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- Title
- FINITE ELEMENT SIMULATION OF REPAIR OF DELAMINATED COMPOSITE STRUCTURES USING PIEZOELECTRIC LAYERS.
- Creator
-
Navale, Kunal, Wang, Quan, University of Central Florida
- Abstract / Description
-
Damage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In...
Show moreDamage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In most conditions, the service life of damaged components is extended with repair instead of immediate replacement. Effective repair of structural damage is therefore an important and practical topic. Repair can extend the service life and can be a cost efficient alternative to immediate replacement of the damaged component. Most conventional repair methods involve welding, riveting or mounting additional patches on the parent structure without removing the damaged portion. These methods tend to be passive and inflexible, faced with the limitations of adjusting the repair to the changes in external loads.Besides, in certain cases these methods may lead to additional damage to the structure. For example, the in-situ drilling required in some cases can cause damage to items such as hidden or exposed hydraulic lines and electrical cables. Welding or bonding patches can cause significant stress alterations and serious stress corrosion problems, apart from burdening the weight sensitive structures. Above all, effective repair applying conventional analytical methods hinges on calculation of the singularity of stress and strain in the vicinity of the damage, which is be a difficult as only approximate solutions are available. Thus, a need is felt to update the repair methods with the advancement in fields of materials, sensing and actuating. This can make the repair more effective and efficient than conventional repair methodology. Current research proposes the use of piezoelectric materials in repair of delaminated composite structures. A detailed mechanics analysis of the delaminated beams, subjected to concentrated static loads and axial compressive loads, is presented. The discontinuity of shear stresses induced at delamination tips due to bending of the beams, under action of concentrated static load and axially compressive load, is studied. This discontinuity of the shear stresses normally leads to the sliding mode of fracture of the beam structures. In order to ensure proper functioning of these beam structures, electromechanical characteristics of piezoelectric materials are employed for their repair. Numerical simulations are conducted to calculate the repair voltage to be applied to the piezoelectric patches to erase the discontinuity of horizontal shear stress at the delamination tips and thus, render the beam repaired. The variation of repair voltage with location and size of the delamination is considered. FE simulations are performed to validate the numerically calculated voltage values. The research presented serves to provide information on the design of piezoelectric materials for the repair of delaminated composite structures.
Show less - Date Issued
- 2005
- Identifier
- CFE0000873, ucf:46662
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000873
- Title
- HYBRID CARBON FIBER ALUMINA NANOCOMPOSITE FOR NON-CONTACT STRESS SENSING VIA PIEZOSPECTROSCOPY.
- Creator
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Hanhan, Imad, Raghavan, Seetha, University of Central Florida
- Abstract / Description
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Carbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Recently, scientists have begun investigating hybrid composites that include fibers and particulate fillers, since they allow for advanced tailoring of mechanical properties, such as improved fatigue life. This project investigated a hybrid carbon fiber reinforced polymer (HCFRP) that includes carbon fiber and additional alumina nanoparticle...
Show moreCarbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Recently, scientists have begun investigating hybrid composites that include fibers and particulate fillers, since they allow for advanced tailoring of mechanical properties, such as improved fatigue life. This project investigated a hybrid carbon fiber reinforced polymer (HCFRP) that includes carbon fiber and additional alumina nanoparticle fillers, which act as embedded nano stress-sensors. Utilizing the piezospectroscopic effect, the photo-luminescent spectral signal of the embedded nanoparticles has been monitored as it changes with stress, enabling non-contact stress detection of the material. The HCRFP's stress-sensitive properties have been investigated in-situ using a laser source and a tensile mechanical testing system. Hybrid composites with varying mass contents of alumina nanoparticles have been studied in order to determine the effect of particle content on the overall stress sensing properties of the material. Additionally, high resolution photo-luminescent maps were conducted of the surfaces of each sample in order to determine the particulate dispersion of samples with varying alumina content. The dispersion maps also served as a method of quantifying particulate sedimentation, and can aid in the improvement of the manufacturing process. The results showed that the emitted photo-luminescent spectrum can indeed be captured from the embedded alumina nanoparticles, and exhibits a systematic trend in photo-luminescent peak shift with respect to stress. The stress maps showed a linear increase in peak shift up to a certain critical stress, and matched closely with the DIC strain results. Therefore, the non-contact stress sensing results shown in this work have strong implications for the future of structural health monitoring and nondestructive evaluation (NDE) of aerospace structures.
Show less - Date Issued
- 2015
- Identifier
- CFH0004750, ucf:45384
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004750
- Title
- ASSESSING THE IMPACT OF OYSTER REEF AND LIVING SHORELINE RESTORATION ON MACROINVERTEBRATE COMMUNITY ASSEMBLAGES IN MOSQUITO LAGOON, FLORIDA.
- Creator
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Searles, Adam, Cook, Geoffrey, University of Central Florida
- Abstract / Description
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As the world continues to experience substantial rates of habitat loss, habitat restoration has become of prime interest to ecologists worldwide. Restoration has shown to be successful in recovering targeted components of certain ecosystems but it is important to achieve a holistic understanding of the resulting ecological impacts it has on communities. To address this, four oyster reefs and three living shorelines were restored during the summer of 2017. These sites, along with four dead...
