Browsing by Author "Smith, Scott A."

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    On the Characterization of Nonlinearities in Assembled Structures
    (ASME, 2020) Smith, Scott A.; Brake, Matthew R.W.; Schwingshackl, Christoph W.
    This work refines a recently formalized methodology proposed by D.J. Ewins consisting of ten steps for model validation of nonlinear structures. This work details, through a series of experimental studies, that many standard test setup assumptions that are made when performing dynamic testing are invalid and need to be evaluated for each structure. The invalidation of the standard assumptions is due to the presence of nonlinearities, both known and unrecognized in the system. Complicating measurements, many nonlinearities are currently characterized as constant properties instead of variables that exhibit dependency on system hysteresis and actuation amplitude. This study reviews current methods for characterizing nonlinearities and outlines gaps in the approaches. A brief update to the CONCERTO method, based on the accelerance of a system, is derived for characterizing a system’s nonlinearities. Finally, this study ends with an updated methodology for model validation and the ramifications for modeling assemblies with nonlinearities are discussed.
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    The Influence of Additively Manufactured Nonlinearities on the Dynamic Response of Assembled Structures
    (ASME, 2020) Shu, Hang; Smith, Scott A.; Brake, Matthew R.W.; Tribomechadynamics Laboratory
    Structural dynamic techniques have been proven accurate at predicting the vibrations of single parts (i.e., monolithic specimens), which are widely used in industrial applications. However, vibration analysis of such assemblies often exhibits high variability or nonrepeatability due to jointed interfaces. Inspired by advances in additive manufacturing (AM) and nonlinear vibration absorber theory, this research seeks to redesign jointed structures in an attempt to reduce the nonlinear effects introduced by the jointed interfaces. First, the nonlinear dynamics of a conventionally manufactured beam and an AM beam are measured in both a traditional (flat) lap joint assembly and also a “linearized” lap joint configuration (termed the small pad). Second, the internal structure of the AM beam is varied by printing specimens with internal vibration absorbers. With the two interface geometries studied in this experiment, the flat interface is found to be predominantly nonlinear, and introducing a vibration absorber fails to reduce the nonlinearities from the jointed interface. The small-pad responses are relatively linear in the range of excitation used in the analysis, and the nonlinear effects are further reduced with the presence of a center vibration absorber. Overall, the energy dissipation at the interface is highly dependent on the design of the contact interface and the internal vibration absorber. Adding a nonlinear vibration absorber alone is insufficient to negate the interfacial nonlinearity from the assembly|| therefore, future work is needed to study the shape, location, and material for the design and fabrication of nonlinear vibration absorbers.