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Description
In a collaborative environment where multiple robots and human beings are expected
to collaborate to perform a task, it becomes essential for a robot to be aware of multiple
agents working in its work environment. A robot must also learn to adapt to
different agents in the workspace and conduct its interaction based on the presence
of these agents. A theoretical framework was introduced which performs interaction
learning from demonstrations in a two-agent work environment, and it is called
Interaction Primitives.
This document is an in-depth description of the new state of the art Python
Framework for Interaction Primitives between two agents in a single as well as multiple
task work environment and extension of the original framework in a work environment
with multiple agents doing a single task. The original theory of Interaction
Primitives has been extended to create a framework which will capture correlation
between more than two agents while performing a single task. The new state of the
art Python framework is an intuitive, generic, easy to install and easy to use python
library which can be applied to use the Interaction Primitives framework in a work
environment. This library was tested in simulated environments and controlled laboratory
environment. The results and benchmarks of this library are available in the
related sections of this document.
to collaborate to perform a task, it becomes essential for a robot to be aware of multiple
agents working in its work environment. A robot must also learn to adapt to
different agents in the workspace and conduct its interaction based on the presence
of these agents. A theoretical framework was introduced which performs interaction
learning from demonstrations in a two-agent work environment, and it is called
Interaction Primitives.
This document is an in-depth description of the new state of the art Python
Framework for Interaction Primitives between two agents in a single as well as multiple
task work environment and extension of the original framework in a work environment
with multiple agents doing a single task. The original theory of Interaction
Primitives has been extended to create a framework which will capture correlation
between more than two agents while performing a single task. The new state of the
art Python framework is an intuitive, generic, easy to install and easy to use python
library which can be applied to use the Interaction Primitives framework in a work
environment. This library was tested in simulated environments and controlled laboratory
environment. The results and benchmarks of this library are available in the
related sections of this document.
ContributorsKumar, Ashish, M.S (Author) / Amor, Hani Ben (Thesis advisor) / Zhang, Yu (Committee member) / Yang, Yezhou (Committee member) / Arizona State University (Publisher)
Created2017
Description
This dissertation uncovers the contemporary impressions of Song cities represented in Song narratives and their accounts of the interplay between people and urban environments. It links these narratives to urban and societal changes in Hangzhou 杭州 (Lin’an 臨安) during the Song dynasty, cross-referencing both literary creations and historical accounts through a close reading of the surviving corpus of Song narratives, in order to shed light on the cultural landscape and social milieu of Hangzhou. By identifying, reconstructing, and interpreting urban changes throughout the “pre-modernization” transition as well as their embodiments in the narratives, the dissertation links changes to the physical world with the development of Song narratives. In revealing the emerging connection between historical and literary spaces, the dissertation concludes that the transitions of Song cities and urban culture drove these narrative writings during the Song dynasty. Meanwhile, the ideologies and urban culture reflected in these accounts could only have emerged alongside the appearance of a consumption society in Hangzhou. Aiming to expand our understanding of the literary value of Song narratives, the dissertation therefore also considers historical references and concurrent writings in other genres. By elucidating the social, spatial, and historical meanings embedded in a variety of Song narrative accounts, this study details how the Song literary narrative corpus interprets the urban landscapes of the period’s capital city through the private experiences of Song authors. Using a transdisciplinary methodology, it situates the texts within the cultural milieu of Song society and further reveals the connections of these narratives to the transformative process of urbanization in Song society.
ContributorsHan, Ye (Author) / West, Stephen H. (Committee member) / Bokenkamp, Stephen R (Committee member) / Ling, Xiaoqiao (Committee member) / Arizona State University (Publisher)
Created2017
Description
In a typical living cell, millions to billions of proteins—nanomachines that fluctuate and cycle among many conformational states—convert available free energy into mechanochemical work. A fundamental goal of biophysics is to ascertain how 3D protein structures encode specific functions, such as catalyzing chemical reactions or transporting nutrients into a cell. Protein dynamics span femtosecond timescales (i.e., covalent bond oscillations) to large conformational transition timescales in, and beyond, the millisecond regime (e.g., glucose transport across a phospholipid bilayer). Actual transition events are fast but rare, occurring orders of magnitude faster than typical metastable equilibrium waiting times. Equilibrium molecular dynamics (EqMD) can capture atomistic detail and solute-solvent interactions, but even microseconds of sampling attainable nowadays still falls orders of magnitude short of transition timescales, especially for large systems, rendering observations of such "rare events" difficult or effectively impossible.
