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Mahmoudi, Amir Hossein. "Influence of residual stresses on fracture." Thesis, University of Bristol, 2005. http://hdl.handle.net/1983/4026a13c-3d83-49a6-815c-1bdf50e37f0a.
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This thesis presents numerical and experimental research concerned with developing laboratory test specimens containing well-characterised residual stress fields. These specimens were then used to examine how residual stresses influenced fracture conditions. Three different materials were used in this work; an A508 ferritic steel, and two aluminium alloys, 2650 and 2024. Residual stresses were generated using a technique called local compression on both uncracked plates and cracked compact tension, C(T), specimens. Residual stresses introduced by single punching tools on the uncracked specimens were examined theoretically and numerically to benchmark further developments. Also residual stresses were measured using three techniques, deep-hole drilling (DHD), centre-hole drilling (ICHD) and synchrotron diffraction (HEXRD) and excellent agreement between measurement methods was obtained. A parametric study was carried out to determine the features of the residual stress field generated in cracked specimens. The position of single and double pairs of punching tools relative to the crack tip as well as the size of the punches were examined systematically. The numerical analyses revealed that positioning a single punching tool tangentially to the crack tip resulted in the generation of a tensile residual stress field ahead of a crack. Furthermore, double pairs of punching tools were shown to generate either tensile or compressive residual stresses normal to the crack plane depending on the relative position of the tools to the crack tip. The numerical findings were confirmed experimentally through HEXRD measurements and fracture tests. Local compression and prior overloading were applied to C(T) specimens to generate a residual stress field, either independently or in combination. It was found that tensile residual stresses reduced the apparent fracture toughness and that compressive residual stresses resulted in increased the fracture toughness. The shift in the apparent fracture toughness depended on the magnitude of the residual stresses and material, with the aluminium alloys being more susceptible to the presence of tensile residual stresses. A local approach based on the Beremin model was used to predict failure in the presence of residual stress fields in terms of fracture toughness for cleavage fracture in steel specimens. The overall trends from predictions were similar to the experiments, but there remain limitations in the model. For aluminium specimens, a method based on the William's series was employed to predict the stress intensity corresponding to a residual stress field (Kres). The measured changes in initiation toughness matched the predicted values of K1es.
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Wilks, Martin David Bernard. "The influence of residual stresses on fatigue." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240439.
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Ntsoane, T. P. "Residual stress in Pt coatings under thermal influence." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/8778.
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Includes bibliographical references.Resistance thermometers are commonly employed when accurate temperature measurements are required. The detection part consists of a thin metallic film deposited on a ceramic substrate. In this work, commercially manufactured Pt-Al₂O₃ composites annealed at 0°C, 300°C, 600°C and 1170°C above room temperature were investigated for residual stress using the non-destructive X-ray diffraction technique. The apparatus used for the investigation was a Ψ-goniometer with a scintillation detector. The measured data were analysed with "sin²Ψ"-method. The total stress yielded was found to be a superposition of both the thermal and intrinsic stress in the layer. Analytical model, following the method of Tsui and Clyne, was used to resolve the two stress contributions. With the thermal component being constant, the variation of the observed total stress was attributed to the relaxing intrinsic components. Further investigations of the samples included the microstructure studies using Scanning Electron Microscopy (SEM).
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LaRue, James Edward. "The Influence of Residual Stress on Fatigue Crack Growth." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04072005-095303/.
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This thesis discusses the analysis of fatigue crack growth in the presence of residual stresses to determine a suitable method for fatigue life predictions. In the research discussed herein, the prediction methodologies are compared to determine the most accurate prediction technique. Finite element analysis results are presented as well as laboratory test data. The validity of each methodology is addressed and future work is proposed.
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Östlund, Magnus. "Residual stresses in paperboard and the influence of drying conditions." Doctoral thesis, KTH, Solid Mechanics (Div.), 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-469.
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The drying sequence in the manufacturing process for paperboard involves evaporation of water, primarily from within the fibres. The vapour is then transported out of the web by pressure or concentration gradients. As the moisture transport from the paper web to the ambient is quicker than the moisture transport within the fibre network to the surfaces of the web, moisture gradients develop through the thickness of the web. This work concerns effects on the mechanics of paper drying from the variation in moisture through the relatively thin structures of paper and paperboard.
Distributions of inplane residual stresses through paper materials in the unloaded state after drying are believed to be caused by the varying moisture through the thickness during drying. The distributions in general exhibit compressive stress near the board surfaces and tensile stress in the interior of the board. This may be modified after drying and is also affected by structural variation in the material between different plies of multi-ply paperboards.
The stress development during drying is important because it influences the resulting material properties of the paper and because it can lead to curl, which is a quality problem. The residual stresses themselves are an error source in simulation or evaluation of the mechanical behaviour of paper.
In this work, residual stress distributions in paperboard were determined experimentally, to clarify the mechanisms of residual stress build-up. An experimental method for such tests was also developed. Based on the experimental findings, the mechanics of paper drying was modelled and the stress build-up simulated. Simulation offers a way of studying how the properties of paper develop during drying of wet paper webs.
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Östlund, Magnus. "Residual stresses in paperboard and the influence of drying conditions /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-469.
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Ngiam, Shi Song. "The influence of surface residual stress on fatigue crack growth." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444870/.
