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- Title
- DEFINING A PERSON: THE NURSE AT RISK FOR COMPASSION FATIGUE.
- Creator
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Johnston, Ellen, Andrews, Diane, University of Central Florida
- Abstract / Description
-
The intent of this thesis was to examine compassion fatigue in nurses through analysis of research studies conducted within the past five years in an effort to identify predisposing factors to the experience of compassion fatigue. Individual and institutional factors were identified as well as current strategies to assist with management of compassion fatigue. Findings indicated that being new to practice, having a trait negative affect, being younger in age, having a history of exposure to...
Show moreThe intent of this thesis was to examine compassion fatigue in nurses through analysis of research studies conducted within the past five years in an effort to identify predisposing factors to the experience of compassion fatigue. Individual and institutional factors were identified as well as current strategies to assist with management of compassion fatigue. Findings indicated that being new to practice, having a trait negative affect, being younger in age, having a history of exposure to trauma and working in high emotionally stressful units predisposed individuals to the experience of compassion fatigue. Institutional factors included a lack of managerial support, organizational commitment, group cohesion, work engagement and conflicting expectations of the nurse. Institutional interventions to assist in mitigating compassion fatigue include improving managerial support, developing group cohesion and communication and providing continuing education opportunities. Institutions can also assist by offering training in resiliency techniques such as negative thought pattern identification, meditation, peer-to-peer discussions, journaling about traumatic experiences, identification and maintenance of personal/professional boundaries and physical wellness through exercise and yoga. These proposed interventions address institutional accountability in health care worker wellness as defined by the quadruple aim. Such interventions also address use of Watson's Caring Theory to emphasize the importance of nurse wellness as essential to creating caring nurse-patient relationships.
Show less - Date Issued
- 2017
- Identifier
- CFH0000222, ucf:44675
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0000222
- Title
- CANINE-ASSISTED THERAPIES AMONG U.S. VETERANS WITH POST TRAUMATIC STRESS DISORDER: AN INTEGRATIVE REVIEW OF THE LITERATURE.
- Creator
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Kondos, Olivia A, Bushy, Angeline, University of Central Florida
- Abstract / Description
-
A sizeable number of U.S. veterans of all ages experience post-traumatic stress disorder (PTSD) which can impact their quality of life; physically, mentally and socially. Consequences of PTSD are associated with physical and emotional disabilities, including ideation of self-harm and even suicide. Increasingly, animal-assisted therapies (AAT) are used to treat PTSD and other physical and behavioral conditions in veterans. Over the decades, AATs have used dogs, cats, horses, and dolphins among...
Show moreA sizeable number of U.S. veterans of all ages experience post-traumatic stress disorder (PTSD) which can impact their quality of life; physically, mentally and socially. Consequences of PTSD are associated with physical and emotional disabilities, including ideation of self-harm and even suicide. Increasingly, animal-assisted therapies (AAT) are used to treat PTSD and other physical and behavioral conditions in veterans. Over the decades, AATs have used dogs, cats, horses, and dolphins among other animals. The purpose of this integrative review is to examine the use of AAT focusing on canine assisted therapy (CAT) among veterans diagnosed with PTSD. The methodology involved database searches, including MEDLINE, PubMed, PsychInfo, EBSCOhost, along with textbooks and popular media published from 2000 to 2016. Associated with the lack of more recent research, relevant articles published before 2000 were included in the review. Search terms included, 'veterans,' 'service dogs,' 'service animals,' 'animal-assisted therapy,' 'canine therapy,' 'PTSD,' 'post-traumatic stress disorder,' 'psychiatric,' 'U.S. veterans,' 'equine therapy,' 'horse therapy,' 'pet therapy,' and 'military veterans.' A total of ten relevant studies were identified which focused on the use of AAT among veterans diagnosed with PTSD. Different populations diagnosed with PTSD and other behavioral and psychiatric health conditions using AAT were examined as well. These articles were read, analyzed, and synthesized. Results of the review offer some support that AAT has psychological, physiological and psychosocial benefits for some populations across the lifespan with various diagnoses. Consistent and conflicting findings along with gaps in the literature are highlighted. Limitations and implications for nursing practice, research, policy and education also are noted in this thesis.
Show less - Date Issued
- 2017
- Identifier
- CFH0000239, ucf:44680
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0000239
- Title
- THE EFFECTS OF PREOPERATIVE EDUCATION ON STRESS IN THE PEDIATRIC POPULATION.
- Creator
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Howard, Amy, Allred, Kelly, University of Central Florida
- Abstract / Description
-
The purpose of this research was to critically analyze relevant literature regarding the effects of preoperative education on levels of stress in the pediatric population. The goal of this research is to review and analyze the available literature to determine best practice as it relates to educating the pediatric preoperative patient in order to relieve stress. Research was retrieved from Cumulative Index to Nursing and Allied Health Literature, PsycINFO, and MEDLINE-EBSCOhost databases...
Show moreThe purpose of this research was to critically analyze relevant literature regarding the effects of preoperative education on levels of stress in the pediatric population. The goal of this research is to review and analyze the available literature to determine best practice as it relates to educating the pediatric preoperative patient in order to relieve stress. Research was retrieved from Cumulative Index to Nursing and Allied Health Literature, PsycINFO, and MEDLINE-EBSCOhost databases using keywords pediatric, preoperative, anxiety, stress, fear, children, hospitalized child, education, play therapy, and surgery. Inclusion criteria included research that focused on relieving anxiety or stress in the pediatric surgical patient. Seven research-based articles were found that met the inclusion criteria. Findings indicate surgery is stressful in pediatric patients at all developmental stages. Preoperative education was found to reduce this stress. Verbal, written, and visual means of education all led to a decrease in stress prior to surgery. More research is needed to determine the best developmentally appropriate educational program to relieve stress in the pediatric patient.
Show less - Date Issued
- 2011
- Identifier
- CFH0003809, ucf:44738
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0003809
- Title
- EVALUATION OF CLIMATIC AND ECOHYDROLOGICAL EFFECTS ON LONGWAVE RADIATION AND EVAPOTRANSPIRATION.