Advanced path-sampling methods exploit reduced physical models or biasing to produce plausible transitions while balancing accuracy and efficiency, but quantifying their accuracy relative to other numerical and experimental data has been challenging. Indeed, new horizons in elucidating protein function necessitate that present methodologies be revised to more seamlessly and quantitatively integrate a spectrum of methods, both numerical and experimental. In this dissertation, experimental and computational methods are put into perspective using the enzyme adenylate kinase (AdK) as an illustrative example. We introduce Path Similarity Analysis (PSA)—an integrative computational framework developed to quantify transition path similarity. PSA not only reliably distinguished AdK transitions by the originating method, but also traced pathway differences between two methods back to charge-charge interactions (neglected by the stereochemical model, but not the all-atom force field) in several conserved salt bridges. Cryo-electron microscopy maps of the transporter Bor1p are directly incorporated into EqMD simulations using MD flexible fitting to produce viable structural models and infer a plausible transport mechanism. Conforming to the theme of integration, a short compendium of an exploratory project—developing a hybrid atomistic-continuum method—is presented, including initial results and a novel fluctuating hydrodynamics model and corresponding numerical code.
Advanced path-sampling methods exploit reduced physical models or biasing to produce plausible transitions while balancing accuracy and efficiency, but quantifying their accuracy relative to other numerical and experimental data has been challenging. Indeed, new horizons in elucidating protein function necessitate that present methodologies be revised to more seamlessly and quantitatively integrate a spectrum of methods, both numerical and experimental. In this dissertation, experimental and computational methods are put into perspective using the enzyme adenylate kinase (AdK) as an illustrative example. We introduce Path Similarity Analysis (PSA)—an integrative computational framework developed to quantify transition path similarity. PSA not only reliably distinguished AdK transitions by the originating method, but also traced pathway differences between two methods back to charge-charge interactions (neglected by the stereochemical model, but not the all-atom force field) in several conserved salt bridges. Cryo-electron microscopy maps of the transporter Bor1p are directly incorporated into EqMD simulations using MD flexible fitting to produce viable structural models and infer a plausible transport mechanism. Conforming to the theme of integration, a short compendium of an exploratory project—developing a hybrid atomistic-continuum method—is presented, including initial results and a novel fluctuating hydrodynamics model and corresponding numerical code.
ContributorsSeyler, Sean L (Author) / Beckstein, Oliver (Thesis advisor) / Chamberlin, Ralph (Committee member) / Matyushov, Dmitry (Committee member) / Thorpe, Michael F (Committee member) / Vaiana, Sara (Committee member) / Arizona State University (Publisher)
Created2017
Description
The electric power system is monitored via an extensive network of sensors in tandem with data processing algorithms, i.e., an intelligent cyber layer, that enables continual observation and control of the physical system to ensure reliable operations. This data collection and processing system is vulnerable to cyber-attacks that impact the system operation status and lead to serious physical consequences, including systematic problems and failures.
This dissertation studies the physical consequences of unobservable false data injection (FDI) attacks wherein the attacker maliciously changes supervisory control and data acquisition (SCADA) or phasor measurement unit (PMU) measurements, on the electric power system. In this context, the dissertation is divided into three parts, in which the first two parts focus on FDI attacks on SCADA and the last part focuses on FDI attacks on PMUs.
The first part studies the physical consequences of FDI attacks on SCADA measurements designed with limited system information. The attacker is assumed to have perfect knowledge inside a sub-network of the entire system. Two classes of attacks with different assumptions on the attacker's knowledge outside of the sub-network are introduced. In particular, for the second class of attacks, the attacker is assumed to have no information outside of the attack sub-network, but can perform multiple linear regression to learn the relationship between the external network and the attack sub-network with historical data. To determine the worst possible consequences of both classes of attacks, a bi-level optimization problem wherein the first level models the attacker's goal and the second level models the system response is introduced.
The second part of the dissertation concentrates on analyzing the vulnerability of systems to FDI attacks from the perspective of the system. To this end, an off-line vulnerability analysis framework is proposed to identify the subsets of the test system that are more prone to FDI attacks.
The third part studies the vulnerability of PMUs to FDI attacks. Two classes of more sophisticated FDI attacks that capture the temporal correlation of PMU data are introduced. Such attacks are designed with a convex optimization problem and can always bypass both the bad data detector and the low-rank decomposition (LD) detector.