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Residual stress exists in most structures and although it has been recognised for a long time, its complex mechanism and characteristics are still being intensively studied. Residual stress can be stratified into damaging residual stress and beneficial residual stress. Surface tensile residual stresses are generally known to reduce the mechanical properties of materials while compressive residual stresses improve the fatigue performance of components. This Ph.D. thesis reports the analytical and experimental work conducted to investigate both the damaging and beneficial effects of residual stress on fatigue crack growth in structural components. The detrimental effect of tensile residual stresses is studied through large scale fatigue testing of T-butt welded plates fabricated from High Strength Steels (HSS). Despite the growing use of HSSs in the offshore industry, the fatigue performance and corrosion resistance of welded joints made from such steels are still not clear. Due to their complex metallurgy and relatively poor weldability, there is still a lack of understanding of the residual stresses that arise from the welding process. This study involved modification and development conducted on a variable amplitude (VA) load-time sequence generator for the investigation of long life fatigue performance of HSS. Emphasis was given to the generation of a stationary load-time history and numerous analyses were presented to demonstrate the importance of the long term statistical nature of the load-time sequence on fatigue testing. Fatigue test results obtained were extensively compared with previous HSS corrosion fatigue studies. The effect of tensile residual stress on fatigue crack growth was investigated using a SIF weight function-based fatigue crack growth model. Two newly developed preferential cold working techniques termed stitch cold rolling and stitch shot peening were explored to investigate the beneficial effect of surface compressive residual stress on fatigue crack growth in mild steel plates. One of the main objectives of this study was to control the fatigue crack shape by the manipulation of surface residual stress fields. The stitch cold rolling technique was implemented using a custom-built cold rolling jig. The feasibility of preferential cold working techniques was further investigated by the fatigue testing of stitch shot peened specimens. Both experimental programmes yielded unprecedented fatigue crack growth results. A residual stress monitoring programme was conducted to study the residual stress relaxation behaviour under cyclic loading. The experimental test results enabled the investigation of SIF solutions in non-uniform stress fields. A novel fatigue crack growth evolution model, which takes into account residual stress relaxation effects, was developed using the powerful SIF weight function methods.
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Royston, Jonathan M. "The influence of posterior corneal surface astigmatism on residual astigmatism." Thesis, Aston University, 1990. http://publications.aston.ac.uk/14636/.
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It has often been found that corneal astigmatism exceeds the amount exhibited by the eye as a whole. This difference is usually referred to as residual astigmatism. Scrutiny of the studies of corneal astigmatismreveal that what has actually been measured is the astigmatic contributionof the anterior corneal surface alone. This anterior surface is easily measured whereas measurement of the posterior corneal surface is much moredifficult. A method was therefore developed to measure the radius and toricity of the posterior corneal surface. The method relies upon photography of the first and second Purkinje images in three fixed meridians. Keratometry, comparison of anterior and posterior corneal Purkinje images and pachometricdata were applied to three meridional analysis equations, allowing the posterior corneal surface to be described in sphero-cylindrical form. Measurements were taken from 80 healthy subjects from two distinct age groups. The first consisted of 60 young subjects, mean age 22.04 years and the second consisted of 20 old subjects, mean age 74.64 years. The young group consisted of 28 myopes, 24 emmetropes and 8 hyperopes. The old group consisted of 6 myopes and 14 hyperopes. There was an equal number of males and females in each group. These groupings allowed the study of the effects of age, ametropia and gender on the posterior corneal toricity. The effect of the posterior corneal surface on residual astigmatism was assessed and was found to cause an overall reduction. This reduction was due primarily to the posterior corneal surface being consistently steeper relative to the anterior surface in the vertical meridian compared to the horizontal meridian.
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Silva, Neto Luiz Vieira da 1987. "Efeito residual no triathlon : como nadar influência nas etapas seguintes." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/275116.
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Orientador: Orival Andries JúniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Educação Física
Made available in DSpace on 2018-08-24T05:58:49Z (GMT). No. of bitstreams: 1 SilvaNeto_LuizVieirada_M.pdf: 895752 bytes, checksum: 969b92939cb56474d2c75ca0ebb18906 (MD5) Previous issue date: 2014
Resumo: O Triathlon é uma modalidade esportiva composta por três etapas, que são nadar, pedalar e correr. Diversos estudos vem investigando como nadar influencia etapas seguintes, mas os resultados ainda são controversos em alguns aspectos. Existem estudos, que falam da importância de nadar para o desempenho geral da prova, pois à medida em que às distâncias das provas variam, a correlação com o resultado final varia. Com isso o objetivo do presente estudo foi analisar como nadar 375 metros pode influenciar durante o pedalar e o correr, além do resultado geral em uma prova simulada de triathlon super sprint (nadar 375m- pedalar 10Km-correr 2.5Km). Foram avaliados 8 triatletas amadores, (27 ± 4 anos; 75 ± 6 kg; 179 ± 7 cm), que assinaram o termo de consentimento livre e esclarecido (TCLE), que foi aprovado junto ao projeto de pesquisa pelo comitê de ética em pesquisa da Unicamp com o Nº8999/2012. Foram realizados três protocolos de avaliação: 1º Triathlon (Tri) que consistia em nadar 375m, pedalar 10Km e correr 2.5Km, no 2º Pedalar e Correr (PC) onde o voluntário deveria pedalar 10Km e correr 2.5Km e no 3º Correr (C) e último o voluntário teve de correr 2.5Km. Todas as coletas foram randomizadas e obedeceram um intervalo que tinha o mínimo de 48 horas. Os dados foram analisados através de estatística descritiva, a normalidade foi testada através do teste de Shapiro-Wilk e após a normalidade dos dados aceita, foi usado o teste "t" pareado para se comparar duas situações e a correlação de Pearson de um momento com o outro, os resultados da presente pesquisa foram expostos em dois artigos. No primeiro estudo, nadar reduziu o desempenho do pedalar (-8,4%) e o tempo total (pedalar + correr; -5,4%) quando comparados à realização das mesmas sem a presença prévia do nadar, todas as etapas analisadas, com exceção do correr em PC, houveram correlações significativas com o tempo total de prova. No segundo estudo, houve diferença significativa nas variáveis, potência média e máxima, potência relativa média e máxima, além de velocidade média e máxima, entre os protocolos Tri e PC. Com base nos achados da presente pesquisa, concluímos que nadar previamente, reduz o desempenho do pedalar, mas não influencia no desempenho do correr, mesmo dessa forma o tempo total de prova foi influenciado, pelo nadar previamente
Abstract: Triathlon is a sport consisting of three stages, which are swimming, biking and running. Several studies have been investigating how swimming may influence on biking and how biking may influence on running, but the results still controversial in some aspects. There are studies that pointed out the importance of swimming for the overall performance in the competition. As the shorter the competition, the bigger the correlation with the final result were found. Therefore, the aim of this study is to analyze how to swim 375 meters may influence biking and running and the overall outcome in a simulated competition of super sprint triathlon (375m swim, 10km cycle, run 2,5 Km). Eight amateur triathletes (27 ± 4 years, 75 ± 6 kg, 179 ± 7 cm), who signed the consent form which was approved by UNICAMP research and ethics committee with number 8999/2012. Three protocols of evaluation were performed: 1st Tri which consisted of swimming 375m, cycling 10km and running 2.5 km; in the 2nd CR the volunteer should cycle 10km and run 2.5 km and in the 3rd R and the last one, the volunteer had to run 2, 5km. All samples were randomized and they had a minimum of 48 hours rest. The data was analyzed using descriptive statistics. Normality was tested by the Shapiro-Wilk. "t" paired test was used to compare the situations and the correlation of Pearson of one moment with other. In the first study, swimming reduced biking performance (-8.4%) and the total time (cycling + running; -5.4%) when compared to the performance of biking and running without the prior presence of swimming. All stages analyzed, with exception of running on BR had significant correlations with the total time of the competition. In the second study, there were significant differences in the variables, average power, maximum power and maximum average relative, and average and maximum speed between the Tri and BR protocols. Based on the results of this research, we concluded that to perform swimming first reduces cycling performance, but does not influence the performance of the run. Finally the total time of the competition was influenced by the pre-swim
Mestrado
Biodinamica do Movimento e Esporte
Mestre em Educação Física
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Wafa, Al-Dajani Waleed. "On the bleachability of alkaline pulps : the influence of residual lignin structure /." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3231.
