Advanced test protocols for rapid detection and quantification of nonlinear dynamic responses in aeroengine casing assemblies

Abstract

In this research, computationally efficient testing protocols were developed for the accurate detection and quantification of nonlinearities in the bolted flange interfaces of aeroengine casing assemblies. Aeroengine casings are joined by bolted flanges that are exposed to high loading amplitudes, leading to bending and large deflections that cause structural nonlinearities. Initially, to assess these structural nonlinearities, a computationally efficient finite element (FE) modelling methodology was developed to accurately capture the vibrational characteristics of the casings while also significantly improving computational efficiency. The technical accuracy of the vibrational characteristics obtained from the FE modelling technique developed here was validated using simulation methods and experimental vibration testing such as modal analysis, the modal assurance criterion, and mode shape assessment. The modes most susceptible to nonlinear dynamic response were then theoretically identified using the mode shape results acquired through the FE model. Thus, a two-step experimental approach is proposed for achieving the accurate and time-efficient quantification of nonlinearities. In the first stage, a rapid experimental nonlinear assessment is performed using a stinger–shaker set-up to validate the FE simulation results of the susceptible nonlinear modes identified. In the second stage, a precise high-resolution measurement is taken with respect to the modes identified in order to precisely capture the nonlinear characteristics. The integration of the proposed theoretical FE modelling technique with advanced experiment formulations results in a significantly more time-efficient and accurate nonlinear testing protocol for aeroengine structures. Furthermore, the nonlinear damping and stiffness parameters of aeroengine casings were also explored in this research and analysed to improve the existing design and development strategies.