Show moreAs the world continues to experience substantial rates of habitat loss, habitat restoration has become of prime interest to ecologists worldwide. Restoration has shown to be successful in recovering targeted components of certain ecosystems but it is important to achieve a holistic understanding of the resulting ecological impacts it has on communities. To address this, four oyster reefs and three living shorelines were restored during the summer of 2017. These sites, along with four dead oyster reefs, four living oyster reefs, and three undisturbed (control) living shorelines, were sampled before restoration and regularly post-restoration for one year using lift nets. Macroinvertebrates were collected and enumerated in the lab. Diversity indices, community composition, and similarity percentages were then calculated and compared across treatments, time, and treatment-by-time. Live reefs displayed significantly higher species richness and Shannon diversity than restored and dead reefs. Simpson diversity did not differ between live and restored oyster reefs but both were significantly higher than dead reefs. Though not statistically detectable, species richness and Shannon diversity on restored reefs were relatively similar to dead reefs before restoration but became increasingly similar to live reefs over the course of the study. Additionally, analyses revealed significantly different community compositions between live reefs and restored reefs, as well as between live and dead reefs. Living shorelines showed no significant differences in diversity indices but did experience similar seasonal fluctuations in diversity across treatments. Just as with oyster reefs, restored and control living shorelines harbored significantly different communities across time. The findings of this study emphasize the need for dedication to thorough monitoring and multi-metric evaluation of success in restoration efforts. This study and future research will equip resource managers with ways to quantify the effects of restoration that will consider several important ecosystem components.
Show less - Date Issued
- 2019
- Identifier
- CFH2000545, ucf:45646
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000545
- Title
- PEDAGOGICAL RE-MEDIATION IN HYBRID COURSES: A CASE STUDY OF FIVE FIRST-YEAR COMPOSITION INSTRUCTORS.
- Creator
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Middlebrook, Rebecca, Wallace, David, University of Central Florida
- Abstract / Description
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As the move to increase availability of composition courses in the online environment continues, it is important to understand the ways in which composition instructors have taken on the challenges associated with moving their teaching online and how they modify, or re-mediate, their pedagogy for the this new teaching and learning environment. This study takes on the task of examining re-mediation as it occurs in the pedagogical practices used by instructors to facilitate peer review...
Show moreAs the move to increase availability of composition courses in the online environment continues, it is important to understand the ways in which composition instructors have taken on the challenges associated with moving their teaching online and how they modify, or re-mediate, their pedagogy for the this new teaching and learning environment. This study takes on the task of examining re-mediation as it occurs in the pedagogical practices used by instructors to facilitate peer review activities in hybrid, first-year composition courses. At the same time, it is important to understand the varying factors that may influence the degree to which instructors re-mediate their pedagogy for this hybrid environment. This study also uncovers four factors that appeared to influence the degree to which the instructors re-mediated their pedagogical practices over the course of the semester in which this study was conducted. Results from this study will contribute to the field by serving as a guide to instructors and administrators who will teach and design hybrid composition courses or curricula in the future.
Show less - Date Issued
- 2009
- Identifier
- CFE0002881, ucf:48040
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002881
- Title
- Reimagining Composition I as a Study in Storytelling Across Disciplines and Media.
- Creator
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O'Keeffe, Angel, Janz, Bruce, Flammia, Madelyn, Underberg-Goode, Natalie, Adams, JoAnne, Malala, John, University of Central Florida
- Abstract / Description
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This dissertation focuses on the role that College Composition courses can and should play in addressing the digital divide and the literacy divide. For this project, digital divide refers to the space between those students who have opportunity to participate in online discourse communities and to contribute to the collective intelligence described by Henry Jenkins and those who have not had this opportunity even though they do have access to current technology. The literacy divide discussed...
Show moreThis dissertation focuses on the role that College Composition courses can and should play in addressing the digital divide and the literacy divide. For this project, digital divide refers to the space between those students who have opportunity to participate in online discourse communities and to contribute to the collective intelligence described by Henry Jenkins and those who have not had this opportunity even though they do have access to current technology. The literacy divide discussed is created when literacy is defined simply as the ability to read and write. Students need to be visually, digitally, and technologically literate.In response to these gaps, I propose reimagining the first-year writing course as a course in storytelling across disciplines and media. Story, oral storytelling, digital narrative, and transmedia narrative are explained. An analysis of several stories including a canonical comic book, a commercial, and a long-term narrative television show are analyzed using Aristotle, Propp, Saussure, Jenkins, Birkerts, and other theorists important to work in Texts and Technology. The guiding question for this project is How can a focus on storytelling using new and digital media in the first-year English composition course create an authentic and relevant learning experience for contemporary students while bridging the digital divide created by the lack of opportunity to participate in the collective intelligence of the convergence culture?Finally, the dissertation includes a research protocol which describes and justifies future research to test the claims made in this dissertation.
