Strengthening of metals using a graphene monolayer

A practical route to exploiting graphene’s supreme properties for a variety of applications is to incorporate graphene layers in composite materials. Harnessing the high stiffness, intrinsic strength as well as transport properties of graphene in its composites requires the combination of high-quality graphene having low defect density, and the precise control of the interfacial interactions between the graphene and the matrix. These requirements equally hold for polymer and metal matrices, and enable the use of graphene in applications ranging from tough thin films for use in flexible electronics to the design of advanced aerospace structures. My dissertation addresses the synthesis, understanding and control of these composites and their mechanical properties probed from the nano- to the microscales. To this end, a model system of ultrathin metal films coated with graphene monolayer via chemical vapor deposition (CVD) is designed and used to study as-grown graphene’s contributions in graphene-metal composite thin films. Due to the thinness of the metal layer - typically less than 300 nm - individual or few graphene layers have a strong contribution on the composite thin film’s mechanics. To create the most ideal interface between the metal and the graphene, CVD synthesis is used to grow the graphene wrapping around the surface of the films. A highly dynamic CVD synthesis route is developed to achieve high-quality graphene monolayer growth on ultrathin metal films while avoiding solid-state dewetting instability which takes place at the extremely high synthesis temperatures. We study how the competition between temperature-driven segregation and precipitation of carbon radicals governs the graphene’s nucleation and growth kinetics on ultrathin metal catalysts. The result of the dynamic recipe is repeatable growth of graphene monolayers with ultralow defect density as confirmed by Raman spectroscopy. Precise mechanical characterization of ultrathin films is carried using various nanoindentation modalities including indentation of supported and freestanding thin films. CVD grown graphene-metal thin film composites exhibit unusual increase in the elastic modulus, strength and toughness. For example, there is 35 % and 57 % increases in the Young’s modulus and tensile strength in graphene-palladium thin film composites compared to those for a bare palladium film having a thickness of 66 nm. Notably, this enhancement exhibits scale effects, where the composite modulus increase varies with the thickness, and is highest for the thinnest metal thicknesses. My work demonstrates that the inherent strong interfaces between graphene and strongly interacting metals like Ni and Pd after synthesis could lead to the manufacturing of composites with significantly higher performances. I also observed increase in toughness and qualitatively different modes of crack propagation owing to the addition of the high stiffness graphene shield on the metal surface during synthesis. Raman spectroscopy and electron imaging of surface reconstructions confirm the high interfacial stresses due to the combination of the lattice mismatch between the graphene and the metals and the kinetics of growth. The findings of this dissertation promote graphene-based thin film composites for flexible electronic devices, and enable fundamental studies of exploiting strain engineering at the graphene-metal interface for electronics, chemistry and mechanics. Furthermore, the results of this dissertation are broadly relevant to the design of bulk graphene-based composite materials

Agency as dynamic and rhizomatic: An exploration of learner identities in two secondary classrooms