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Johns, Eyioma Izuwah. "Influence of weldiing modes to strength and residual of low carbon steel joints." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140617_122036-53782.
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In this study, microstructural, micro hardness evaluation and residual stress distribution, of low carbon steel after single pass gas metal arc welding technique (GMAW) were investigated. The goal of this investigation were to reveal the microstructures, micro hardness, residual stress distribution and tensile strength of welded joints by using welding current as varying parameter. In order to realize this objective, welded plate of low carbon steel with thickness of 2.5mm and 250mm long by 200mm wide were welded together with different welding current of 70A, 100A through MIG process. Four different parts of samples were tried. The first part of samples was annealed in a furnace to a temperature of 750 and allowed to cool in air before welding. While the second was not heated, third and fourth trials were heated to a temperature of 200˚C and 580˚C respectively after the welding and allowed cooling in air. Nikon optic microscope and CSM micro hardness testing instrument were used to determine the microstructure of the weld bead and HAZ of the samples, and hardness tests were carried out at different zones of welded joint.
Micro hardness behavior was observed by using CSM instrument using 20N load for indentation, which reveals the correlation between hardness, elasticity and plasticity on the heat affected zone (HAZ) and weld bead of the welded plates. The samples were subjected to tensile strength and the distribution of residual stress of the weld. Tensile strength test... [to full text]Šiame darbe aprašomi mikrostruktūros, mikrokietumo nustatymo bei liekamųjų įtempimų pasiskirstymo tyrimai mažo anglingumo plienuose po lankinio suvirinimo. Tyrimo tiksla - nustatyti suvirintos jungties mikrostuktūros ir mikrokietųmo priklausomybę nuo suvirinimo srovės, kaip kintamo dydžio. Remiantis užduotimi buvo suvirintos 2.5 mm storio, 250 mm ilgio ir 200 mm pločio mažaanglio plieno plokštės, naudojant skirting dydžio (70A ir 100A) suvirininant apsauginių dujų aplinkoje (MIG) srovę. Buvo paruoštos keturios partijos bandinių. Pirmoji partija, proies suvirinant, buvo atkaitinta 750°C temperatųroje, ir ataušintas ore. Tuo tarpu antroji partija nebuvo apdorojama, o trečioji ir ketvirtoji atleista 200 C° ir 580°C temperatūroje ir atvėsinta ore. Suvirinimo vonelės ir erminio poveikio zonos mikrostruktūrai tirti bei mikrokietumui nustatyti buvo naudotas Nicon optinis mikroskopas bei CSM mikrokietumo bandymų įrenginys. Matuojant CSM įrenginiu, 20N įspaudimo apkrova, buvo pastebėtas įdomus kietuvo būvis, kuris atskleidė ryšį tarp kietumo, elastingumo ir plastiškumo esantį suvirintų plokštelių terminio poveikio zonoje bei suvirinimo vonelėje. Buvo matuojamas suvirintų bandinių stiprumas tempiant ir liekamųjų įtempimų pasiskirstymas. Tempimo stiprumo bandymų duomenys parodė ducharakteringus suirimo atvejus – plastiio-elastinio bei trapaus tipo. Liekamųjų įtempimų bandymų rezultati neparodė rėikšmingos liekamųjų įtempimų įtakos pasirinktomis sąlygomis suvirintuose bandiniuose.
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Li, Bocheng. "Influence of Petroleum Deposit Geometry on Long Term Persistence of Residual Crude Oil." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/54007.
