Nonlinear bending compliance of closed-sectioned composite beam structures by local compression flange buckling

Abstract

Passive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. This paper presents a passive spanwise bending shape-adaption concept for highly loaded wing-like structures based on local buckling of the compression flange at a prescribed external bending moment. Buckling reduces the in-plane stiffness of the compression flange and thus yields a beam design with a high prebuckling and a low postbuckling bending stiffness. The investigated concept is experimentally validated using a composite four-point bending beam, which is designed to experience compression flange buckling between the load introductions. The point of buckling is at 374.80 Nm, and ultimate failure occurred in the experiment at 524 Nm, which results in a postbuckling range of 149.2 Nm. The bending stiffness was reduced by more than 41% after the point of buckling which shows the effectiveness of compression flange buckling for nonlinear bending compliance. This proof of concept has demonstrated for the first time, that compression flange buckling is a viable structural concept for highly loaded composite beam structures to achieve nonlinear bending compliance.