Browsing by Author "Brake, Matthew RW"

Now showing 1 - 4 of 4
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    Dissipative Dynamics of Bolted Joints
    (2021-08-11) Balaji, Nidish; Brake, Matthew RW
    Bolted Joints finds ubiquitous applications in mechanical and allied industries, spanning from household appliances to advanced aerospace applications. The currently prevalent practice in the design industry, when it comes to bolted joints, is to over-design these components to a very large extent so one needs not pay too much attention to the exact physical properties of these joints, which are fundamentally nonlinear. The current study seeks to advance understanding of the fundamental physical phenomena typifying bolted joints through a two-pronged approach: theoretical and modeling. In the theoretical portion of the work, advances in computational modeling techniques pertinent to the nonlinear characterization of such structures, including a novel Nonlinear Modal Analysis (NMA) approach and interface reduction approaches, are presented which enable the studies in the final portion of the work. In the Modeling portion of the work, two approaches, an empirical and a physics-based approach, are presented. While in the former, the exact form of the contact representation is of secondary importance and the parameters are optimized against experimental data, the latter is an attempt at making blind predictions of the dynamics of a structure assembled through bolted joints. Additionally, the physics-based model is studied using an uncertainty quantification approach in order to throw light on the exact manner in which each parameter of the model influences the predictions. Finally, the thesis closes with recommendations for future work based on the investigations undertaken herein.
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    Investigating the Influence of the Radius of Curvature in Elastic-Plastic Spherical Contact
    (2020-04-23) ONeill, Eoghan Oisin; Brake, Matthew RW
    The study of elastic-plastic contact mechanics is fundamental in understanding the multi-scale behavior of mechanical systems. The e ects of the varying the radius of curvature in elastic-plastic asperity contact, and resulting impact on contact parameters, has been largely neglected in previous studies. A typical approach for elastic-plastic contact models is to assume the equivalent radius of curvature from Hertzian theory is valid in this regime. To assess the applicability of this assumption, contact between two spheres is modeled with FEA. For two elastic- plastic spheres, the ratio of the radii of curvature and material models are varied to encompass the range of flattening to indentation scenarios. Comparisons to contact models are shown and trends are observed indicating the significance of the effect of the radius of curvature on elastic-plastic contact. Finally, a formulation for contact parameters as a function of radii of curvature during contact is proposed.
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    Modal Interactions and Jointed Structures
    (2024-08-01) Porter, Justin H.; Brake, Matthew RW
    Understanding the nonlinear vibration behavior of structures is critical to ensuring reliability and improving efficiency. Jointed connections, integral to assembled structures, introduce contact and friction resulting in nonlinear vibration behavior. Specifically, properties of linear modal analysis including constant modal frequencies and damping and the decoupling of modes break down in the case of nonlinear vibration. Of interest here, modal interactions occur when multiple nonlinear modes respond simultaneously modifying the total response characteristics, potentially increasing vibration amplitudes and causing structural failures. An understanding of modal interactions is predicated on capturing the nonlinear effects of friction in joints, so this thesis investigates physics-based friction modeling to numerically simulate responses of benchmark jointed structures. To address computational costs, a new method is developed to analyze modal interactions utilizing the developed friction model. In the case of a single mode, frictional contact results in a decrease in modal frequency and an increase in modal damping as the vibration amplitude increases. This behavior is well captured by the proposed friction modeling approach. Beyond the single mode case, the state of the art for modeling modal interactions is thoroughly reviewed, and open challenges are discussed. To better understand modal interactions, a numerical method termed variable phase resonance nonlinear modes (VPRNM) is proposed for tracking superharmonic resonances, a specific type of modal interaction. Superharmonic resonances occur at steady-state when a mode responds in resonance at an integer multiple of the forcing frequency (e.g., with amplitude on the order of the response at the forcing frequency). When a superharmonic resonance occurs simultaneously with a primary resonance, the response is further complicated and termed an internal resonance. Utilizing VPRNM, a reduced order modeling approach (VPRNM ROM) is proposed to reconstruct frequency response curves with significantly reduced computational cost compared to existing approaches. This thesis compares the proposed modeling approaches to new experimental results for the Half Brake-Reuss Beam, a benchmark jointed structure. Overall, this thesis provides significant insights into the phenomena of modal interactions for jointed connections and approaches for computationally efficiently modeling such interactions.
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    Thermal Spray Coating Characterization via Higher Dimensional Surfaces
    (2022-12-02) Ahadzie, Senyo Evan; Brake, Matthew RW
    Thermal spray coatings are microscale coatings used to improve the surface properties of surfaces they are applied to. Statistical quantification can improve understanding of a thermal coating's microstructure; however, doing so in an automatic and autonomous manner from image data is non-trivial. A new methodology is developed to characterize thermal spray coatings from serial sectioning images (or other analogous image data) using manifold surfaces in higher dimensions, as well as associated operators on such data.