Passive twisting of composite beam structures by elastic instabilities

This paper introduces a purely passive shape adaptation mechanism for applications in lift generating structures, such as wings. We focus on tailoring the bending-twisting response to a spanwise loading of thin-walled rectangular composite beam structures by intentionally inducing elastic instabilities. For this purpose, the component is designed with a particular material anisotropy utilising unidirectional fibre reinforced composites. Tailoring the fibre orientation and web thickness enables the onset of buckling to be triggered purely passively at a prescribed level of external loading. We utilise the modified load-structure interaction resulting from the deliberate occurrence of externally triggered elastic instabilities to achieve a desired buckling-induced sectional twist. Analytical and numerical models are developed to obtain bounds on the attainable stiffness and shape adaptability by exploiting purposely induced elastic instability. The accuracy and validity of the obtained predictions are confirmed with experimental results from composite beam demonstrators. The study demonstrates the possibility of creating functionality exploiting elastic instabilities, resulting in a novel passive shape adaptation mechanism for simple composite structures.