This dissertation studies the physical consequences of unobservable false data injection (FDI) attacks wherein the attacker maliciously changes supervisory control and data acquisition (SCADA) or phasor measurement unit (PMU) measurements, on the electric power system. In this context, the dissertation is divided into three parts, in which the first two parts focus on FDI attacks on SCADA and the last part focuses on FDI attacks on PMUs.
The first part studies the physical consequences of FDI attacks on SCADA measurements designed with limited system information. The attacker is assumed to have perfect knowledge inside a sub-network of the entire system. Two classes of attacks with different assumptions on the attacker's knowledge outside of the sub-network are introduced. In particular, for the second class of attacks, the attacker is assumed to have no information outside of the attack sub-network, but can perform multiple linear regression to learn the relationship between the external network and the attack sub-network with historical data. To determine the worst possible consequences of both classes of attacks, a bi-level optimization problem wherein the first level models the attacker's goal and the second level models the system response is introduced.
The second part of the dissertation concentrates on analyzing the vulnerability of systems to FDI attacks from the perspective of the system. To this end, an off-line vulnerability analysis framework is proposed to identify the subsets of the test system that are more prone to FDI attacks.
The third part studies the vulnerability of PMUs to FDI attacks. Two classes of more sophisticated FDI attacks that capture the temporal correlation of PMU data are introduced. Such attacks are designed with a convex optimization problem and can always bypass both the bad data detector and the low-rank decomposition (LD) detector.
ContributorsZhang, Jiazi (Author) / Sankar, Lalitha (Thesis advisor) / Kosut, Oliver (Committee member) / Hedman, Kory (Committee member) / Vittal, Vijay (Committee member) / Arizona State University (Publisher)
Created2017
Description
This dissertation examines how contemporary ideologies of race and “colorblind” discourse are reproduced, deployed, and reimagined in Mexican American literature. It demonstrates that the selected narratives foreground inconsistencies in colorblind ideologies and problematize the instability and perennial reformulation of race definitions in the United States. This study also contributes to the discussion of racial formation in Mexican American literary studies from 1970 to 2010. Chapter One provides the critical and literary context of Mexican American literature from 1970 to 2010. Chapter Two details the process of racial formation in the United States according to Michael Omi and Howard Winant. Simultaneously, this chapter describes the theoretical framework and concepts of experience and epistemic privilege, mestizaje, and intercultural relations as offered respectively by Paula M. L. Moya, Rafael Pérez-Torres, and Marta E. Sánchez. Chapter Three offers an analysis of racial discourse and assimilation via two autobiographical texts: Oscar Acosta’s The Autobiography of a Brown Buffalo (1972) and Richard Rodriguez’s Hunger of Memory: The Education of Richard Rodriguez (1982). Chapter Four examines the colorblind racial ideology in two texts by Mexican American women authors: Erlinda Gonzales-Berry’s Paletitas de guayaba (1991) and Mona Ruiz’s Two Badges: The Lives of Mona Ruiz (1998). Chapter Five explores the rearticulation of colorblind racial discourse in the “postracial” United States. In this chapter, we examine three works of speculative fiction: The Rag Doll Plagues (1992) by Alejandro Morales, Texas 2077: A Futuristic Novel (1998) by Carlos Miralejos, and Lunar Braceros 2125-2148 (2009) by Rosaura Sánchez and Beatrice Pita. By combining theories from Chicana/o Studies, Critical Race and Gender Studies, and Cultural Studies in my textual analysis, my dissertation challenges notions of contemporary colorblind or postracial ideologies that regard present day discussions of race as counterproductive to U.S. race relations.
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ContributorsFlores, José Roberto (Author) / Rosales, Jesus (Thesis advisor) / Foster, David W (Committee member) / Gil-Osle, Juan P (Committee member) / Arizona State University (Publisher)
Created2017
Description
The purpose of this project is to analyze Jane Austen's unfinished novel Sanditon (1817) and its inclusion of a character of color. This thesis discusses Austen's mixed-race heiress, Miss Lambe, in the context of two other pieces of fiction that feature mixed-race heroines--the anonymously published The Woman of Colour (1808) and Mary Ann Sullivan's Owen Castle (1816). Scholarship on Austen's awareness of the Abolitionist movement and her sympathy for its politics has previously been published. I advance our conversations on the subject by discussing Austen's Miss Lambe as a mixed-race heiress in the context of gender, race, and ethnicity in late eighteenth- and early nineteenth-century novels. My thesis considers literary and historical treatments of people of color and provides a trans-Atlantic approach to female characters identified as mixed race.
