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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Fabricação de ferramentas de corte em gradação funcional por Spark Plasma Sintering (SPS). / Fabrication of cutting tools from functionally graded materials using Spark Plasma Sintering (SPS).

Carneiro, Marcelo Bertolete 23 January 2014 (has links)
O objetivo do trabalho foi fabricar ferramentas de corte para usinagem a partir de materiais em gradação funcional (Functionally Graded Materials FGM), fazendo uso da técnica de sinterização por plasma pulsado (Spark Plasma Sintering SPS), a qual permite taxa de aquecimento e resfriamento maior do que as técnicas tradicionais, menor temperatura e tempo de operação, melhor controle energético e alta repetibilidade. Os materiais utilizados foram pós cerâmicos a base de alumina (Al2O3-ZrO2 e Al2O3-TiC) e metal duro (WC-Co), de modo que dois insertos foram desenvolvidos, um de cerâmica branca (Al2O3-ZrO2) em gradação com metal duro e outro de cerâmica mista (Al2O3-TiC) em gradação com metal duro. A metodologia experimental levou em conta a aplicação de um modelo termomecânico para estimar a tensão residual térmica ao longo da espessura da ferramenta, estudo da influência dos parâmetros de sinterização por SPS (Temperatura e Pressão) sobre a qualidade do sinterizado (caracterização da propriedade física, densidade), com base nesses dados foi escolhida a melhor condição de operação para fabricar corpos de prova (CPs) para os ensaios mecânicos de resistência à flexão, dureza e tenacidade à fratura, além de insertos em FGM para os ensaios de usinagem em ferro fundido cinzento fazendo uso da operação de torneamento. Os resultados mostraram que o parâmetro de máquina que mais influenciou a densidade foi a Temperatura, os FGMs de AlTiC e AlZr obtiveram um aumento de 126 e 73% na resistência à flexão em relação às suas respectivas cerâmicas homogêneas, seguindo a sequência dos materiais, a dureza foi avaliada em 13,8 e 15,8 GPa, enquanto a tenacidade à fratura em 4,91 e 5,04 MPa.m1/2. Quanto aos ensaios de usinagem, as ferramentas de FGM AlZr apresentaram menor desgaste do que as de FGM AlTiC, as forças de corte foram influenciadas pelas variáveis Avanço e Velocidade de corte, finalmente, o Avanço foi a variável que mais influenciou os resultados de rugosidade. / The aim was fabricating cutting tools from functionally graded materials (FGM) by spark plasma sintering method (SPS), which allow heating and cooling rates higher than traditional methods, lower temperature and shorter time sintering, better energy control and high reproducibility. The materials used were ceramic powders based on alumina (Al2O3-ZrO2 and Al2O3-TiC) and cemented carbide (WC-Co), so that two inserts were developed, one of white ceramic (Al2O3-ZrO2) graded with cemented carbide and the other of mixed ceramic (Al2O3- TiC) graded with cemented carbide. The experimental methodology was developed from thermo-mechanical model application to estimate thermal residual stress along with tool thickness, study into the influence of SPS sintering parameters (Temperature and Pressure) over sintered quality (physical properties characterization, density), on the basis of these data, the best operating condition was chosen to fabricate workpieces for mechanical tests of flexural strength, hardness and fracture toughness, besides FGM inserts to machining tests in grey cast iron using turning operation. The results showed the machine parameter that mostly influenced density was Temperature; the AlTiC and AlZr FGMs got an increase of 126 and 73% in flexural strength in relation to their homogeneous ceramics. Following the materials sequence, the hardness was evaluated at 13.8 and 15.8 GPa, whereas the fracture toughness was 4.91 and 5.04 MPa.m1/2. For the machining tests, FGM AlZr cutting tools showed lower wear than FGM AlTiC ones; the cutting forces were influenced by Feed Rate and Cutting Speed. Finally, the Feed Rate was the variable that mostly influenced the roughness results.
2

Fabricação de ferramentas de corte em gradação funcional por Spark Plasma Sintering (SPS). / Fabrication of cutting tools from functionally graded materials using Spark Plasma Sintering (SPS).

