Pre-test Predictions of Next-Level Assembly Using Calibrated Nonlinear Subcomponent Model 13 5 Conclusions This research is built upon the experimental study of the isolated fixture-pylon assembly from previous research. A nonlinear reduced order model of their test assembly was used to identify the nonlinearity localized in the pylon when the thin beam contacts the surrounding support blocks. A penalty spring element was used to describe this nonlinear contact behavior and produced frequency backbone curves that agreed well with measured results. This model was validated through comparison of displacement response from stepped-sine simulations to those measured during the previous tests. A nonlinear reduced order model of the next-level assembly comprising the pylon, wing, and fixture block was created using this calibrated nonlinear pylon model to generate pre-test predictions in the form of frequency-energy curves for the first two nonlinear normal modes. These were both shown to have internal resonances due to the dynamics of the next-level assembly, providing valuable insight into the design of future experiments and potential nonlinear phenomena to be observed in the data. The results presented on the wing-pylon-fixture reveal the complex physics associated with the dynamics of the next-level assembly and fixturing. The NNM framework combined with nonlinear system identification can serve as a useful design tool to understand potential regimes in response when modes can interact. Depending on the objective of the structure, the tools utilized throughout this study can be used to tailor the dynamics of the system for the intended needs, i.e., either exploit or eliminate the modal interactions. Future work will seek to validate these findings on test hardware with a variable length wing. Acknowledgments This research was conducted at the 2020 Nonlinear Mechanics and Dynamics (NOMAD) Research Institute supported by Sandia National Laboratories and hosted by the University of New Mexico. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the US Department of Energy or the US Government. This research was also supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc. for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. The authors would like to thank Amy Chen of Sandia National Laboratories for her efforts in creating the finite element meshes used throughout this study. References 1. 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