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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Thrombus Formation under High Shear in Arterial Stenotic Flow

Flannery, Conor James 28 April 2005 (has links)
Acute thrombotic and thromboembolic occlusion of atherosclerotic vessels are events that precipitate most heart attacks and strokes. In arterial stenotic flow, thrombus formation is shear dependent and may or may not lead to complete occlusion of the vessel. Platelets in whole blood adhere to collagen-coated surfaces and as they accumulate the resistance of the stenosis increases because of the decreasing passageway of the occluded stenosis. As a model of blood clotting in stenoses, porcine blood is heparinized and perfused over tubular glass test sections that are coated with collagen type I. Each test section has a preexisting stenosis and its severity varies so that higher percent stenoses produce higher shear rates on the blood. The hypothesis of this thesis is that high shear rates due to stenosis in arteries are a necessary feature for occlusive thrombosis.
52

Deformation Mechanism and Shear Banding Behavior in Amorphous/Nanocrystalline Multilayer System

Lin, I-Chin 26 July 2010 (has links)
Over the past decades, bulk metallic glasses (BMGs) have attracted extensive interests because of their unique physical and chemical properties such as good corrosion resistance, larger elastic elongation limit and high strength and hardness. They are also seen as the potential material for micro-electro-mechanical systems (MEMS). However, despite many extraordinary properties in BMGs, BMGs might be difficult to be made into MEMS, different from thin film metallic glasses (TFMGs). Compared with BMGs, few studies have been carried out on TFMGs and their application for MEMS. In this study, efforts have been made to study the properties of multilayered TFMGs. The multilayer thin film selected in this thesis is amorphous/nanocrystalline nanolaminate systems. The micro-pillars of multilayered TFMGs with diameter of 1 £gm are fabricated by using focus ion beam (FIB) and tested in microcompression at room temperature. On nano-indentation test, the phenomenon of strain burst decreases by way of multilayer system. It means that the multilayer system can retard the shear band propagation initiated from the amorphous layers. Under the microcompression test, the deformation of both ZrCu (100 nm)/Cu (50 nm) and ZrCu (100 nm)/Cu (10 nm) multilayer micro-pillars are still dominated by the emission of shear bands in a manner of strain burst to release the energy, but the ZrCu (100 nm)/Cu (100 nm) multilayer thin films reveal continuous deformation and smooth stress-strain curve with no strain burst. First, the sufficient thick of copper layer can absorb more energy from shear deformation of amorphous layer. Second, the copper layer exhibits plastic flow along the transverse direction under the iso-stress deformation. The transverse plastic flow acts as a shear force at interface causing non-stress concentration at amorphous layer. It means that the amorphous layer can be deformed to large plastic strain without stress concentration, causing a homogeneous deformation. According to these two deformation mechanisms, it is possible that the ZrCu (100 nm)/Cu (100 nm) multilayer thin film is better system for improving the ductility of amorphous alloy with a good strength.
53

Effect of confinement on shear dominated reinforced concrete elements

Powanusorn, Suraphong 17 February 2005 (has links)
It has been demonstrated that transverse reinforcement not only provides the strength and stiffness for reinforced concrete (RC) members through direct resistance to external force demands, but also helps confine the inner core concrete. The confinement effect can lead to improved overall structural performance by delaying the onset of concrete fracture and allowing more inelastic energy dissipation through an increase in both strength and deformability of RC members. The objective of this research was to evaluate the effect of confinement due to the transverse reinforcement on enhancing the shear performance of RC members. A new constitutive model of RC members was proposed by extending the Modified Compression Field Theory (MCFT) to incorporate the effect of confinement due to transverse reinforcement by adjusting the peak stress and peak strain of confined concrete in compression. The peak stress of confined concrete was determined from the five-parameter failure surface for concrete developed by Willam and Warnke (1974). The peak strain adjustment was carried out using a relationship proposed by Mander et al. (1988). The proposed analytical model was compared with results from an experimental program on sixteen RC bent caps with varied longitudinal and transverse reinforcement details. Two-dimensional Finite Element Modeling (FEM) using the proposed constitutive model was conducted to numerically simulate the RC bent cap response. Results showed that the proposed analytical model yielded good results on the prediction of the strength but significantly overestimated the post-cracking stiffness of the RC bent cap specimens. The results also indicated that the confinement effect led to enhanced overall performance by increasing both the strength and deformability of the RC bent caps. Two potential causes of the discrepancy in the underestimation of the RC bent cap deformations, namely the effects of concrete shrinkage and interfacial bond-slip between the concrete and main flexural reinforcement in the bent caps, were discussed. Parametric studies showed that the tension-stiffening in the proposed constitutive models to implicitly take into account the bond-slip between the concrete and main flexural reinforcement was the major cause of the overestimation of the post-cracking stiffness of RC bent caps. The explicit use of bond-link elements with modified local bond stress-slip laws to simulate the slip between the concrete and main flexural reinforcement led to good predictions of both strength and deformation.
54

