Verification study on buckling behaviour of composite cylinder with eccentric supports

摘要

Imperfection sensitive structures such as unstiffened or skin-dominant shell structuresrnare commonly used for aeronautic and aerospace applications. Cylindrical shells arerndominating satellite launcher structures and a reliable methodology to calculate theirrnbehaviour in the early stages of design is fundamental to achieve optimum results.rnLauncher design requires fast and precise prediction of structural weight as well itsrnweight distribution already in the early design phase, because in that phase differentrnconcepts of the whole launcher system have to be evaluated in order to identify thernoptimal one. The prediction has to be precise, because less reliable ones might lead tornbasic changes, later in the detailed design phase, which might also influence the designrnof the whole system. Such changes in later design phases are extremely costly in termsrnof time and money; they definitely have to be avoided.rnThe dimensioning criterion with the design of launcher structures is buckling notrnbefore ultimate load, thus they do not have an exploitable post-buckling area. The mostrncritical aspect for numerical buckling prediction is the structure’s sensitivity to geometricrnand loading imperfections. Currently, imperfection sensitive shell structures prone tornbuckling are designed according to the NASA SP-8007 guideline [1], from 1968, usingrnits conservative lower bound curve. In this guideline the structural behaviour ofrncomposite materials is not appropriately considered, since the imperfection sensitivityrnand the buckling load of shells made of such materials depend on the lay-up design.rnThere is no specific design guideline for imperfection sensitive composite structuresrnprone to buckling. NASA performed high investments for the last 5 years with onernproject called “Shell Buckling Knock-down Factor” (SBKF) in order to develop a newrnguideline to calculate the knock-down factor of cylindrical shells prone to buckling [2],rnand also the European project DESICOS [3] (New Robust DESign Guideline forrnImperfection Sensitive COmposite Launcher Structures) is working on newrnmethodologies to estimate the ultimate load of such structures. An example ofrnapplicability of these new design guidelines could be the next generation of thernEuropean launchers family “Ariane” in order to maintain the actual position in thernsatellite launchers market [4].