- Creator
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Rizou, Maria, Nnadi, Fidelia, University of Central Florida
- Abstract / Description
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Modern tools, nontraditional datasets and a better understanding of the interaction between climate and ecohydrology are continuously being developed as today's society is in critical need for improving water management, predicting hydrometeorological hazards and forecasting future climate. In particular, the study of the intra- and inter-annual variations in grass productivity and evapotranspiration caused by variations in precipitation/soil moisture and other biophysical factors is of...
Show moreModern tools, nontraditional datasets and a better understanding of the interaction between climate and ecohydrology are continuously being developed as today's society is in critical need for improving water management, predicting hydrometeorological hazards and forecasting future climate. In particular, the study of the intra- and inter-annual variations in grass productivity and evapotranspiration caused by variations in precipitation/soil moisture and other biophysical factors is of great significance due to their relation to future climatic changes. The research presented here falls in three parts. In the first part of the dissertation, a land use adaptable model, based on the superposition of the temperature and water vapor pressure effects, is proposed for the effective clear sky emissivity. Ground radiometer and meteorological data, applicable in the subtropical climate of Saint Johns River Water Management District, Florida, were utilized for the model development over the spring season of 2004. The performance of this model was systematically evaluated by pertinent comparisons with previously established models using data over various land covers. The second part of the thesis investigates the dynamics of evapotranspiration with respect to its significant environmental and biological controls over an unmanaged bahia grassland. Eddy correlation measurements were carried out at a flux tower in Central Florida over the annual course of 2004. The main focus was on the sensitivity of the water vapor flux to wetness variables, namely the volumetric soil water content and the current precipitation index. It was shown that the time scales involved with the dynamics of evapotranspiration were on the order of six days, suggesting that depletion of the soil moisture was mostly responsible for the temporal fluctuations in evapotranspiration. Finally, simple models for the Priestley-Taylor factor were employed in terms of water availability, and the modeled results closely matched the eddy covariance flux values on daily time scale during all moisture conditions. In the third part of this work, the partitioning between latent and sensible heat fluxes was systematically examined with respect to biophysical factors. It was found that the seasonal variations in leaf area index, soil water content and net radiation were reflected in a strong seasonal pattern of the energy balance. Calculations of the bulk parameters, namely Priestley-Taylor parameter and decoupling coefficient, indicated that evapotranspiration of this grassland was controlled by water supply limitations and surface conductance. At an annual basis, the cumulative evapotranspiration was 59 percent of the precipitation received at the site. The results of this research complemented with other studies will promote better understanding of land-atmosphere interactions, accurate parameterizations of hydroclimatic models, and assessment of climate impact of grassland ecosystems.
Show less - Date Issued
- 2008
- Identifier
- CFE0002279, ucf:47851
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002279
- Title
- Mechanical Properties of Brittle Ceramics: Case Study of Boron Rich Ceramics and Acropora cervicornis Coral Skeleton.
- Creator
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Carrasco-Pena, Alejandro, Kwok, Kawai, Orlovskaya, Nina, Gou, Jihua, Uribe Romo, Fernando, University of Central Florida
- Abstract / Description
-
Ceramics are ubiquitous in man-made and natural structures. Their mechanical properties highly depend on their composition, microstructure and level of defects in the bulk of the material, the latter affecting the integrity of the components; such is the case of boron-rich ceramics where large agglomerates create high stressed regions, or coral skeleton where porosity determines their strength against hydrodynamic forces present in the ocean tides. Therefore, studying the properties of...
Show moreCeramics are ubiquitous in man-made and natural structures. Their mechanical properties highly depend on their composition, microstructure and level of defects in the bulk of the material, the latter affecting the integrity of the components; such is the case of boron-rich ceramics where large agglomerates create high stressed regions, or coral skeleton where porosity determines their strength against hydrodynamic forces present in the ocean tides. Therefore, studying the properties of ceramic materials using invasive and non-invasive methods helps in the understanding of the link between the properties and the performance of the structures. The aim of this research was to test the novel ceramic component ZrB2-30wt%SiB6 and Acropora cervicornis coral skeleton using non-conventional techniques that allow for the study of their mechanical properties and their behavior when exposed to external loads present in their environments of application. The first part of this study focuses on understanding the effects of adding SiB6 to enhance the mechanical properties of ZrB2 ceramics for their ultra-high temperature use. The second part will emphasize in the behavior of Acropora cervicornis coral skeleton when exposed to compressive forces and the effects porosity has on this structure when subjected to such loads. It was found that the SiB6 phase was not stable after sintering of the composite and large agglomerates were present in the surface of the material acting as stress concentrators, thus compromising the biaxial strength of the component that resulted to be 224.9 MPa. It was also found that coral skeletons are highly susceptible to porosity which creates variability on the elastic modulus ranging from 60-1 GPa for simulated porosity of 0-90% respectively and a strength of 3.56 (&)#177; 0.31 GPa obtained through Vickers indentation. Finite element models were developed and validated against experimental results for the ZrB2-30wt%SiB6 and Acropora cervicornis coral skeleton.
Show less - Date Issued
- 2019
- Identifier
- CFE0007440, ucf:52696
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007440
- Title
- Analysis of residual stress and damage mechanisms of thermal barrier coatings deposited via PS-PVD and EB-PVD.
- Creator
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Rossmann, Linda, Raghavan, Seetha, Sohn, Yongho, Vaidyanathan, Raj, Ghosh, Ranajay, University of Central Florida
- Abstract / Description
-
Thermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of...
