Browsing by Author "Porter, Justin H."

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    A quantitative assessment of the model form error of friction models across different interface representations for jointed structures
    (Elsevier, 2022) Porter, Justin H.; Balaji, Nidish Narayanaa; Little, Clayton R.; Brake, Matthew R.W.
    Hysteretic models are widely used to model frictional interactions in joints to recreate experimental behavior. However, it is unclear which models are best suited for fitting or predicting the responses of structures. The present study evaluates 26 friction model/interface representation combinations to quantify the model form error. A Quasi-Static Modal Analysis approach (termed Rayleigh Quotient Nonlinear Modal Analysis) is adopted to calculate the nonlinear system response, and a Multi-Objective Optimization is solved to fit experimental data of the first mode of the Brake-Reuß Beam. Optimized parameters from the first mode are applied to the second and third bending modes to quantify the predictive ability of the models. Formulations for both tracing full hysteresis loops and recreating hysteresis loops from a single loading curve (Masing assumptions) are considered. Smoothly varying models applied to a five patch representation showed the highest flexibility (for fitting mode 1) and good predictive potential (for modes 2 and 3). For a second formulation, which uses 152 frictional elements to represent the interface, the physically motivated spring in series with a Coulomb slip model (elastic dry friction) has high error for fitting mode 1 and performs near the middle for predicting higher modes. For both interface representation, the best fit models are not the most physical, but rather the ones with the most parameters (as expected); however, the more physical models perform somewhat better for predicting the higher modes.
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    Constitutive Modeling of Friction in Bolted Connections
    (2021-11-16) Porter, Justin H.; Brake, Matthew R.W.
    Bolted joints are ubiquitous in mechanical engineering, requiring accurate models to optimize designs. However, the exact nature of frictional contact between components is unknown and poses a significant challenge to modeling the nonlinear vibration of assemblies. This thesis applies empirical and physics-based modeling approaches to identify improvements to current models and a potential path towards predictive models of friction in bolted joints. The empirical modeling approach solves a multi-objective optimization to fit 26 friction model/interface representation combinations to experimental data and quantify the model form error. While the empirical models are not physical, the optimized results highlight the benefits of using smooth friction models and the limitations of a common physically motivated model. The physics-based model formulates the frictional force based on contact interactions of surface features and derives parameters from surface scans. While the physics-based model is not completely predictive, results show promising agreement with experiments.
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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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    Towards a predictive, physics-based friction model for the dynamics of jointed structures
    (Elsevier, 2023) Porter, Justin H.; Brake, Matthew R.W.
    Bolted connections are ubiquitous in mechanical designs and pose a significant challenge to understanding and predicting the vibration response of assembled structures. The present paper develops a physics-based rough contact model of the frictional interactions within a joint. This model sums over the probable interactions of asperities – defined as locally maximum surface features – to determine the contact forces. Here, the tangential contact forces vary smoothly between sticking and slipping and allow the model to better capture the qualitative trends of experimental amplitude dependent frequency and damping than previous studies. Furthermore, the novel model is generalized to allow for arbitrarily varying normal pressure including potential separation to better represent the interfacial dynamics. This includes developing a new, computationally tractable approximation to the analytical Mindlin partial slip solution for tangential loading of contacting spheres. The results highlight the importance of accurately characterizing the as-built topology of the interface, the plastic behavior of the contacting asperities, the relevant length scale of asperities, and the eccentricity of asperities. A predictive friction coefficient based on plasticity provides a poor match to experiments, so fitting the friction coefficient is also considered. Numerical results are compared to experiments on the Brake-Reuß Beam to assess the predictive potential of the models. While blind predictions over-predict the slip limit, the current model presents a significant improvement in physics-based modeling and highlights areas for ongoing research.