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Following the DWH oil spill event, crude oil reaching the shoreline of Gulf of Mexico produced petroleum oil deposit with a range of distinct geometries, including sphere tar balls and horizontal tar sheets. Numerical models were developed based on the Deep Water Horizon oil spill conditions to evaluate the influence of deposit geometry on long term persistence of residual NAPL oil. Two extreme deposit geometries were modeled in this study: the horizontal tar sheet and the spherical tar ball. Both two-dimensional modeling approach and three-dimensional modeling approach were applied to compare two contrasting geometries. The two-dimensional model results showed that sheet geometry deposits exhibited a greater obstruction to groundwater flow relative to the spherical deposits and induced a larger sulfate reducing zone downgradient of the NAPL source, resulting in significantly greater sulfate-based biodegradation of benzene. Three-dimensional models were constructed to assess the influence of key geometry parameters on oil deposit fate and persistence. Three parameters affecting deposit's geometric structure were recognized, including the upper horizontal area of the sheet deposit, the thickness of the sheet deposit, and the radius of the sphere deposit. The three-dimensional model results suggested that thickness of the sheet deposit and radius of the sphere deposit were important geometry factors impacting the fate and long term persistence of residual NAPL oil in the coastal environment. However, the influence of deposit geometry differed depending on the solubility of the different NAPL components. When high solubility compound and low solubility compound both exist in the oil deposit, the influence of deposit geometry on benzene degradation was significant, while the influence on naphthalene was almost negligible.Master of Science
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Malmberg, Andreas. "The influence of carbonitriding on hardness, retained austenite and residual stress in 52100 steel." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173804.
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High rolling contact fatigue parts are vital for the long service life of fuel pumps. Cummins Fuel Systems are currently using an M2 tool steel for one of the most important roller bearing application in their pumps, namely the cam follower. The future design of the cam follower is a pin-less tappet roller. The wear and fatigue properties of the roller is vital to ensure reliability of the fuel system. M2 tool steel is an expensive material and becomes even more so if diamond like coating (DLC) is needed to decrease the friction coefficients. To cut costs of the fuel pump it might be possible to replace the M2 tool steel with 52100 steel (100Cr6). Competitive methods have proven that carbonitrided 52100 can reach excellent wear and fatigue properties making it a candidate to replace M2 tool steel. How the properties of hardness, toughness and compressive residual stresses are developed in 52100 and how they affect the fatigue and wear resistance has been researched from the literature. A big part of this project was to do an extensive analysis of a roller bearing that was believed to have gone through one of these competitive methods that produce excellent wear and fatigue resistance. The analysis was done with background to the knowledge gathered from the literature. Finally process trials were set up to carbonitride 52100 steel samples. The trials were done to develop a better understanding of how adding carbon together with nitrogen to the surface of 52100 steel will influence the metallurgical parameters that results in good wear and fatigue resistance. From this analysis Cummins hope to create a process recipe that can be used for carbonitriding the cam follower and maybe other components in their fuel systems.
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Sedighi, Mohammad. "Modelling the influence of manufacturing parameters on variation of residual stresses in quenched parts." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262815.
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Hunt, Christopher Paul. "Influence of residual elements on the intergranular stress corrosion cracking of carbon manganese steel." Thesis, University of Surrey, 1987. http://epubs.surrey.ac.uk/847543/.
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The Influences of five common tramp elements P, S, Sn, Cu, and Ni at typical residual levels on the intergranular stress corrosion cracking (IGSCC) of a typical mild steel. (0.15%C, 0.8%Mn and 0.05%Si), are studied in nitrate solutions and a mixture of carbonate and bicarbonate solutions. The relative effects of these impurities are examined in terms, of the electrochemical properties of unstressed material, of the IGSCC susceptibility in a constant strain rate test, and of the grain boundary and surface oxide compositions via surface analysis. Results show that in general only phosphorus can be detrimental. A slight beneficial effect is apparent for Cu in both electrolytes. Phosphorus has small adverse effects in certain narrow potential regions in the NH[4]NO[3] electrolyte. These occur just above the free corrosion potential and above the active-passive transition (1100 mV). There are no detrimental effects due to the impurities in the carbonate/bicarbonate electrolyte. The negligible effects of impurities occurs in spite of impurity concentrations at the grain boundaries being significantly enhanced above the bulk to 10%. as confirmed by Auger electron spectroscopy. Hence, the IGSCC susceptibility is shown to be dominated by the carbon present in the steel. XPS measurements indicate that carbon is present throughout the oxide, and importantly up to the electrolyte interface. IGSCC susceptibility is thought to occur principally by a breakdown in the oxide integrity, which leads to prolonged chemical attack. This mechanism is attibuted to the action of carbon and possibly the impurities, however under certain conditions some secondary mechanisms are needed to account for ail the effects due to the impurities. These include improved passivation by reaction products and a remedial influence on the detrimental effect of carbon.
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Aird, Christopher John. "The influence of long-range residual stress on the cleavage fracture of ferritic steel." Thesis, University of Bristol, 2010. http://hdl.handle.net/1983/518cc704-b7bd-4ebf-a063-6cdcede108b9.
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This dissertation considers the influence of long-range residual stress on the cleavagefracture of ferritic steel. The existing body of work related to the influence ofmacro scale residual stress on fracture is reviewed. It is shown that although long-rangeresidual stress, resulting from misfits between components of an engineeringstructure, was discussed by a number of researchers in the late 1970s, it wasneither treated comprehensively nor developed by more recent researchers. Consequently, the design of a test rig capable of generating long-range residual stressin a laboratory compact-tension (C(T)) specimen, for the purpose of investigatingthe effects associated with combined residual and applied loading, is described. Results from fracture tests, carried out using this rig in conjunction with ferriticsteel C(T) specimens below the ductile to brittle transition temperature, are presentedand assessed within the context of a whole-structure model. The developmentof this whole-structure model leads to the central thesis that the strength ofa cracked structure containing long-range residual stress is not dependent solelyon the level of residual stress but also on the amount of plastic deformation priorto fracture, the position of the applied load relative to the cracked element and,crucially, on the relative stiffness of the cracked and uncracked parts of the structure. Finally, the treatment of long-range residual stress within the R6 Revision4 structural integrity assessment procedure is considered and a critical specimento rig stiffness ratio is identified, above which classifying a given long-rangeresidual stress as a ‘secondary’ stress leads to a non-conservative estimate of theload carrying ability of the structure.
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Pasic, Anel. "The influence of the cooling rate during induction hardening on residual stresses and fatigue strength." Thesis, KTH, Hållfasthetslära (Avd.), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103718.