Show moreThermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of producing a variety of customizable microstructures as well as non-line-of-sight deposition, which allows more complex geometries to be coated, or even multiple parts at once. The pseudo-columnar microstructure that can be produced with PS-PVD is a possible alternative to EB-PVD. However, before PS-PVD can be used to its full potential, its mechanical properties and behavior must be understood. This work contributes to this understanding by characterizing PS-PVD TBCs that have been thermally cycled to simulate multiple lifetimes (0, 300, and 600 thermal cycles). Residual stress in the thermally grown oxide (TGO) layer is characterized by photoluminescence piezospectroscopy as TGO residual stress is correlated with the lifetime of the coating. Residual stress in the top coat is characterized by Raman spectroscopy, because this stress drives cracking in the top coat that can lead to failure. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are performed to observe microstructural and phase evolution to provide context and possible explanations for the stress results. In addition, EB-PVD samples of the same thermal cycling history are characterized in the same way so that PS-PVD can be benchmarked against the industry standard. The compressive residual stress in the TGO in both coatings was relieved with thermal cycling due to the TGO lengthening as well as microcracking. The PS-PVD samples had slightly lower TGO stress than the EB-PVD, which is attributed to the greater extent of cracking within the TGO, whereas cracking in the EB-PVD samples was at the TGO/topcoat interface. The PS-PVD cycled samples had significant cracking within the topcoat near the TGO due to both greater porosity than EB-PVD samples and regions of unmelted particles that provide little resistance to cracking. The greater convolution of the TGO in the PS-PVD samples results in greater out-of-plane tensile stresses that cause crack initiation, as well as diverts cracks away from the difficult-to-follow interface. The TGO stress results agree with existing literature and extend the thermal cycling beyond what has previously been reported for PS-PVD coatings, revealing a trend of stress relief and stress values similar to that of EB-PVD coatings in this study and in the literature. Residual stress in the topcoat for both coating types became increasingly compressive with thermal cycling, indicating loss of strain tolerance by sintering. The trend of the YSZ stress for both coating types to become more compressive with cycling and with depth agrees with the literature, and the thermal cycling is longer than has been previously reported for PS-PVD. The two coating types had quite different microstructures and crack modes as well as different as-deposited residual stresses, but after thermal cycling had similar stresses in both the TGO and top coat. No samples experienced spallation. These results indicate that, while PS-PVD coatings have different properties and behavior from EB-PVD coatings, they had comparable levels of damage to EB-PVD coatings of the same lifetime and are a viable alternative to EB-PVD. Further tuning of the processing parameters may result in PS-PVD coatings with even more similar behavior to EB-PVD coatings.
Show less - Date Issued
- 2019
- Identifier
- CFE0007717, ucf:52429
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007717
- Title
- Preservice Teachers and Perceived Stress: A Comparative Study.
- Creator
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Evans, Kelsey, Russell, William, Hewitt, Randall, Hynes, Mike, Jahani, Shiva, University of Central Florida
- Abstract / Description
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Teachers are being pushed to the brink of burnout and leaving the profession, placing teachers' health and wellness in jeopardy (Daniels (&) Strauss, 2009; Maslach (&) Leiter, 2008; Stephenson, 2012; Vladut (&) Kallay, 2010; Wilkerson, 2009). Yet, it has become increasingly clear teacher stress may start prior to entering the profession (Brown (&) Ryan, 2003, Darling-Hammond, 2006). The researcher used a non-experimental design to evaluate the perceived stress among pre-service teachers...
Show moreTeachers are being pushed to the brink of burnout and leaving the profession, placing teachers' health and wellness in jeopardy (Daniels (&) Strauss, 2009; Maslach (&) Leiter, 2008; Stephenson, 2012; Vladut (&) Kallay, 2010; Wilkerson, 2009). Yet, it has become increasingly clear teacher stress may start prior to entering the profession (Brown (&) Ryan, 2003, Darling-Hammond, 2006). The researcher used a non-experimental design to evaluate the perceived stress among pre-service teachers enrolled in internship, and if the coping style of mindfulness had any correlation on self-reported stress levels. The quantitative study surveyed 332 student interns using the Perceived Stress Survey (Cohen (&) Williams, 1988) to depict perceived stress levels of pre-service teachers. A demographic questionnaire was also administered. The results indicated an increase in perceived stress, suggesting that stress may vary across the demographic variables of gender. Mindfulness was researched as a potential solution, however, there was no correlation between mindfulness and stress levels. education is necessary in the discussion and implementation of mindfulness as a potential intervention tool for stress. Further research is needed for a deeper understanding of gender, and how mindfulness may be a positive intervention to perceived stress.
Show less - Date Issued
- 2019
- Identifier
- CFE0007628, ucf:52546
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007628
- Title
- An Exploration of the Relationship between Work Climate, the Utilization of Support Resources, and Compassion Fatigue Level in Child Protective Investigators.
- Creator
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Holliker, Shannon, Leon, Ana, Yegidis, Bonnie, Dziegielewski, Sophia, Rosa-Lugo, Linda, University of Central Florida
- Abstract / Description
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The impact of child maltreatment is far reaching, affecting the abused child, the family system, and the professionals tasked with providing support during the moments of crisis. As child protective investigators (CPIs) provide care and support to others, they are at high risk of experiencing secondary traumatic stress and/or burnout, both aspects of compassion fatigue. Researchers suggest that work climate, utilization of resources, and worker characteristics can impact CPI compassion...
Show moreThe impact of child maltreatment is far reaching, affecting the abused child, the family system, and the professionals tasked with providing support during the moments of crisis. As child protective investigators (CPIs) provide care and support to others, they are at high risk of experiencing secondary traumatic stress and/or burnout, both aspects of compassion fatigue. Researchers suggest that work climate, utilization of resources, and worker characteristics can impact CPI compassion-fatigue level. Drawing on extant literature, this study examined three research questions and seven hypotheses aiming to explore the relationship between work climate, resource utilization, CPI characteristics, and CPI compassion-fatigue level. This dissertation research used a cross-sectional study design that included collecting data from 165 CPIs using three instruments: (a) CPI demographic form, (b) Professional Quality of Life-5, and (c) Safety Attitudes Questionnaire. Descriptive, nonparametric, and regression analyses were conducted on the returned surveys of 165 Florida-based CPIs. Results of data analyses indicated that statistically significant inverse relationships exist between the independent variable, compassion fatigue, and the dependent variables of teamwork climate, CPI supervision utilization, CPI age, and CPI trauma history (verbal abuse). The study presents implications for addressing compassion fatigue in CPIs from a public-affairs, a practice, and a research perspective.
Show less - Date Issued
- 2019
- Identifier
- CFE0007654, ucf:52496
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007654
- Title
- How does Jay-customer Affect Employee Job Stress and Job Satisfaction?.
