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No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph.D.) -- Virginia Commonwealth University, 2005. / Title from title-page of electronic thesis. Prepared for: Dept. of Mechanical Engineering. Bibliography: p. 112-123.

<p> Bio-structures owe their remarkable mechanical properties to their hierarchical geometrical arrangement as well as heterogeneous material properties. This dissertation presents an integrated, interdisciplinary approach that employs computational mechanics combined with flow network analysis to gain fundamental insights into the failure mechanisms of high performance, light-weight, structured composites by examining the stress flow patterns formed in the nascent stages of loading for the rostrum of the paddlefish. The data required for the flow network analysis was generated from the finite element analysis of the rostrum. The flow network was weighted based on the parameter of interest, which is stress in the current study. The changing kinematics of the structural system was provided as input to the algorithm that computes the minimum-cut of the flow network. The proposed approach was verified using two classical problems &ndash; three- and four-point bending of a simply-supported concrete beam. The current study also addresses the methodology used to prepare data in an appropriate format for a seamless transition from finite element binary database files to the abstract mathematical domain needed for the network flow analysis. A robust, platform-independent procedure was developed that efficiently handles the large datasets produced by the finite element simulations. Results from computational mechanics using Abaqus and complex network analysis are presented. The complex network strategy successfully identified failure mechanisms in the bio-structure by identifying strain localization in regions of tension, and buckling/crushing in regions of compression. The transdisciplinary strategy used in this study identified the failure mechanisms early, when the material was still in the linearly elastic regime, thereby tremendously reducing the computational time and cost as compared to running a finite element analysis to failure. This work also developed five proof-of-concept, bio-inspired models with varying lattice complexity based on the rostrum. Performance of these bio-inspired models was analyzed with respect to the stress and deformation. Numerical experiments were carried out on one of the bio-inspired model to demonstrate the application of newly developed similitude laws for blast loading. This research has laid the groundwork for an efficient design-test-build cycle for rapid prototyping of novel bio-inspired structures by using flow network analysis, finite element analysis, and similitude laws.</p><p>

<p> A theoretical model is proposed for the buckling of a three-dimensional vein subjected to torsion, internal pressure, and axial tension using energy conservation methods. The vein is assumed to be an anisotropic hyperelastic cylindrical shell which obeys the Fung constitutive model. Finite deformation theory for thick-walled blood vessels is used to characterize the vessel dilation in the pre-buckling state. </p><p> The pre-buckling state is identified by its midpoint and then perturbed by a displacement vector field dependent on the circumferential and axial directions to define the buckled state. The total potential energy functional of the system is extremized by minimizing the first variation with respect to the elements of the set of all continuous bounded functions on <b>R </b>³. The Euler-Lagrange equations form three coupled linear partial differential equations with Dirichlet boundary conditions characterizing the buckling displacement field under equilibrium. </p><p> A second solution method approximates the first variation of the total potential energy functional using a variational Taylor series expansion. The approximation is minimized and combined with equations of equilibrium derived from elasticity theory to yield a polynomial relating buckling eigenmodes, material parameters, geometric parameters, and the critical angle of twist which induces buckling. Various properties of the total potential energy functional specific to the problem are proved. Another solution method is outlined using the first variation approximation and the basis of the kernel of the linear transformation which maps buckling displacement amplitudes during static equilibrium. </p><p>

No description available.

The formation of channel segregates or freckles during vertical solidification of Pb-Sn alloys is simulated. The simulation is based on a mathematical model of dendritic solidification, in which the solid plus liquid zone is modeled as an anisotropic porous medium of variable porosity. The alloy solidifies from an initial melt and proceeds until the alloy is completely solidified, and the final macrosegregation can be predicted. The growth process is calculated by solving the fully coupled equations of momentum, energy and solute transport, as well as by maintaining the thermodynamic constraints dictated by the equilibrium phase diagram of the alloy. It is found that the thermosolutal convection that occurs during solidification, under certain growth conditions, can produce localized segregation zones, varying in shape from short streaks or pockets to long and narrow channels or freckles rich in solute. Several numerical examples show how these defects originate and why they subsist or die, depending on whether they face a favorable or adverse convection pattern ahead of the solidification front. The response, in both appearance and location, of channels to the variation of the cooling conditions is in good agreement with experiments, although the preference of channels to form on the outer surface of the casting, rather than in the interior, is greater than what is normally observed in Pb-Sn alloys. A mechanism that favors the formation of freckles within the body of the casting, because of defects in the dendritic mushy zone, is proposed and illustrated numerically.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xii, 134 p.; also includes graphics. Includes abstract and vita. Advisor: Noriko Katsube, Dept. of Mechanical Engineering. Includes bibliographical references (p. 121-125).

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.