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University of Colorado, Boulder

Theses/Dissertations

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Full-Text Articles in Engineering Science and Materials

Experimental Validation For The Theory Of Blisters’ Instabilities, Hongtian Zhu Jan 2018

Experimental Validation For The Theory Of Blisters’ Instabilities, Hongtian Zhu

Mechanical Engineering Graduate Theses & Dissertations

Blister formation is a universal problem that can be witnessed within a wide range of contents. It is first documented as a side effect of syringomyelia and other diseases. Later on, the forming of blisters are also observed during the cell apoptosis, which leads to the hypothesis that it could have some intricate relationships with the death of living organisms. Other than biological problems, blister forming is also a common phenomenon in thin film technologies. Therefore, the research in the forming of blisters is essential and critical in both engineering and science fields.

In this thesis, we study the problem ...


Lamb Waves With Conical Dispersion At Zero Wavenumber, David M. Stobbe Jan 2018

Lamb Waves With Conical Dispersion At Zero Wavenumber, David M. Stobbe

Mechanical Engineering Graduate Theses & Dissertations

Lamb waves are guided elastic waves in plates. These waves are dispersive, with the frequency and wavenumber related by the well-known Rayleigh-Lamb equation. Generally, at zero wavenumber the dispersion curves are parabolic and the waves are non-propagating thickness resonances. For distinct values of Poisson’s ratio, however, degeneracy can occur between thickness resonance modes. At these coincidence frequencies the dispersion curves become linear and in a three-dimensional representation the dispersion surface is shaped like a cone. This behavior is referred to as conical dispersion. Waves excited at coincidence frequencies maintain the infinite phase velocity associated with thickness resonances but transport ...


Investigating The Physical Mechanisms That Impact Electric Fields In The Atmosphere, Greg M. Lucas Jan 2017

Investigating The Physical Mechanisms That Impact Electric Fields In The Atmosphere, Greg M. Lucas

Aerospace Engineering Sciences Graduate Theses & Dissertations

The underlying physics and dynamics of the atmosphere drive electric currents and establish electric fields in a phenomenon known as the global electric circuit (GEC). The GEC has been observed and modeled with limiting assumptions and parameterizations in previous research. This thesis describes the incorporation of a physics-based GEC modeling scheme into a sophisticated climate model to describe the evolution of GEC currents, ground-ionosphere potential, electric fields, and conductivity within the atmosphere. Supporting measurements of atmospheric electric fields over time were used to describe the impact of local meteorological changes and assess the GEC contribution to near-surface electric fields.

The ...


Hierarchical Multiscale Modeling To Inform Continuum Constitutive Models Of Soils, Erik Wallace Jensen Jan 2017

Hierarchical Multiscale Modeling To Inform Continuum Constitutive Models Of Soils, Erik Wallace Jensen

Civil Engineering Graduate Theses & Dissertations

The behavior of soils is fundamentally the combined interactions between billions and billions of individual particles and particle matrices. For computational tractability and despite this fact, many soil models assume the material is a continuum essentially averaging the inter-particle interactions to predict the behavior of the bulk material. In recent years, multiscale modeling techniques have been developed to reintroduce the effect of the grain-scale interactions to help model situations where the continuum assumption fails, such as shear band development in triaxial tests or soil disaggregation under blast loading. One of such multiscale models called hierarchical upscaling, or global-local analysis, model ...


Finite Strain Micromorphic Elasticity, Elastoplasticity, And Dynamics For Multiscale Finite Element Analysis, Farhad Shahabi Jan 2017

Finite Strain Micromorphic Elasticity, Elastoplasticity, And Dynamics For Multiscale Finite Element Analysis, Farhad Shahabi

Civil Engineering Graduate Theses & Dissertations

This study stands as an attempt to consider the micro-structure of materials in a continuum framework by the aid of micromorphic continuum theory in the sense of Eringen. Since classical continuum mechanics do not account for the micro-structural characteristics of materials, they cannot be used to address the macroscopic mechanical response of all micro-structured materials. In the “representative volume element (RVE)” based methods, classical continuum mechanics may be applied to analyze mechanical deformation and stresses of materials at the relevant micro-structural length-scale (such as grains of a polycrystalline metal, or sand, or metal matrix composite, etc), but when applying standard ...