- Creator
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Kim, Gawon, Ro, Hee Jung, Kwun, David, Hutchinson, Joe, University of Central Florida
- Abstract / Description
-
Guest-contact employees interact with various types of customers, and they are often exposed to stressful conditions caused by the deviant, or jay-customers. The purpose of this study is to examine how jay-customer behaviors (customer incivility and customer aggression) affect employees' job stress, and consequently, job satisfaction. Surveys of 210 participants, currently working as guest-contact employees in the hospitality industry, were analyzed for the study. The results of hierarchical...
Show moreGuest-contact employees interact with various types of customers, and they are often exposed to stressful conditions caused by the deviant, or jay-customers. The purpose of this study is to examine how jay-customer behaviors (customer incivility and customer aggression) affect employees' job stress, and consequently, job satisfaction. Surveys of 210 participants, currently working as guest-contact employees in the hospitality industry, were analyzed for the study. The results of hierarchical multiple regression analyses show a positive relationship between the experience of customer incivility and employees' job stress. Additionally, the results indicate a full mediation effect of employees' job stress on the relationship between customer incivility and employees' job satisfaction. Unfortunately, the study was not able to analyze customer aggression, because the majority of the participants did not report customer aggression. The findings of this study make a contribution to the hospitality service management literature by providing empirical evidence of customer incivility and its negative impact on guest-contact employees. Hospitality managers should acknowledge the existence of jay-customer behaviors and recognize their significant impact on employees' job stress and job satisfaction.
Show less - Date Issued
- 2012
- Identifier
- CFE0004563, ucf:49223
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004563
- Title
- The relationship between caregiver intimate partner violence, posttraumatic stress, child cognitive self-development, and treatment attrition among child sexual abuse victims.
- Creator
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Delorenzi, Leigh, Daire, Andrew, Young, Mark, Lambie, Glenn, Abel, Eileen, University of Central Florida
- Abstract / Description
-
Child sexual abuse (CSA) is a worldwide problem, with two-thirds of all cases going unreported. A wealth of research over the last 30 years demonstrates the negative emotional, cognitive, physical, spiritual, academic, and social effects of CSA. As a result, researchers and mental health professionals frequently attempt to measure the efficacy of treatment modalities in order to assess which treatments lead to better outcomes. However, in order to effectively study treatment outcomes,...
Show moreChild sexual abuse (CSA) is a worldwide problem, with two-thirds of all cases going unreported. A wealth of research over the last 30 years demonstrates the negative emotional, cognitive, physical, spiritual, academic, and social effects of CSA. As a result, researchers and mental health professionals frequently attempt to measure the efficacy of treatment modalities in order to assess which treatments lead to better outcomes. However, in order to effectively study treatment outcomes, researchers must be able to track the status of child functioning and symptomology before, during, and after treatment. Because high levels of treatment attrition exist among CSA victims, researchers are unable to effectively study outcomes due to large losses in research participants, loss of statistical power, and threats to external validity (Kazdin, 1990). Moreover, due to the high prevalence of concurrent family violence, caregivers with intimate partner violence are more than twice as likely to have children who are also direct victims of abuse (Kazdin, 1996). Caregivers ultimately make the decisions regarding whether or not a child stays in treatment, and therefore, it is important to examine the influence of both parent factors (e.g., intimate partner violence) and child factors (e.g., traumatization and/or disturbances in cognitive self-development) on treatment attrition. This two-pronged approach of examining both child and family characteristics simultaneously with attrition patterns offers a more complete picture for the ways concurrent family violence influences treatment than looking at child and caregiver factors separately.The purpose of this study was to investigate the relationships between caregiver intimate partner violence, child posttraumatic stress (Trauma Symptom Checklist for Children [TSCC]; Briere, 1996), child cognitive self-development (Trauma and Attachment Belief Scale [TABS]; Pearlman, 2003), and treatment attrition. The statistical analyses in this study included (a) Logistic Regression, (b) Poisson Regression, and (c) Chi-square Test for Independence. Elevated TSCC subscale scores in posttraumatic stress predicted both an increased number of sessions attended and increased number of sessions missed. Elevated TABS subscale scores in self-trust predicted an increased number of sessions attended and decreased number of sessions missed. Elevated TABS subscale scores of other-intimacy and self-control predicted an increased number of sessions missed. Moreover, the presence of past or current caregiver intimate partner violence predicted a decrease in number of sessions attended. While no relationship existed between child posttraumatic stress or cognitive self-development and whether a child graduated or prematurely terminated from treatment, children with parents who confirmed past or current intimate partner violence were 2.5 times more likely to prematurely terminate from treatment.
Show less - Date Issued
- 2012
- Identifier
- CFE0004369, ucf:49439
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004369
- Title
- CONVENTIONAL AND ZVT SYNCHRONOUS BUCK CONVERTER DESIGN, ANALYSIS, AND MEASUREMENT.
- Creator
-
Cory, Mark, Yuan, Jiann, University of Central Florida
- Abstract / Description
-
The role played by power converting circuits is extremely important to almost any electronic system built today. Circuits that use converters of any type depend on power that is consistent in form and reliable in order to properly function. In addition, todayÂÂ's demands require more efficient use of energy, from large stationary systems such as power plants all the way down to small mobile devices such as laptops and cell phones. This places a need to reduce any losses...
Show moreThe role played by power converting circuits is extremely important to almost any electronic system built today. Circuits that use converters of any type depend on power that is consistent in form and reliable in order to properly function. In addition, todayÂÂ's demands require more efficient use of energy, from large stationary systems such as power plants all the way down to small mobile devices such as laptops and cell phones. This places a need to reduce any losses to a minimum. The power conversion circuitry in a system is a very good place to reduce a large amount of unnecessary loss. This can be done using circuit topologies that are low loss in nature. For low loss and high performance, soft switching topologies have offered solutions in some cases. Also, limited study has been performed on device aging effects on switching mode power converting circuits. The impact of this effect on a converterÂÂ's overall efficiency is theoretically known but with little experimental evidence in support. In this thesis, non-isolated buck type switching converters will be the main focus. This type of power conversion is widely used in many systems for DC to DC voltage step down. Newer methods and topologies to raise converter power efficiency are discussed, including a new synchronous ZVT topology . Also, a study has been performed on device aging effects on converter efficiency. Various scenarios of voltage conversion, switching frequency, and circuit components as well as other conditions have been considered. Experimental testing has been performed in both cases, ZVTÂÂ's benefits and device aging effects, the results of which are discussed as well.
