Wright-Patterson Air Force Base

About: Wright-Patterson Air Force Base is a other organization based out in Wright-Patterson AFB, Ohio, United States. It is known for research contribution in the topics: Laser & Microstructure. The organization has 5817 authors who have published 9157 publications receiving 292559 citations. The organization is also known as: Wright-Patterson AFB & FFO.

Structural evolution and kinetics in Cu-Zr metallic liquids from molecular dynamics simulations

Abstract: The atomic structure of the supercooled liquid has often been discussed as a key source of glass formation in metals. The presence of icosahedrally coordinated clusters and their tendency to form networks have been identified as one possible structural trait leading to glass-forming ability in the Cu-Zr binary system. In this paper, we show that this theory is insufficient to explain glass formation at all compositions in that binary system. Instead, we propose that the formation of ideally packed clusters at the expense of atomic arrangements with excess or deficient free volume can explain glass forming by a similar mechanism. We show that this behavior is reflected in the structural relaxation of a metallic glass during constant pressure cooling and the time evolution of structure at a constant volume. We then demonstrate that this theory is sufficient to explain slowed diffusivity in compositions across the range of Cu-Zr metallic glasses.

Ab initio based empirical potential used to study the mechanical properties of molybdenum

Abstract: Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for molybdenum. The accuracy and transferability of the potential are verified by comparison to experimental and density-functional data for point defects, phonons, thermal expansion, surface and stacking fault energies, and ideal shear strength. Searching the energy landscape predicted by the potential using a genetic algorithm verifies that it reproduces not only the correct bcc ground state of molybdenum but also all low-energy metastable phases. The potential is also applicable to the study of plastic deformation and used to compute energies, core structures, and Peierls stresses of screw and edge dislocations. Molybdenum's high strength and high-temperature stability make this refractory metal very attractive for use in advanced process technologies. The motion of dislocations is generally accepted to be responsible for the complex deformation behavior of this transition metal. 1-8 In recent years progress has been made on the description of the properties of screw dislocations using density-functional theory (DFT), tight- binding calculations, and empirical potentials. 9-19 However, DFT and tight-binding techniques are limited to small system sizes, which is problematic due to the long-range strain field of dislocations, and current empirical potentials lack the required accuracy for the description of the dislocation structure. Simulations of dislocation motion and interactions require efficient interatomic potentials which accurately describe the dislocation energies, core structures, and motion. In this work we develop an empirical potential for Mo which predicts the ideal shear strength, generalized stacking fault en- ergies, energies of dislocations, and the Peierls stress and core structure of the � 111� /2 screw dislocation. The potential form is given by the modified embedded-atom method (MEAM) and the potential parameters are optimized usingabinitio energies, lattice parameters, forces, and elastic constants. Section II describes the calculations for the DFT database, the functional form of the MEAM potential, and the optimization of the potential parameters to the DFT database. The accuracy of the potential for structural, elastic, and defect properties is verified in Sec. III by comparison to DFT results and experiments. A genetic algorithm search of the energy landscape of the MEAM potential confirms that the potential reproduces the correct bcc ground state and predicts several low-energy metastable structures whose energies agree well with DFT results. Results of the MEAM potential for formation energies of point defects, phonon dispersion, thermal expansion, surface energies, ideal shear strength, and generalized stacking faults for the MEAM potential closely match DFT results and available experimental data. In Sec. IV we apply the potential to determine energies and Peierls stresses of the screw and edge dislocation in bcc Mo. The results show that the MEAM potential accurately describes the structural and mechanical properties of Mo and should be applicable to simulate the motion of dislocations and the plastic deformation of Mo.

Peptide Functionalized Gold Nanorods for the Sensitive Detection of a Cardiac Biomarker Using Plasmonic Paper Devices

Abstract: The sensitivity of localized surface plasmon resonance (LSPR) of metal nanostructures to adsorbates lends itself to a powerful class of label-free biosensors. Optical properties of plasmonic nanostructures are dependent on the geometrical features and the local dielectric environment. The exponential decay of the sensitivity from the surface of the plasmonic nanotransducer calls for the careful consideration in its design with particular attention to the size of the recognition and analyte layers. In this study, we demonstrate that short peptides as biorecognition elements (BRE) compared to larger antibodies as target capture agents offer several advantages. Using a bioplasmonic paper device (BPD), we demonstrate the selective and sensitive detection of the cardiac biomarker troponin I (cTnI). The smaller sized peptide provides higher sensitivity and a lower detection limit using a BPD. Furthermore, the excellent shelf-life and thermal stability of peptide-based LSPR sensors, which precludes the need for special storage conditions, makes it ideal for use in resource-limited settings.

The effect of process parameters on residual stress evolution and distortion in the laser powder bed fusion of Ti-6Al-4V

Abstract: Laser powder bed fusion (LPBF) is a popular additive manufacturing (AM) process that has shown promise in fabricating novel components that can be utilized for a wide variety of applications. However, one of the main drawbacks of LPBF is that it produces large thermal gradients and fast cooling rates during the solidification of each layer, which can lead to large levels of residual stress/distortion, sometimes resulting in build failure/rejection. In the present work, several experimental techniques (x-ray diffraction, hole drilling, contour method, and laser line profilometry) were utilized to establish the effect of LPBF process parameters (scan speed, laser power, build height, build plan area, and substrate condition) on residual stress evolution and distortion. X-ray diffraction and hole-drilling measurements were performed on the surfaces of the LPBF deposits and substrates, while bulk residual stresses were measured using the contour method. In addition, a laser line profilometer was used to measure the distortion after fabrication. The results obtained by the non-destructive and destructive measurement techniques suggested that process parameters greatly influence the development of residual stress and distortion throughout the LPBF deposit and the substrate. Furthermore, the experimental results in this work provide a valuable foundation for future modeling and simulation of the evolution of residual stress and distortion.