This thesis is premised on “a politics of becoming” (Gowlett, 2013, p. 149), a Deleuzo-Guattarian notion which speaks to social justice research. Rather than a focus on reductionist reformist politics, I explore moments of possibility as lines of flight that disrupt dominant discourses. As outlined in the New Zealand Curriculum, New Zealand schools are charged with the task of strengthening students’ key competencies (Ministry of Education, 2007a) to lay a foundation for lifelong learning. Learner agency is embedded in a dispositional view of these competencies but there is a paucity of research from a poststructural perspective in this area from New Zealand. Agency is also fundamental to a sociocultural conception of assessment for learning (AfL) where learners initiate, participate and contribute to learning in their classroom communities. Positioned in theoretical landscapes of socioculturalism and feminist poststructuralism, this study investigates agency through a rhizo-textual analysis in two year nine classrooms. The dynamic poststructural view of agency theorised in this thesis is derived from Judith Butler’s (1993) notion of performativity which precludes any prediscursive autonomous subject. Using data from episodes in two year nine classrooms I explore: how students engage as authoritative, active participants, authoring and directing their own actions in social activity within multiple discourses; how students move themselves from one set of culturally and socially structured subjectivities to another; and how agency can look, sound and feel in the discursive space of the classroom. In keeping with a rhizoanalytic approach, I construct plateaus of discourse based on episodes of classroom activity. These three short episodes of classroom discourse serve to illuminate the subjectivities in play. There are two forms of analysis used to construct these plateaus. Firstly, I conduct a discourse analysis of identity affordances and discourses to examine the nature of learner positioning. I then use rhizo-textual analysis (Honan & Sellers, 2006) to map the students’ and teachers’ moves in discourse and shifting subjectivities. The findings highlight how agency can appear as a rapid series of rhizomatic discourse moves that take place as students and teachers deterritorialize and reterritorialize discourses as they enact specific identities. They resonate with Davies’ (2000) observation that learners can accept, resist, subvert and change or ignore a range of discourse positions. The study also illustrates that what can appear to be ‘off-task’ behaviour can be also read as highly agentic. The dynamic and rhizomatic theory of agency proposed illustrates that learners can inhabit multiple subject positions across discourses as they respond to the interpellations of their teachers and peers. Rather than a performance where individuals act out roles as pre-discursive identities, students exercise performativity within and across classroom discourses as they are constituted agentically through their lines of flight. The research makes a methodological contribution through combining sociocultural and poststructural theories to explore the discursively constructed social and cultural environments of two classrooms. This is a deterritorializing move away from conventional sociocultural learning theory to incorporate an ecological (Boylan, 2010), rhizomatic view of classroom participation. This research has implications for how educators conceptualise learners’ identities and provide affordances for learners to initiate learning and take up agentic positions in classroom discourse. It also has implications for the ways in which the key competencies can be interpreted and strengthened in classrooms. Rather than ‘having’ agency to transfer competencies from one situation to the next, competencies are produced and enacted as learners shift subjectivities within and across discourses. The findings also offer students, teachers and policy makers insight into the learning dynamics of classrooms which embody the ‘spirit’ of AfL (Marshall & Drummond, 2006) where students can be afforded opportunities for lines of flight to initiate learning. Through being aware of learners’ rhizomatic moves, teachers may be able to notice, recognise and respond to learner initiatives more readily, and assist them to develop their capacity to be agentic learners

An investigation of yarn spinning from electrospun nanofibres

The aim of the thesis is to investigate yarn spinning from electrospun nanofibres. The concepts of staple and core yarn spinning on electrospun nanofibres has been investigated by examining nanofibre uniformity, alignment, twist insertion and yarn take up by engining and engineering a new take up mechanism. Nylon 6 nanofibres have been fabricated and used throughout this work. The effects of varying the electrospinning parameters such as applied voltage, polymer solution concentration and electrospinning distance on fibre morphology have been established for process optimization. A novel nanofibre aligning mechanism has been devised and systematically revised to enable optimization of alignment process parameters. MWCNTs have been successfully dispersed into nylon 6 nanofibres and have been aligned along the nanofibre body by manipulating the electric and stretching forces with the aid of the alignment mechanism. Novel mechanisms for spinning continuous twisted nanofibre/composite nanofibre yarn and core electrospun yarn have been researched, developed and implemented by making samples. It has been found that defining the velocity and count of the nanofibres entering the spinning zone is important for controlling the yarn count and twist per unit length. By modelling the electrospinning jet, mathematical equations for theoretically calculating the velocity of the jet and nanofibres and their count have been established, necessary for process control. Aspects of practical measurement and comparison of jet and nanofibre velocities have been described and discussed. Tensile testing of single nanofibre and nanofibre mats has been attempted for mechanical characterization. Initial results show the range of tensile strength of nylon 6 nanofibre assemblies and indicate the effect of change of process parameters. A review of those engineering mechanisms related to various nanofibre architectures and their industrial and commercial importance has also been reviewed, described and discussed

NASA space biology accomplishments, 1982

Summaries of NASA's Space Biology Program projects are provided. The goals, objectives, accomplishments, and future plans of each project are described in this publication as individual technical summaries

