Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

”cell”, containing this solution and 50mm long by 15mm high by 155mm wide, was placed in a superconducting magnet at Marshall
Space Flight Center. The magnetic field was measured at various positions within the bore of the magnet using a Hall effect
probe. In this way, a position was found where the magnetic field gradient was predominantly upward; the magnitude of the gradient
could then be adjusted by adjusting the current of the magnet. The ends of the cell consisted of machined copper blocks maintained
at controlled temperatures by circulating water from constant temperature baths. The walls of the cell were of rectangular
section glass tubing so that the cell contents could be seen. Velocities arising from thermal gradients within the cell were measured
by particle image velocimetry (PIV). Particles used for this purpose were silver-coated hollow glass spheres of micrometers diameter
and nearly the same density as the solution. A central vertical plane of the cell was illuminated by a laser beam passing through
a cylindrical lens. Digital images of the particles were captured on a CCD camera and fed to a computer so that frame-to-frame
movements of particles traveling with the fluid were captured. These images were employed to compute velocity maps using commercial
PIV software. In a typical experiment the cold end of the cell was maintained at 10C and the warm end at 30 C. With no
current in the magnet, i.e.- with natural -convection allowed to occur, the fluid was observed to circulate with an average speed
of approximately 0.3 millimeters per second. It was visually apparent that this circulation was diminished as the current was
increased. At currents of approximately 20A the flow was halted, to within the precision of the PIV measurements. At yet higher
currents the convection was reversed with the hotter solution sinking and the cooler solution rising. At 40A this reversed convection
had speeds averaging 0.43 millimeters per second. The measurements of susceptibility and density allow an estimate of the
field gradient necessary to halt convection in the experiment. That estimate was 7.8T (squared) per meter and the convection was
observed to halt in the magnet at a current giving 7.21T (squared) per meter from the magnetic field measurements. Calculations
of the flow have been carried out using the computational fluid dynamics software FLUENT and show good agreement with the
measurements.
Author
Convection; Magnetic Permeability; Solidification; Temperature Dependence; Computational Fluid Dynamics
50
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METALS AND METALLIC MATERIALS
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20000061970 NASA Glenn Research Center, Cleveland, OH USA
Bithermal Low-Cycle Fatigue Evaluation of Automotive Exhaust System Alloy SS409
Lu, Gui-Ying, Arvin Exhaust Systems, USA; Behling, Mike B., Arvin Exhaust Systems, USA; Halford, Gary R., NASA Glenn
Research Center, USA; [2000]; 32p; In English, 1 Nov. 1999, Cincinnati, OH, USA; Sponsored by American Society for Metals,
USA; No Copyright; Avail: CASI; A03, Hardcopy; A01, Microfiche
This investigation provides, for the first time, cyclic strainrange-controlled, thermomechanical fatigue results for the ferritic stainless
steel alloy SS409. The alloy has seen extensive application for automotive exhaust system components. The data were generated to calibrate
the Total Strain Version of the Strainrange Partitioning (TS-SRP) method for eventual application to the design and durability assessment
of automotive exhaust systems. The thermomechanical cyclic lifetime and cyclic stress-strain constitutive behavior for alloy SS409 were
measured using bithermal tests cycling between isothermal extremes of 400 and 800 C. Lives ranged up to 10,000 cycles to failure with
hold-times of 0.33 to 2.0 minutes. The bithermal fatigue behavior is compared to isothermal, strain-controlled fatigue behavior at both 400
and 800 C. Thermomechanical cycling was found to have a profound detrimental influence on the fatigue failure resistance of SS409
compared to isothermal cycling. Supplementary bithermal cyclic stress-strain constitutive tests with hold-times ranging from 40 seconds
up to 1.5 hours were conducted to calibrate the TS-SRP equation for extrapolation to longer lifetime predictions. Observed thermomechanical
(bithermal) fatigue lives correlated well with lives calculated using the calibrated TS-SRP equations: 70% of the bithermal fatigue data
fall within a factor of 1.2 of calculated life; 85% within a factor of 1.4; and 100% within a factor of 1.8.
Author
Cycles; Fatigue Life; Fatigue (Materials); Alloys; Ferritic Stainless Steels; Stress-Strain Relationships
20000064082 United Engineering Foundation, Inc., New York, NY USA
An Interdisciplinary Approach to the Science of Alloys in Metals, Minerals and Other Materials Systems, 7 Jan. 1999 -
6 Mar. 2000
Gonis, A.; Melke, A.; Rajan, K.; Turchi, P. E.; Sep. 15, 1999; 19p; In English; 2nd; Alloy, 8-13 Aug. 1999, Davos, Switzerland
Contract(s)/Grant(s): N00014-99-1-0895
Report No.(s): AD-A368788; 99-BS; No Copyright; Avail: CASI; A01, Microfiche; A03, Hardcopy; Abstract Only; Abstract
Only