Show less - Date Issued
- 2010
- Identifier
- CFE0003106, ucf:48650
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003106
- Title
- INVESTIGATION AND TRADE STUDY ON HOT CARRIER RELIABILITY OF THE PHEMT FOR DC AND RF PERFORMANCE.
- Creator
-
Steighner, Jason, Yuan, Jiann-Shiun, University of Central Florida
- Abstract / Description
-
A unified study on the hot carrier reliability of the Pseudomorphic High Electron Mobility Transistor (PHEMT) is carried out through Sentaurus Device Simulation, measurement, and physical analyses. A trade study of devices with four various geometries are evaluated for DC and RF performance. The trade-off of DC I-V characteristics, transconductance, and RF parameters versus hot carrier induced gate current is assessed for each device. Ambient temperature variation is also evaluated to observe...
Show moreA unified study on the hot carrier reliability of the Pseudomorphic High Electron Mobility Transistor (PHEMT) is carried out through Sentaurus Device Simulation, measurement, and physical analyses. A trade study of devices with four various geometries are evaluated for DC and RF performance. The trade-off of DC I-V characteristics, transconductance, and RF parameters versus hot carrier induced gate current is assessed for each device. Ambient temperature variation is also evaluated to observe its impact on hot carrier effects. A commercial grade PHEMT is then evaluated and measured to demonstrate the performance degradation that occurs after a period of operation in an accelerated stress regime-one hour of high drain voltage, low drain current stress. This stress regime and normal operation regime are then modeled through Sentaurus. Output characteristics are shown along with stress mechanisms within the device. Lastly, a means of simulating a PHEMT post-stress is introduced. The approach taken accounts for the activation of dopants near the channel. Post-stress simulation results of DC and RF performance are then investigated.
Show less - Date Issued
- 2011
- Identifier
- CFE0003994, ucf:48659
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003994
- Title
- The Impact of Mobbing and Job-related Stress on Burnout and Health-related Quality of Life: The Case of Turkish Territorial State Representatives.
- Creator
-
Yesilbas, Mehmet, Wan, Thomas, Dziegielewski, Sophia, Steen, Julie, Zhang, Ning, University of Central Florida
- Abstract / Description
-
Job-related stress occurs as one of the most serious issues in modern era in developed nations. It has direct and negative effects on employees' productivity and it may have negative impacts on employees' health. One of the potential results of prolonged stressors at work place is burnout and this response may lead to physical, emotional, and psychological exhaustion that can occur at both individual and organizational levels. Burnout is a job related threat that provokes social stress and...
Show moreJob-related stress occurs as one of the most serious issues in modern era in developed nations. It has direct and negative effects on employees' productivity and it may have negative impacts on employees' health. One of the potential results of prolonged stressors at work place is burnout and this response may lead to physical, emotional, and psychological exhaustion that can occur at both individual and organizational levels. Burnout is a job related threat that provokes social stress and can directly affect an individual's health. Health-related quality of life (HRQoL) is commonly used to measure an individual's overall/global health and quality of life. Another serious issue, mobbing, usually leads to some individual and organizational complications. It affects the organizational commitment, motivation and efficiency of staff, job satisfaction of employee, and may lead to potential burnout of the employees. The primary objective of this study is to determine whether stress and mobbing are directly related to burnout; and, whether burnout leads to an adverse effect on the HRQoL of Turkish territorial state representatives (TSRs). This study examines four specific research questions: 1) Whether and to what extent do the levels of perceived job related stress and mobbing affect the level of perceived burnout syndrome of TSRs? 2) Whether and to what extent is the level of perceived burnout syndrome associated with HRQoL of TSRs? 3) To what extent does the level of perceived burnout mediate the effects of job-related stress on HRQoL of TSRs? 4) What are the mediating factors between job burnout and HRQoL? This study is expected to offer valuable and insightful information about the role of job burnout factors influencing the variability in TSRs' HRQoL.The study utilized two statistical analyses, which were descriptive analysis and Structural Equation Modelling (SEM) which allows for the assessment of the relationships specified in the hypotheses and the SEM was used to validate the theoretically driven model. The findings of the study supported the hypotheses of the study, which asserted that there were correlations between job-related stress and burnout, mobbing and burnout, and burnout and HRQoL. The CFA results established that job-related stress was positively and significantly associated with the burnout of TSRs, while perceived mobbing was positively and significantly related to the burnout of TSRs. Moreover, perceived HRQoL of TSRs was negatively associated with the burnout of TSRs. Further, the findings indicated that the relationship between job-related stress and burnout and the relationship between burnout and HRQoL of TSRs were statistically significant. Thus the variable had a positive effect on burnout and a negative effect on the HRQoL of TSRs. In summary, the findings of the study showed that results and propositions of the theoretical frameworks of the study and literature were consistent with one another.
Show less - Date Issued
- 2015
- Identifier
- CFE0006236, ucf:51071
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006236
- Title
- Mechanistic Behavior of UHPC and UHPC Composite Structural Components.
- Creator
-
Al-Ramahee, Munaf, Mackie, Kevin, Makris, Nicos, Nam, Boo Hyun, Gou, Jihua, University of Central Florida
- Abstract / Description
-
The resistance of reinforced concrete is mobilized through the composite action of two materials with different mechanical behaviors and physical features. Enabling the composite action requires a transfer mechanism between the concrete and the reinforcement which is referred to as bond. The bond model can be defined as a traction-slip relation tangent to the interface. The bond strength between different types of concrete, internal reinforcement, and external reinforcement has been of...
