Digital Commons Network^™

Multiscale Numerical Modeling And Characterization Of Carbon/Carbon Composites, Borys Drach

Doctoral Dissertations

Carbon/carbon composite is a high-performance material with a unique set of physical and thermo-mechanical properties making it irreplaceable for severe environment aerospace applications. Its complex hierarchical microstructure presents materials scientists and engineers with substantial modeling challenges when it comes to predicting material's behavior under various loading conditions. My research has been focused on characterization, mutliscale modeling and mechanical testing of this composite. A set of new elasticity solutions for the carbon fiber surrounded by multiple layers of pyrolytic carbon represented as a multicoated cylinder is presented on the microscale. On the mesoscale, deterministic and statistical approaches to evaluation of contributions …

Utilization Of Copper Alloys For Marine Applications, Andrew Drach

Doctoral Dissertations

Utilization of copper alloy components in systems deployed in marine environment presents potential improvements by reducing maintenance costs, prolonging service life, and increasing reliability. However, integration of these materials faces technological challenges, which are discussed and addressed in this work, including characterization of material performance in seawater environment, hydrodynamics of copper alloy components, and design procedures for systems with copper alloys.

To characterize the hydrodynamic behavior of copper alloy nets, mesh geometry of the major types of copper nets currently used in the marine aquaculture are analyzed and formulae for the solidity and strand length are proposed. Experimental studies of …

Mean Force Structure And Scaling Of Rough-Wall Turbulent Boundary Layers, Faraz Mehdi

Doctoral Dissertations

The combined roughness-Reynolds number problem is explored from the perspective of ordering of terms in the mean momentum balance. Existing mean velocity and Reynolds shear stress data from zero pressure gradient, rough-wall turbulent boundary layers are used to clarify the nature of the leading order balances across the boundary layer. These existing data are augmented by data from a judiciously chosen set of experiments performed at the University of New Hampshire. These low speed, Laser Doppler velocimetry based experiments were performed over three types of roughnesses. Their purpose is to clarify the trends found in the existing data sets.

By …

Analytical And Numerical Prediction Of Localized Necking In Sheet Metal Forming Processes, Raed Zuhair Hasan

Doctoral Dissertations

The goal of this research is to investigate, develop and validate analytical and numerical tools that can accurately predict failure in sheet metal forming operations. The strain-based forming limit curve (FLC) is one of the tools to predict the maximum permissible strains of thin metallic sheets which are loaded in the plane of the sheet to different states of stress. It may be used to assess forming operations in the press shops as well as unintentional deformations, such as vehicle, aircraft, or train crashes. The accurate prediction of failure in sheet metal stamping can shorten product lead times, decrease tooling …

A Computational Fluid Dynamics Study Of Two-Phase Flows In The Presence Of Surfactants, Yuanyuan Cui

Doctoral Dissertations

Drop formation in co-flowing fluids and drops rising in a tube are important in applications such as microencapsulation and enhanced oil recovery. A hybrid volume-of-fluid method with a front-tracking scheme is developed to study two-phase flows in the presence of surfactants at finite Reynolds numbers. Both fluids can be Newtonian or shear-thinning, and surfactants are soluble in the adsorption-desorption limit. A drop in the co-flowing geometry typically breaks up at the primary neck. The drop breaks faster with smaller volumes as the outer flow rate increases or the drop viscosity decreases. When surfactants are present, they accumulate in the neck …

Development Of Engineering Tools To Analyze And Design Flexible Structures In Open Ocean Environments, Judson Decew

Doctoral Dissertations

Methods to effectively predict system response in marine settings are critical in the engineering design process. The high energy ocean environment can subject structures to large wave and current forces, causing complex coupled motions and loads. This research focused on the development of effective methods to predict flexible system response and the structural integrity of marine High Density Polyethylene (HDPE) components. Numerical modeling tools were developed to analyze and design flexible structures in open ocean environments. Enhancements to the University of New Hampshire's Aqua-FE finite element computer program were performed, including expansion of the element library to include spherical geometries …

Wireless Sensor Integrated Tool For Characterization Of Machining Dynamics In Milling, Christopher Adam Suprock

