Chapter 5 Investigating Nonlinearities in a Demo Aircraft Structure Under Sine Excitation S. B. Cooper, S. Manzato, A. Borzacchiello, L. Bregant, and B. Peeters Abstract Developing on the basic idea behind parametric and non-parametric identification of nonlinear systems, another case study on integrating system identification and finite element modelling of nonlinear structures is presented. The first step, which is the focus of this paper, involves using acquired input and output data to derive an experimental model for both the underlying linear model and nonlinear model of the proposed structure, no information about the system is required and only the applied excitations and corresponding accelerations are implemented in the nonlinear identification step. The proposed case study is demonstrated on a nonlinear simple metallic plane assembly with localized stiffness and damping nonlinearities; in this case, an updated linear finite element model of the structure is derived and the nonlinearities experimentally characterised. Keywords Nonlinear identification · Experimental data · Finite element model · Numerical simulation and system integration 5.1 Introduction Nonlinearities often originate from different sources in engineering structures most especially in an industrial application, a large majority of these nonlinearities are narrowed down to the design of the structure, nature of the joints, material and geometric properties. Research on bolted joints and other types of nonlinear features have been proven to introduce large uncertainties in the stiffness and damping properties of a structure which can often render the response of the structure nonlinear, identifying and predicting the effect of these nonlinearities at operational conditions is of current challenge to present structural engineers dealing with complex nonlinear structures. In this context the integration of experimental nonlinear identification and finite element modelling of engineering structures would be of great advantage to the present structural dynamics society. Experimental nonlinear identification is important in many structural dynamic applications, for example in complex aerospace and mechanical structures [1], micromechanical systems with magnetic or friction forces [2], machineries with rubber isolation mounts and assembled structures with bolted interfaces [3]. In most engineering design, the base line structure is often linear, but the vibration testing and operational performance of some of these structures exhibit a level of nonlinear phenomena which can no longer be ignored or assumed as linear [4]. Hence, the accurate representation of these nonlinear behavior in the finite element model of the structure or built up assembly would be of extreme benefit in obtaining better response prediction at the forcing range of interest. Examples on the real life application of some of these developed nonlinear identification methods are also available in the literature where the identification of weak nonlinearities was studied on a more complex aerospace structure in [5] where a strategy for non-linear modal identification of weak nonlinear effects on a large aircraft was presented. An aluminum plate S. B. Cooper Test Division, Siemens Industry Software NV, Leuven, Belgium Department of Mechanical Engineering, University of Bristol, Bristol, UK S. Manzato ( ) · B. Peeters Test Division, Siemens Industry Software NV, Leuven, Belgium A. Borzacchiello Test Division, Siemens Industry Software NV, Leuven, Belgium Department of Engineering and Architecture, Università degli Studi di Trieste, Trieste, Italy L. Bregant Department of Engineering and Architecture, Università degli Studi di Trieste, Trieste, Italy © Society for Experimental Mechanics, Inc. 2020 R. Barthorpe (ed.), Model Validation and Uncertainty Quantification, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-12075-7_5 41
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