Local and global buckling of ultra-lightweight IsoTruss® structures

The local and global compressive buckling behavior of stability-critical, high-aspect ratio, cantilevered composite IsoTruss® grid structure columns was examined. The influence of local bay length and number of carbon fiber tows in the longitudinal and helical members on the compressive strength of IsoTruss® columns was examined. Four 3-m (118.0 in.) long IsoTruss® specimens were fabricated and tested in axial compression with fixed-free boundary conditions. The test results exhibit the same trend as the finite element predictions, although the error is higher for shorter bay lengths. Local buckling depends on bay length, with higher buckling loads observed for shorter bay lengths. Global buckling, on the other hand, is independent of bay length; although increasing the bay length reduces the weight and thus increases the overall efficiency of an IsoTruss® structure. The Euler column buckling prediction only considers the overall diameter and the axial stiffness of the longitudinal members; therefore, Euler buckling predictions are accurate only for IsoTruss® configurations that fail in global buckling.