Show moreThe resistance of reinforced concrete is mobilized through the composite action of two materials with different mechanical behaviors and physical features. Enabling the composite action requires a transfer mechanism between the concrete and the reinforcement which is referred to as bond. The bond model can be defined as a traction-slip relation tangent to the interface. The bond strength between different types of concrete, internal reinforcement, and external reinforcement has been of interest to structural engineers for decades. Experimental tests have been carried out to validate the existing bond models and introduce new bond models for special cases of concrete or reinforcement. The effect of various parameters on the bond stress, such as bar diameter, concrete compressive strength, presence of fibers, cyclic loading, etc. have been investigated. However, little attention has been directed to the contribution of normal (to the interface) stress and state of stress of the substrate layer on the mechanical response of the interface. Since the state of stress (tangential, normal, and substrate) within each type of experimental test is different, the resulting bond models are not consistent.Behavior of ultra-high performance concrete (UHPC) composite flexural members are studied using experimental, analytical, and numerical approaches in this research. A new bond-slip model is proposed that contains an explicit representation of the normal stress and constitutive model of the substrate. The parameters of the model were calibrated from beam and pullout tests using UHPC and HSS. The calibrated results showed consistency in the material point behavior between the pullout and beam test although the states of stress were different. The effect of the normal force was verified throughout a numerical model compared with experimental flexural tests. Single and double lap shear tests were carried out for UHPC and FRP, and parameters of the bilinear model were calibrated and used in the finite element model of the new composite deck.A new lightweight composite deck system is proposed that uses fiber reinforced polymers (FRP) bonded to UHPC using vacuum-assisted resin transfer molding. The high-performance deck system has application in deck design and replacement for bridges with weight restrictions as well as for accelerated bridge construction. Results show the deck satisfies strength and serviceability criteria under monotonic load. The bond strength between the UHPC and the glass fiber reinforced polymers (GFRP) plays a significant role in the performance of the proposed deck and controls the behavior of the system. However, live loads on bridges are inherently cyclic and therefore research on serviceability and fatigue behavior of UHPC and UHPC composite members were carried out. The UHPC beams were strengthened using glass GFRP plates on compression side to obtain data that could be utilized for the future design. The effect of fatigue loading on the interfacial shear stress between UHPC and GFRP was also investigated and it is found to be minor under low load level. However, a noticeable progression in the interfacial shear stress was found for the higher load ratio.
Show less - Date Issued
- 2016
- Identifier
- CFE0006431, ucf:51464
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006431
- Title
- POLYURETHANE FIBER REINFORCED POLYMER STRENGTHENING OF SHEAR DEFICIENT REINFORCED CONCRETE BEAMS.
- Creator
-
Al-Lebban, Yasir, Mackie, Kevin, Chopra, Manoj, Makris, Nicos, Gou, Jihua, University of Central Florida
- Abstract / Description
-
The use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and...
Show moreThe use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and five large-scale (132 in span, 12 in width, and 17 in height) flexural specimens were tested, considering FRP system type (polyurethane versus epoxy), size effect, shear span-to-depth ratio, FRP configuration (U-wraps versus side bonding), and FRP scheme (sheets versus strips with 45o or 90o). Experimental strength testing under four-point loading demonstrated similar or enhanced shear capacity when strengthening by the polyurethane compared to the epoxy composite systems.The shear behavior of polyurethane-based FRP composite system is investigated in this research using analytical and numerical approaches. A closed-form mechanics-based analytical model, utilizing the principle of effective FRP stress and upper-bound theorem, illustrated that the shear behavior and debonding mechanism were dependent on both FRP composite and bond characteristics. The analytical model is expressed in terms of shear crack opening crossed by the FRP laminate and gives good agreement with experimental results. The finite element analysis (FEA) model shows that the stresses in the FRP are not in single direction as in the coupon tests, and the biaxial stress states should be taken into consideration.The structural behavior of RC members strengthened with externally-bonded FRP composites is mobilized through the composite action technique. Bond stress can be defined as the shear stress acting in the interface between FRP and concrete. It is of crucial importance to evaluate the failure mode behavior. Debonding (loss of adhesion) failure is one of the most common modes of failure encountered in shear strengthening RC members in practice. Numerous constitutive bond-slip models have been proposed and derived numerically and mathematically based on experimental data with an assumption that the FRP width bp is taken as a variable and all stresses or strains at the same longitudinal coordinate (L direction) are uniform. No attention has been given to study the bond states of stress which are mainly altered by the inclined shear cracks in concrete. A new bond-slip law was proposed to address the biaxial two-dimensional (2D) states of stress problem. Numerical solution by finite difference (FD) was conducted to solve four partial differential equations per node (2 for FRP and 2 for concrete in each direction) with appropriate boundary conditions to obtain the stresses, slips, and strains based on the proposed bond-slip model. A new experimental setup was proposed to represent the 2D bond-slip model by lap shear tests in both directions by laminating two perpendicular strips on concrete blocks with the proposed strain profile. Experimental calibration has been carried out by using nonlinear least-squares regression (fitting) of the experimental strain data with the numerical FD equations to obtain the bond-slip parameters for the 2D FRP-to-concrete polyurethane interface system.
Show less - Date Issued
- 2017
- Identifier
- CFE0006852, ucf:51737
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006852
- Title
- Health Behaviors in Military Veterans with and without Posttraumatic Stress Disorder.
- Creator
-
Kitsmiller, Emily, Neer, Sandra, Beidel, Deborah, Bowers, Clint, University of Central Florida
- Abstract / Description
-
A link between posttraumatic stress disorder and health behaviors, such as exercise, alcohol, smoking, and caffeine has been suggested. However, it is unknown whether veterans with combat-related PTSD differ from combat veterans without PTSD and whether health behaviors change over the course of exposure therapy for PTSD or differ based on PTSD severity. This study examined the relationship between health behaviors and PTSD. More specifically, combat veterans with and without PTSD were...
Show moreA link between posttraumatic stress disorder and health behaviors, such as exercise, alcohol, smoking, and caffeine has been suggested. However, it is unknown whether veterans with combat-related PTSD differ from combat veterans without PTSD and whether health behaviors change over the course of exposure therapy for PTSD or differ based on PTSD severity. This study examined the relationship between health behaviors and PTSD. More specifically, combat veterans with and without PTSD were compared across self-reported levels of alcohol use, smoking, exercise, and caffeine. Health behaviors of combat veterans with PTSD were compared before and after a 17-week treatment for PTSD. Results showed a significant number of participants decreased alcohol use at post-treatment by an average of eight drinks over 30 days, regardless of their PTSD severity level or amount of improvement in PTSD symptoms. No significant differences were found for other health behaviors.
