NASA Scientific and Technical Aerospace Reports

20060001806 North Carolina State Univ., Raleigh, NC USA
Promotion or Retention of Desired Metastable and Ultrafine Microstructures with an Electric Field or Current
Conrad, H.; Jung, K.; Narayan, J.; Oct. 13, 2005; 28 pp.; In English; Original contains color illustrations
Contract(s)/Grant(s): DAAD19-02-1-0315
Report No.(s): AD-A440284; 5-21616F; ARO-41893.29-MS; No Copyright; Avail.: Defense Technical Information Center
(DTIC)
The influence of an electric field on the equlibria and kinetics of grain growth and phase transformations in metals and
the resulting mechanical properties were determined, with attention to ultrafine and nanometer microstructures. The
phenomena and materials considered were: (a) precipitation in Al-Mg-Si alloys, (b) phase coarsening in 60Sn40Pb solder
joints, (c) grain growth in electrodeposited Cu and (d) dependence of the plastic flow stress on grain size. Regarding (a), a
field applied during solutionizing increased the solubility of the pertinent constituents and in turn the tensile properties in the
naturally-aged temper. Thermodynamic considerations along with HRTEM and SAED studies indicated that the field reduced
the Gibbs free energy of solution, increased the size of the naturally-aged precipitates and changed their crystal structure.
Regarding (b), a field retarded coarsening of the Sn and Pb phases and changed their volume fractions. The effect of the field
on phase coarsening appeared to be through its effect on the diffusion coefficient. Regarding (c), a field retarded grain growth.
Whether the field retarded grain boundary mobility or enhanced the annihilation of the crystal defects responsible for the
driving force was not clear. Regarding (d), analysis of the effect of grain size d on the flow stress of metals and compounds
over the range from nanometers to millimeters indicated three regimes: Regime I (d\g^10-6m), Regime II (d=10-8-10-6m) and
Regime III (d\h10-6m). Dislocations are active in I and II and obscent in III. The mechanism governing Regime III appears
to be grain boundary shear accommodated by grain boundary diffusion. Unique pulsed laser vapor deposition techniques were
employed to fabricate: (a) metals and compounds with nanometer grain size, (b) La0.7Sr0.3MnO3/ZnO heterostructures and
(c) nanodot metals embedded in ceramic matrices, and their respective novel mechanical or electrical properties were
determined.
DTIC
Electric Current; Electric Fields; Metastable State; Microstructure
20060001808 Ohio State Univ., Columbus, OH USA
Dynamic Analysis of Sliding Friction in Rotorcraft Geared Systems
Singh, Rajendra; Sep. 17, 2005; 7 pp.; In English
Contract(s)/Grant(s): DAAD19-02-1-0334
Report No.(s): AD-A440286; ARO-42571.3-EG; No Copyright; Avail.: CASI: A02, Hardcopy
This comprehensive study has examined the key effects of sliding friction in spur and helical gear dynamic models,
vibro-acoustic sources and geared system responses. First, many dynamic phenomena that emerge due to the interactions
between time-varying mesh stiffness, sliding friction and/or surface finish are successfully formulated. Second, new
multi-degree-of-freedom models considering both torsional and translational dynamics of spur and helical gear pairs have been
developed. These include time-varying mesh stiffness, sliding friction excitation and shaft/bearing compliances. Line-of-action
and off-line-of-action motion predictions, based on the lumped gear dynamic models, match well with a benchmark finite
element/contact mechanics code. Third, new mathematical models have been proposed to examine structure-borne and
air-borne noise that should arise due to surface asperities as a function of operating speed and surface finish. Fourth, mobility
type frequency response studies of the system vibro-acoustic characteristics provide new insights into dynamic forces at the
bearings and sound radiation. Fifth, two sets of experimental studies at ARL/NASA Glenn were conducted. Gear noise source
and lumped system models match well with experiments on ARL/NASA spur gears. Finally, a set of helical gears has been
designed that clearly isolate the effects of sliding friction. Suggestions for future research are included.
DTIC
Rotary Wing Aircraft; Sliding Friction
20060001812 Air Force Inst. of Tech., Wright-Patterson AFB, OH USA
Effects of Boundary Layer Flow Control Using Plasma Actuator Discharges
Newcamp, Jeffrey M.; Sep. 1, 2005; 125 pp.; In English; Original contains color illustrations
Report No.(s): AD-A440294; AFIT/GAE/ENY/05-S05; No Copyright; Avail.: Defense Technical Information Center (DTIC)
This study addresses the usage and effects of atmospheric plasma discharges on the near wall flow conditions for a Pak-B
low-pressure turbine blade. A plasma actuator was built normal to the freestream flow in a low-speed wind tunnel. The test
section of the wind tunnel had a contoured upper wall geometry designed to mimic the suction side of a Pak-B turbine blade.
A high frequency ac voltage source supplied three voltages in the kilovolt range at four Reynolds numbers in the experiment,
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