Show less - Date Issued
- 2018
- Identifier
- CFE0007350, ucf:52082
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007350
- Title
- Chemical Composition of Preclassic-Period Maya Slips: Analysis and Interpretation of Flores Waxy Ware and Paso Caballo Waxy Ware Sherds from Holtun, Guatemala Using pXRF Spectrometry.
- Creator
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Kebler, Anna, Callaghan, Michael, Kovacevich, Brigitte, Walker, John, University of Central Florida
- Abstract / Description
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Slip, a fluid suspension of clay that is applied to the surface of a piece of ceramic, allows for increased control over the functional and aesthetic properties of a finished vessel. The potter can select a slip to provide a more appealing color, texture, and/or luster to the vessel's surface, while maintaining the favorable functional qualities of the paste. Though slip color has long been used as an attribute for classification in the Maya lowlands, only recently have the raw materials of...
Show moreSlip, a fluid suspension of clay that is applied to the surface of a piece of ceramic, allows for increased control over the functional and aesthetic properties of a finished vessel. The potter can select a slip to provide a more appealing color, texture, and/or luster to the vessel's surface, while maintaining the favorable functional qualities of the paste. Though slip color has long been used as an attribute for classification in the Maya lowlands, only recently have the raw materials of slips been used to inform studies of production and exchange, with much of this work using Late and Terminal Classic-period ceramics and analysis techniques that require taking small samples of each ceramic to be analyzed. Such studies present an incomplete picture of Maya slips, since they only include later ceramics and exclude vessels from which samples cannot be taken. This thesis broadens our understanding of Maya slips by 1) establishing portable x-ray fluorescence (pXRF) spectrometry as a nondestructive analysis technique that can be used to chemically characterize slips on a wide range of sherd sizes and whole vessels, and 2) determining the chemical compositions of red, cream, and black slips on Middle and Late Preclassic-period ceramic sherds excavated in 2017 from Holtun, Guatemala. The data produced through pXRF spectrometry revealed that red slips were chemically distinct from the other two colors, while white and black slips were chemically indistinct. Iron, zinc, molybdenum, tin, and antimony concentrations were the principal determinants of compositional groups. These results indicate that these elements are of primary interest in sourcing the clays used to make the slips, and trends in the chemical composition of each color have the potential to reveal much about Maya potters' processes and standardization in slip production.
Show less - Date Issued
- 2019
- Identifier
- CFE0007475, ucf:52668
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007475
- Title
- Qualitative and Quantitative Elemental Composition Analysis of the Surrounding Pollen Coating via ICP-MS.
- Creator
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Voyer, Brandy, Baudelet, Matthieu, Rex, Matthew, Sigman, Michael, University of Central Florida
- Abstract / Description
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Pollen evidence has proven to be a powerful forensic tool to trace a suspect or item to a victim or a crime scene. This is possible because it is microscopic, abundant in nature, resistant to degradation and decay; it presents dispersal patterns that can be used to generate a 'fingerprint' within specific areas, and has illustrated a unique morphology that can be used to classify species. While the pollen grain morphology has been extensively used to characterize the specific species, not...
Show morePollen evidence has proven to be a powerful forensic tool to trace a suspect or item to a victim or a crime scene. This is possible because it is microscopic, abundant in nature, resistant to degradation and decay; it presents dispersal patterns that can be used to generate a 'fingerprint' within specific areas, and has illustrated a unique morphology that can be used to classify species. While the pollen grain morphology has been extensively used to characterize the specific species, not much has been investigated as pertains to the coating that surrounds the pollen grain aside from it being categorized as waste. This Master thesis focuses on the qualitative and quantitative determination of the elemental composition of this coating surrounding pollen via Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Two methodologies for sample preparation were compared: a complete digestion and analysis of (i) the entire pollen and (ii) the surrounding pollen coating alone removed from the pollen grain by Soxhlet extraction in ethanol. The goal was to discern the elemental composition of the coating and its specific elemental composition in comparison with the whole pollen grain. The results of both F-test and T-test performed for three pollen species indicated that, of the 19 elements investigated, B, Mg, Mn, K, Ti, and Cs resulted in significant differences between the whole grain and the coating alone; while Se, V, Pb, Cr, Al, and Zn can be recognized as being characteristic of the coating surrounding the pollen grain.
Show less - Date Issued
- 2018
- Identifier
- CFE0007261, ucf:52189
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007261
- Title
- MECHANICAL CHARACTERIZATION AND NUMERICAL SIMULATION OF A LIGHT-WEIGHT ALUMINUM A359 METAL-MATRIX COMPOSITE.
- Creator
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DeMarco, James, Gordon, Ali, University of Central Florida
- Abstract / Description
-
Aluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of...
Show moreAluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of material through edge cracking during the hot rolling process which is applied to reduce thick billets of as-cast material to usable sheets. In the current work, mechanical characterization and numerical modeling of as-cast aluminum A359-SiCp-30% is employed to determine the properties of the composite and identify their dependence on strain rate and temperature conditions. Tensile and torsion tests were performed at a variety of strain rates and temperatures. Data obtained from tensile tests were used to calibrate the parameters of a material model for the composite. The material model was implemented in the ANSYS finite element software suite, and simulations were performed to test the ability of the model to capture the mechanical response of the composite under simulated tension and torsion tests. A temperature- and strain rate-dependent damage model extended the constitutive model to capture the dependence of material failure on testing or service conditions. Trends in the mechanical response were identified through analysis of the dependence of experimentally-obtained material properties on temperature and strain rate. The numerical model was found to adequately capture strain rate and temperature dependence of the stress-strain curves in most cases. Ductility modeling allowed prediction of stress and strain conditions which would lead to rupture, as well as identification of areas of a solid model which are most likely to fail under a given set of environmental and load conditions.
