Manufacturing Imperfections of Open Cross-Section Ultrathin Composite Deployable Shells

Accurate characterization of the geometric imperfections in thin-shell deployable structures is important, since both local and global deviations from nominal design shapes can result in significant reductions in buckling loads. Hence, to enable high-fidelity modeling of thin-shell composite Triangular Rollable and Collapsible (TRAC) longerons for future applications, this work develops a method for measuring and analyzing the geometric imperfections in longerons that were manufactured using two different methods. The mean geometrical parameters, axial twist, and the lengths, amplitudes and locations of local radial imperfections were measured and quantified. The dominant imperfections introduced by both manufacturing methods were determined and categorized into local outward (bump) and inward (dimple), and circumferential outward (ridge) and inward (valley) radial deviations. The overall mean imperfection amplitude was found to be six to seven times the shell thickness for bumps, dimples and ridges, and about ten times the thickness for valleys.