Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Magnetomechanical damping capacity of Tb/sub x/Dy/sub 1-x/Fe/sub 1.92/(0.30/spl les/x/spl les/0.50) alloys

Abstract: The stress-strain hysteresis losses of Tb/sub x/Dy/sub 1-x/Fe/sub 1.92/(x=0.30, 0.33, 0.40, 0.45, and 0.50) were measured at a variety of magnetic fields between 0 and 1600 Oe. Stress ranges from /spl sim/0 to -10, -20, -40, and -60 MPa (the minus sign indicates compressive stresses) were used. The hysteresis loop area increased from 5.7 kJ/m/sup 3/ at x=0.30 to 10 kJ/m/sup 3/ at x=0.50 as the Tb concentration and the magnetic anisotropy increased. The position of the hysteresis loop shifted to larger compressive stresses as the magnetic field was increased allowing the strength of the damping to be controlled by the magnetic field.

Dislocation Mechanics Based analysis of Material Dynamics Behavior : Enhanced Ductility, Deformation Twinning, Shock Deformation, Shear Instability, Dynamic Recovery

Abstract: Further developments are described for the dislocation mechanics based constitutive equation analysis previously used to describe the separate dynamic stress-strain behavior of fcc and bcc metal polycrystals. An enhanced hardening and ductility in copper and certain tantalum materials at higher strain rates in split Hopkinson pressure bar tests and in shock loading are attributed to enhanced dislocation generation rather than to dislocation drag. Added material strengthening is accounted for also by deformation twinning in ARMCO iron and titanium and in shocked copper and tantalum. The separate equations are applied to calculate the critical strain for shear banding in copper, iron, and the titanium alloy, Ti-6Al-4V. In the two latter cases, the results are very sensitive to the details of the strain-hardening behavior and the need is demonstrated for a dynamic recovery factor to account for the onset of shear banding. Consideration is given also to the possibility that shear band behavior requires explanation on a more fundamental Hall-Petch dislocation pile-up basis.

Microwave Nondestructive Detection of Corrosion Under Thin Paint and Primer in Aluminum Panels

Abstract: Detection of corrosion, under paint and primer, in various metallic structural components, particularly when used in moist and salty environments is an important practical concern. Moreover, nondestructive testing techniques that do not require paint removal are desired. Near-field microwave nondestructive inspection techniques, employing open-ended rectangular waveguide probes, have shown tremendous potential for detecting and evaluating the presence of corrosion under paint in steel substrates. The objective of this investigation has been to investigate the potential of these techniques for detecting corrosion under paint and primer in aluminum substrates. To accomplish this goal, an electromagnetic formulation, simulating detection of corrosion in layered structure using open-ended rectangular waveguide probes, was used to gain an insight into the functionality of measurement parameters such as the frequency of operation and standoff distance. In conjunction with this simulation, the dielectric properties of paint, primer, real and chemically produced aluminum oxide were measured in a wide range of microwave frequencies (2.6–18 GHz). The results showed that the dielectric properties of paint, primer and aluminum oxide are very similar to each other. Subsequently, the theoretical simulation was conducted in a wide frequency band (8.2–40 GHz). The overall result of the simulation effort was that higher frequencies and standoff distances of a few mm are more optimal for detecting thin corrosion layers under paint. Two specially prepared aluminum panels with induced areas of corrosion and surface pitting were produced as well. Using these panels and several phase sensitive measurement systems, experiments were conducted producing 2-D images of various areas of these panels. Images were produced at different standoff distances and at frequencies of 9, 11.725, 24.1, and 33.5 GHz. The overall results of the experimental investigation were extremely promising when detecting the thin regions of corrosion in these panels. This paper presents the approach and results of this investigation.

Magnetostriction of Terfenol-D heat treated under compressive stress

Abstract: Heat treatment at temperatures >835/spl deg/C and compressive stresses >80 MPa substantially increased the magnetostrictive performance of Terfenol-D (Tb/sub 0.3/Dy/sub 0.7/Fe/sub 1.92/) under the condition of zero loading. This heat treatment created a built-in prestress which significantly increased the low stress magnetostriction and substantially altered the magnetization curve by reducing its initial susceptibility. For measurements at compressive stresses >15 MPa the effect of the built-in stress was minimal and the magnetostrictive performance was not appreciably altered.