Show less - Date Issued
- 2017
- Identifier
- CFE0006891, ucf:51711
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006891
- Title
- How does brief cognitive behavioral therapy work? Potential mechanisms of action for veterans with physical and psychological comorbidities.
- Creator
-
Deavers, Frances, Cassisi, Jeffrey, Bowers, Clint, Eldridge, Gloria, University of Central Florida
- Abstract / Description
-
Depression and anxiety are commonly comorbid among patients with chronic medical conditions. These comorbidities are associated with negative outcomes including poorer quality of life and worse physical functioning. Evidence that traditional cognitive behavioral therapy (CBT) is less effective for these populations has led to the development of brief CBT protocols that incorporate physical health self-management skills and are delivered in primary care. To continue refining treatment packages...
Show moreDepression and anxiety are commonly comorbid among patients with chronic medical conditions. These comorbidities are associated with negative outcomes including poorer quality of life and worse physical functioning. Evidence that traditional cognitive behavioral therapy (CBT) is less effective for these populations has led to the development of brief CBT protocols that incorporate physical health self-management skills and are delivered in primary care. To continue refining treatment packages, it is important to understand how brief CBT works. The present study used the transactional model of stress and coping as a framework for investigating potential mechanisms of action of brief CBT. Veterans with chronic obstructive pulmonary disease and/or heart failure and elevated symptoms of depression and/or anxiety were randomized to receive brief CBT (n =180) or enhanced usual care (EUC; n = 122). At 4-month follow-up, depression and anxiety symptoms were significantly lower in veterans who received brief CBT, compared to EUC. Multiple mediation analyses revealed that brief CBT was associated with higher self-efficacy and less avoidant coping at 4-month follow-up, which were in turn associated with less depression and anxiety symptoms. Illness intrusiveness was also a significant mediator of the relationship between brief CBT and anxiety symptoms, but not depression symptoms. In contrast, increases in active coping attributable to brief CBT were not associated with improvements in depression or anxiety symptoms. These results demonstrate the utility of the transactional model of stress and coping as a framework for understanding mechanisms of action of brief CBT in patients with comorbid physical and psychological conditions.
Show less - Date Issued
- 2017
- Identifier
- CFE0006733, ucf:51884
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006733
- Title
- Is Conflict a Factor in a Population's Quality of Life? A Comparative Study of University Students in the Palestinian Territories and Jordan.
- Creator
-
Asi, Yara, Unruh, Lynn, Ramirez, Bernardo, Liu, Albert/Xinliang, Sadri, Houman, University of Central Florida
- Abstract / Description
-
As nearly one third of the world's population lives in an area that is in some way touched by war, researchers have long been interested in the varied impacts of conflict on civilians. Many indicators, measuring both physical and mental constructs, have been assessed in war-torn populations from around the world, one of which is health-related quality of life (HRQoL). The occupied Palestinian Territories (oPt) are one region in which copious research on health indicators has been undertaken...
Show moreAs nearly one third of the world's population lives in an area that is in some way touched by war, researchers have long been interested in the varied impacts of conflict on civilians. Many indicators, measuring both physical and mental constructs, have been assessed in war-torn populations from around the world, one of which is health-related quality of life (HRQoL). The occupied Palestinian Territories (oPt) are one region in which copious research on health indicators has been undertaken in an effort to understand how long-term conflict manifests itself in noncombatant populations. However, existing studies focus primarily on indicators within the Palestinian population itself that impact HRQoL, and not on the extent to which the presence of the conflict and its consequences disturb physical and mental health outcomes compared to areas without conflict. The purpose of this study is to evaluate the impact of long-term conflict by comparing HRQoL in the oPt and the neighboring country of Jordan, as well as to assess how demographic factors such as socioeconomic status and household size can moderate or aggravate this impact. The potential mediating factors of insecurity and perceived stress will also be assessed. This study found that the presence of conflict was not the most significant predictor of low HRQoL. The mitigating factor of a traditional foundation of mental resilience in Palestinian culture is addressed as a potential explanation for this result. The implications of this study are wide-ranging, particularly in their ability to contribute to healthcare policy recommendations in war-affected areas, and to bolster our understanding of the health status and needs of those living in these areas.
Show less - Date Issued
- 2015
- Identifier
- CFE0005574, ucf:50233
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005574
- Title
- Physiological Constraints on Warm-Water Habitat Site Selection and Utilization by the Florida Manatee (Trichechus manatus latirostris) in East Central Florida.
- Creator
-
Spellman, Ann, Worthy, Graham, Noss, Reed, Hinkle, Ross, DeFreese, Duane, University of Central Florida
- Abstract / Description
-
Living at the northern limits of its geographic range, the Florida manatee is particularly susceptible to cold stress-related mortality during the winter months, with most deaths occurring in the lower two-thirds of the state. Contributing to this cold stress susceptibility is the manatee's limited physiological and behavioral responses available when thermally stressed. While capable of migrating south in response to falling water temperatures, manatees must still find warm water when...