Marcelo Bertolete Carneiro 23 January 2014 (has links)
O objetivo do trabalho foi fabricar ferramentas de corte para usinagem a partir de materiais em gradação funcional (Functionally Graded Materials FGM), fazendo uso da técnica de sinterização por plasma pulsado (Spark Plasma Sintering SPS), a qual permite taxa de aquecimento e resfriamento maior do que as técnicas tradicionais, menor temperatura e tempo de operação, melhor controle energético e alta repetibilidade. Os materiais utilizados foram pós cerâmicos a base de alumina (Al2O3-ZrO2 e Al2O3-TiC) e metal duro (WC-Co), de modo que dois insertos foram desenvolvidos, um de cerâmica branca (Al2O3-ZrO2) em gradação com metal duro e outro de cerâmica mista (Al2O3-TiC) em gradação com metal duro. A metodologia experimental levou em conta a aplicação de um modelo termomecânico para estimar a tensão residual térmica ao longo da espessura da ferramenta, estudo da influência dos parâmetros de sinterização por SPS (Temperatura e Pressão) sobre a qualidade do sinterizado (caracterização da propriedade física, densidade), com base nesses dados foi escolhida a melhor condição de operação para fabricar corpos de prova (CPs) para os ensaios mecânicos de resistência à flexão, dureza e tenacidade à fratura, além de insertos em FGM para os ensaios de usinagem em ferro fundido cinzento fazendo uso da operação de torneamento. Os resultados mostraram que o parâmetro de máquina que mais influenciou a densidade foi a Temperatura, os FGMs de AlTiC e AlZr obtiveram um aumento de 126 e 73% na resistência à flexão em relação às suas respectivas cerâmicas homogêneas, seguindo a sequência dos materiais, a dureza foi avaliada em 13,8 e 15,8 GPa, enquanto a tenacidade à fratura em 4,91 e 5,04 MPa.m1/2. Quanto aos ensaios de usinagem, as ferramentas de FGM AlZr apresentaram menor desgaste do que as de FGM AlTiC, as forças de corte foram influenciadas pelas variáveis Avanço e Velocidade de corte, finalmente, o Avanço foi a variável que mais influenciou os resultados de rugosidade. / The aim was fabricating cutting tools from functionally graded materials (FGM) by spark plasma sintering method (SPS), which allow heating and cooling rates higher than traditional methods, lower temperature and shorter time sintering, better energy control and high reproducibility. The materials used were ceramic powders based on alumina (Al2O3-ZrO2 and Al2O3-TiC) and cemented carbide (WC-Co), so that two inserts were developed, one of white ceramic (Al2O3-ZrO2) graded with cemented carbide and the other of mixed ceramic (Al2O3- TiC) graded with cemented carbide. The experimental methodology was developed from thermo-mechanical model application to estimate thermal residual stress along with tool thickness, study into the influence of SPS sintering parameters (Temperature and Pressure) over sintered quality (physical properties characterization, density), on the basis of these data, the best operating condition was chosen to fabricate workpieces for mechanical tests of flexural strength, hardness and fracture toughness, besides FGM inserts to machining tests in grey cast iron using turning operation. The results showed the machine parameter that mostly influenced density was Temperature; the AlTiC and AlZr FGMs got an increase of 126 and 73% in flexural strength in relation to their homogeneous ceramics. Following the materials sequence, the hardness was evaluated at 13.8 and 15.8 GPa, whereas the fracture toughness was 4.91 and 5.04 MPa.m1/2. For the machining tests, FGM AlZr cutting tools showed lower wear than FGM AlTiC ones; the cutting forces were influenced by Feed Rate and Cutting Speed. Finally, the Feed Rate was the variable that mostly influenced the roughness results.
3

Analysis of smart functionally graded materials using an improved third order shear deformation theory

