature and dilute alloys addition, using electron microscopy
Transport mechanism for holes in polycrystalline Ge films based on Matthiessen rule, considering surface scattering and dislocation
Elastic cracks and screw dislocation pile-ups crossing bimaterial interface, deriving dual singular integral equations