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A vital part in the transmission for Scania lorries is the shaft in the rear axle. Since this shaft is divided into two identical parts, these are termed half shafts. Close control of the manufacturing process of these is required. Influence of flow rate, temperature and polymer concentration of the quenchant was investigated. An important controlling factor is the cooling rate used in the hardening process. This factor was selected for investigation in the present study. It was found that high flow rate, low temperature and low polymer concentration gives high cooling rates. Further investigation was performed how the residual stresses, surface hardness and the case depth of the half shafts were affected by the cooling rate. The results show that residual stresses are particularly affected by the cooling rate. Higher cooling rates results in higher residual stresses. Since residual stresses are important for fatigue lifer, a fatigue study was also undertaken. Five half shafts were quenched with a polymer concentration of 5%, and another five with 15%. All ten half shafts were fatigue tested in torsion, using a Scania standardized method. The shafts were loaded in torsion torque with company confidential amplitude, mean equal to zero number of cycles to failure was recorded. In normal production the half shafts are quenched with 10% polymer concentration. No tests with a polymer concentration of 10% were carried out in this investigation since results from this concentration are available from earlier studies. Residual stresses were measured using a relatively new method developed by Scania, called the core drilling method. A 20 cm long portion of the shaft was center drilled in steps, gradually increasing the drill diameter. After each step, the relaxation of surface strain was measured in the longitudinal and transversal directions. Having obtained these data, stresses can be calculated. Residual stresses were also measured by x-ray diffraction. Only surface stresses are obtained in this way, however. These measurements were made for each of the three polymer concentrations. An attempt was also made on trying to simulate the stress formation in the shafts during the heat treatment with FEM and also to calculate the residual stresses after the treatment. Results from the measurements were then compared with the FEM calculated results. Since the number of tested shafts is small, results are not statistically relevant. One may conclude, though, that fatigue life increases with increasing cooling rate, i.e. with decreasing polymer concentration. The fatigue life requirement for all tested shafts was fulfilled. The compressive residual stresses for 5% and 10% polymer concentration are of same magnitude and higher than for those quenched with 15% polymer concentration. The result also shows that the cooling rate does not affect the surface hardness, nor the case depth.
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LOPES, MARIA BERNADETE LUCIANO. "INFLUENCE OF SUCTION ON THE SHEAR STRENGTH OF A FILITE RESIDUAL SOIL FROM BELO HORIZONTE, MG." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9536@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORFUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE APOIO A NÚCLEOS DE EXCELÊNCIA
FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS
Neste trabalho, analisou-se a influência da sucção na resistência ao cisalhamento de um solo residual jovem de filito da região metropolitana de Belo Horizonte (MG). A fim de determinar a resistência ao cisalhamento do solo não saturado, foram realizados ensaios de cisalhamento direto com sucção controlada em amostras indeformadas e teor de umidade natural. Foram feitos também ensaios de cisalhamento direto convencional, em corpos de prova indeformados e submersos. Tais ensaios foram executados com diferentes níveis de tensão. Determinaram-se as curvas de retenção de umidade através do método do papel filtro, para se obter a relação entre a sucção e o teor de umidade do solo. O programa experimental compreendeu também ensaios de caracterização geotécnica, análises químico- mineralógicas. A partir da análise dos resultados de ensaios de cisalhamento direto convencional e com sucção controlada foi possível estabelecer uma envoltória de resistência ao cisalhamento em três dimensões para o solo estudado, função das variáveis de tensão ((sigma)-ua) e (ua-uw). Também são apresentadas algumas considerações sobre a influência da sucção na compressibilidade do material. Por fim, fez-se uma comparação dos resultados obtidos para a resistência ao cisalhamento com estimativas indiretas através de formulações simplificadas que usam os parâmetros efetivos de resistência e a curva característica de sucção (i.e. Lytton, 1995; Vanapalli et al., 1996; Fredlund et al., 1996; Oberg e Sallfors, 1997), assim como com outros resultados encontrados na literatura técnica.
This work intends to evaluate the influence of suction in the shear strength of a young residual filite soil from Belo Horizonte city, of Minas Gerais, Brazil. The experimental program included conventional tests of geotechnical, chemical and mineralogical characterization. The relationship between suction and water content of soil was obtained by the filter paper method and represented graphically by soil-water characteristic curves (SWCC). In order to determine the shear strength of unsaturated soil, direct shear tests with controlled suction were executed with soil samples in their natural state. In addition, conventional shear strength tests were performed with undisturbed and submersed specimens. Both types of tests were performed with different values of stress. From the analysis of the tests´ results it was possible to establish a three- dimensional shear strength envelope in function of the stress state variables ((sigma)-ua) and (ua-uw). Moreover, some considerations about the influence of stress variables in compressibility of soil are discussed. Finally, a comparison of the results obtained for the soil´s shear strength was made with different prediction models using the SWCC and the effective strength parameters (i.e. Lytton, 1995; Vanapalli et al., 1996; Fredlund et al., 1996; Oberg e Sallfors, 1997). The results were also compared with other data found in the literature.
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Dawkins, Jeremy James. "Influence of crystallographic orientation in normal and sliding contacts." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24713.
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Abebe, Tarekegn. "The influence of selective logging on residual stand and regeneration in a rain forest in southwestern Ethiopia /." Umeå : Swedish University of Agricultural Sciences, 2003. http://diss-epsilon.slu.se/archive/00000213/.
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Thesis (doctoral)--Swedish University of Agricultural Sciences, 2003.Thesis documentation sheet inserted. Appendix includes five manuscripts submitted for publication elsewhere, four co-authored with others. Includes bibliographical references.
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Wu, Guiyi. "The influence of long-range residual stress on plastic collapse of pressurised pipes with and without flaws." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.681731.