Juxtaposing Sanditon, The Woman of Colour, and Owen Castle provides insight into how Austen was working within a set of established literary traditions, while creating ways to disrupt some of its problematic elements. This project looks at conventions of the mixed-race female characters in five ways. To begin, I discuss the mixed-race heroine and the compulsion to define her place of origin. Second, I consider the convention of describing mixed-race heiresses' rights to their inheritance. An analysis of the significance of naming mixed-race heiresses follows. I discuss literary conventions of the betrayal of mixed-race females. Lastly, I explore the common use of black maid figures in novels of this era to advance social critique against prejudice. Comparative analysis of Austen with other novels featuring mixed-race heroines in this era allows us to reach new understandings of Sanditon. Austen's unfinished last novel is shown to question the power of fortune, to undermine the orthodoxy of categorizing race and ethnicity, and to unsettle the hierarchy among characters of different races and ethnicities.
Juxtaposing Sanditon, The Woman of Colour, and Owen Castle provides insight into how Austen was working within a set of established literary traditions, while creating ways to disrupt some of its problematic elements. This project looks at conventions of the mixed-race female characters in five ways. To begin, I discuss the mixed-race heroine and the compulsion to define her place of origin. Second, I consider the convention of describing mixed-race heiresses' rights to their inheritance. An analysis of the significance of naming mixed-race heiresses follows. I discuss literary conventions of the betrayal of mixed-race females. Lastly, I explore the common use of black maid figures in novels of this era to advance social critique against prejudice. Comparative analysis of Austen with other novels featuring mixed-race heroines in this era allows us to reach new understandings of Sanditon. Austen's unfinished last novel is shown to question the power of fortune, to undermine the orthodoxy of categorizing race and ethnicity, and to unsettle the hierarchy among characters of different races and ethnicities.
ContributorsBaugh, Victoria (Author) / Looser, Devoney (Thesis advisor) / Justice, George (Committee member) / Wernimont, Jacqueline (Committee member) / Arizona State University (Publisher)
Created2017
Description
Membranes are a key part of pervaporation processes, which is generally a more
efficient process for selective removal of alcohol from water than distillation. It is
necessary that the membranes have high alcohol permeabilities and selectivities.
Polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) have
demonstrated very promising results. Zeolitic imidazolate framework-71 (ZIF-71)
demonstrated promising alcohol separation abilities. In this dissertation, we present
fundamental studies on the synthesis of ZIF-71/PDMS MMMs.
Free-standing ZIF-71/ PDMS membranes with 0, 5, 25 and 40 wt % ZIF-71
loadings were prepared and the pervaporation separation for ethanol and 1-butanol from
water was measured. ZIF-71/PDMS MMMs were formed through addition cure and
condensation cure methods. Addition cure method was not compatible with ZIF-71
resulting in membranes with poor mechanical properties, while the condensation cure
method resulted in membranes with good mechanical properties. The 40 wt % ZIF-71
loading PDMS nanocomposite membranes achieved a maximum ethanol/water selectivity
of 0.81 ± 0.04 selectivity and maximum 1-butnaol/water selectivity of 5.64 ± 0.15.
The effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle
size and the effect of particle size on membrane performance were studied. Temperature
had the greatest effect on ZIF-71 particle size as the synthesis temperature varied from -
20 to 35 ºC. The ZIF-71 synthesized had particle diameters ranging from 150 nm to 1
μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance
for alcohol removal from water through pervaporation. The membranes made with
micron sized ZIF-71 particles showed higher alcohol/water selectivity than those with
smaller particles. Both alcohol and water permeability increased when larger sized ZIF-
71 particles were incorporated.
ZIF-71 particles were modified with four ligands through solvent assisted linker
exchange (SALE) method: benzimidazole (BIM), 5-methylbenzimidazole (MBIM), 5,6-
dimethylbenzimidazole (DMBIM) and 4-Phenylimidazole (PI). The morphology of ZIF-
71 were maintained after the modification. ZIF-71/PDMS composite membranes with 25
wt% loading modified ZIF-71 particles were made for alcohol/water separation. Better
particle dispersion in PDMS polymer matrix was observed with the ligand modified ZIFs.
For both ethanol/water and 1-butanol/water separations, the alcohol permeability and
alcohol/water selectivity were lowered after the ZIF-71 ligand exchange reaction.
efficient process for selective removal of alcohol from water than distillation. It is
necessary that the membranes have high alcohol permeabilities and selectivities.
Polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) have
demonstrated very promising results. Zeolitic imidazolate framework-71 (ZIF-71)
demonstrated promising alcohol separation abilities. In this dissertation, we present
fundamental studies on the synthesis of ZIF-71/PDMS MMMs.
