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From:
Scott Malaznik (Senior Staff Engineer, Lockheed Martin Aeronautics Company, Palmdale, California),
“Crippling of thin-walled composite sections using progressive failure analysis”, Lockheed Report AM-CONF13-43, 2013
Summary: Aircraft structures, both metallic and composite, are often stiffened with thin-walled sections of various shapes to resist compression loads efficiently. Analysis of these structures can be challenging, and empirical methods are often used for design purposes. Since initial buckling is not necessarily indicative of structural failure, the analysis must be carried into the post-buckling range, where geometric and material nonlinearities are present. Final failure in this context is called crippling, which corresponds to the maximum load carried by the section.
In this paper, the nonlinear capabilities of MSC Nastran SOL 400 are used to perform post- buckling analysis of graphite/epoxy composite I-section stiffeners. After performing an eigenvalue buckling analysis, initial imperfections in the shape of the buckling modes are applied to the model to start the large displacement analysis. Composite material failures are modeled using the Progressive Failure Analysis (PFA) feature of SOL 400. Results are plotted as load- displacement curves, and crippling failure is defined as the maximum load carried. Results are compared to published test data as well as MIL-HDBK-17 design equations.
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