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An investigation was carried out to characterize the effect of aging, environment (include [NaCl] concentration), and load ratio on fatigue crack growth kinetics of Al 7075 alloy. The materials investigated were peakaged Al 7075-T651 and overaged Al 7075-T7351. The results indicate: (1) the fatigue crack growth rates and fatigue crack growth threshold, Kth, for Al 7075-T651 and Al 7075-T7351 are comparable at similar stress ratios in each of the three test environments (vacuum, ambient air, and 1% NaCl solution); (2) irrespective of Al 7075 aging conditions and stress ratios, the fatigue crack growth rates are lowest in vacuum, followed by those in ambient air, and are highest in 1% NaCl; (3) for both Al 7075-T651 and Al 7075-T7351, the fatigue crack growth rates initially increase rapidly when [NaCl] increases from 0.001 to 1% and then remain unchanged when [NaCl] further increases from 1 to 15%; and (4) for both Al 7075-T651 and Al 7075-T7351, the fatigue crack growth rates are higher at higher stress ratio in all three environments and the Kth progressively decreases as the load ratio increases., The original document contains color images.

In pulsed laser deposition of YBa2Cu3O7-delta films, defect introduction into the films tends to anisotropically improve the pinning along the Hc direction due to the columnar growth mode of the process. In Eu-substituted samples, however, even though an increase in critical current density (Jc) in the Hc direction was observed for low fields (H = 0.2 T), the improvement was more notable for the Hab-plane at both low and higher fields. Herein we present detailed TEM microstructural studies to understand these new trends in Jc(H), which are markedly different than flux pinning increases achieved with other methods, for example, with nanoparticle additions. Threading dislocations, observed in the Eu-substituted samples along the c-axis, account for Jc enhancement with Hc at low field. The enhanced ab-planar pinning in the Eu-substituted samples is attributed to the extensive bending of the {0 0 1} lattice planes throughout the film, and the crystal lattice defects with excess Cu-O planes, that were effective in increasing the Jc for Hab at both low and high fields., Published in Physica C, Vol. 470, p318-322, 2010. Prepared in cooperation with the Naval Research Laboratory, Washington, DC. Sponsored in part by ONR.

High temperature superconducting (HTS) motors and generators will enable high-efficiency, high power density naval propulsion, and compact electrical generators for weapons and ship systems. The second-generation high temperature superconductors (2G-HTS) based on yttrium-barium-copper- oxide (YBCO) coated conductor architectures have undergone a processing technology breakthrough that has led to manufacturability of long lengths of these materials, sufficient for demonstrations of large motors and generators. Ensuring superior fatigue properties of the HTS materials compatible with the life-cycle of naval machinery is a key issue. NRL has been working closely with superconductor manufacturer Superpower, Inc., electric motor manufacturer Baldor Reliance, General Dynamics Electric Boat Division, and Naval Surface Warfare Center Carderock Division (Philadelphia) on risk mitigation demonstrations for a 10 MW HTS generator design. NRL's responsibility in this collaboration is assessment of the reliability of HTS coil design, particularly with respect to thermomechanical fatigue associated with cooling/warming between room temperature and the cryogenic temperatures at which the machines operate., Published in NRL Review, p180-181, 2009. Sponsored in part by NRL.

Strain localization in the presence of a stress gradient is a phenomenon common to many systems described by continuum mechanics. Variations of this complex phenomenon lead to interesting nonlinear effects in materials/engineering science as well as in other fields. Here, the synchrotron based energy dispersive x-ray diffraction (EDXRD) technique is used for high spatial resolution profiling of both compression and tension induced strain localization in important materials/engineering problems. Specifically, compression induced strain localization in shot peened materials and tension induced strain localization in the plastic zones adjoining the faces of a fatigue crack are profiled. The utility of the EDXRD synchrotron technique for nondestructively cross-sectioning strain variations on small length scales is described. While the strain field profiling relies on the shift of the Bragg lines, the data show that plastic deformation regions can also consistently be seen in the broadening of the Bragg peaks through the full width at half maximum parameter., Published in the Journal of Engineering Materials and Technology, v130 p1-10, April 2008. In-house contract.

As the Navy moves to the all-electric warship, superconducting materials will play a key enabling role. High temperature superconducting (HTS) motors and generators will enable extended range, high-efficiency, high-power density naval propulsion, and compact generators for weapons and ship systems. Compact mobile HTS generators also may provide portable/mobile power for littoral and expeditionary operation, naval air, and homeland security. The "second generation" high-temperature superconductors (2G-HTS) based on yttrium-bariumcopper- oxide (YBCO) "coated conductor" architectures are undergoing a processing technology breakthrough that will lead to large-scale manufacture by 2008. NRL is working with manufacturers to address key issues in the processing and performance of these conductors during this fast-paced stage of technology development. In particular, 2G-HTS process development is accelerated by fundamental understanding of the materials microstructures gained at NRL. Key goals include reduction of AC losses in the HTS motors and generators, as well as novel inductor designs for power electronics. Ensuring superior fatigue properties of the HTS materials compatible with the lifecycle of naval machinery is a key objective., Published in NRL Review, Materials Science and Technology, 2006.

A review of fatigue of coatings/substrates is presented. Fatigue damage is either local or general, depending on the range of cyclic loads. Local fatigue damage includes rolling contact fatigue (RCF), fretting fatigue, fatigue-wear and general wear. Applied loads are localized consisting of rolling contacts or sliding contacts, and the resulting damage is mostly surface related. Crack initiation, surface pitting, delamination, spalling, buckling and enhanced wear can result from local fatigue damage of coatings. General fatigue damage results when the loads are of longer range such as cyclic bending, torsion or uniaxial or biaxial tension/compression etc. The mechanics of fatigue, role of microstructure, micromechanics in terms of crack nucleation, growth and fracture are reviewed. Defects produced during processing form precursors for crack nucleation. It is shown that optimization of the processing conditions to minimize defect density is essential to enhance fatigue resistance of coatings/substrates., Final proceedings of the NATO Advanced Research Workshop on Nanostructured Films and Coatings, Santorini, Greece on 28-30 Jun 1999, p283-295. Prepared in cooperation with Dept. of Materials Science, National Univ. of Singapore, Kent Ridge, Republic of Singapore and Dept. of Ceramics and Materials Engineering, Rudgers Univ., NJ. This article is from ADA399041 NATO Advanced Research Workshop on Nanostructured Films and Coatings. Series 3. High Technology - Volume 78