Isogrid Structural Tests and Stability Analyses

Test results and related structural instability analyses are presented for a 10-ft-diam, 37-in.-long cylinder, and a 10-ft-diam, 40 in.-long, 45-deg. conical frustum. Both structures are based upon flanged isogrids and are fabricated in 2024-T851 aluminum. Peak edge load intensities at failure were 1,654 Ib/in. for the cylinder, and 1,457 Ib/in. at the small diam of the frustum. General instability cylindrical-monocoque-structure equivalent knockdown factors for both were in good agreement (7 = 0.48). Design analysis is also derived for estimating critical cylinder instability edge loads from the performance of two tandem isogrid members. Evaluation is made of effective skin contributing to isogrid load-carrying cross-section.