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Structural integrity assessments of pressurised pipes include plastic collapse as a potential failure mode. This dissertation uses analytical and numerical models as well as experiments to explore the effect of displacement controlled loading conditions and fixed load conditions on the collapse pressure of pipes with and without flaws. Open- and closed-ended pipes are considered. The displacement controlled uniform stress and bending stress represent long-range or fit-up residual stress. Such long-range residual stress, resulting from misfit between components of an engineering structure, is associated with significant elastic follow-up and is commonly treated as primary stress which contributes to plastic collapse. However, this approach may be incorrect as residual stress can be relaxed. There is little evidence that explores the relationship between longrange residual stress and plastic collapse in a pressurised pipe. In this thesis the finite element method and experiments are developed to consider the effect of long-range residual stress on plastic collapse of pressurised pipes. Pipes in a number of states are considered: short and long pipes with no flaws, part and full circumferential flaws. The flaws consist of either a crack or a slot on the internal or external surface of the pipe. Both local and global collapse pressures are considered. It is found that global collapse of pressurised pipes containing longrange residual stress is not dependent solely on the level of initial stress but also on the length of the pipe, the flaw geometries and the collapse dominated stress. It is shown that the displacement controlled stress can act either as secondary stress or as primary stress. Finally, before considering the role of long-range residual stress in failure assessment diagrams, the level of elastic follow-up for full circumferentially flawed pipes is quantified and closed-form approximations of plastic collapse pressures are proposed to consider when a long-range residual stress is treated as either a secondary stress or a primary stress. The results from this work show that conservative assessments will be made of the collapse pressures of pipes containing flaws if a long-range residual stress is simply taken to be an equivalent form of mechanical loading.
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Suhr, Robert W. "The influence of surface defects and residual stress on the fatigue properties of 12%Cr and low alloy steels." Thesis, Coventry University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367123.
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Verma, Shwetabh [Verfasser], and Jürgen W. [Akademischer Betreuer] Hesser. "Determining the Influence of Environment and Minimizing Residual Roughness in Laser Corneal Refractive Surgery / Shwetabh Verma ; Betreuer: Jürgen W. Hesser." Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://d-nb.info/1209677458/34.
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Verma, Shwetabh [Verfasser], and Jürgen [Akademischer Betreuer] Hesser. "Determining the Influence of Environment and Minimizing Residual Roughness in Laser Corneal Refractive Surgery / Shwetabh Verma ; Betreuer: Jürgen W. Hesser." Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://nbn-resolving.de/urn:nbn:de:bsz:16-heidok-281492.
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Adjaye, John. "Influence of source/drain residual implant lattice damage traps on silicon carbide metal semiconductor field effect transistor drain I-V characteristics." Diss., Mississippi State : Mississippi State University, 2007. http://sun.library.msstate.edu/ETD-db/theses/available/etd-09242007-081525.
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Davis, Michael Patrick Kerley Monty Stephen. "Influence of diet, production traits, blood hormones and metabolites, and mitochondrial complex protein concentrations on residual feed intake in beef cattle." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/7034.
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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 26, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Monty Kerley. Vita. Includes bibliographical references.
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Nobre, Juvencio Santos. "Métodos de diagnóstico para modelos lineares mistos." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/45/45133/tde-22082007-181254/.
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Muitos fenômenos podem ser representados por meio de modelos estatísticos de forma satisfatória. Para validar tais modelos é necessário verificar se as suposições envolvidas estão satisfeitas e se o modelo é sensível a pequenas perturbações; este é o objetivo da análise de diagnóstico. Neste trabalho apresentamos, discutimos e propomos técnicas de diagnóstico em modelos lineares mistos e as ilustramos com um exemplo prático.Many phenomena can be represented through statistical models in a satisfactory way. To validate such models it is necessary to verify whether the assumptions are satisfied and whether the model is sensitive to small deviations; this constitutes the objective of diagnostic analysis. In this work we present, discuss and propose diagnostic techniques for mixed linear models and illustrate them with a practical example.
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SILVA, THAIANA ALVIM. "EVALUATION OF THE INFLUENCE OF MATRIC SUCTION AND DEGREE OF WEATHERING ON THE COEFFICIENT OF EARTH PRESSURE AT REST (K0) IN RESIDUAL SOIL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=31407@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A necessidade da determinação do comportamento tensão-deformação de solos sob carregamento para fins de projeto de Engenharia exige o conhecimento prévio do estado natural de tensões ao que o solo está imposto. Quando se trata de solos residuais tropicais, este desafio amplia-se ainda mais devido à ação do intemperismo e variação de umidade. O estado natural do solo é usualmente expresso pelo coeficiente de empuxo no repouso (K0). Para a determinação de K0 três classes de métodos são utilizadas: métodos de correlação, de determinação in situ e em laboratório. Neste estudo, é utilizada uma célula rígida com sistema de controle de sucção para a obtenção de K0 em laboratório. Foram analisadas três amostras de solo residual de Gnaisse com diferentes graus de intemperismo, provenientes de São Conrado, Rio de Janeiro, denominadas: solo residual jovem (SRJ); solo residual de transição (SRT); e solo residual maduro (SRM). Para a análise da influência da sucção no valor do coeficiente de empuxo, cada amostra de solo foi ensaiada sob três diferentes condições de umidade, que tentaram representar as seguintes condições: mais úmida, com sucção de 10 kPa; intermediária, com 40 kPa de sucção; e mais seca, com 100 kPa. Os valores de K0 obtidos nos ensaios variaram de 0,50 a 0,65. Os resultados seguiram, em parte, a tendência esperada. Entretanto, devido à heterogeneidade do material estudado, é necessário realizar repetições dos ensaios a fim de obter dados representativos.
