Modeling and validation of residual stress distribution in an HSLA-100 disk

The residual stress distribution in a GTA spot we 100 steel disk was analyzed using thermomechanically uncoupled and semi-coupled finite element (FE) formulations and measured with the neutron diffraction technique. The computations used temperature-dependent the and mechanical properties of the base metal. The thermal analysis was based on the heat conduction formulation with the Gaussian heat input from the arc. The semi-coupled approach is an effective alternative to the fully coupled approach in which the incompatibility in the thermal and mechanical time increments often leads to numerical convergence difficulties. Convergence was achieved in the semi-coupled approach where a larger time increment for temperature calculation was automatically divided into some sub-intervals for the thermal stress calculation. The temperature, deformation configurations, and state variables were updated at the end of the temperature increment. The predictions from the FE models are in very good agreement with the neutron measurement results in the far heat-affected zone (HAZ) and in the base metal. Both models over-predicted the residual stress field in the fusion zone and near HAZ as measured by the neutron diffraction method. The discrepancy could be attributed to the changes in microstructures and material properties in the HAZ and fusion zone due to phase transformations during the welding thermal cycle. The formation of cracks in the fusion zone is another factor that possibly contributes to the lower measured residual stress values

Polycapillary optics based neutron focusing for small sample neutron crystallography.

This work presents preliminary measurements designed to explore a new approach to neutron diffraction that is somewhat analogous to the pseudo-Laue technique, except that instead of using a broad energy (wavelength) bandwidth it uses a broad angular bandwidth. We have used a polycapillary focusing optic to focus neutrons from a monochromatic beam (using the BT-8 spectrometer on the NIST research reactor) and from a polychromatic beam at a pulsed spallation source (the Intense Pulsed Neutron Source, IPNS at Argonne National Laboratory) into a small, intense spot and have carried out preliminary diffraction measurements. Using the single crystal diffraction (SCD) facility on IPNS, diffraction of a 3{sup o} convergent beam from an alpha quartz crystal showed six diffraction beams in the 1-5{angstrom} wavelength bandwidth transmitted by the optic. The diffraction spots showed an intensity gain of 5.8 {+-} 0.9 compared to a direct beam diffracting from the same sample volume as that illuminated by the convergent beam

Magnetic trapping of ultracold neutrons

Three-dimensional magnetic confinement of neutrons is reported. Neutrons are loaded into an Ioffe-type superconducting magnetic trap through inelastic scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low energy and in the appropriate spin state are confined by the magnetic field until they decay. The electron resulting from neutron decay produces scintillations in the liquid helium bath that results in a pulse of extreme ultraviolet light. This light is frequency downconverted to the visible and detected. Results are presented in which 500 +/- 155 neutrons are magnetically trapped in each loading cycle, consistent with theoretical predictions. The lifetime of the observed signal, 660 s +290/-170 s, is consistent with the neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review

NEUTRON INELASTIC SCATTERING FROM SOLID HCl

$^{1}$K. Shimaoka, et al., J. Phys. Soc. Japan 27, 1078 (1969). $^{2}$S. F. Trevino, Applied Spectroscopy 22, 659 (1968). Gault, Trevino and Prask were guests at AMMRC, Watertown, Mass. 02172. Gault was an NRC-FRL Postdoctoral Research Associate.""Author Institution: Explosives Laboratory, Feltman Research LaboratoriesHigh resolution neutron inelastic scattering spectra in the region below $250 cm^{-1}$ have been obtained from solid HCl at temperatures corresponding to the low temperature ferroelectric phase, the high temperature disordered phase and the recently $reported^{1}$ (120$^\circ K$--98.4$^\circ K$) intermediate phase. These data were obtained utilizing a time-of-flight spectrometer with a crystal monochromator. The resolution of this instrument is sufficient to enable previously unresolved structure to be observed. The low temperature phase data are compared to cross-sections calculated by using a full lattice dynamical $model^{2}$ and good agreement is obtained

Polycapillary Optics Based Neutron Focusing for Small Sample Neutron Crystallography”, (these proceedings

ABSTRACT This work presents preliminary measurements designed to explore a new approach to neutron diffraction that is somewhat analogous to the pseudo-Laue technique, except that instead of using a broad energy (wavelength) bandwidth it uses a broad angular bandwidth. We have used a polycapillary focusing optic to focus neutrons from a monochromatic beam (using the BT-8 spectrometer on the NIST research reactor) and from a polychromatic beam at a pulsed spallation source (the Intense Pulsed Neutron Source, IPNS at Argonne National Laboratory) into a small, intense spot and have carried out preliminary diffraction measurements. Using the single crystal diffraction (SCD) facility on IPNS, diffraction of a 3 o convergent beam from an alpha quartz crystal showed six diffraction beams in the 1-5 Å wavelength bandwidth transmitted by the optic. The diffraction spots showed an intensity gain of 5.8±0.9 compared to a direct beam diffracting from the same sample volume as that illuminated by the convergent beam. INTRODUCTION Rapid, accurate, high-resolution structural analysis of proteins is central to the success of rational drug design and other medical and scientific applications. Neutron diffraction has powerful and unique potential for determination of the structure and dynamics of proteins including direct determination of hydrogen positions, solvent association, etc

Neutron residual stress measurements in rails

Rails were among the first objects of study by neutron diffraction strain measurement and the first experiments were done as early as the late 1980s [1, 2]. This interest is easy to explain: the problem of rail fracturing is critical from the public safety point of view and the penetrating ability of neutrons suggested the possibility of breakthrough experiments and fast progress in this field. It was well-established that residual stresses, both near-surface and interior, played a signifi cant role in the development of defects which led to rail failure. This suggested three distinct approaches of neutron diffraction strain measurement that could contribute to various problems of the rail industry. The first method was to map the complete triaxial stress distribution non-destructively in the interior of an intact rail, ideally before and after significant service. Another approach was to use slices, for example to characterize how different processing methods produce favourable or detrimental stress distributions in rails. A third technique was to make non-destructive measurements, but in critical and not very deep portions of rails, for example, to examine defects and their relation to rail failure in the top running surface of rails, e.g. white layer formation