Free-standing ZIF-71/ PDMS membranes with 0, 5, 25 and 40 wt % ZIF-71
loadings were prepared and the pervaporation separation for ethanol and 1-butanol from
water was measured. ZIF-71/PDMS MMMs were formed through addition cure and
condensation cure methods. Addition cure method was not compatible with ZIF-71
resulting in membranes with poor mechanical properties, while the condensation cure
method resulted in membranes with good mechanical properties. The 40 wt % ZIF-71
loading PDMS nanocomposite membranes achieved a maximum ethanol/water selectivity
of 0.81 ± 0.04 selectivity and maximum 1-butnaol/water selectivity of 5.64 ± 0.15.
The effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle
size and the effect of particle size on membrane performance were studied. Temperature
had the greatest effect on ZIF-71 particle size as the synthesis temperature varied from -
20 to 35 ºC. The ZIF-71 synthesized had particle diameters ranging from 150 nm to 1
μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance
for alcohol removal from water through pervaporation. The membranes made with
micron sized ZIF-71 particles showed higher alcohol/water selectivity than those with
smaller particles. Both alcohol and water permeability increased when larger sized ZIF-
71 particles were incorporated.
ZIF-71 particles were modified with four ligands through solvent assisted linker
exchange (SALE) method: benzimidazole (BIM), 5-methylbenzimidazole (MBIM), 5,6-
dimethylbenzimidazole (DMBIM) and 4-Phenylimidazole (PI). The morphology of ZIF-
71 were maintained after the modification. ZIF-71/PDMS composite membranes with 25
wt% loading modified ZIF-71 particles were made for alcohol/water separation. Better
particle dispersion in PDMS polymer matrix was observed with the ligand modified ZIFs.
For both ethanol/water and 1-butanol/water separations, the alcohol permeability and
alcohol/water selectivity were lowered after the ZIF-71 ligand exchange reaction.
ContributorsYin, Huidan (Author) / Lind, Mary Laura (Thesis advisor) / Mu, Bin (Committee member) / Nielsen, David (Committee member) / Seo, Don (Committee member) / Lin, Jerry (Committee member) / Arizona State University (Publisher)
Created2017
Description
The Space Race (1957–1975), a period of rapid technological advancements prompted by the uncertainty and fear of the Cold War, captured the curiosity and attention of many artists, filmmakers and composers. Their responses, recorded in a multitude of works from various genres, reflect the overall tone and mirror societal views in the midst of uncertain, politically-charged times.
My thesis explores two seminal American artists who explored outer space in numerous works. John Cage (1912–1992), an avant-garde classical composer, wrote such works as Atlas Eclipticalis (1961), Etudes Australes (1974–75), and the Freeman Etudes (1977–1980), all composed using star-maps. Sun Ra (1914–1993), an American Afrofuturist jazz composer, created hundreds of iconic experimental jazz works on the theme of outer space, with albums such as We Travel the Space Ways (1967), Space Is the Place (1973), and Cosmos (1976).
The works of these two composers span across several decades, encompassing the Space Race and Cold War. In this thesis, I will specifically discuss the details of two works: Cage’s Atlas Eclipticalis, and Ra’s composition Space Is the Place (later included in the soundtrack of a film by the same name). Discussion will elaborate on the cultural, political, philosophical, and societal influences that played a part in the creation of these two compositions.
My research materials for this thesis includes a collection of primary sources in the form of recordings, early musical sketches, and in the case of Ra, film footage from Space Is the Place (1974), as well as multitude of secondary sources. By choosing works from two different genres I hope to present a wider, more nuanced snapshot of artist responses to space exploration during the Cold War.
My thesis explores two seminal American artists who explored outer space in numerous works. John Cage (1912–1992), an avant-garde classical composer, wrote such works as Atlas Eclipticalis (1961), Etudes Australes (1974–75), and the Freeman Etudes (1977–1980), all composed using star-maps. Sun Ra (1914–1993), an American Afrofuturist jazz composer, created hundreds of iconic experimental jazz works on the theme of outer space, with albums such as We Travel the Space Ways (1967), Space Is the Place (1973), and Cosmos (1976).
The works of these two composers span across several decades, encompassing the Space Race and Cold War. In this thesis, I will specifically discuss the details of two works: Cage’s Atlas Eclipticalis, and Ra’s composition Space Is the Place (later included in the soundtrack of a film by the same name). Discussion will elaborate on the cultural, political, philosophical, and societal influences that played a part in the creation of these two compositions.