Doctoral Dissertations

A first step towards practical sensing in the machining environment is the development and use of low cost, reliable sensors. Historically, the ability to record in-process data at an end mill tool tip has been limited by the sensor location. Often, these sensors are mounted on the material workpiece or the machine spindle at significant physical distance from the cutting process. Of specific interest are the problems of tool chatter which causes limitations to productivity and part quality. Although tool chatter is a substantial issue in machining, it remains an open research topic. In this research, a sensor integrated cutting …

Fabrication And Tribology Of Composite Coatings Incorporating Solid Lubricant Micro-Reservoirs, Canan Gamze Guleryuz

Doctoral Dissertations

The tribological behavior of composite coating incorporating solid lubricant reservoirs has been investigated in this study. A new method, termed " microbeading" was devised to create microscopic reservoirs on the surface of sputter-deposited hard coatings. Pin-on-disk tests were used to evaluate the lubricating performance of these newly devised composite coatings. Three sizes of the reservoirs were investigated: 1.5, 5 and 10 microm. The 10 microm-sized-reservoirs performed better in terms of reducing friction and extending wear life. These coatings were also evaluated with finite element models. It was found that during ball-coating surface interaction, the lowest stresses and calculated work done …

Milling Cutter Software Architecture For Force And Surface Finish Modeling, Cuneyt Yalcin

Doctoral Dissertations

The main goal of this dissertation is to pave the way towards a milling simulation software platform that enables academic modeling research to be easily incorporated into industrial practice. The most significant contribution is creation of numeric structures that enable utilization of any milling cutting force model with any type of milling cutting tool in a computationally efficient manner. Efficiency and accuracy of the force and surface finish modeling are the main focus of this study.

Force modeling is an important part of milling research since it is directly connected to tool health and workpiece quality. A number of force …

Investigation And Characterization Of Size Effects In Microforming Processes, Sunal Ahmet Parasiz

Doctoral Dissertations

The products of miniaturization, such as mobile phones, personal digital assistants, computers and other electronic devices have become an indispensable part of our daily lives. Nowadays, more and more industrial products including some medical and electromechanical products contain micro scale metal parts such as connector pins, resistor caps, screws, contact springs and chip lead frames. Miniaturization brings the challenge of realizing the production of these microscale metals parts. Microforming, due to its well known advantages of high production rates, excellent material utilization, and low costs, is a promising manufacturing method compared to the alternative processes in this field. However, well-established …

Improved Estimation Of Fourier Coefficients For Ill-Posed Inverse Problems, Mikhail V. Shubov

Doctoral Dissertations

In this dissertation we present and solve an ill-posed inverse problem which involves reproducing a function f(x) or its Fourier coefficients from the observed values of the function. The observations of the f(x) are made at n equidistant points on the unit interval with p observations being made at each point. The observations are effected by a random error with a known distribution.

First of all we present a very simple estimator for the Fourier coefficients of f(x). Then we present an iteration algorithm for improving the estimator for the Fourier coefficients. We show that the improved estimator we use …

Smart Machining System Platform For Cnc Milling With The Integration Of A Power Sensor And Cutting Model, Min Xu

Doctoral Dissertations

Novel techniques and strategies are investigated for dynamically measuring the process capability of machine tools and using this information for Smart Machine System (SMS) research. Several aspects of the system are explored including system integration, data acquisition, force and power model calibration, feedrate scheduling and tool condition monitoring.

A key aspect of a SMS is its ability to provide synchronization between process measurements and model estimates. It permits real time feedback regarding the current machine tool process. This information can be used to accurately determine and keep track of model coefficients for the actual tooling and materials in use, providing …

Analytical Model Development And Experimental Investigation Of Process Model Size Effects In Microforming, Richard M. Onyancha

Doctoral Dissertations

With the emergence of micromanufacturing technologies, a critical need to develop process models that can accurately predict the required parameters, such as process forces, has arisen. As with the manufacturing processes themselves, macroscale process models can not effectively be used at the microscale due to size effects, i.e. changes in material and process parameters with miniaturization. Size effects with respect to material properties and frictional conditions have been demonstrated in past research. This dissertation demonstrates the existence of size effects due to process model assumptions and specimen deformation.

