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The objective of this investigation was to establish the relationship between mechanical property anisotropy, microstructure and crystallographic texture in integrally 'T'-stiffened extruded panels fabricated from the Al-Li alloys 2195, 2098 and 2096. In-plane properties were measured as a function of orientation at two locations in the panels, namely mid-way between (Skin), and directly beneath (Base), the integral 'T' stiffeners. The 2195 extrusion exhibited the best combination of strength and toughness, but was the most anisotropic. The 2098 extrusion exhibited lower strength and comparable toughness, but was more isotropic than 2195. The 2096 extrusion exhibited the lowest strength and poor toughness, but was the most isotropic. All three alloys exhibited highly elongated grain structures and similar location-dependent variations in grain morphology. The textural characteristics comprised a beta + fiber texture, similar to rolled product, in the Skin regions and alpha + fiber texture, comparable to axisymmetric extruded product, in the Base regions. In an attempt to quantitatively correlate texture with yield strength anisotropy, the original 'full constraint' Taylor model and a variant of the 'relaxed constraint' model, explored by Wert et al., were applied to the data. A comparison of the results revealed that the Wert model was consistently more accurate than the Taylor model.Hales, Stephen J. and Hafley, Robert A.Langley Research CenterCORRELATION; MICROSTRUCTURE; MECHANICAL PROPERTIES; CRYSTALLOGRAPHY; ALUMINUM-LITHIUM ALLOYS; ANISOTROPY; EXTRUDING; YIELD STRENGTH
This chapter describes the development of crystallographic texture and its effects on mechanical properties in aluminum-lithium alloys. Crystallographic texture evolves during the forming of wrought products from cast ingots of Al-Li alloys and consequently affects the mechanical properties. Practical approaches to control the texture have been developed and have been successfully used in the products obtained from industrial-scale ingots. This texture tailoring has significantly reduced the yield strength anisotropy. In addition, theoretical approaches have been used to model the yield strength anisotropy of aluminum alloys in the presence of complex precipitates.
Mechanical, thermal fatigue and stress corrosion properties were determined for the two lots of Al-Li X2096-T8A3 extruded beams. Based on the test results, the beams were accepted as the construction material for fabrication of the Hubble Space Telescope new Solar Array Support Structure.Flom, Y. and Viens, M. and Wang, L.Goddard Space Flight CenterALUMINUM-LITHIUM ALLOYS; SPACECRAFT CONSTRUCTION MATERIALS; HUBBLE SPACE TELESCOPE; BEAMS (SUPPORTS); CORROSION TESTS; FATIGUE TESTS; THERMAL CYCLING TESTS; STRESS CORROSION; THERMAL FATIGUE; MECHANICAL PROPERTIES; THERMODYNAMIC PROPERTIES; SOLAR ARRAYS; EXTRUDING
The mechanical properties of (1) a 7049-T73 bar extrusion, (2) a 7049-T73 integrally stiffened extrusion and (3) a 7049-T76 bar extrusion were evaluated. The evaluation encompassed tensile, fracture toughness, axial fatigue, stress corrosion, and fatigue crack growth testing at several temperatures from -65 F to 500 F.