Show less - Date Issued
- 2011
- Identifier
- CFE0004007, ucf:49177
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004007
- Title
- Writing for Change and Changing Writing: Service Learning, First-Year Composition and Writing about Writing.
- Creator
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Bormann, Vanessa, Scott, John, Wardle, Elizabeth, Young, Beth, University of Central Florida
- Abstract / Description
-
Through a piloted model of curriculum designed for ENC 1101 this teacher-research study investigated how service-learning can shape the experiences of both teachers and students in the first-year composition classroom. The research aimed to determine the ways in which enhancement occurred for students and teachers through evaluation of student coursework, a post-semester student focus group and a faculty interview. Focusing on the impacts of this curriculum on a part-time teacher, this study...
Show moreThrough a piloted model of curriculum designed for ENC 1101 this teacher-research study investigated how service-learning can shape the experiences of both teachers and students in the first-year composition classroom. The research aimed to determine the ways in which enhancement occurred for students and teachers through evaluation of student coursework, a post-semester student focus group and a faculty interview. Focusing on the impacts of this curriculum on a part-time teacher, this study also aimed to bring to light some of the challenges inherent in service-learning within FYC, while offering ways to mediate those challenges in both course design and departmental implementation. As a result of this project, recommendations were made for modification of this curriculum to be used as an option for instructors alongside appropriate professional development, which is essential to the success of service-learning in FYC. Continued research dealing with various approaches to using service-learning in FYC was also recommended.
Show less - Date Issued
- 2012
- Identifier
- CFE0004292, ucf:49479
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004292
- Title
- PROSPECTS FOR CHANGE: CREATING A BLENDED LEARNING PROGRAM THROUGH A CULTURE OF SUPPORT.
- Creator
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Leach, Bill, Murphy, Patrick, University of Central Florida
- Abstract / Description
-
Blended learning, a combination of traditional face to face (F2f) instruction and computer-mediated communication (CMC), is a popular trend in many universities and corporate settings today. Most universities provide faculty members course management systems, such as Blackboard, Angel, and others as a way to organize and transmit course materials to students. In order to assess the pedagogical value of blended learning in a university-level first year composition (FYC) environment, it is...
Show moreBlended learning, a combination of traditional face to face (F2f) instruction and computer-mediated communication (CMC), is a popular trend in many universities and corporate settings today. Most universities provide faculty members course management systems, such as Blackboard, Angel, and others as a way to organize and transmit course materials to students. In order to assess the pedagogical value of blended learning in a university-level first year composition (FYC) environment, it is necessary to view the environment through a critical lens and adequately train faculty in the need for and use of the features of the learning management software (LMS). The setting for this study is the Humanities and Communication Dept. of Florida Institute of Technology, a private university on FloridaÂÂ's east coast, consisting of around 6000 students. As I investigate the various pedagogical and theoretical issues of incorporating blended learning into the FYC environment, I critically examine the issues involved in implementing the program. I employ a blended research method to join the tracks of implementing a blended learning program and developing a culture of support together in the Humanities and Communication Department of Florida Tech. In examining program implementation, I use a combination of institutional critique, as advanced by Porter et al., together with an ÂÂ"ecologicalÂÂ" methodology, as outlined by Nardi and OÂÂ'Day. In examining the feasibility of creating a culture of support through the design of a faculty workshop, I mainly use Richard SelfeÂÂ's methodology, although elements of the previous two methods operate as well. The results of my study provide a means by which faculty members can experience and realize the benefits, while avoiding the pitfalls, of implementing CMC into a f2f classroom and provide an action plan for other researchers to utilize in their own educational settings.
Show less - Date Issued
- 2010
- Identifier
- CFE0003057, ucf:48303
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003057
- Title
- FLEXURAL MECHANICAL DURABILITY OF CONCRETE BEAMS STRENGTHENED BY EXTERNALLY BONDED CARBON FIBER REINFORCED POLYMER SHEETS.
- Creator
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Olka, Michael, Mackie, Kevin, University of Central Florida
- Abstract / Description
-
About 77,600 bridges throughout the United States in the Federal Highway Association (FHWA) bridge database are listed as structurally deficient. This has created a need to either replace or strengthen bridges quickly and efficiently. Due to high costs for total replacement of deficient bridges, strengthening of existing bridges is a more economical alternative. A technique that has been developing over the past two decades is the strengthening of bridges using carbon fiber reinforced polymer...
