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Description
Understanding damage evolution, particularly as it relates to local nucleation and growth kinetics of spall failure in metallic materials subjected to shock loading, is critical to national security. This work uses computational modeling to elucidate what characteristics have the highest impact on damage localization at the microstructural level in metallic materials, since knowledge of these characteristics is critical to improve these materials. The numerical framework consists of a user-defined material model implemented in a user subroutine run in ABAQUS/Explicit that takes into account crystal plasticity, grain boundary effects, void nucleation and initial growth, and both isotropic and kinematic hardening to model incipient spall. Finite element simulations were performed on copper bicrystal models to isolate the boundary effects between two grains. Two types of simulations were performed in this work: experimentally verified cases in order to validate the constitutive model as well as idealized cases in an attempt to determine the microstructural characteristic that define weakest links in terms of spall damage. Grain boundary effects on damage localization were studied by varying grain boundary orientation in respect to the shock direction and the crystallographic properties of each grain in the bicrystal. Varying these parameters resulted in a mismatch in Taylor factor across the grain boundary and along the shock direction. The experimentally verified cases are models of specific damage sites found from flyer plate impact tests on copper multicrystals in which the Taylor factor mismatch across the grain boundary and along the shock direction are both high or both low. For the idealized cases, grain boundary orientation and crystallography of the grains are chosen such that the Taylor factor mismatch in the grain boundary normal and along the shock direction are maximized or minimized. A perpendicular grain boundary orientation in respect to the shock direction maximizes Taylor factor mismatch, while a parallel grain boundary minimizes the mismatch. Furthermore, it is known that <1 1 1> crystals have the highest Taylor factor, while <0 0 1> has nearly the lowest Taylor factor. The permutation of these extremes for mismatch in the grain boundary normal and along the shock direction results in four idealized cases that were studied for this work. Results of the simulations demonstrate that the material model is capable of predicting damage localization, as it has been able to reproduce damage sites found experimentally. However, these results are qualitative since further calibration is still required to produce quantitatively accurate results. Moreover, comparisons of results for void nucleation rate and void growth rate suggests that void nucleation is more influential in the total void volume fraction for bicrystals with high property mismatch across the interface, suggesting that nucleation is the dominant characteristic in the propagation of damage in the material. Further work in recalibrating the simulation parameters and modeling different bicrystal orientations must be done to verify these results.
ContributorsVo, Johnathan Hiep (Author) / Peralta, Pedro (Thesis director) / Oswald, Jay (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2014-12
Description
The United States criminal justice system seemingly contradicts the staples of freedom that the country was founded upon. Given that the U.S. leads the world in rate of imprisonment, "the land of the free" is actually better described as "the land of the imprisoned". Yet despite such meteoric imprisonment rates, there is no evidence that United States citizens commit more crimes than citizens of other countries. This leads to the deduction that there is a fundamental difference between the United States criminal justice system and that of other countries. While different does not always mean worse, it is undoubtable that the United States is currently facing a financial dilemma due to housing so many criminals. Further, prosecution of such a large number of citizens has led to a dichotomy in society that perpetuates recidivism among those imprisoned. Thus, reform activists are growing in number as the incarceration problem continues to perpetuate. Information Measurement Theory, a modern school of thought, is applied in this paper in order to develop practical improvements to the American criminal justice system. Information Measurement Theory is aptly named because it proposes universal axioms based upon the various levels of information perceived by human beings. It has already improved performance dynamics in various areas of business; therefore it has a great opportunity for success in refining the American prison industry. Staples of Information Measurement Theory allow the individual to simplify complex situations. Hence, it can be applied to simplify the conditions that have led to the current U.S. incarceration predicament. Three different specific areas of U.S. criminal justice will be addressed, and solutions will be presented that are complimentary to Information Measurement Theory fundamentals.