Permeability characterization of shear zones in the Hickory sandstone member, Riley Formation, Texas

Nieto Camargo, Jorge Enrique 17 February 2005 (has links)
Reservoir compartments, typical targets for new infill locations, are commonly created by faults that may reduce or enhanced permeabilities. Faults often contain narrow zones of intense shear comprised of geometrically complex elements that reduce permeability and compartmentalize blocks as a function of time and pressure. This thesis characterizes the permeability structure of shear zones and the relationship between fault permeability, host rock properties and the relative degree of deformation. The main objectives of this work are to (1) characterize the geometry and permeability of deformation elements within shear zones; (2) determine permeability anisotropy in shear zones according to fault characteristics and host lithology; and (3) develop a process to predict permeability anisotropy of faults in reservoirs using probabilistic approaches. The study results give a better understanding of fluid flow behavior of shear zones and their potential to create reservoir heterogeneity and compartmentalization. Fluid flow in a reservoir with faults is controlled by variables such as fault throw, shear-zone thickness, undeformed and deformed rock permeability and the geometry of all deformation elements. Methodology to predict permeability structure was developed using analytical and numerical simulation of selected core samples and laboratory measurements. We found useful relationships between permeability of the host rock and highly deformed elements according to the amount of throw of the fault. The high lateral continuity of the highly deformed elements and their predictable low permeability make these elements most important in controlling permeability in shale-free and low-shale shear zones created by low displacement (subseismic) faulting. Probe permeameter data is a precise, inexpensive and non-destructive source of permeability information that can be effectively incorporated in detailed models to investigate the effect of individual deformation elements in the whole shear zone permeability and their effect at the field scale.
55

Development of skew correction factors for live load shear and reaction distribution in highway bridge design a dissertation presented to the faculty of the Graduate School, Tennessee Technological University /

Zhang, Qinghe, January 2009 (has links)
Thesis (Ph.D.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on Mar. 18, 2010). Bibliography: leaves 170-174.
56

Hessert transonic free shear layer facility

Chouinard, Mitchell. January 2004 (has links)
Thesis (M.S.)--University of Notre Dame, 2004. / Thesis directed by Eric J. Jumper for the Department of Aerospace and Mechanical Engineering. "April 2004." Includes bibliographical references (leaves 66-68).
57

Particle-wall shear stress measurements within the standpipe of a circulating fluidized bed

Sarra, Angela M. January 2001 (has links)
Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xi, 137 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 136-137).
58

Shear strength of concrete joints under dynamic loads.

Lui, Lup-moon. January 1977 (has links)
Thesis--M. Phil., University of Hong Kong.
59

Behaviour under lateral loading of rectangular framed structures stiffened with shear walls.

Ko, Jan-ming. January 1969 (has links)
Thesis--Ph. D., University of Hong Kong. / Mimeographed.
60

Quasi-static testing of cantilever masonry shear wall segments

Hernandez, Jaime F. 25 June 2012 (has links)
The primary objective of this thesis was to study how the behavior of flexure-dominated masonry shear-wall segments is affected by changes in the normalized axial load and the percentage of vertical reinforcement. Six reinforced masonry shear-wall segment were constructed and tested at the Ferguson Structural Engineering Laboratory of the University of Texas at Austin. Specimens were 96-in. wide and 96-in. high (aspect ratio equal to 1.0) and were tested with different combinations of axial load ratio (zero and 0.10) and vertical reinforcement ratios (0.33% and 0.16%). Specimens met the 2011 MSJC Code requirements for special reinforced masonry shear walls, and were tested under quasi-static in-plane reversed cyclic loads. The specimens exhibited predominantly flexural behavior, as expected. Specimens exhibited high displacement ductility (5.6 to 16.7), as expected for flexure-dominated specimens. Specimens constructed with "green" units behaved essentially like otherwise identical specimens constructed with conventional ("gray") units. / text

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