The necessity to determine the stress-strain behavior of soils under loading for the purpose of engineering projects requires early knowledge of the natural state of stress that acting on the mass of soil. When it comes to tropical residual soils, this challenge is even greater due to weathering and moisture variation. The natural state of the soil is usually expressed by the coefficient of earth pressure at rest (K0). For the determination of K0 three classes of methods can be used: correlation meth-ods, in situ determination and laboratory tests. On this research, one rigid cell with system of suction control is used to obtain values of K0 in laboratory tests. Were analyzed three samples of Gneiss residual soil with different degrees of weathering. The samples were provenient to São Conrado, Rio de Janeiro and namely: young residual soil (SRJ), transition residual soil (SRT) and mature residual soil (SRM). To evaluate the influence of suction on the value of coefficient of earth pressure at rest, each sample of soil were tested into three different levels of moisture which correspond of following conditions: more humid, with suction of 10 kPa; interme-diate, with 40 kPa of suction; and more dry, with 100 kPa. The K0 values obtained in the tests ranged from 0,50 to 0,65. In general, the results attended the expected trend. However, due to the great heterogeneity of the studied material, it is neces-sary to perform repetitions of tests in order to obtain representative data.
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Mishurova, Tatiana [Verfasser], Guillermo Carlos [Akademischer Betreuer] Requena, Sandra [Akademischer Betreuer] Korte-Kerzel, and Giovanni [Akademischer Betreuer] Bruno. "Influence of residual stress and microstructure on mechanical performance of LPBF TI-6AL-4V / Tatiana Mishurova ; Guillermo Carlos Requena, Sandra Korte-Kerzel, Giovanni Bruno." Aachen : Universitätsbibliothek der RWTH Aachen, 2020. http://d-nb.info/1231542160/34.
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Nagel, Herbert, and Reinhold Hatzinger. "Diagnostics in some Discrete Choice Models." Department of Statistics and Mathematics, WU Vienna University of Economics and Business, 1990. http://epub.wu.ac.at/506/1/document.pdf.
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Discrete choice models form a class of models widely used in econometrics for modelling the individual choice from a finite set of alternatives. The most widely used model is the multinomial logit model, implicitly assuming independence of irrelevant alternatives. A generalization is the nested multinomial logit model, relaxing this strong assurnp tion. Viewing both models as nonlinear regression models a set of diagnostics is derived. This includes a hat matrix, measures of leverage, influence and residuals and an approximation to the parameters for case deletion. In an example for the multinomid logit model a good performance of these diagnostics is observed and the parameter approximation by the proposed formula is better than a one step Newton-Raphson procedure. In an example for the nested logit model a constructed outlier with high influence is revealed by the measures of leverage and residual, but the parameter approximation is insufficient. (author's abstract)Series: Forschungsberichte / Institut für Statistik
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Collins, Shane. "Residue composition influences nutrient release from crop residues." University of Western Australia. School of Earth and Geographical Sciences, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0171.
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[Truncated abstract] A greater adoption of stubble retention, minimum-till and no-till farming practices for the purposes of conserving soil, water and fertility requires a greater understanding of the complexity of physical and chemical interactions between the soil and crop residues. There is currently insufficient knowledge to allow reliable predictions of the effects of different residue types in different environments on soil fertility and crop growth, owing to the many residue characteristics and environmental interactions that have been shown to affect decomposition or nutrient release. The role of fibre and nutrient composition in nutrient release from crop residues, and implications for residue management techniques, were studied. Canola, lupin and field pea residues, obtained from farmland in Meckering and Northam, Western Australia, were separated into upper and basal stems, leaves, and siliques or pods. This was done to provide materials with a wide range of chemical and physical characteristics, and also allowed consideration of differential residue management of plant organs, such as comparing harvested canola siliques and retained canola stubble. Pre-treatment by chopping and/or humidification was applied to residues to provide some information about the processes of nutrient release. Residues were subjected to simulated rainfall to assess nutrient leaching from plant material, and placed on soil in pots in constant-temperature glasshouse conditions to assess decomposition. Amounts and rates of change of residue fibre and nutrients were determined throughout leaching and decomposition. Energy Dispersive X-ray (EDX) microanalysis was used to assess the location of diffusible ions in air-dried residues and the effects of humidification on nutrient positioning and release. ... However, the release of calcium and magnesium depended on the decomposition of the more recalcitrant components such as cellulose and lignin, as supported by microscopy results showing changes in nutrient distribution following humidification. The proportionality of amounts of calcium and magnesium leached and released during decomposition is likely to suggest a similarity of chemical form more than similarity of function or position of the two elements. Management of crop residues for maximising and optimising the timing of release of different nutrients will need to take into account the placement of different plant types and parts, particle sizes distribution and pre-treatment of material to efficiently manage short- and long-term soil fertility to sustain crops, particularly on degraded soils. Significant nutrient release of potassium, sulphur and magnesium from crop residues can be achieved from surface placement, with the release of potassium and sulphur managed by modifying residue particle size through appropriate harvesting, ploughing or sowing implement selection. High nutrient uptake crops and plant parts where they can be economically viable to grow or separated by the harvesting technique are particularly valuable as sources of nutrients and soil organic matter.
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Rawls, Michael M. "Assessing Research Productivity from an Institutional Effectiveness Perspective: How Universities Influence Faculty Research Productivity." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5471.
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Faculty research productivity studies typically focus on the scholarly performance of the individual researcher, although environmental and organizational conditions that are largely outside of the researcher’s control can significantly impact that performance. From an institutional effectiveness perspective, it is imperative for the higher education administrators and leaders who share the responsibility of managing and supporting their university’s research enterprise to understand how the institutional environment itself impacts the productivity of its research community. In this sequential mixed methods study, a quantitative framework was tested for assessing institutional effectiveness in research administration based on the assertion that this concept can be measured indirectly, at the departmental level, based on the calculation of a program’s residual scholarly output. This is the difference between the actual amount of scholarly output a program produces compared to the predicted amount of scholarly output that its resources suggest it is capable of producing. The assumption is that the institution’s effectiveness in supporting research is largely reflected by the extent to which a program over- or under-produces scholarship based on its level of resources. The residual scholarly output was calculated for each Ph.D.-granting biomedical engineering program in doctoral universities with a Carnegie classification of “highest research activity” for the period of 2014 through 2016. A sampling of those programs that achieved among the highest and lowest residual productivity levels then became the subject of a qualitative inquiry where researchers and administrators were interviewed with two goals in mind. The more ostensive goal was to reveal what factors, characteristics, resources, and conditions distinguish under- and over-producing programs for the purpose of informing best and worst practices in research administration. Equally important, the second goal was to determine if the quantitative framework was actually successful in distinguishing institutional effectiveness in supporting research. The study concludes that the quantitative framework proved to be a successful method for detecting institutional effectiveness in supporting research, and that the primary distinguishing characteristic between high and low-functioning environments was how well programs were able to reduce the general administrative burdens that researchers face, particularly in grant management and the operation of research laboratories.
