Predictions of mechanical collisions between two bodies frequently cannot be completed by the impulse-momentum equation together with a complete description of the motion of the system at the initial contact. Additional account must be taken of the deformations and frictional interaction induced by the impulsive reaction force, where the bodies contact one another, as these play an important role in the outcome of the collision. During the time the bodies are in contact, elastic, friction and inertia properties combine to produce a complex variation of sliding and sticking through out the contact surface. For accurately predicting the impulse and velocity changes during contact, a considerably simplified, coupled, conservative model, which captures the essential characteristics of the elastic-friction interaction during contact loading, is investigated in this thesis. In this simplified model, the interface between two colliding bodies resembles the behavior of a pair of mutually perpendicular, non-linear springs which react independently with the exception that the stiffness of the tangential "spring" is influenced by the normal displacement. These elastic properties, in combination with inertial properties derived from generalized impulse-momentum laws, form a "spring-mass" system for which numerical integration yields the prediction of rebound velocities. For comparison, an explicit non-linear finite element code, DYNA3D, developed at Lawrence Livermore National Laboratory for analyzing the transient dynamic response of three-dimensional solids, is used to predict the responses of an elastic sphere and elastic rod, each colliding with a rigid plane with varying initial velocities and configurations. Results are also compared with results of a complex analysis of collisions of spheres by Maw, Barber, and Fawcett (1976). / Graduation date: 1999

The finite element stress analysis method was utilized to determine the effects of thermal expansion in small scale crystal deformation with the entire study conducted within the elastic limits of failure. A 5 by 25 km model was simulated, with accepted physical properties of rock and heated to an average geothermal gradient 30° C/km. Parameters independently examined included 1) variance of the coefficient of thermal expansion; 2) variance of temperature magnitude; and 3) variance of temperature geometry.The variations in coefficient of thermal expansion, studied here produced slight alterations in stress patterns produced by body weight and the normal geothermal gradient. It was suggested that general ranges of coefficients were sufficient to predict the behavior of the body. Temperature magnitudes have also resulted in small changes in displacements and stress patterns.Displacements due to thermal expansion were of minimal geologic significance. However, the stress could alter stress patterns generated by other tectonic forces. This may dictate the time and location of the initial failure of the body; in turn controling any subsequent tectonic activity.Ball State UniversityMuncie, IN 47306

In the present study, we propose a computational model for the linear and nonlinear analysis of shell structures. We consider a tensor-based finite element formulation which describes the mathematical shell model in a natural and simple way by using curvilinear coordinates. To avoid membrane and shear locking we develop a family of high-order elements with Lagrangian interpolations. The approach is first applied to linear deformations based on a novel and consistent third-order shear deformation shell theory for bending of composite shells. No simplification other than the assumption of linear elastic material is made in the computation of stress resultants and material stiffness coefficients. They are integrated numerically without any approximation in the shifter. Therefore, the formulation is valid for thin and thick shells. A conforming high-order element was derived with 0 C continuity across the element boundaries. Next, we extend the formulation for the geometrically nonlinear analysis of multilayered composites and functionally graded shells. Again, Lagrangian elements with high-order interpolation polynomials are employed. The flexibility of these elements mitigates any locking problems. A first-order shell theory with seven parameters is derived with exact nonlinear deformations and under the framework of the Lagrangian description. This approach takes into account thickness changes and, therefore, 3D constitutive equations are utilized. Finally, extensive numerical simulations and comparisons of the present results with those found in the literature for typical benchmark problems involving isotropic and laminated composites, as well as functionally graded shells, are found to be excellent and show the validity of the developed finite element model. Moreover, the simplicity of this approach makes it attractive for future applications in different topics of research, such as contact mechanics, damage propagation and viscoelastic behavior of shells.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 140-146). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 100-104). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 100-104). Also available on the Internet.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: product geometry; hot rolling; high speed rolling; rolling simulation; bar and rod rolling; free surface; finite element analysis. Includes bibliographical references (p. 69-75).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2003. / On t.p. "[infinity]" appears as the infinity symbol. Includes bibliographical references (leaves 88-92). Also available in electronic version. Access restricted to campus users.

This bachelor thesis has been carried out at GKN Aerospace. GKN is a member of European Space Agency, designing and manufacturing rocket-nozzles for the Ariane rockets. The manufacturing process entails many welds. Weld-simulations have been made to investigate stresses and plastic strains on simplified geometries. Plastic strains have been evaluated parallel and normal to the weld for plate geometries of shell-elements with rectangular cross-section and sandwich-cross-section, using the FEM-program MSC.marc. Results shows that plate width and length have negligible effect on the plastic strains when one weld is made. A comparison between a sandwich-sector cone and a sandwich plate was made, to investigate how plastic strains and stresses were affected of geometry. Plastic strains and stresses parallel the weld are the same. Plastic strains and stresses normal the weld are affected by changing geometry. Studies on differences in stresses between solid and shell elements propose use of solid elements near the weld region, if stresses are of interest.

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