Notes on the Practice of Osteopathy: From the Lectures of Dr. George M. Laughlin, Dr. George A. Still, and Dr. Frank L. Bigsby

It is always a difficult matter for the student to get the full benefit of the Lectures and at the same time take a complete set of notes for future reference. To overcome this difficulty and also to furnish a trustworthy set of notes are the purposes of this little book. Such examples as Asthma (bronchial) provide a definition of causes, symptoms and treatments. That it may accomplish these purposes is the sincere hope of the compilers.https://digitalcommons.pcom.edu/classic_med_works/1004/thumbnail.jp

Linerless Eutectic Al-Si Engine Wear: Microstructural Evolution

The wear mechanisms of novel linerless eutectic Al-Si engines subjected to extensive dynamometer testing have been thoroughly investigated using an array of surface and subsurface techniques to elucidate the effects of alloying, surface preparation, and temperature on the overall wear progression of linerless Al-Si engines. The efforts of this research have revealed that the long term wear resistance of linerless eutectic Al-Si engine bores is derived from the combined effects of oil deposits, silicon exposure, and the formation of reduced grain structures in the aluminum-matrix. Under this criterion, silicon particles maintained exposure at an equilibrium height of ~0.4 to 0.6 um. Amorphous structured oil deposits, abundant on the worn surface, were shown to fill/protect uneven areas on the aluminum-matrix. The evolution of the bore microstructure is explained in terms of fragmentation of silicon particles and subsequent polishing of the entire worn surface caused by sliding contact with the rings

Morphology and Evolution of the Ceratopsian Skull

PhD ThesisSocio-sexual selection has long been recognised as an important driver of evolution and is known to be an important influence on the morphology and behaviour of extant organisms. The long term macroevolutionary effects of socio-sexual selection are difficult to observe because they operate over long timescales. Theoretical work has suggested that socio-sexual selection can possibly influence speciation, adaptation and extinction rates, but these predictions remain largely untested. The fossil record provides a potential solution for testing macroevolutionary hypotheses regarding socio-sexual selection over millions of years. Recent studies have suggested that the growth patterns of cranial ornamentation in Ceratopsian dinosaurs resemble the growth patterns predicted for a trait under socio-sexual selection. Identifying the presence of socio-sexual selection in extinct organisms is problematic, but evidence from extant taxa provide important evidence in detecting its effects on morphology. In this project, I use a combination of traditionally defined character states and three-dimensional geometric morphometrics, on a large scale for the first time in a dinosaur clade, to test competing macroevolutionary hypotheses of socio-sexual selection. I first test the hypothesis that morphological diversity in ceratopsian dinosaurs is driven by species recognition by comparing differences in character states between ceratopsian clades. I evaluate morphological evidence for socio-sexual selection in fossil specimens, employing novel techniques to assess growth and morphological variation in the skull of the ceratopsian that is best-represented by fossil specimens, Protoceratops andrewsi. Lastly, I extend the morphological dataset to encompass other ceratopsian taxa and examine modularity, morphological disparity and evolutionary rates across the clade. My results refute the hypothesis that exaggerated ceratopsian traits evolved for species recognition and provide support for predictions that ceratopsian traits associated with socio-sexual selection, namely the frill and horns, formed distinct units that both developed and evolved at comparatively rapid rates

Precision and Scalability in Ultrasonic Machining for Microscale Features.