ContributorsMcLeod, Ian Nicholas (Author) / Kashiwagi, Dean (Thesis director) / Kashiwagi, Jacob (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Mechanical Engineering Program (Contributor) / Del E. Webb School of Construction (Contributor)
Created2015-05
Description
The following document addresses two grand challenges posed to engineers: to make solar energy economically viable and to restore and improve urban infrastructure. Design solutions to these problems consist of the preliminary designs of two energy systems: a Packaged Photovoltaic (PPV) energy system and a natural gas based Modular Micro Combined Cycle (MMCC) with 3D renderings. Defining requirements and problem-solving approach methodology for generating complex design solutions required iterative design and a thorough understanding of industry practices and market trends. This paper briefly discusses design specifics; however, the major emphasis is on aspects pertaining to economical manufacture, deployment, and subsequent suitability to address the aforementioned challenges. The selection of these systems is based on the steady reduction of PV installation costs in recent years (average among utility, commercial, and residential down 27% from Q4 2012 to Q4 2013) and the dramatic decline in natural gas prices to $5.61 per thousand cubic feet. In addition, a large number of utility scale coal-based power plants will be retired in 2014, many due to progressive emission criteria, creating a demand for additional power systems to offset the capacity loss and to increase generating capacity in order to facilitate the ever-expanding world population. The proposed energy systems are not designed to provide power to the masses through a central location. Rather, they are intended to provide economical, reliable, and high quality power to remote locations and decentralized power to community-based grids. These energy systems are designed as a means of transforming and supporting the current infrastructure through distributed electricity generation.
ContributorsSandoval, Benjamin Mark (Author) / Bryan, Harvey (Thesis director) / Fonseca, Ernesto (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
Description
In recent years, networked systems have become prevalent in communications, computing, sensing, and many other areas. In a network composed of spatially distributed agents, network-wide synchronization of information about the physical environment and the network configuration must be maintained using measurements collected locally by the agents. Registration is a process for connecting the coordinate frames of multiple sets of data. This poses numerous challenges, particularly due to availability of direct communication only between neighboring agents in the network. These are exacerbated by uncertainty in the measurements and also by imperfect communication links. This research explored statistically based registration in a sensor network. The approach developed exploits measurements of offsets formed as differences of state values between pairs of agents that share a link in the network graph. It takes into account that the true offsets around any closed cycle in the network graph must sum to zero.
ContributorsPhuong, Shih-Ling (Author) / Cochran, Douglas (Thesis director) / Berman, Spring (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
DescriptionThe heat island effect has resulted in an observational increase in averave ambient as well as surface temperatures and current photovoltaic implementation do not migitate this effect. Thus, the feasibility and performance of alternative solutions are explored and determined using theoretical, computational data.
ContributorsCoyle, Aidan John (Author) / Trimble, Steven (Thesis director) / Underwood, Shane (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
Description
This work describes the numerical process developed for use of rocket engine nozzle ejectors. Ejector nozzles, while applied to jet engines extensively, have not been applied to rockets, and have great potential to improve the performance of endoatmospheric rocket propulsion systems. Utilizing the low pressure, high velocity flow in the plume, this secondary structure entrains a secondary mass flow to increase the mass flow of the propulsion system. Rocket engine nozzle ejectors must be designed with the high supersonic conditions associated with rocket engines. These designs rely on the numerical process described in this paper.
ContributorsGibson, Gaines Sullivan (Author) / Wells, Valana (Thesis director) / Takahashi, Timothy (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
Description
The main field of study research through this project is to study the effect of history of deformation in materials subjected to complex loading, useful for producing lightweight alloys and composites optimized for absorbing shock and impact. This is accomplished by creating a digital model of a system in which the material undergoes tension and compression through colliding bars. The results show that the system generated is accurate when compared to real tests, so the program used to create the model can be used in the future for simulated tests using different materials or applied loads.