Show moreAbout 77,600 bridges throughout the United States in the Federal Highway Association (FHWA) bridge database are listed as structurally deficient. This has created a need to either replace or strengthen bridges quickly and efficiently. Due to high costs for total replacement of deficient bridges, strengthening of existing bridges is a more economical alternative. A technique that has been developing over the past two decades is the strengthening of bridges using carbon fiber reinforced polymer (CFRP) sheets. The CFRP sheets are attached to the bottom of the bridge girders using structural adhesives so that the CFRP becomes an integral part of the bridge and carries a portion of the flexural loading. The CFRP sheets allow for an increase in the capacity of the bridge with minimal increase in the weight of the structure due to CFRP having a low density. Because the CFRP is expected to be an integral component and carry some of the long-term loading it is important to understand the long-term durability of the composite section. This thesis is part of a larger project, in which the long-term durability of the CFRP composite on concrete beams is investigated experimentally. The CFRP strengthened beams are exposed to fatigue testing and thermal-humidity cycling followed by failure testing. The testing scheme for this experiment allows for the investigation of the individual effects of fatigue and thermal-humidity loading as well as to explore the effects from combined fatigue and thermal-humidity loading. The investigation of the combined effects is a unique aspect of this experiment that has not been performed in prior studies. Results indicate that a polyurethane-based adhesive could provide a more durable bond for the CFRP-concrete interface than possible with epoxy-based adhesives.
Show less - Date Issued
- 2009
- Identifier
- CFE0002585, ucf:48252
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002585
- Title
- Understanding the Dynamics of Peer Review and Its Impact on Revision.
- Creator
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Kopp, Julie, Roozen, Kevin, Rounsaville, Angela, Hall, Mark, University of Central Florida
- Abstract / Description
-
Research in writing studies has focused on what happens as students, and often their teachers, talk about student writing. This line of inquiry has identified several strategies for productive peer interactions, including spontaneous talk (Danis; Dipardo and Freedman; Johnson, The New Frontier; Bruffee; Lam), a flexible environment (Dipardo (&) Freedman; Johnson, (")Friendly Persuasion(")), positive rapport (Rish; Thompson; Wolfe), feedback and support (Barron; Covill; Flynn; Grimm; Lam;...
Show moreResearch in writing studies has focused on what happens as students, and often their teachers, talk about student writing. This line of inquiry has identified several strategies for productive peer interactions, including spontaneous talk (Danis; Dipardo and Freedman; Johnson, The New Frontier; Bruffee; Lam), a flexible environment (Dipardo (&) Freedman; Johnson, (")Friendly Persuasion(")), positive rapport (Rish; Thompson; Wolfe), feedback and support (Barron; Covill; Flynn; Grimm; Lam; Yucel, Bird, Young, and Blanksby; Zhu), and reflection (Yucel, Bird, Young, and Blanksby). However, research invested in understanding the extent to which such interactions result in better revisions or make students better writers has been slower to emerge. To address this gap in the existing scholarship, this thesis involved case studies of two first-year undergraduates as they navigated multiple peer review interactions throughout one semester of ENC 1101. Data collection for this inquiry included observations of three peer review sessions, retrospective interviews with each participant, and participants' end of semester e-portfolios. Using conversation analysis as a lens (Black; Ford and Thompson; Kerschbaum), this project explores the extent to which peer interactions inform students' revision of their writing. The analysis of the data suggests that the amount of interruptions and control during peer interactions influences the amount of comments a student takes up in the revision process. The results of conversation analysis identify a power structure within peer interactions that are developed and constantly changing. Those power structures also show the relationship between social interaction and revision. Teachers can use this study to motivate students to use the comments given during peer review toward revising their papers. Also, with the development of more diverse case studies, researchers would be able to identify if these phenomena show up more consistently.
Show less - Date Issued
- 2017
- Identifier
- CFE0006613, ucf:51284
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006613
- Title
- Characterization of mechanical properties in nanoparticle reinforced hybrid carbon fiber composites using photoluminescence piezospectroscopy.
- Creator
-
Jahan, Sanjida, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, University of Central Florida
- Abstract / Description
-
Carbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Hybrid carbon fiber reinforced polymer (HCFRP) composites with alumina nanoparticles reinforcement display improved material properties such as fracture toughness, resistance to crack propagation and improved fatigue life. However, homogeneous dispersion of nanoscale materials in the matrix is important for even distribution of the improved...
