Extraction of the Descriptive Function of a Folding Wing With Free-Play Using the Modal Test Results to Be Used in the Nonlinear Motion Equation of the Structure

Structures can exhibit non-linear behavior due to the presence of free-play. To analyze this behavior, different numerical and analytical methods like the substructure synthesis method or the harmonic balance method are used. To determine the effect of non-linarites caused by free-play, descriptive functions must be identified. The restoring force approach is frequently used in systems where mass and stiffness matrices are known, such as finite element models. Another approach involves frequency response functions obtained through vibration tests.

This article discusses the second approach, which involves extracting the free-play function using frequency response functions obtained from tests. The tests include a modal test with random excitation to determine the frequency response functions for the linear mode of the modes with low excitation amplitude. Additionally, sinusoidal excitation is used with increasing amplitude for the frequency response functions in the nonlinear state of the modes. The laboratory method used to determine the nonlinear modes involves increasing the amplitude of sinusoidal stimulation in the frequency range of each resonance. This article presents a practical method for analyzing the dynamic behavior of structures related to the folding wing of a flying system. Using simple techniques and vibration test results, it deals with extracting the free-play function of the structure.