NASA Scientific and Technical Aerospace Reports

texture during fatigue cycling of rolled aluminum 2024-T3 sheet was monitored using x-ray diffraction techniques. The texture
development was calculated as a function of number of fatigue cycles: (1) to determine whether texture changes as a material
is fatigued and (2) to correlate the development of texture to crack formation. X-ray diffraction measurements show that the
rolling direction initially lies normal to the preferred plane on which grains are oriented. In Millers indices, the rolling
direction and the normal plane are denoted as (100) and (100) respectively. Upon fatigue cycling, an initially rapid
development of texture is found to occur. Prior to cracking, the grains rotate such that the (100) direction lies along the stress
axis. The rate of texture development is dependent on the direction of the strain axis with respect to the rolling direction of
the aluminum and the number of cycles to failure. After crack initiation, the texture development slows down and changes
gradually until the point of failure. This demonstrates that texture development does indeed occur with fatigue and plays a role
in the development of cracks in the aluminum sheet. A more detailed study is required to develop a diagnostic test for
proximity to crack initiation.
NTIS
Airframes; Fatigue (Materials); Crack Initiation
20040111232 NASA Langley Research Center, Hampton, VA, USA
Experimental Results on the Feasibility of an Aerospike for Hypersonic Missiles
Huebner, Lawrence D.; Mitchell, Anthony M.; Boudreaux, Ellis J.; [1995]; 11 pp.; In English; 33rd Aerospace Sciences
Meeting and Exhibit, 9-13 Jan. 1995, Reno, NV, USA
Report No.(s): AIAA Paper 95-0737; Copyright; Avail: CASI; A03, Hardcopy
A series of wind tunnel tests have been performed on an aerospike-protected missile dome at a Mach number of 6 to obtain
quantitative surface pressure and temperature-rise data, as well as qualitative flow visualization data. These data were used
to determine aerospike concept feasibility and will also provide a database to be used for calibration of computational fluid
dynamics codes. Data were obtained on the hemispherical missile dome with and without an aerospike that protrudes ahead
of the dome along the axisymmetric center line. Data were obtained on two models (one pressure, one temperature) in the
NASA Langley 20-Inch Mach 6 Tunnel at a freestream Reynolds number of 8.0 x 10(exp 6) per feet and angles of attack from
0 to 40 degrees. Surface pressure and temperature-rise results indicate that the aerospike is effective for very low angles of
attack (less than 5 degrees) at Mach 6. Above 5 degrees, impingement of the aerospike bow shock and the flow separation
shock from the recirculation region created by the aerospike causes pressure and temperature increases on the windward side
of the dome which exceed values observed in the same region with the aerospike removed. Flow characterization obtained via
oil-flow and schlieren photographs provides some insight into the quantitative surface data results, including vortical flow and
shock-wave impingement.
Author
Aerospike Engines; Computational Fluid Dynamics; Feasibility; Missiles; Hypersonic Wind Tunnels; Hypersonic Speed
20040111293 NASA Langley Research Center, Hampton, VA, USA
Grid Sensitivity and Aerodynamic Optimization of Generic Airfoils
Sadrehaghighi, Ideen; Smith, Robert E.; Tiwari, Surendra N.; [1995]; 8 pp.; In English
Contract(s)/Grant(s): NCC1-68; Copyright; Avail: CASI; A02, Hardcopy
An algorithm is developed to obtain the grid sensitivity with respect to design parameters for aerodynamic optimization.
The procedure is advocating a novel (geometrical) parameterization using spline functions such as NURBS (Non-Uniform
Rational B- Splines) for defining the airfoil geometry. An interactive algebraic grid generation technique is employed to
generate C-type grids around airfoils. The grid sensitivity of the domain with respect to geometric design parameters has been
obtained by direct differentiation of the grid equations. A hybrid approach is proposed for more geometrically complex
configurations such as a wing or fuselage. The aerodynamic sensitivity coefficients are obtained by direct differentiation of the
compressible two-dimensional thin-layer Navier-Stokes equations. An optimization package has been introduced into the
algorithm in order to optimize the airfoil surface. Results demonstrate a substantially improved design due to maximized
lift/drag ratio of the airfoil.
Author
Airfoil Profiles; Algorithms; Optimization; Sensitivity Analysis; Grid Generation (Mathematics); Sensitivity; Aerodynamic
Configurations
20040111295 NASA Langley Research Center, Hampton, VA, USA
Rapid Airplane Parametric Input Design(RAPID)
Smith, Robert E.; Bloor, Malcolm I. G.; Wilson, Michael J.; Thomas, Almuttil M.; [2004]; 11 pp.; In English
Report No.(s): AIAA Paper 95-1687; Copyright; Avail: CASI; A03, Hardcopy
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