Micro ultrasonic machining, µUSM, is a non-thermal, nonchemical and non-electrical process that is especially suitable for hard, brittle, and inert insulators such as ceramics. Typically, the µUSM process is capable of machining rates ≥300nm/sec; the resulting surface roughness is Sa≥250nm. There is a compelling need to extend this micromachining approach in precision and resolution for a variety of MEMS, such as for the high resolution trimming of timing references. However, a number of challenges must be addressed including the development of appropriate equipment, methodology of tool design and fabrication, and optimization of machining parameters. The research described in this thesis addresses the challenges for high resolution micro ultrasonic machining (HR-µUSM), providing high resolution and high surface quality, and precise control of machining rates. Experimental results demonstrate that the HR-µUSM process achieves machining rates as low as 10nm/sec averaged over the first minute of machining of fused silica substrates. This corresponds to a mass removal rate of ≈20ng/min. The average surface roughness, Sa, achieved is as low as 30nm, which is an order of magnitude lower than conventional µUSM. The process is used to demonstrate trimming of hemispherical 3-D shells made of fused silica. Additionally, this thesis addresses a challenge of slurry precipitation or settling during 3-D machining using µUSM, which drastically reduces the machining rates to negligible values. A mode of μUSM is developed in which the workpiece is vibrated and not the tool. Experimental evaluations of this process result in machining rates ranging typically from 5–50 nm/sec for vibration levels ranging from 1–8 μm. The workpiece vibration agitated the abrasive particles, alleviating slurry settling. Finally, this thesis explores the resolution limit of µUSM using lithographically patterned silicon micromachined tools. The use of lithography enables the batch mode transfer of complex patterns, greatly enhancing the throughput of the process. Silicon microstructures with high resolution(≤10 µm) and high aspect ratio(≥20:1) can be readily made using deep reactive ion etching (DRIE). Fine featured Si cutting tools are lithographically patterned and fabricated. Machining evaluations result in the successful transfer of patterns with sub-10 μm feature sizes and ≈3:4 aspect ratios.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/108849/1/anupamv_1.pd

Development of a machine-tooling-process integrated approach for abrasive flow machining (AFM) of difficult-to-machine materials with application to oil and gas exploration componenets

This thesis was submitted for the degree of Doctor of Engineering and awarded by Brunel UniversityAbrasive flow machining (AFM) is a non-traditional manufacturing technology used to expose a substrate to pressurised multiphase slurry, comprised of superabrasive grit suspended in a viscous, typically polymeric carrier. Extended exposure to the slurry causes material removal, where the quantity of removal is subject to complex interactions within over 40 variables. Flow is contained within boundary walls, complex in form, causing physical phenomena to alter the behaviour of the media. In setting factors and levels prior to this research, engineers had two options; embark upon a wasteful, inefficient and poor-capability trial and error process or they could attempt to relate the findings they achieve in simple geometry to complex geometry through a series of transformations, providing information that could be applied over and over. By condensing process variables into appropriate study groups, it becomes possible to quantify output while manipulating only a handful of variables. Those that remain un-manipulated are integral to the factors identified. Through factorial and response surface methodology experiment designs, data is obtained and interrogated, before feeding into a simulated replica of a simple system. Correlation with physical phenomena is sought, to identify flow conditions that drive material removal location and magnitude. This correlation is then applied to complex geometry with relative success. It is found that prediction of viscosity through computational fluid dynamics can be used to estimate as much as 94% of the edge-rounding effect on final complex geometry. Surface finish prediction is lower (~75%), but provides significant relationship to warrant further investigation. Original contributions made in this doctoral thesis include; 1) A method of utilising computational fluid dynamics (CFD) to derive a suitable process model for the productive and reproducible control of the AFM process, including identification of core physical phenomena responsible for driving erosion, 2) Comprehensive understanding of effects of B4C-loaded polydimethylsiloxane variants used to process Ti6Al4V in the AFM process, including prediction equations containing numerically-verified second order interactions (factors for grit size, grain fraction and modifier concentration), 3) Equivalent understanding of machine factors providing energy input, studying velocity, temperature and quantity. Verified predictions are made from data collected in Ti6Al4V substrate material using response surface methodology, 4) Holistic method to translating process data in control-geometry to an arbitrary geometry for industrial gain, extending to a framework for collecting new data and integrating into current knowledge, and 5) Application of methodology using research-derived CFD, applied to complex geometry proven by measured process output. As a result of this project, four publications have been made to-date – two peer-reviewed journal papers and two peer-reviewed international conference papers. Further publications will be made from June 2014 onwards.Engineering and Physical Sciences Research Council (EPSRC) and the Technology Strategy Board (TSB