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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. [ABSTRACT FROM AUTHOR]

This paper describes the analyses performed to determine why nominally flat composite isogrid panels designed for the Clementine I satellite were warping during the autoclave cure cycle. Analytical models indicated that the largest factor was the mismatch in the coefficient of thermal expansion of different parts of the tooling. The next most important factor was the coefficient of thermal expansion mismatch between the skin and rib materials of the composite isogrid itself. A new tooling design eliminated the first factor, producing a rib-only panel with no warping. An analytical model was developed, which predicted that warping caused by the rib/skin mismatch would be 3.31 mm over a length of 147.32 cm. A panel with the skin was manufactured and found to have a warp of 3.80 mm. Further improvements in producing flat panels will depend on finding appropriate materials for the rib and skin. [ABSTRACT FROM AUTHOR]