Show moreLiving at the northern limits of its geographic range, the Florida manatee is particularly susceptible to cold stress-related mortality during the winter months, with most deaths occurring in the lower two-thirds of the state. Contributing to this cold stress susceptibility is the manatee's limited physiological and behavioral responses available when thermally stressed. While capable of migrating south in response to falling water temperatures, manatees must still find warm water when ambient river temperature drops below 20(&)deg;C for more than a few days. This is in part due to the species low metabolic rate, limited capacity for thermogenesis, and limited ability to raise its metabolic rate. Prolonged exposure to cold temperatures may result in cold stress syndrome, which involves a number of potentially life-threatening, if not fatal physiological changes. Survival during the winter months is therefore, dependent upon the manatee's ability to balance basic physiological needs, primarily the need to forage and to obtain fresh water with the need to stay warm.When identifying which animals are most susceptible and where, analyses of statewide manatee mortality records from 1996 through 2011 (n = 823) indicated that, size and location matter. Medium to large-sized calves accounted for the majority of documented death from cold stress (46.6%), while subadults and small calves were the least represented size classes (14.3 % and 9.5%, respectively). Adults slightly outnumbered subadults (15.8%). Males outnumbered females in all size classes but gender differences were not statistically significant. With regards to location, two areas of the state, the southwest and central east coasts showed the highest incidents of cold stress-related mortality. Both are regions with no primary, natural warm-water springs and whose principal warm-water refugia are power plant effluents. Brevard County on the central east coast is the area most at risk during cold weather events accounting for more than 25% of all cold stress deaths statewide. Warm-water sites within this region are few and relatively underrepresented in the literature in an area well-studied in terms of manatee abundance and distribution relative to the operational power plant. Results from cold stress data analyses emphasize the importance of identifying and characterizing the physical attributes of both known and suspected secondary warm-sites used by manatees in this region for both long and short term protection of the species, and its critical habitat.Three locations within Brevard County identified as passive thermal basins (PTBs), and classified as secondary warm-water sites, have been documented supporting in excess of 100 manatees on numerous occasions, and during winters of varying severity. Unique in physical appearance, distance to forage, hydrology including thermal profiles, and when it was used by manatees, each site challenged the accepted definitions and criteria of what constitutes an acceptable and appropriate warm-water site.Through analyses of photo-identification records, site fidelity at two of these warm-water sites, the Berkeley Canal and the Desoto Canal, was established for a minimum of 20 highly identifiable animals, 15 of which used adjacent sites within the same year, and 6 that used both sites but during different years. Observations of daily use patterns within the sites supported optimization of thermoregulation through adjustments in both vertical and horizontal movement, the latter of which seemed to follow the path of the sun. Manatees using the sites also made use of bottom sediment presumably to stay warm at all three locations. Temperature data indicated that water temperatures monitored in the sediment at secondary sites were some of the highest in the county. The predictable movements during all but the coldest weather fronts indicated that manatees utilized these sites during the early morning and afternoon hours when ambient river temperatures were coldest, gradually returning to the river to feed as ambient temperatures began to rise later in the afternoon.The availability of PTBs in proximity to primary warm-water sites within the region may provide an important component needed for manatees to successfully balance the need to forage with the need to stay warm by providing a network that allows for more efficient foraging while reducing exposure to sub-critical ambient river temperatures. The challenge of balancing the need to forage and to maintain homeostasis in the face of thermal stress is complex. This complexity was best approached and better understood through use of a manatee energetics model. The model was designed to facilitate simulation of an unlimited number of different case scenarios involving the exposure of virtually created manatees to a variety of winter conditions as might be experienced by real manatees in a natural system. Sixty-four different simulations were run using six virtual manatees of differing ages, gender, physical parameters, and knowledge of warm-water sites. Simulations were conducted using actual winter water temperature data from Brevard secondary sites and the ambient river from both a mild and a severe winter season. Outcomes, measured as changes in physical parameters indicative of body condition (i.e. mass, percent body fat, blubber depth, girths, etc.), showed that all else being equal, calves in the 2 year-old range fared poorly in all scenarios when compared to individuals of larger size. Subadults fared better than larger adults. This outcome illustrates the complex relationship between size, energy requirements and the synergistic effects of body mass, body fat and blubber thickness on SA:V ratio. Model outcomes agree closely with manatee cold stress mortality analyses predicting that medium to large-sized calves are most susceptible to CS, followed by adults, then subadults.Because all models are simplifications of complex systems, the manatee energetics model is not without its flaws and limitations. The current version of the model could not predict the point at which cold stress mortality would occur. However, a cold stress warning system incorporated into the design alerts the user if potential CSS is likely based on changing physical parameters. Another limitation was the inability of the model to account for the behavioral plasticity of individual subjects since virtual manatees respond to water temperatures based on the user defined rules. A number of additional limitations related to gaps in existing manatee data the gaps were identified and defined. Despite these gaps, the model is designed to allow for incorporation of additional interactions, feedback loops and relevant data as it becomes available and as additional physiological interactions and energy requirements are more clearly defined. Sensitivity analyses, a feature of the model that allowed for modifications in a number of physical as well as environmental parameters, provided an otherwise unlikely opportunity to see how incremental changes in input values, specifically the starting values for mass, percent body fat and blubber depth affected the model's outcome. Ultimately the goal of the model was to facilitate a better understanding of complex relationships by challenging our preconceived understanding of the manatee and its environment
Show less - Date Issued
- 2014
- Identifier
- CFE0005419, ucf:50428
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005419
- Title
- The Characterization of the Effects of Stress Concentrations on the Mechanical Behavior of a Micronic Woven Wire Mesh.
- Creator
-
Kraft, Steven, Gordon, Ali, Bai, Yuanli, Gou, Jihua, University of Central Florida
- Abstract / Description
-
Woven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material...
Show moreWoven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material knowledge gap that exists for characterizing the behavior of a metallic woven structure, composed of stainless steel wires on the order of 25 microns in diameter, and subjected to various loading conditions and stress risers. Uniaxial and biaxial tensile experiments, employing Digital Image Correlation (DIC) as a strain measurement tool, are conducted on woven wire mesh specimens incised in various material orientations, and with various notch geometries. Experimental results, supported by an ample analytic modeling effort, indicate that an orthotropic elastic constitutive model is reasonably capable of governing the macro-scale elasticity of the subject material. Also, the Stress Concentration Factor (SCF) associated with various notch geometries is documented experimentally and analytically, and it is shown that the degree of stress concentration is dependent on both notch and material orientation. The Finite Element Method (FEM) is employed on the macro-scale to expand the experimental test matrix, and to judge the effects of a homogenization assumption when modeling metallic woven structures. Additionally, plasticity of the stainless steel woven wire mesh is considered through experimental determination of the yield surface, and a thorough analytic modeling effort resulting in a modified form of the Hill yield criterion. Finally, meso-scale plasticity of the woven structure is considered, and the form of a multi-scale failure criterion is proposed and exercised numerically.
Show less - Date Issued
- 2013
- Identifier
- CFE0004707, ucf:49825
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004707
