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: Sonar & Radar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

J and CTOD Estimation Equations for Shallow Cracks in Single Edge Notch Bend Specimens

Abstract: Fracture toughness values determined using shallow cracked single edge notch bend, SE(B), specimens of structural thickness are useful for structural integrity assessments. However, testing standards have not yet incorporated formulas that permit evaluation of J and CTOD for shallow cracks from experimentally measured quantities (i.e. load, crack mouth opening displacement (CMOD), and load line displacement (LLD)). Results from two dimensional plane strain finite - element analyses are used to develop J and CTOD estimation strategies appropriate for application to both shallow and deep crack SE(B) specimens. Crack depth to specimen width ( a/W ) ratios between 0.05 and 0.70 are modelled using Ramberg Osgood strain hardening exponents ( n ) between 4 and 50. The estimation formulas divide J and CTOD into small scale yielding ( SSY ) and large scale yielding ( LSY ) components. For each case, the SSY component is determined by the linear elastic stress intensity factor, K I . The formulas differ in evaluation of the LSY component. The techniques considered include: estimating J or CTOD from plastic work based on load line displacement ( A pl | LLD ), from plastic work based on crack mouth opening displacement ( A pl | CMOD ), and from the plastic component of crack mouth opening displacement (CMOD pl ). A pl | CMOD provides the most accurate J estimation possible. The finite - element results for all conditions investigated fall within 9% of the following formula:

Frontiers in Thermionic Cathode Research

Abstract: The high electron emission resulting from low-work-function scandate-added dispenser cathodes has generated a great deal of interest and research since the late 1970s. Despite the reported high current density at low temperatures, scandate cathodes have not yet seen wide-scale industrial adoption due to poor emission uniformity, inadequate reproducibility, and short lifetimes. This lack of industrial adoption stemming from the above issues is likely due to insufficient fundamental understanding of the role that scandium plays in the emission process. Recent work by five research teams under the U.S. Defense Advanced Research Projects Agency Innovative Vacuum Electronics Science and Technology Program aims at advancing this fundamental understanding and the cathode manufacturing processing. Emission microscopy of model surfaces of adsorbed Ba–Sc–O on single crystal tungsten and detailed characterization techniques, such as Wulff shape analysis, are being used to understand the morphology, composition and phase of each of the species that comprise the cathode emitting surfaces. The structure of tungsten grains at the cathode surface of activated and unactivated scandate cathodes and the resulting emission performance are observed. 3-D printing is being investigated as an advanced manufacturing method to meet the demanding requirements of modern vacuum electron devices. Finally, density functional theory is being employed to study the work function of perovskite oxides as a novel class of alternative materials to tungsten dispenser cathodes.

Total-energy local-spin-density approach to structural and electronic properties of ferromagnetic iron.

Abstract: Obtention des proprietes structurales du fer bcc a partir de calculs de structure electronique d'energie totale comme fonction de la constante de reseau et grâce a l'utilisation de la methode d'onde plane augmentee, polarisee par un potentiel entier et a l'approximation de densite de spin local. Presentation des structures de bandes electroniques, de la densite des etats et de la surface de Fermi a la constante de reseau d'equilibre calculee, comparaison aux donnees de de Haas-van Alphen

High-repetition-rate hydrogen spark gap

Abstract: A high-power spark-gap switch capable of 100- mu s recovery times can be constructed without gas flow by using high-pressure hydrogen gas and by triggering the main gap in a highly undervolted state. These techniques have been demonstrated to work at voltages up to 120 kV, peak currents of up to 170 kA, and energy transfers of up to 12.5 kJ. Tests underway to test the concepts at 600 kV and for multiple-pulse bursts are discussed. >