ContributorsShoemaker, Bradley Dean (Author) / Oswald, Jay (Thesis director) / Solanki, Kiran (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
Description
This study aims to showcase the results of a quadrotor model and the mathematical techniques used to arrive at the proposed design. Multicopters have made an explosive appearance in recent years by the controls engineering community because of their unique flight performance capabilities and potential for autonomy. The ultimate goal of this research is to design a robust control system that guides and tracks the quadrotor's trajectory, while responding to outside disturbances and obstacles that will realistically be encountered during flight. The first step is to accurately identify the physical system and attempt to replicate its behavior with a simulation that mimics the system's dynamics. This becomes quite a complex problem in itself because many realistic systems do not abide by simple, linear mathematical models, but rather nonlinear equations that are difficult to predict and are often numerically unstable. This paper explores the equations and assumptions used to create a model that attempts to match roll and pitch data collected from multiple test flights. This is done primarily in the frequency domain to match natural frequency locations, which can then be manipulated judiciously by altering certain parameters.
ContributorsDuensing, Jared Christopher (Author) / Takahashi, Timothy (Thesis director) / Garrett, Frederick (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
Description
An automated test system was developed to characterize detectors for the Kilopixel Array Pathfinder Project (KAPPa). KAPPa is an astronomy instrument that detects light at terahertz wavelengths using a 16-pixel heterodyne focal plane array. Although primarily designed for the KAPPa receiver, the test system can be used with other instruments to automate tests that might be tedious and time-consuming by hand. Mechanical components of the test setup include an adjustable structure of aluminum t-slot framing that supports a rotating chopper. Driven by a stepper motor, the chopper alternates between blackbodies at room temperature and 77 K. The cold load consists of absorbing material submerged in liquid nitrogen in an open Styrofoam cooler. Scripts written in Matlab and Python control the mechanical system, interface with receiver components, and process data. To calculate the equivalent noise temperature of a receiver, the y-factor method is used. Test system operation was verified by sweeping the local oscillator frequency and power level for two room temperature Schottky diode receivers from Virginia Diodes, Inc. The test system was then integrated with the KAPPa receiver, providing a low cost, simple, adaptable means to measure noise with minimal user intervention.
ContributorsKuenzi, Linda Christine (Author) / Groppi, Christopher (Thesis director) / Mauskopf, Philip (Committee member) / Kulesa, Craig (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
Description
The ideal function of an upper limb prosthesis is to replace the human hand and arm, but a gulf in functionality between prostheses and biological arms still exists, in large part due the absence of the sense of touch. Tactile sensing of the human hand comprises a key component of a wide variety of interactions with the external environment; visual feedback alone is not always sufficient for the recreation of nuanced tasks. It is hoped that the results of this study can contribute to the advancement of prosthetics with a tactile feedback loop with the ultimate goal of replacing biological function. A three-fingered robot hand equipped with tactile sensing fingertips was used to biomimetically grasp a ball in order haptically explore the environment for a ball-in-hole task. The sensorized fingertips were used to measure the vibration, pressure, and skin deformation experienced by each fingertip. Vibration and pressure sensed by the fingertips were good indicators of changes in discrete phases of the exploratory motion such as contact with the lip of a hole. The most informative tactile cue was the skin deformation of the fingers. Upon encountering the lip of the test surface, the lagging digit experienced compression in the fingertip and radial distal region of the digit. The middle digit experienced decompression of the middle region of the finger and the lagging digit showed compression towards the middle digit and decompression in the distal-ulnar region. Larger holes caused an increase in pressure experienced by the fingertips while changes in stroke speed showed no effect on tactile data. Larger coefficients of friction between the ball and the test surface led to an increase in pressure and skin deformation of the finger. Unlike most tactile sensing studies that focus on tactile stimuli generated by direct contact between a fingertip and the environment, this preliminary study focused on tactile stimuli generated when a grasped object interacts with the environment. Findings from this study could be used to design experiments for functionally similar activities of daily living, such as the haptic search for a keyhole via a grasped key.
ContributorsLoges, Shea Remegio (Author) / Santos, Veronica (Thesis director) / Artemiadis, Panagiotis (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05