Show moreCarbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Hybrid carbon fiber reinforced polymer (HCFRP) composites with alumina nanoparticles reinforcement display improved material properties such as fracture toughness, resistance to crack propagation and improved fatigue life. However, homogeneous dispersion of nanoscale materials in the matrix is important for even distribution of the improved properties. Implementing silane coupling agents (SCAs) improves dispersion by acting as a bridge between organic and inorganic materials, which increases interfacial strength and decreases sedimentation by bonding the particulate filler to the fiber reinforcement. This research is aimed at quantifying the improvement in dispersion of nanoparticles and elucidating the effects on the mechanical property of HCFRP samples through the novel use of photoluminescent characteristic peaks emitted by the alumina reinforcement particles. Photo-luminescene emission from secondary reinforcement particles of alumina embedded within the hybrid carbon fiber composites is leveraged to reveal microstructural effects of functionalization and particle weight fraction as it relates to overall composite mechanics.6, 9 and 12 weight percentage of alumina particle loading with Reactive Silane Coupling Agents, Non-reactive Silane Coupling Agent surface treatments and untreated condition are investigated in this research. Uniaxial tensile tests were conducted with measurements using piezospectroscopy (PS) and concurrent digital image correlation (DIC) to quantify the mechanical property and load distribution between the carbon fiber/epoxy and the reinforcing nanoparticles. The piezospectroscopic data were collected in an in-situ configuration using a portable piezospectroscopy system while the sample was under tensile load. Photoluminescence results show the dispersion and sedimentation behavior of the nanoparticles in the material for different surface treatment and weight percentage of the alumina nanoparticles. The piezospectroscopic maps capture and track the residual stress and its change under applied load. The results reveal the effect of varying particle loading on composite mechanical properties and how this changes with different functionalization conditions. The role of the particles in load transfer in the hybrid composite is further investigated and compared with theory. This work extends the capability of spectroscopy as an effective non-invasive method to study, at the microstructural level, the material and manufacturing effects on the development of advanced composites for applications in aerospace structures and beyond.
Show less - Date Issued
- 2017
- Identifier
- CFE0006886, ucf:51715
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006886
- Title
- Escape Artist.
- Creator
-
Mujica, Alejandro, Rushin, Patrick, Bartkevicius, Jocelyn, Neal, Mary, University of Central Florida
- Abstract / Description
-
My thesis, Escape Artist, is a composite novel written as a fictitious memoir, similar in style to Tim O'Brien's The Things They Carried, that describes my experiences between the years 2001 and 2011. During that time I went through Marine Corps Boot Camp, became a military police officer, patrolled Yuma, AZ, was sent to Iraq for a seven-month tour as a security detail just before the start of Operation Iraqi Freedom, and made it back home four years later. The novel also looks into my...
Show moreMy thesis, Escape Artist, is a composite novel written as a fictitious memoir, similar in style to Tim O'Brien's The Things They Carried, that describes my experiences between the years 2001 and 2011. During that time I went through Marine Corps Boot Camp, became a military police officer, patrolled Yuma, AZ, was sent to Iraq for a seven-month tour as a security detail just before the start of Operation Iraqi Freedom, and made it back home four years later. The novel also looks into my struggles with Post-Traumatic Stress Disorder symptoms, how they affected the people around me, and what I've been trying to do to remedy them (or ignore them).
Show less - Date Issued
- 2012
- Identifier
- CFE0004788, ucf:49732
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004788
- Title
- MECHANICAL AND THERMAL CHARACTERIZATION OF CONTINUOUS FIBER-REINFORCED PYROLYSIS-DERIVED CARBON-MATRIX COMPOSITES.
- Creator
-
Lui, Donovan, Gou, Jihua, Raghavan, Seetha, Lin, Kuo-Chi, University of Central Florida
- Abstract / Description
-
Maturity of high-temperature polymer-reinforced composites defer to conventionally expensive and intensive methods in both material and manufacturing aspects. Even traditional carbon-carbon, aerogel, and ceramic approaches are highly limited by difficult manufacturing techniques and are subject to sensitive handling throughout their processing and lifetime. Despite their utility in extreme environments, the high costs of existing high-temperature composites find limited practical...
Show moreMaturity of high-temperature polymer-reinforced composites defer to conventionally expensive and intensive methods in both material and manufacturing aspects. Even traditional carbon-carbon, aerogel, and ceramic approaches are highly limited by difficult manufacturing techniques and are subject to sensitive handling throughout their processing and lifetime. Despite their utility in extreme environments, the high costs of existing high-temperature composites find limited practical applicability under high-performance applications. The development of continuous fiber-reinforced pyrolysis-derived carbon-matrix composites aim to circumvent the issues surrounding the manufacturing and handling of conventional high-temperature composites.Polymer matrix composites (PMCs) have a number of attractive properties including light weight, high stiffness-to-weight and strength-to-weight ratios, ease of installation on the field, potential lower system-level cost, high overall durability and less susceptibility to environmental deterioration than conventional materials. However, since PMCs contain the polymer matrix, their applications are limited to lower temperatures. In this study, a pyrolysis approach was used to convert the matrix material of phenolic resin into carbon-matrix to improve the mechanical and thermal properties of the composites. Composite material consisting of basalt fiber and phenolic resin was pyrolyzed to produce basalt-carbon composites through a novel method in which the pyrolysis promoted in-situ carbon nanotube growth to form (")fuzzy fibers("). The carbon phenolic composites were pyrolyzed to produce carbon-carbon composites. Several types of composites are examined and compared, including conventional phenolic and carbon-matrix composites. Through Raman spectroscopy and scanning electron microscopy, the composition of materials are verified before testing. Investigation into the improvements from in-situ carbon growth was conducted with an open-flame oxyacetylene test (ASTM-E285), to establish high-temperature thermal behavior, in addition to mechanical testing by three-point bending (ASTM-D790), to evaluate the mechanical and thermal properties of the pyrolyzed composites.
