Optimization of Composite Structures to Delay Mode Jump Instabilities

摘要

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 remove a mode jump by increasing the skin thickness of the postbuckling region. A lay up optimization methodology, 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 secondary instabilities. This routine was linked to the genetic algorithm to find a revised layup for the skin bay, 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.