Aliaga Salazar, James Wilson 02 June 2009 (has links)
Smart materials are very important because of their potential applications in the biomedical, petroleum and aerospace industries. They can be used to build systems and structures that self-monitor to function and adapt to new operating conditions. In this study, we are mainly interested in developing a computational framework for the analysis of plate structures comprised of composite or functionally graded materials (FGM) with embedded or surface mounted piezoelectric sensors/actuators. These systems are characterized by thermo-electro-mechanical coupling, and therefore their understanding through theoretical models, numerical simulations, and physical experiments is fundamental for the design of such systems. Thus, the objective of this study was to perform a numerical study of smart material plate structures using a refined plate theory that is both accurate and computationally economical. To achieve this objective, an improved version of the Reddy third-order shear deformation theory of plates was formulated and its finite element model was developed. The theory and finite element model was evaluated in the context of static and dynamic responses without and with actuators. In the static part, the performance of the developed finite element model is compared with that of the existing models in determining the displacement and stress fields for composite laminates and FGM plates under mechanical and/or thermal loads. In the dynamic case, coupled and uncoupled electro-thermo-mechanical analysis were performed to see the difference in the evolution of the mechanical, electrical and thermal fields with time. Finally, to test how well the developed theory and finite element model simulates the smart structural system, two different control strategies were employed: the negative velocity feedback control and the Least Quadratic Regulator (LQR) control. It is found that the refined plate theory provides results that are in good agreement with the those of the 3-D layerwise theory of Reddy. The present theory and finite element model enables one to obtain very accurate response of most composite and FGM plate structures with considerably less computational resources.
4

The Effects of Female Genital Mutilation on Women of Sierra Leone

Kalokoh, Nenneh Kalokoh 01 January 2017 (has links)
Female genital mutilation or cutting (FGM/C), a common practice among Sierra Leonean women, carries significant psychological and physical risks. Prior to this study, a substantial need existed for inquiry of the experiences and belief systems within this cultural group to better understand the effects of FGM/C on women and girls. Guided by feminist theory and the theory of cultural relativism, the goal of this phenomenological study was to review the cultural perspectives and experiences of Sierra Leonean women who underwent FGM/C to investigate their concerns about safety and their perceptions of the practices. In addition, this study explored concerns among Sierra Leonean women about the procedure performed on their daughters and to what they attributed the continued practice of FGM/C. Participants included a purposeful sample of 12 women from Sierra Leone who had experienced FGM/C. Data were collected via in-person, semi-structured interviews and analyzed thematically. Analysis revealed differences in participant definitions of FGM/C, cultural and social aspects of the procedure, personal beliefs and perceptions of the procedures. Results provide new understandings to help health and human rights organizations implement proactive safety measures for these women and girls. Positive social change from this investigation may occur via proper education about FGM/C. Goals include helping women understand the risks associated with the practice and to make their own informed decisions regarding the procedure. Findings revealed that a powerful strategy for protecting women's health and well-being related to FGM/C may be through education on the facts of the procedure.
5

The Association between Female Genital Mutilation (FGM) and the Risk of HIV/AIDS in Kenyan Girls and Women (15-49 Years)

Kinuthia, Rosemary G 04 May 2010 (has links)
INTRODUCTION: Kenya like the rest of Sub-Saharan Africa continues to be plagued with high rates of AIDS/HIV. Research has shown that cultural practices have serious implications for the spread of HIV/AIDS, as well as other communicable diseases. One of the practices that have been speculated to have an impact on AIDS/HIV is female genital mutilation (FGM). Despite efforts to eradicate the practice, prevalence of FGM in Kenya remains relatively high. Researchers have postulated that various forms of FGM may be associated with the spread of HIV/AIDS. OBJECTIVE: The purpose of this study is to determine the relationship between FGM and HIV/AIDS using a representative sample of Kenyan girls and women. METHODS: Data (n=3271) from the Kenya 2003 Demographic and Health Survey was used for this study. Chi-square test was used to examine the distribution of selected risk factors across HIV/AIDS status. Odds ratios from multivariate logistic regression analyses were used to determine association between FGM and HIV/AIDS. RESULTS: This study shows an inverse association (OR=0.508; 95% CI: 0.376-0.687) between FGM and HIV/AIDS, after adjusting for confounding variables. DISCUSSION: The inverse association between FGM and HIV/AIDS established in this study suggests a possible protective effect of female circumcision against HIV/AIDS. This finding suggests therefore the need to authenticate this inverse association in different populations and also to determine the mechanisms for the observed association.
6

Services for women with female genital mutilation in Christchurch : perspectives of women and their health providers

