Thesis (Ph.D.) - University of Glasgow, 2008. / Ph.D. thesis submitted to the Department of Mathematics, Faculty of Information and Mathematical Sciences, University of Glasgow, 2008. Includes bibliographical references. Print version also available.

A nonlinear finite element model of the hot and cold rolling processes has been developed for flat rolling stock with rectangular cross section. This model can be used to analyze the flat rolling of cold and hot steel rectangular strips under a series of different parameters, providing the rolling designer with a tool that he can use to understand the behavior of the steel as it flows through the different passes. The models developed, take into account all of the non-linearities present in the rolling problem: material, geometric, boundary, and heat transfer. A coupled thermal-mechanical analysis approach is used to account for the coupling between the mechanical and thermal phenomena resulting from the pressure-dependent thermal contact resistance between the steel slab and the steel rolls. The model predicts the equivalent stress, equivalent plastic strain, maximum strain rate, equivalent total strain, slab temperature increase, increase in roll temperature, strip length increase, slab thickness % reduction (draft), and strip's velocity increase, for both the cold and hot rolling processes. The FE model results are an improvement over the results obtained through the classical theory of rolling. The model also demonstrates the role that contact, plastic heat generation and friction generated heat plays in the rolling process. The analysis performed shows that the steel in cold rolling can be accurately modeled using the elastic-plastic (solid Prandtl-Reuss) formulation, with a von Mises yield surface, the Praguer kinematic hardening rule, and the Ramberg-Osgood hardening material model. The FE models also demonstrate that the steel in hot rolling can be modeled using the rigid-viscoplastic (flow Levy-Mises) formulation, with a von Mises yield surface, and Shida's material model for high temperature steel where the flow stress is a function of the strain, strain rate, and the temperature. Other important contributions of this work are the demonstration that in cold rolling, plane sections do not remain plane as the classic theory of rolling assumes. As a consequence, the actual displacements, velocity, and stress distributions in the workpiece are compared to and shown to be an improvement over the distributions derived from the classical theory. Finally, the stress distribution in the rolls during the cold rolling process is found, and shown to be analogous to the stress distribution of the Hertz contact problem. / Master of Science

Este estudo foca uma análise comparativa de diferentes painéis internos de capôs de veículos, com o objetivo de minimizar as lesões ao pedestre em caso de um atropelamento. As lesões na cabeça do pedestre são medidas através de um modelo em elementos finitos de uma cabeça padrão de acordo com o comitê europeu de melhorias da segurança de veículos. Os valores de desaceleração obtidos nas análises são comparados com valores toleráveis de acordo com o critério HIC (Head Injury Criteria), criado pela NHTSA (National Highway Traffic Safety Administration). Baseando-se nos resultados obtidos demonstra-se a influência dos tipos de estruturas internas de capô e recomenda-se a melhor estrutura para aplicações na indústria automobilística. / This study focus on comparative analysis of different vehicle hood inner panels, with the objective to minimize the injuries to the pedestrian in case of a running over accident. The method to measure the injuries in the head of the pedestrian will be made through a finite element model of a standard head in accordance with the European committee of improvements of the security of vehicles. The values of decelerations obtained in the analysis are compared with human tolerance levels according to HIC criteria (Head Injury Criteria), created by NHTSA (National Highway Traffic Safety Administration). Based on the finite element analysis results, this study demonstrate the influence of different hood inner panels and recommends the best structure to be applied by automobile industry.

Materially non-linear analysis of reinforced concrete frame structures with infill walls requires appropriate mathematical models to be adopted for the beams and the columns as well as the infill walls. This study presents a mathematical model for frame elements based on a 3D Hermitian beam/column finite element and an equivalent strut model for the infill walls. The spread-of-plasticity approach is employed to model the material nonlinearity of the frame elements. The cross-section of the frame element is divided into triangular sub regions to evaluate the stiffness properties and the response of the element cross-section. By the help of the triangles spread over the actual area of the section, the bi-axial bending and the axial deformations are coupled in the inelastic range. A frame super-element is also formed by combining a number of frame finite elements. Two identical compression-only diagonal struts are used for modeling the infill. The equivalent geometric and material properties of the struts are determined from the geometry of the infill and the strength of the masonry units A computer code is developed using the object-oriented design paradigm and the models are implemented into this code. Efficiency and the effectiveness of the models are investigated for various cases by comparing the numerical response predictions produced by the program with those obtained from experimental studies.

Este estudo foca uma análise comparativa de diferentes painéis internos de capôs de veículos, com o objetivo de minimizar as lesões ao pedestre em caso de um atropelamento. As lesões na cabeça do pedestre são medidas através de um modelo em elementos finitos de uma cabeça padrão de acordo com o comitê europeu de melhorias da segurança de veículos. Os valores de desaceleração obtidos nas análises são comparados com valores toleráveis de acordo com o critério HIC (Head Injury Criteria), criado pela NHTSA (National Highway Traffic Safety Administration). Baseando-se nos resultados obtidos demonstra-se a influência dos tipos de estruturas internas de capô e recomenda-se a melhor estrutura para aplicações na indústria automobilística. / This study focus on comparative analysis of different vehicle hood inner panels, with the objective to minimize the injuries to the pedestrian in case of a running over accident. The method to measure the injuries in the head of the pedestrian will be made through a finite element model of a standard head in accordance with the European committee of improvements of the security of vehicles. The values of decelerations obtained in the analysis are compared with human tolerance levels according to HIC criteria (Head Injury Criteria), created by NHTSA (National Highway Traffic Safety Administration). Based on the finite element analysis results, this study demonstrate the influence of different hood inner panels and recommends the best structure to be applied by automobile industry.