Analysis and Compression Testing of 2024 and 8009 Aluminum Alloy Zee-Stiffened Panels

Zee-stiffened compression test panels, fabricated with dispersion-strengthened, high-temperature 8009 aluminum alloy sheet, were evaluated to determine the alloy’s feasibility for compression-critical applications. A compression panel design configuration was obtained using a strength analysis program that predicts the post-skin buckling strength of flat or curved-skinned, metallic-stiffened structure. Three short-column panels were tested to failure at room temperature: (a) a baseline riveted panel fabricated with 2024-T62 aluminum zee stringers and a 2024-T81 aluminum skin, (b) a riveted panel fabricated with 8009 aluminum zee stringers and skin, and (c) a resistance spot-welded panel fabricated with 8009 aluminum zee stringers and skin. The 8009 alloy exhibited pronounced, compressive strength anisotropy, necessitating panel orientation to take advantage of the higher compressive yield in the sheet transverse direction. Compression test results were in good agreement with the predicted compression allowables since they were within 5 percent of the test strength. The 8009 aluminum riveted panel exhibited superior skin buckling resistance and failed in the wrinkling mode, as predicted, at a load approximately 15 percent higher than that of the baseline 2024 panel. The spotwelded 8009 panel did not fail in the wrinkling mode since the spot welds failed in tension shortly after the skin locally buckled. The latter test indicates that the spot welded skin-stringer combinations should not be used above the buckling stress. Due to its excellent microstructural stability at elevated temperatures, high-temperature compression panels of 8009 alloy offer potential weight savings of 25 percent compared with conventional aluminum alloys.