Nonlinear Dispersive Elastic Waves In Solids: Exact, Approximate, And Numerical Solutions, Romik Khajehtourian Jan 2017

Nonlinear Dispersive Elastic Waves In Solids: Exact, Approximate, And Numerical Solutions, Romik Khajehtourian

Aerospace Engineering Sciences Graduate Theses & Dissertations

Wave motion lies at the heart of many disciplines in the physical sciences and engineering. For example, problems and applications involving light, sound, heat, or fluid flow are all likely to involve wave dynamics at some level. A particular class of problems is concerned with the propagation of elastic waves in a solid medium, such as a fiber-reinforced composite material responding to vibratory excitations, or soil and rock admitting seismic waves moments after the onset of an earthquake, or phonon transport in a semiconducting crystal like silicon. Regardless of the type of wave, the dispersion relation provides a fundamental characterization ...


Autonomous Mission Design In Extreme Orbit Environments, David Allen Surovik Jan 2016

Autonomous Mission Design In Extreme Orbit Environments, David Allen Surovik

Aerospace Engineering Sciences Graduate Theses & Dissertations

An algorithm for autonomous online mission design at asteroids, comets, and small moons is developed to meet the novel challenges of their complex non-Keplerian orbit environments, which render traditional methods inapplicable. The core concept of abstract reachability analysis, in which a set of impulsive maneuvering options is mapped onto a space of high-level mission outcomes, is applied to enable goal-oriented decision-making with robustness to uncertainty. These nuanced analyses are efficiently computed by utilizing a heuristic-based adaptive sampling scheme that either maximizes an objective function for autonomous planning or resolves details of interest for preliminary analysis and general study. Illustrative examples ...


Roll-To-Roll Atomic Layer Deposition Of Ultrabarriers, Alexander Yersak Jan 2016

Roll-To-Roll Atomic Layer Deposition Of Ultrabarriers, Alexander Yersak

Mechanical Engineering Graduate Theses & Dissertations

Atomic layer deposition (ALD) is a bottom-up, gas phase, thin film deposition technique based on sequential, self-limiting binary surface reactions. The precise sub-nanometer film thickness control and conformal nature of this process have led to various commercial applications of ALD. However, ALD films are most commonly deposited in batch processes at low pressures, which raises throughput and/or cost concerns for many otherwise promising applications. This problem can be solved by spatial ALD (S-ALD) which is a version of the ALD technique where the precursors are separated in space rather than time. We have demonstrated the first atmospheric pressure roll-to-roll ...


The Particle Based Moving Interface Method For Soft Matter Mechanics And Fluid/Membrane Interactions With Applications To Biological Cells, Louis Cyrille Foucard Jan 2014

The Particle Based Moving Interface Method For Soft Matter Mechanics And Fluid/Membrane Interactions With Applications To Biological Cells, Louis Cyrille Foucard

Civil Engineering Graduate Theses & Dissertations

The mechanics of the interaction between a fluid and a soft interface (such as an elastic membrane or shell) undergoing large deformations appears in many places, such as in biological systems or industrial processes. We present here an Eulerian approach that describes the mechanics of an interface and its interactions with a surrounding fluid via the so-called Navier boundary condition. The interface is modeled as a curvilinear surface with arbitrary mechanical properties across which discontinuities in pressure and tangential fluid velocity can naturally be enforced using a modified version of the extended finite element method. The tracking and evolution of ...


Fish Skin: A Thin, Flexible, Protective Membrane, Natasha Elaine Funk Jan 2014

Fish Skin: A Thin, Flexible, Protective Membrane, Natasha Elaine Funk

Civil Engineering Graduate Theses & Dissertations

Although there have been recent efforts to characterize the important structural characteristics of fish scales and fish skin (e.g., the tensile strength [9], puncture strength [19], bending rigidity [10]), attempts to fabricate materials that mimic natural fish skins have remained limited. This thesis presents a synthetic fish skin material designed to replicate the structural, dimensional, mechanical, and functional aspects of natural teleost fish skin comprised of leptoid-like scales. The material design and fabrication has been simplified to include (i) a low modulus elastic mesh or dermis layer that holds (ii) relatively (in comparison to the mesh) rigid, plastic scales ...


Confined Masonry: Theoretical Fundamentals, Experimental Test, Finite Element Models, And Future Uses, Lan T. Nguyen Jan 2014

Confined Masonry: Theoretical Fundamentals, Experimental Test, Finite Element Models, And Future Uses, Lan T. Nguyen

Civil Engineering Graduate Theses & Dissertations

Inspired from the MS thesis that investigated the underlying relationship between the implicit level of risk accepted for natural hazards and the level of economic, social and political development of Haiti, a developing country, this dissertation focuses structurally on the use of low-rise confined masonry (CM) buildings in natural hazard consideration areas. The research emphasizes the responses of the CM shear wall structure as a whole, as well as the material conditions in detail. Key findings are presented from experimental tests, computational modeling procedures, analytical results, and reliability analysis for CM structures followed with the summary of the behavior of ...