Show less - Date Issued
- 2014
- Identifier
- CFE0005654, ucf:50196
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005654
- Title
- Processing and Characterization of Continuous Basalt Fiber Reinforced Ceramic Matrix Composites Using Polymer Derived Ceramics.
- Creator
-
Cox, Sarah, Gou, Jihua, Kapat, Jayanta, Sohn, Yongho, University of Central Florida
- Abstract / Description
-
The need for high performance vehicles in the aerospace industry requires materials which can withstand high loads and high temperatures. New developments in launch pads and infrastructure must also be made to handle this intense environment with lightweight, reusable, structural materials. By using more functional materials, better performance can be seen in the launch environment, and launch vehicle designs which have not been previously used can be considered. The development of high...
Show moreThe need for high performance vehicles in the aerospace industry requires materials which can withstand high loads and high temperatures. New developments in launch pads and infrastructure must also be made to handle this intense environment with lightweight, reusable, structural materials. By using more functional materials, better performance can be seen in the launch environment, and launch vehicle designs which have not been previously used can be considered. The development of high temperature structural composite materials has been very limited due to the high cost of the materials and the processing needed. Polymer matrix composites can be used for temperatures up to 260(&)deg;C. Ceramics can take much higher temperatures, but they are difficult to produce and form in bulk volumes. Polymer Derived Ceramics (PDCs) begin as a polymer matrix, allowing a shape to be formed and cured and then to be pyrolized in order to obtain a ceramic with the associated thermal and mechanical properties. The use of basalt in structural and high temperature applications has been under development for over 50 years, yet there has been little published research on the incorporation of basalt fibers as a reinforcement in the composites. In this study, continuous basalt fiber reinforced PDCs have been fabricated and tested for the applicability of this composite system as a high temperature structural composite material. The oxyacetylene torch testing and three point bend testing have been performed on test panels and the test results are presented.
Show less - Date Issued
- 2014
- Identifier
- CFE0005320, ucf:50530
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005320
- Title
- Development and Characterization of Nanoparticlee Enhancements in Pyrolysis-Derived High Temperature Composites.
- Creator
-
McKee, James, Gou, Jihua, Kapat, Jayanta, Xu, Chengying, University of Central Florida
- Abstract / Description
-
Thermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because...
Show moreThermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because they are not capable of supporting larger structures. The limitations of polymer reinforced composites have limited their entry into these applications, except for pyrolyzed composite materials, such as carbon-carbon and ceramic composites. These materials have been successfully demonstrated their utility in extreme environments, such as spacecraft heat shields, but their high costs and the difficulty to manufacture them have limited their use to similarly high performance applications where the costs are justifiable. Previous work by others with (")fuzzy fiber(") composites have shown that aligned carbon nanotubes (CNTs) grown on fibers can improve their thermal conductivity and wettability. To this end vertically aligned CNTs were studied for their potential use, but found to be difficult to process with current conventional techniques. A composite material comprised of basalt, a relatively new reinforcing fiber, and phenolic, which has been used in high-temperature applications with great success was made to attempt to create a new material for these applications. To further improve upon the favorable properties of the resulting composite, the composite was pyrolyzed to produce a basalt-carbon composite with a higher thermal stability than its pristine state. While testing the effects of pyrolysis on the thermal stability, a novel technique was also developed to promote in-situ carbon nanotube growth of the resulting basalt-carbon composite without using a monolithic piece of cured phenolic resin in place of the standard aromatic hydrocarbon-catalyst precursor. The in-situ growth of carbon nanotubes (CNTs) was explored as their thermal stability and effectiveness in improving performance has been previously demonstrated when used as a resin additive. The specimens were examined with SEM, EDS, and TGA to determine the effects of both pyrolysis and CNT growth during pyrolysis of the basalt phenolic composites. These tests would confirm the presence of CNTs/CNFs directly grown in the composite by pyrolysis, and confirm their composition by EDS and Raman spectroscopy. EDS would additionally confirm that the surface of the basalt fibers possess a composition suitable for CNT growth, similar to the parameters of CVD processing. Additional testing would also show that the growth behavior of the CNTs/CNFs is dependent on temperature as opposed to composition, indicating that there is a threshold temperature necessary to facilitate the availability of catalysts from within the basalt fibers. The thermal stability shown by TGA indicates that the process of pyrolysis leaves the newly formed composite with a high degree of thermal stability, making the new materials potentially usable in applications such as turbines, in addition to large-scale thermal protection systems.
Show less - Date Issued
- 2013
- Identifier
- CFE0005380, ucf:50458
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005380
- Title
- Development of Nitrogen Concentration During Cryomilling of Aluminum Composites.
- Creator
-
Hofmeister, Clara, Sohn, Yongho, Suryanarayana, Challapalli, Coffey, Kevin, University of Central Florida
- Abstract / Description
-
The ideal properties of a structural material are light weight with extensive strength and ductility. A composite with high strength and tailorable ductility was developed consisting of nanocrystalline AA5083, boron carbide and coarser grained AA5083. The microstructure was determined through optical microscopy and transmission electron microscopy. A technique was developed to determine the nitrogen concentration of an AA5083 composite from secondary ion mass spectrometry utilizing a nitrogen...
