Postbuckled behavior of composite isogrid stiffened shell structure

This paper investigated reliability of a postbuckled composite isogrid stif fened 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 weigh t of the cylinder was 3.24 kg. A finite element buckling analysis result wa s compared with the axial compression experimental data. The average critic al buckling load of 186.56 kN was obtained by using the Patran finite eleme nt analysis (FEA). The isogrid shell was modeled using 3-node triangular el ements and the stiffeners were modeled using 4-node quad elements with a to tal of 504 nodes and 900 elements. The postbuckled isogrid cylinder was com pression tested to the failure load of 177.35 kN. The postbuckled cylinder continued to resist compression loading even after one or more stiffeners h ad fractured. The testing evaluation revealed that the stiffener buckling w as the critical failure mode and it has been demonstrated to be tolerant to structural damage due to the multiplicity of load paths. The lower experim ental bucking load was due to the small imperfections in the cylinder but t his problem can be overcome by advancement in the manufacturing methods.