Evaluation of Joint Modeling Techniques Using Calibration and Fatigue Assessment of a Bolted Structure Moheimin Khan, Patrick Hunter, Benjamin R. Pacini, Daniel R. Roettgen, and Tyler F. Schoenherr Abstract Calibrating a finite element model to test data is often required to accurately characterize a joint, predict its dynamic behavior, and determine fastener fatigue life. In this work, modal testing, model calibration, and fatigue analysis are performed for a bolted structure, and various joint modeling techniques are compared. The structure is designed to test a single bolt to fatigue failure by utilizing an electrodynamic modal shaker to axially force the bolted joint at resonance. Modal testing is done to obtain the dynamic properties, evaluate finite element joint modeling techniques, and assess the effectiveness of a vibration approach to fatigue testing of bolts. Results show that common joint models can be inaccurate in predicting bolt loads, and even when updated using modal test data, linear structural models alone may be insufficient in evaluating fastener fatigue. Keywords Bolted joint · Joint stiffness · Modal analysis · Model calibration · Fatigue 1 Introduction Bolted joints are commonly used to connect parts and assemblies but are still a source of error in analytical structural models. Various joint modeling techniques can be utilized, depending on the application and quantities of interest. For structures subjected to dynamic loading, it is important to consider the frequency response of the structure. When fastener fatigue is a concern, predicting failure requires a joint model that can accurately represent the loading through the bolt. In order to evaluate and improve current joint modeling techniques, enhance fatigue analysis, and advance testing capabilities, an experimental structure is developed. The structure is designed to fail a bolt in fatigue using a modal shaker forced at the axial resonant mode of the structure. Free-free and fixed base mode shapes of the structure are obtained, and finite element (FE) analyses are performed using the SIERRA finite element code suite developed at Sandia National Laboratories [1]. Several different joint models are explored in this work, and analysis results along with test data are used to compare these models and evaluate the viability of using the structure to perform fatigue testing of bolts. 2 Hardware Description A structure is designed for use in joint model calibration and fatigue testing for a single ¼ inch bolt (¼ -20 UNC). It consists of a large mass with a small support structure that is attached to a plate, shown in Fig. 1. The large mass, denoted the Kettlebell (KB), directly attaches to the Adapter Plate (AP), which has eight bolts to attach to a seismic mass. The structure was designed such that its axial mode imparts a large force on the single bolt when the KB is driven with a modal shaker, Sandia National Laboratories is 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. 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. M. Khan ( ) · P. Hunter · B. R. Pacini · D. R. Roettgen · T. F. Schoenherr Sandia National Laboratories, Albuquerque, NM, USA e-mail: mkhan@sandia.gov; pshunte@sandia.gov; brpacin@sandia.gov; drroett@sandia.gov; tfschoe@sandia.gov © The Society for Experimental Mechanics, Inc. 2022 G. Kerschen et al. (eds.), Nonlinear Structures & Systems, Volume 1, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-77135-5_4 33
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