Simplified methods for the buckling analysis of composite multi-spar wing boxes

Abstract

Two simplied methods for the buckling analysis of multi-spar wing boxes made from composite materials are presented. The spars divide such boxes into cells. Both methods, called the lower bound method and the repetitive analysis method, are computationally much quicker than analysing a complete wing box because they consider only one cell at a time. The lower bound method has only been briefly considered previously and the lower bounding property is guaranteed by theory. This method gives guaranteed conservatism when designing. The repetitive analysis method is very quick and the data preparation small. However it is not guaranteed to give lower bound answers and is thus not favoured by the authors except for structures that are nearly repetitive. Both methods are illustrated by using the computer program VICONOPT to analyse six variants of a laboratory test specimen of the type used when developing multi-spar wing boxes. The results indicate that the lower bound method usually achieves an accuracy well within 10%.