The new models were evaluated by comparing the predicted results to both …

Modeling Of Diffusional Creep And Stress Relaxation In Copper Grains During Manufacturing Of Microelectronic Integrated Circuits, Vasyl M. Grychanyuk

Doctoral Dissertations

The finite element technique was developed to study diffusional creep and stress relaxation in Cu grains with several atomic monolayers thick grain boundary region of enhanced diffusivity. The model was motivated by the need to study nanoscale back-end interconnect structures of microelectronic circuits. These structures have the length scale that does not conform to the assumptions of classical dimensional theories of diffusional creep.

Both diffusion and elasticity governing equations are considered in the coupled formulation of mass flow and stress analysis. Vacancy concentration field in the grains subjected to external load is coupled to stress field through diffusional creep strains. …

Effective Elastic Properties Of Two -Dimensional Solids With Inhomogeneities Of Irregular Shapes, Jindrich Novak

Doctoral Dissertations

This work investigates the effective elastic properties of two-dimensional solids with inhomogeneities of various shapes. We develop a special procedure to evaluate the contribution of irregularly shaped inhomogeneities to these properties. The method can also be used to investigate the stress concentrations around the inhomogeneities. The procedure is based on the analysis of a representative volume element. We express the contribution of each inhomogeneity to the overall moduli of the composite in terms of the compliance contribution tensor. To calculate the components of this tensor, we devise a method that combines analytical and numerical approaches: Kolosov-Muskhelishvili complex variable technique and …

Multiple Steady Solutions And Bifurcations In The Symmetric Driven Cavity, Kahar Bin Osman

Doctoral Dissertations

The symmetric driven cavity with sinusoidal forcing for two- and three-dimensions is considered. Results are obtained via numerical computations of the Navier Stokes equations with constant density. The numerical integration is a splitting method, using the Crank-Nicholson method for linear terms and the second-order Adams-Bashforth method for the non-linear terms. Spatial derivatives are evaluated with finite differences, and matrix equations are treated with SOR by lines. The results show symmetric solutions for low Reynolds numbers and asymmetric solutions for higher Reynolds numbers. Subcritical bifurcations are observed for two-dimensional flow. Unsteady flow behavior occurs at higher Reynolds number. Three-dimensional simulations for …

Discrete Modeling Of Sculptured Surface Machining For Robust Automatic Feedrate Selection, Jeffrey Gordon Hemmett

Doctoral Dissertations

Traditional feedrate selection techniques currently used in three and five-axis CNC machining reduces milling efficiency. Manually estimated feedrates tend to be conservative and constant, greatly increasing mill time. The goal of this research is to develop robust techniques and software tools for automatically generating optimized feedrates for use on three and five-axis CNC mills, to both simplify the feed selection process and to increase the safety and efficiency of the milling operation through milling process simulation.

The simulation software estimates milling force vectors for each tool move, and identifies a feedrate that maintains a desired peak force. The desired cutting …

An Experimental And Finite Element Investigation Of Thermally Induced Inelastic Deformation Of Single-Level Damascene Copper High Density Interconnect Structures, Nazri B. Kamsah

Doctoral Dissertations

An atomic force microscope was used to investigate thermally induced deformation mechanisms in the areas of copper and polyimide vias in copper-polyimide interconnect structure, as a result of a thermal cycle to 350°C. The copper films exhibited evidence of copper grain boundary sliding, Coble creep, and voids formation. Cu-Ta interfacial sliding was observed in the Cu and polyimide via areas. The direction of the Cu-Ta sliding changes as the polyimide via size decreases. The polyimide experienced a residual deformation attributed to the Cu-Ta sliding and in-plane deformation of the copper vias.

