Browsing by Subject "Rolling"

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    Plastic analysis of processes involving material-object interaction.
    (2010-06) Hambleton, James Paul
    The dissertation presents theoretical models for processes involving continuous failure and displacement of material via contact with a rigid object. Focus is mainly on processes relating to material-wheel interaction, which are central in a number of engineering applications (e.g., vehicle mobility and metal rolling). The analysis considers indentation, transient rolling, and steady-state rolling on an elastic-perfectly plastic or a rigid-perfectly plastic cohesive-frictional material. Mechanics-based models are developed using two separate approaches. The first is based on comprehensive numerical simulation using the Finite Element Method (FEM), which enables rigorous analysis of the three-dimensional deformation occurring for narrow wheels. The second approach is analytic and formulated by considering the entire process of deformation as a sequence of incipient plastic flow problems. Using the theoretical models, the relationships between dimensionless variables are quantitatively assessed. It is further shown that the predictions display reasonable agreement with experimental data from two types of small-scale indentation and rolling tests: one aimed at measuring the force-penetration relationship for indenting and rolling wheels and the second type concentrated on measuring the incremental displacement field at wheel midplane using Particle Image Velocimetry (PIV). The models and experiments provide insights into how indentation and rolling processes are influenced by three-dimensional effects, non-associativity, localization, and the presence of displaced material.
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    Prediction and Prevention of Tripped Rollovers
    (Intelligent Transportation Systems Institute, Center for Transportation Studies, University of Minnesota, 2012-12) Phanomchoeng, Gridsada; Rajamani, Rajesh
    Vehicle rollovers account for a significant fraction of highway traffic fatalities, causing more than 10,000 deaths in the U.S. each year. While active rollover prevention systems have been developed by several automotive manufacturers, the currently available systems address only untripped rollovers. This project focuses on the development of a new real-time rollover index that can detect both tripped and un-tripped rollovers. A new methodology is developed for estimation of unknown inputs in a class of nonlinear dynamic systems. The methodology is based on nonlinear observer design and dynamic model inversion to compute the unknown inputs from output measurements. The developed approach can enable observer design for a large class of differentiable nonlinear systems with a globally (or locally) bounded Jacobian. The developed nonlinear observer is then applied for rollover index estimation. The rollover index estimation algorithm is evaluated through simulations with an industry standard software, CARSIM, and with experimental tests on a 1/8th scaled vehicle. The simulation and experimental results show that the developed nonlinear observer can reliably estimate vehicle states, unknown normal tire forces, and rollover index for predicting both un-tripped and tripped rollovers. The final chapter of this report evaluates the feasibility of rollover prevention for tripped rollovers using currently available actuation systems on passenger sedans.