Browsing by Author "Peng, Bo"

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    Applying the Newmark Method to the Discontinuous Deformation Analysis
    Peng, Bo (Virginia Tech, 2014-12-08)
    Discontinuous deformation analysis (DDA) is a newly developed simulation method for discontinuous systems. It was designed to simulate systems with arbitrary shaped blocks with high efficiency while providing accurate solutions for energy dissipation. But DDA usually exhibits damping effects that are inconsistent with theoretical solutions. The deep reason for these artificial damping effects has been an open question, and it is hypothesized that these damping effects could result from the time integration scheme. In this thesis two time integration methods are investigated: the forward Euler method and the Newmark method. The work begins by combining the Newmark method and the DDA. An integrated Newmark method is also developed, where velocity and acceleration do not need to be updated. In simulations, two of the most widely used models are adopted to test the forward Euler method and the Newmark method. The first one is a sliding model, in which both the forward Euler method and the Newmark method give accurate solutions compared with analytical results. The second model is an impacting model, in which the Newmark method has much better accuracy than the forward Euler method, and there are minimal damping effects.
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    Discrete Element Method (DEM) Contact Models Applied to Pavement Simulation
    Peng, Bo (Virginia Tech, 2014-08-20)
    Pavement is usually composed of aggregate, asphalt binder, and air voids; rigid pavement is built with hydraulic cement concrete; reinforced pavement contains steel. With these wide ranges of materials, different mechanical behaviors need to be defined in the pavement simulation. But so far, there is no research providing a comprehensive introduction and comparison between various contact models. This paper will give a detail exploration on the contact models that can be potentially used in DEM pavement simulation; in the analysis, it includes both a theoretical part, simulation results and computational time cost, which can reveal the fundamental mechanical behaviors for the models, and that can be a reference for researchers to choose a proper contact model. A new contact model—the power law viscoelastic contact model is implemented into software PFC 3D and is numerically verified. Unlike existing linear viscoelastic contact models, the approach presented in this thesis provides a detailed exploration of the contact model for thin film power-law creeping materials based on C.Y Chueng's work. This model is aimed at simulating the thin film asphalt layer between two aggregates, which is a common structure in asphalt mixtures. Experiments with specimens containing a thin film asphalt between two aggregates are employed to validate the new contact model.
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    High quality factor silica microspheres functionalized with self-assembled nanomaterials
    Kandas, Ishac L. N.; Zhang, Baigang; Daengngam, Chalongrat; Ashry, Islam; Jao, Chih-Yu; Peng, Bo; Ozdemir, Sahin K.; Robinson, Hans D.; Heflin, James R.; Yang, Lan; Xu, Yong (Optical Society of America, 2013-09-01)
    With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e. g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7). We compare experimentally measured Q factors with theoretical estimates, and find good agreement. (C) 2013 Optical Society of America