Hussen, Marian Aden January 2014 (has links)
Abstract In recent decades there has been increased immigration to New Zealand of women from East Africa. These countries have the highest prevalence rates (between 90-97%) of Female Genital Mutilation (FGM) worldwide. FGM therefore has become part of the care experience of some New Zealand health providers. Information on FGM is available on the New Zealand Ministry of Health website. This study captures the experience of a group of East African women in Christchurch who have undergone FGM and given birth in Christchurch Hospitals. Two focus groups, each with ten women, were held so that women could talk about their health services experience. A narrative approach was adopted, listening to their stories in order to explore, to gain insight and to understand how these women felt during reproductive and antenatal care, childbirth and after childbirth. Interviews with three health providers sought their experiences of caring for women with FGM. The study identifies diverse potential explanations with the focus group members telling their stories and identifying issues related to FGM. Several short case histories are presented to illustrate these experiences. The thematic analysis reported four themes: satisfaction with clinical care, concern about infibulation, barriers to knowledge for women, and problems of cross-cultural communication. Health providers reported similar issues, with themes related to their own clinical experience, knowledge gaps, and need for greater cultural understanding and communication. These themes reflect the journey of the East African women with FGM in Christchurch and the challenges faced by them and their providers. This research recommends that women with FGM receive more education and support to manage their relationships with the health system and their own health. Health providers need continuing education and further support in the psychosocial, psychological and physical health needs of East African women living in Christchurch. Service outcomes should be evaluated.
7

Effects of female genital mutilation on childbirth

Khaled, M. A. January 2004 (has links)
Female genital mutilation (FGM) is defined by the World Health Organisation as the deliberate total or partial removal of the external female genitalia, or other deliberate injury to the female genitalia, which is carried out for non-therapeutic purposes. The practice is widely condemned. Even though the adverse effects of the practice have been well documented in many small studies and case reports, FGM is still common in many countries. The effects of this practice are also being felt in many developed countries due to substantial migration in recent years. One of the limiting factors in encouraging eradication is the availability of high quality evidence of the effects of the practice on the process of childbirth. By highlighting the effects of FGM on the process of childbirth, the objective was to encourage policy makers, in co-operation with many relevant organisations, to work together to eradicate the procedure. This original study investigates the effects of FGM on the process of childbirth using a large international epidemiological case control study involving three centres in three different countries. The inclusion criteria were strict and comprised of agreement by the woman and or her husband to participate in the study, for a normal singleton pregnancy at term with a cephalic presentation which resulted in a normal baby, for the women with and without FGM during the period of study. Women who did not fulfil these criteria were excluded. Maternal outcome measures included length of labour, obstruction to the progress of labour, operative delivery, urine retention, perineal complications, intrapartum and postpartum haemorrhage and blood loss during the process of labour. Newborn outcome measures included birth status at delivery, Apgar scores at 5 and 10 minutes, requirement for resuscitation, admission to special care unit and time taken from delivery to the first breast feed. Psychological sequelae were not assessed. The total number of participants in these three centres was 1,970 women; 526 with no FGM (control) and 1444 with different types of FGM. Every effort was taken to keep confidentiality and not to interfere with management of labour during data collection. The results indicate a highly significant difference between the two groups when comparing length of the process of labour, mode of delivery and the need for instrumental deliveries, episiotomies and tears, blood loss during and after delivery, the need for catheterisation following deliveries and duration of hospital stay following birth. Adverse effects were not confined to women and were found to have extended to the new-borns in the two groups again with highly significant difference with regard to birth trauma, requirement for resuscitation and medical attention. The time taken for the first breast contact was different in the two groups with possible effects which may be difficult to establish and require further research. The data provide clear evidence that the practice of FGM is associated with clinical adverse effects, which are not only confined to women but involve the newborn as well. It is hoped that this systematic and comprehensive collection of evidence will make a substantial contribution to the world wide effort to eradicate this harmful practice.
8