The Effect Of Temperature On Moisture Transfer In Concrete, Yao Wang Jan 2014

The Effect Of Temperature On Moisture Transfer In Concrete, Yao Wang

Civil Engineering Graduate Theses & Dissertations

Moisture transfer is a major concern for predicting the durability and serviceability of concrete. To predict moisture transfer in concrete, one should not only analyze the effect of moisture gradient, but also consider the effect of temperature gradient. This effect is called Soret effect. Moreover, depending on the experimental results, the value of coefficient was calculated and used to quantify the Soret effect.

This thesis presents results of an experimental investigation of how the temperature gradient affects the moisture in concrete. The thesis includes two major parts. The first part introduces the background information as well as the theoretical review ...


Thermal Strain Of Concrete Under Low Temperatures And Durability And Processing Techniques Of Concrete With Cnts, Xingang Wang Jan 2013

Thermal Strain Of Concrete Under Low Temperatures And Durability And Processing Techniques Of Concrete With Cnts, Xingang Wang

Civil Engineering Graduate Theses & Dissertations

This thesis consists of two topics: Thermal strain of concrete under low temperatures, and durability and processing techniques of concrete with CNTs. The low temperature test studies the anti-freezing action of concrete under cooling environment. Concrete mixes using different amounts of air-entraining agent and water/cement ratios were made and cured under different humidity environments. During the cooling process from 10 ºC to -25 ºC, the strain of concrete was measured every 3~5 ºC. The strain-temperature curve of concrete under different mixing proportion was produced from these results. A numerical model was developed based on the theory of the ...


Model Development And Experimental Validation Of Pressure Independent Hydronic Circuits, Justin Thomas Bellucci Jan 2012

Model Development And Experimental Validation Of Pressure Independent Hydronic Circuits, Justin Thomas Bellucci

Civil Engineering Graduate Theses & Dissertations

Computer modeling is quickly becoming a more accessible method to evaluate the performance of complex building systems, due in part to the recent advance in computing power over the last decade. Rising energy costs, stricter building codes, the threat of global climate change and governmental pressure have all influenced building owners, architects, engineers and system operators to design and operate the world's building stock in a more energy efficient manner. Particularly important in large buildings and campuses are the hydronic flow networks that deliver chilled water to the cooling coils in air handling units for the purpose of regulating ...


The Influence Of Representative Volume Element Size, Soil Fabric, And Interparticle Elasto-Plasticity In Three-Dimensional Ellipsoidal Discrete Element Modeling Of Granular Assemblies, Yevgeniy Kaufman Jan 2012

The Influence Of Representative Volume Element Size, Soil Fabric, And Interparticle Elasto-Plasticity In Three-Dimensional Ellipsoidal Discrete Element Modeling Of Granular Assemblies, Yevgeniy Kaufman

Civil Engineering Graduate Theses & Dissertations

In this comparative study of RVEs, a DEM code ELLIP3D is utilized to simulate quartz sand in triaxial compression tests with particle assemblies attained from an in situ fabric generated by synchrotron X-ray microcomputed tomography. In order to attain meaningful results for engineered systems at the macroscopic scale using DEM, RVE volume sizes play a significant role in the accuracy of simulating physical experiments. Simulation time or the number of particles limits the capacity of DEM to simulate large-scale granular systems, which is why it is crucial to determine an efficient quantity and quality of RVEs.

ELLIP3D simulations have been ...


Thermomechanics Of Shape Memory Polymers And Composites, Qi Ge Jan 2012

Thermomechanics Of Shape Memory Polymers And Composites, Qi Ge

Mechanical Engineering Graduate Theses & Dissertations

This dissertation presents studies with a combination of experiment, theory, and simulation on a broad range of polymeric material systems (both established and emerging), that exhibit the shape memory (SM) effect. The goals of the studies are to understand complex thermomechanical behaviors of shape memory polymers (SMPs), develop constitutive models to describe the behaviors and use the developed models to advance the development and deployment of SMPs. The general approach used in the studies is independent of the material system and consists of: i) sample fabrication and thermomechanical experiments including dynamic mechanical analysis (DMA), stress-strain behaviors and thermal strain tests ...