My research materials for this thesis includes a collection of primary sources in the form of recordings, early musical sketches, and in the case of Ra, film footage from Space Is the Place (1974), as well as multitude of secondary sources. By choosing works from two different genres I hope to present a wider, more nuanced snapshot of artist responses to space exploration during the Cold War.
ContributorsIvis, Andrea (Author) / Feisst, Sabine (Thesis advisor) / Wells, Christopher (Committee member) / Solís, Ted (Committee member) / Arizona State University (Publisher)
Created2017
Description
Medical errors are now estimated to be the third leading cause of death in the United States (Makary & Daniel, 2016). Look-alike, sound- alike prescription drug mix-ups contribute to this figure. The US Food and Drug Administration (FDA) and Institute for Safe Medication Practices (ISMP) have recommended the use of Tall Man lettering since 2008, in which dissimilar portions of confusable drug names pairs are capitalized in order to make them more distinguishable. Research on the efficacy of Tall Man lettering in differentiating confusable drug name pairs has been inconclusive and it is imperative to investigate potential efficacy further considering the clinical implications (Lambert, Schroeder & Galanter, 2015). The present study aimed to add to the body of research on Tall Man lettering while also investigating another possibility for the mechanism behind Tall Man’s efficacy, if it in fact exists. Studies indicate that the first letter in a word offers an advantage over other positions, resulting in more accurate and faster recognition (Adelman, Marquis & Sabatos-DeVito, 2010; Scaltritti & Balota, 2013). The present study used a 2x3 repeated measures design to analyze the effect of position on Tall Man lettering efficacy. Participants were shown a prime drug, followed by a brief mask, and then either the same drug name or its confusable pair and asked to identify whether they were the same or different. All participants completed both lowercase and Tall Man conditions. Overall performance measured by accuracy and reaction time revealed lowercase to be more effective than Tall Man. With regard to the position of Tall Man letters, a first position advantage was seen both in accuracy and reaction time. A first position advantage was seen in the lowercase condition as well, suggesting the location of the differing portion of the word matters more than the format used. These findings add to the body of inconclusive research on the efficacy of Tall Man lettering in drug name confusion. Considering its impact on patient safety, more research should be conducted to definitively answer the question as to whether or not Tall Man should be used in practice.
ContributorsKnobloch, Ashley (Author) / Branaghan, Russell (Thesis advisor) / Cooke, Nancy J. (Committee member) / Gray, Robert (Committee member) / Arizona State University (Publisher)
Created2017
Description
The stability of nanocrystalline microstructural features allows structural materials to be synthesized and tested in ways that have heretofore been pursued only on a limited basis, especially under dynamic loading combined with temperature effects. Thus, a recently developed, stable nanocrystalline alloy is analyzed here for quasi-static (<100 s-1) and dynamic loading (103 to 104 s-1) under uniaxial compression and tension at multiple temperatures ranging from 298-1073 K. After mechanical tests, microstructures are analyzed and possible deformation mechanisms are proposed. Following this, strain and strain rate history effects on mechanical behavior are analyzed using a combination of quasi-static and dynamic strain rate Bauschinger testing. The stable nanocrystalline material is found to exhibit limited flow stress increase with increasing strain rate as compared to that of both pure, coarse grained and nanocrystalline Cu. Further, the material microstructural features, which includes Ta nano-dispersions, is seen to pin dislocation at quasi-static strain rates, but the deformation becomes dominated by twin nucleation at high strain rates. These twins are pinned from further growth past nucleation by the Ta nano-dispersions. Testing of thermal and load history effects on the mechanical behavior reveals that when thermal energy is increased beyond 200 °C, an upturn in flow stress is present at strain rates below 104 s-1. However, in this study, this simple assumption, established 50-years ago, is shown to break-down when the average grain size and microstructural length-scale is decreased and stabilized below 100nm. This divergent strain-rate behavior is attributed to a unique microstructure that alters slip-processes and their interactions with phonons; thus enabling materials response with a constant flow-stress even at extreme conditions. Hence, the present study provides a pathway for designing and synthesizing a new-level of tough and high-energy absorbing materials.
ContributorsTurnage, Scott Andrew (Author) / Solanki, Kiran N (Thesis advisor) / Rajagopalan, Jagannathan (Committee member) / Peralta, Pedro (Committee member) / Darling, Kristopher A (Committee member) / Mignolet, Marc (Committee member) / Arizona State University (Publisher)
Created2017