Optimization of Composite Structures to Delay Mode Jump Instabilities

Abstract

DOI: 10.2514/1.J050590 Numerous studies have shown that postbuckling stiffened panels may undergo abrupt changes in buckled mode shape when loaded in uniaxial compression. This phenomenon is often referred to as a mode jump or secondary instability. The resulting sudden release of stored energy may initiate damage in vulnerable regions within a structure, for example, at the skin-stiffener interface of a stiffened composite panel. Current design practice is to removeamodejumpbyincreasingtheskinthicknessofthepostbucklingregion.Alayupoptimizationmethodology, based on a genetic algorithm, is presented, which delays the onset of secondary instabilities in a composite structure while maintaining a constant weight and subject to a number of design constraints. A finite element model was developed of a stiffened panel’s skin bay, which exhibited secondary instabilities. An automated numerical routine extracted information directly from the finite element displacement results to detect the onset of initial buckling and secondaryinstabilities.Thisroutinewaslinkedtothegeneticalgorithmto findarevisedlayupfortheskinbay,within appropriate design constraints, to delay the onset of secondary instabilities. The layup optimization methodology, resulted in a panel that had a higher buckling load, prebuckling stiffness, and secondary instability load than the baseline design.