Show moreThe ideal properties of a structural material are light weight with extensive strength and ductility. A composite with high strength and tailorable ductility was developed consisting of nanocrystalline AA5083, boron carbide and coarser grained AA5083. The microstructure was determined through optical microscopy and transmission electron microscopy. A technique was developed to determine the nitrogen concentration of an AA5083 composite from secondary ion mass spectrometry utilizing a nitrogen ion-implanted standard. Aluminum nitride and amorphous nitrogen-rich dispersoids were found in the nanocrystalline aluminum grain boundaries. Nitrogen concentration increased as a function of cryomilling time up to 72hours. A greater nitrogen concentration resulted in an enhanced thermal stability of the nanocrystalline aluminum phase and a resultant increase in hardness. The distribution of the nitrogen-rich dispersoids may be estimated considering their size and the concentration of nitrogen in the composite. Contributions to strength and ductility from the Orowan relation can be more accurately modeled with the quantified nitrogen concentration.
Show less - Date Issued
- 2013
- Identifier
- CFE0004864, ucf:49702
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004864
- Title
- FINITE ELEMENT SIMULATION OF SINGLE-LAP SHEAR TESTS UTILIZING THE COHESIVE ZONE APPROACH.
- Creator
-
Perez, Wilson A, Gordon, Ali P., University of Central Florida
- Abstract / Description
-
Many applications require adhesives with high strength to withstand the exhaustive loads encountered in regular operation. In aerospace applications, advanced adhesives are needed to bond metals, ceramics, and composites under shear loading. The lap shear test is the experiment of choice for evaluating shear strength capabilities of adhesives. Specifically during single-lap shear testing, two overlapping rectangular tabs bonded by a thin adhesive layer are subject to tension. Shear is imposed...
Show moreMany applications require adhesives with high strength to withstand the exhaustive loads encountered in regular operation. In aerospace applications, advanced adhesives are needed to bond metals, ceramics, and composites under shear loading. The lap shear test is the experiment of choice for evaluating shear strength capabilities of adhesives. Specifically during single-lap shear testing, two overlapping rectangular tabs bonded by a thin adhesive layer are subject to tension. Shear is imposed as a result. Debonding occurs when the shear strength of the adhesive is surpassed by the load applied by the testing mechanism. This research develops a finite element model (FEM) and material model which allows mechanicians to accurately simulate bonded joints under mechanical loads. Data acquired from physical tests was utilized to correlate the finite element simulations. Lap shear testing has been conducted on various adhesives, specifically SA1-30-MOD, SA10-100, and SA10-05, single base methacrylate adhesives. The adhesives were tested on aluminum, stainless steel, and cold rolled steel adherends. The finite element model simulates what is observed during a physical single-lap shear test consisting of every combination of the mentioned materials. To accomplish this, a three-dimensional model was created and the cohesive zone approach was used to simulate debonding of the tabs from the adhesive. The thicknesses of the metallic tabs and the adhesive layer were recorded and incorporated into the model in order to achieve an accurate solution. From the data, force output and displacement of the tabs are utilized to create curves which were compared to the actual data. Stress and strain were then computed and plotted to verify the validity of the simulations. The modeling and constant determination approach developed here will continue to be used for newly-developed adhesives.
Show less - Date Issued
- 2016
- Identifier
- CFH2000149, ucf:45973
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000149
- Title
- STRUCTURAL HEALTH MONITORING OF COMPOSITE OVERWRAPPED PRESSURE VESSELS.
- Creator
-
Letizia, Luca, Catbas, F. Necati, University of Central Florida
- Abstract / Description
-
This work is focusing to study the structural behavior of Composite Overwrapped Pressure Vessels (COPVs). These COPVs are found in many engineering applications. In the aerospace field, they are installed onto spaceships and aid the reorientation of the spacecraft in very far and airless, therefore frictionless, orbits to save energy and fuel. The intent of this research is to analyze the difference in performance of both perfectly intact and purposely damaged tanks. Understanding both the...
Show moreThis work is focusing to study the structural behavior of Composite Overwrapped Pressure Vessels (COPVs). These COPVs are found in many engineering applications. In the aerospace field, they are installed onto spaceships and aid the reorientation of the spacecraft in very far and airless, therefore frictionless, orbits to save energy and fuel. The intent of this research is to analyze the difference in performance of both perfectly intact and purposely damaged tanks. Understanding both the source and location of a structural fault will help NASA engineers predict the performance of COPVs subject to similar conditions, which could prevent failures of important missions. The structural behavior of six tanks is investigated by means of experimental modal analysis. Knowledge of statistical signal processing methods allows to sort out and extract meaningful features from the data as to gain understanding of the performance of the structures. Structural identification is carried out using Narrow Band and Broad Band algorithms. A comparison through correlation tables and figures presents the differences in natural frequencies, mode shapes and damping ratios of all structures. A careful analysis displays the deviation of these modal parameters in the damaged tanks, highlighting the evident structural defects.
Show less - Date Issued
- 2016
- Identifier
- CFH2000069, ucf:45514
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000069
