Identification of Nonlinearity Sources in a Flexible Wing

High aspect ratio flexible wings are of increasing interest for enhancing the aerodynamic efficiency of future designs. However, they often exhibit nonlinear dynamic behavior, complicating both testing and analysis. This paper presents a novel framework aimed at identifying the sources of such nonlinearities, focusing on a wing that previously displayed softening behavior during previous ground vibration test campaigns. The framework combines nonlinear modal analysis, backbone curve extraction from free-decay data, and advanced time-frequency analysis using superlets, which provide higher resolution than conventional methods. This analysis confirmed the softening behavior observed in earlier tests. Further testing, visual inspections, and center of mass and shear center calculations were performed to pinpoint the primary sources of nonlinearity. The results show that torsional moments, caused by misalignment between the center of mass and the excitation force, are the dominant contributors to the wing nonlinear response. The main contribution of this work is the development of a comprehensive framework that addresses the complexities of nonlinear behavior in high aspect ratio flexible wings. In addition, this is the first instance in which superlets are employed for the time-frequency analysis of mechanical systems.