Postbuckled behavior of composite isogrid stiffened shell structure

Abstract

This paper investigated reliability of a postbuckled composite isogrid stiffened shell structure under a compression load. The outside diameter of the isogrid cylinder was 624.8 mm, the length was 368.3 mm and the total weight of the cylinder was 3.24 kg. A finite element buckling analysis result was compared with the axial compression experimental data. The average critical buckling load of 186.56 kN was obtained by using the Patran finite element analysis (FEA). The isogrid shell was modeled using 3-node triangular elements and the stiffeners were modeled using 4-node quad elements with a total of 504 nodes and 900 elements. The postbuckled isogrid cylinder was compression tested to the failure load of 177.35 kN. The postbuckled cylinder continued to resist compression loading even after one or more stiffeners had fractured. The testing evaluation revealed that the stiffener buckling was the critical failure mode and it has been demonstrated to be tolerant to structural damage due to the multiplicity of load paths. The lower experimental bucking load was due to the small imperfections in the cylinder but this problem can be overcome by advancement in the manufacturing methods.