A finite element method was used to simulate the …

E -Commerce For The Metal Removal Industry, Okhyun Ryou

Doctoral Dissertations

The popularity of outsourcing fabrication introduces a problem, namely an inevitable loss of data as information is translated from design to fabrication or from one system to another. Unsatisfactory information, delivered to the outsourcing facility, and inefficient communications between design and fabrication certainly cause enormous economic losses from late product delivery or bad product quality. To overcome these data transferring problems and to improve communications between the design and fabrication sides, a design and manufacturing methodology for custom machined parts in E-Commerce is suggested and implemented in this dissertation. This methodology is based on the idea of a "Clean Interface" …

Numerical Simulation Of Acoustic Waves In A Rectangular Chamber, Normah Mohd. Ghazali

Doctoral Dissertations

Numerical simulation of acoustic waves in a closed two-dimensional rectangular chamber is considered. The waves are generated by a membrane or piston boundary condition on one wall. The simulations are performed through many acoustic cycles. A stack of heat exchanger plates are sometimes included. The study is motivated by thermoacoustic refrigeration, a phenomena which uses soundwaves in a chamber to achieve a cooling effect.

The present study treats the flow numerically. The governing equations are the viscous compressible Navier-Stokes system, assuming a perfect gas. The numerical method employs a finite difference spatial discretization and semi-implicit time-marching procedure. Verification is accomplished …

Finite Element Modeling Of Tidal Flow And Bed -Load Transport In The Great Bay Estuarine System, New Hampshire, Ata Bilgili

Doctoral Dissertations

Current, sea level and bed-load transport are investigated in the Great Bay Estuary, New Hampshire---a shallow, well-mixed system with low freshwater input. Main channel tidal currents are over 2 m/sec, and its dynamic balance is dominated by the pressure gradient and bottom friction. Current and sea level forced by the M2, M4, M6 tides at the estuary mouth are simulated by two numerical models---a three-dimensional, harmonic model that solves the linearized shallow water equations (FUNDY5); and a vertically averaged, time stepping, non-linear model (ADAM). ADAM makes use of a kinematic assumption (that is, the local and advective accelerations are neglected) …

Three-Dimensional Imaging Of Turbulent Flows: Optical Tomography With Proper Orthogonal Decomposition, Barbara Jeanne Pelliccia

Doctoral Dissertations

Fluid flows with turbulent characteristics are evident in many important engineering and scientific applications. For years researchers have investigated fluid flow turbulence but have not attained a complete physical understanding and quantitative description of the turbulent fluid motion. One approach has been to identify and classify the organized, or coherent, structures imbedded in the turbulence. Research in this area has been restricted by the lack of complete three-dimensional descriptions of the flow. In many studies, the velocity field is measured in either one or two dimensions using mechanical probes which can disrupt the downstream evolution of the flow and offer …

Fluid-Structure Interaction In Taylor-Couette Flow, Martin Horst Willi Kempf

Doctoral Dissertations

The linear stability of a viscous fluid between two concentric, rotating cylinders is considered. The inner cylinder is a rigid boundary and the outer cylinder has an elastic layer exposed to the fluid. The subject is motivated by flow between two adjoining rollers in a printing press. The governing equations of the fluid layer are the incompressible Navier-Stokes equations, and the governing equations of the elastic layer are Navier's equations. A narrow gap, neutral stability, and axisymmetric disturbances are assumed. The solution involves a novel technique for treating two layer stability problems, where an exact solution in the elastic layer …

An Experimental Investigation Of The Effects Of Elastic Modulus And Yield Strength On Fracture Surface Interference In Shear Loaded Cracks, Ronald U. Goulet

Doctoral Dissertations

An experimental process was developed to study the effects of material properties on fracture surface interference in Mode II loaded cracks in 7075 aluminum. 4340 and 8642 steels. Factors studied included elastic modulus, yield strength, mode mixity and fracture surface geometry. An asymmetric four point bend specimen and fixture was developed to apply pure Mode II and mixed Mode I and II loads to edge cracks. Three dimensional displacement fields were measured as a function of applied load using an electro-optical holographic interferometric facility. Stress intensity factors were obtained by fitting observed 2-D field displacements to basis functions derived from …

Dynamic Response Of Poroelastic Materials Containing Bingham Fluid: Application To Electrorheological Fluids, Mete Kesan