Colonizing Bodies: a Feminist Science Studies Critique of Anti-Fgm Discourse

Njambi, Wairimu Ngaruiya 14 March 2001 (has links)
The contentious topic of female circumcision brings together medical science, women's health activism, and national and international policy-making in pursuit of the common goal of protecting female bodies from harm. To date, most criticisms of female circumcision, practiced mainly in parts of Africa and Southwest Asia, have revolved around the dual issues of control of female bodies by a male-dominated social order and the health impacts surrounding the psychology of female sexuality and the functioning of female sex organs. As such, the recently-evolved campaign to eradicate female circumcision, alternatively termed "Female Genital Mutilation" (FGM), has formed into a discourse intertwining the politics of feminist activism with scientific knowledge and medical knowledge of the female body and sexuality. This project focuses on the ways in which this discourse constructs particular definitions of bodies and sexuality in a quest to generalize the practices of female circumcision as "harmful" and therefore dangerous. Given that the discourse aimed at eradicating practices of female circumcision, referred to in this study as "anti-FGM discourse," focuses mostly on harm done to women's bodies, this project critiques the assumption of universalism regarding female bodies and sexuality that is explicitly/implicitly embedded in such discourse. By questioning such universals, I look at the ways in which different stories regarding bodies and sexuality can emerge at the gaps of the anti-FGM discourse regarding female circumcision practices. I.e., are there other possible avenues for envisioning bodies which are subjugated and hence eliminated from the view by their rhetoric? While the main assumption within anti-FGM discourse is that bodies and sexuality are naturally given and therefore universal, contemporary theories in STS and feminism have stressed that bodies and sexualities are figures of historical and political performances, and that knowledge about them is locally situated. These perspectives redirect the typical assumption of bodies and sexuality as simply "biological" to a view of bodies as products of cultural imagination. This project shows that such perspectives have profound implications for understanding female circumcision practices by allowing different body narratives to emerge in the gaps of already established "truths." / Ph. D.
9

Study of the honeycomb structures and functionally graded materials using the BEM and FEM

Mellachervu, Krishnaveni January 2008 (has links)
No description available.
10

Modelling of Biomass Syngas Combustion with CFD

Papafilippou, Nikolaos January 2022 (has links)
Gas turbines integrated with biomass gasification in a combined cycle power plant (Bio-IGCC) provide a path to power production with very high efficiency. Over 60% fuel-to-power efficiency has been demonstrated with natural gas. The fast ramp and relatively low cost make Bio-IGCC via gas turbines the ideal complement to intermittent power from wind turbines and PV cells. With stricter pollutant regulations and in order to promote the use of renewable fuels there is a great interest in improving fuel flexibility. An important feature of biomass gasification is that its properties vary depending on the feedstock and gasification principle and that the combustion characteristics are significantly different from conventional fuels. This makes it interesting to develop CFD models that can be used to simulate the combustion of syngas in existing gas turbines and for design optimization of new gas turbines.  The TECFLAM swirl burner geometry, which is designed to be representative of common gas turbine burners, was selected for an assessment of the differences between a typical hydrocarbon fuel and syngas. A two-stage approach was employed with development and validation of an advanced CFD model. The validated model was used to compare the flame shape and other characteristics of the flow between methane, 40% hydrogen enriched methane and four typical syngas compositions. The syngas compositions used are representative of practical gasification processes and biomass feedstocks. It was found that the syngas fuels experience lower swirl intensity due to high axial velocities that weaken the inner recirculation zone. A strong correlation was found between the laminar flame speed and the flame shape.  The simulation of a typical combustion geometry with syngas is quite demanding and requires a long computational time. In order to speed up the parametric analysis and to make it possible to test more configurations a Two-Step, One Way coupled method was assessed. This is a common approximation in CFD that is used to solve complex problems with limited computational resources. The test case used for the assessment was the CeCOST burner that uses strong swirl for flame stabilization. Only isothermal flow was investigated to eliminate the influence from flow – chemistry interactions. This method effectively divides the domain in two parts, one downstream and one upstream. The assumption behind this method is that the downstream part should not have a big influence on the upstream part and hence it could be solved separately. From the comparison it was found that the full solution and the approximations were in good qualitative agreement. However, there were some minor quantitative discrepancies, and it was proposed that the explanation for the differences could be the slightly different solution approaches that were used for the full simulation (URANS) and the two approximate solutions (RANS). The speed-up from using the approximate method was close to one order of magnitude.  However, because an artificial steady inlet cannot reproduce all the dynamic phenomena created by a swirler, for the continuation a full CeCOST domain was used. LES modelling was also employed to be able to identify smaller structures that would affect flame stability. Using LES and the Artificially Thickened Flame model, a syngas composition that relates to Black Liquor gasification was modelled. The flame front position using the CH2O mole fraction was estimated and it correlated well with the position estimated by the progress variable. The flame front position found by using the OH mole fraction was different to the two previous ones, predicting the hot part of the flame.

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