Doctoral Dissertations

This work examines the dynamic response to harmonic loading of a disk of poroelastic material containing non-Newtonian Bingham fluid which exhibits a yield stress. Biot's poroelasticity equations and modified Darcy's law for non-Newtonian fluids exhibiting a yield stress are combined together to obtain the governing equations of the system for quasi-static case. Dissipation due to friction arising from the flow of fluid relative to the solid is taken into account but inertia effects are neglected. The response and the complex modulus of the system are calculated using the finite element method taking into account the nonlinear nature of Bingham fluid. …

Numerical Analysis For Blood Distribution In Complete Flow Cross-Section Microvascular Networks, Jewen Xiao

Doctoral Dissertations

As the blood flows through a bifurcation, the axisymmetric red blood cell concentration profile is skewed by plasma skimming. In the downstream segment of the bifurcation the concentration profile of red blood cells recovers symmetry by the red blood cell dispersion process.

In this study, the concentration convective equation, which models the red blood cell dispersion process, is solved with the method of finite differences in cylindrical coordinates. In the computation, a shear-induced diffusivity coefficient is used. The computed hematocrit ratios at the second bifurcation are compared with in vitro experimental data obtained from 50 $\mu$m serial trees with two …

An Experimental Investigation Of Thermally-Induced Deformation Of 1 Micron Thick Copper/Tantalum/Polymide High-Density Interconnect Structures, Dmitry V. Zhmurkin

Doctoral Dissertations

A new technique to estimate the out-of-plane thermal expansion coefficient (CTE) of several 1 $\mu$m thick, spin-coated polyimides is introduced. Arrays of parallel copper and polyimide lines of various aspect ratios on Si substrate were imaged in air at room temperature and at 97$\sp\circ$C using an atomic force microscope (AFM). The out-of-plane CTE of the polyimides was estimated by matching the experimental results with the predictions of finite element models with different out-of-plane parameters. For FPI-135 (6FCDA-TMOB) polyimide the out-of-plane CTE was found to be $\approx$260 ppm/$\sp\circ$C, for FPI-136 (PMDA-6FDA-TFMOB) polyimide $\approx$120 ppm/$\sp\circ$C. Polyimide lines with widths equal to or …

Analysis And Design Of Ac Induction Motors With Squirrel Cage Rotors, Shine Ho

Doctoral Dissertations

The traditional approach to modelling the AC induction motor revolves around the well-known equivalent "T" circuit model. In this approach, the direct connection from geometry to performance is suppressed. For better understanding of magnetic, electrical, and thermal behaviors, three lumped models based on the actual geometry are developed in this dissertation. Based on these lumped models, an iterative design model is also developed.

In order to analyze and design induction motors, the relationships of basic motor variables to motor performance must be known. For determining the relationships, three new mathematical lumped models are developed. The magnetic model describes flux behavior. …

Analysis And Design Considerations Of A High-Power Density, Dual Air Gap, Axial-Field, Brushless, Permanent Magnet Motor, Chahee Peter Cho

Doctoral Dissertations

Until recently, brush dc motors have been the dominant drive system because they provide easily controlled motor speed over a wide range, rapid acceleration and deceleration, convenient control of position, and lower product cost. Despite these capabilities, the brush dc motor configuration does not satisfy the design requirements for the U.S. Navy's underwater propulsion applications.

Technical advances in rare-earth permanent magnet materials, in high-power semiconductor transistor technology, and in various rotor position-sensing devices have made using brushless permanent magnet motors a viable alternative. This research investigates brushless permanent magnet motor technology, studying the merits of dual-air gap, axial-field, brushless, permanent …

The Stability Of Flow Over An Elastic Boundary, Paul Joseph Schall

Doctoral Dissertations

Experiments with printing presses show unusual behavior when a fluid flows between rubber and rigid roller. For better understanding of this behavior, three problems which address the stability near fluid interfaces are considered. First, the stability of a viscous flow between a rigid boundary and an elastic layer is studied. Of particular interest are cases with large Froude number modeling rotational effect, and cases with an elastic layer thin as compared to the depth of the fluid. Linear stability is considered using a spectral method. Second, the inviscid flow between a rigid boundary and an elastic layer is studied. Two …