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Katemi, Richard Jackson [Verfasser], Franz [Akademischer Betreuer] Hoffmann, Franz [Gutachter] Hoffmann, and Udo [Gutachter] Fritsching. "Influence of Carbonitriding Process on Phase Transformation during Case Hardening, Retained Austenite and Residual Stresses / Richard Jackson Katemi ; Gutachter: Franz Hoffmann, Udo Fritsching ; Betreuer: Franz Hoffmann." Bremen : Staats- und Universitätsbibliothek Bremen, 2019. http://d-nb.info/1199003603/34.
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Dufrenoy, Stephane. "Influence des transformations surfaciques induites par traitements thermomécaniques sur la tenue en fatigue du Ti-10V-2Fe-3Al." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCD064/document.
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Les alliages de titane sont largement utilisés dans le secteur de l’aéronautique. Cependant,ces alliages sont très sensibles aux gammes d’élaboration et de mises en forme. Cesdernières ont une grande influence sur l’intégrité de surface des produits finis, ce qui aun impact sur la durée de vie des pièces en service. Il est donc nécessaire de maîtriser lesprocédés afin de pouvoir définir la tenue en service des pièces.Dans ces travaux, les différentes intégrités de surface sont décrites en termes d’évolutionmicrostructurale, de contraintes résiduelles et de micro-géométrie. Des essais de fatigueen flexion 4 points sont réalisés pour tester les performances mécaniques de ces surfaces.Nous avons remarqué une bonne cohérence entre les modèles reliant l’intégrité de surfaceet la tenue en fatigue déterminée expérimentalement.De plus, étant donné que les alliages de titane ont des microstructures complexes etpeuvent être multiphasés, nous nous sommes aussi intéressés au caractère hétérogènede ces matériaux principalement dans l’analyse de contraintes résiduelles déterminées àl’aide de la diffraction des rayons X. Nous avons remarqué que ces hétérogénéités ontun impact sur la détermination des contraintes résiduelles. De fait une méthodologiede détermination de contraintes non standard a été mise en place et validée par dessimulations utilisant un modèle d’homogénéisation auto-cohérent.Ces modèles d’homogénéisation sont intéressants d’un point de vue de la déterminationdes contraintes résiduelles par diffraction des rayons X car ils permettent la prise encompte de l’aspect multiphasé des matériaux ainsi que leur caractère anisotropeTitanium alloys are widely used in aeronautics industries. However, these alloys are highlysensitive to the method for elaboration and transformation processes. These processesimpact on the surface integrity of products. Therefore, they have to be controlled inorder to predict life time of structures.In this work, the study of surface integrity is focused on the description of microstructalevolution, residual stresses and micro-geometry. Four points bending tests were performedin order to determined the fatigue limit of the different studied processes. We find outa good consistency between models used to determinate lifetime from surface integrityinvestigation and experimental results.Moreover, microstructures of titanium alloys are highly complex and they often are twophasedmaterials. Consequently, we studied the heterogeneous behaviour of such materialby X-ray diffraction investigation.We found out that these heterogeneities have an impacton residual stresses determination. Therefore, a non-standard methodology was definedand validate by simulation using a micro-mechanic model : a self-consistent model.Micro-mechanical models are interesting for the residual stresses determination using Xraydiffraction because they allow to take into account heterogeneous and anisotropicbehaviours through anisotropic elasticity and anisotropic texture
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Guinard, Caroline. "Influence des propriétés morphologiques et mécaniques des barrières thermiques sur la fissuration interfaciale induite par perçage laser impulsionnel." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM068/document.
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De nombreuses pièces aéronautiques telles que les chambres de combustion sont percées d'une multitudes de trous de refroidissement. Ce perçage, généralement effectué par un laser de puissance peut induire des endommagements dans la matière percée. Sur les systèmes barrières thermiques, une fissuration pouvant conduire à l'écaillage de la barrière thermique se produit à l'interface céramique/sous-couche lors du perçage laser. Cette thèse présente des éléments de compréhension des phénomènes de formation et de propagation de la fissure interfaciale. Pour cela, un protocole spécifique a été utilisé, consistant en la réalisation de perçage interrompus. De plus, afin de comprendre l'influence de la sous-couche et de l'interface sous-couche / céramique sur cette fissuration, une large gamme d'échantillons aux propriétés morphologiques et mécaniques bien distincts ont été sélectionnés. Pour cela, la sous-couche a été modifiée par la variation des paramètres de projection, du procédé de projection ainsi que par des post traitements sur la sous-couche. Le lien entre ces interfaces et les endommagements liés au perçage laser sont présentés au travers d'observations 2D et 3D, destructives et non destructives ainsi que par l'étude des modifications des contraintes résiduelles avant et après perçage laser pour différentes barrières thermiques. De manière a réduire encore la fissure interfaciale, plusieurs stratégies de perçage sont étudiées via la variation de la puissance laser entre les différentes impulsions laser nécessaires pour percer le matériau multicouches. Les résultats obtenus offrent des perspectives intéressantes pour améliorer la résistance à la fissuration des pièces aéronautiquesMany aircraft engines parts such as combustion chambers are drilled with numerous cooling holes. These holes, generally performed by a high power laser machine can induce damages in the part materials. On thermal barrier coatings systems, cracking can lead to spalling of the coating occurs at the ceramic / bond-coat layer interface during laser drilling. This thesis presents elements of understanding of the interfacial crack formation end propagation phenomena. In this purpose, a specific protocol was used, consisting of interrupted drilling process. Moreover, in order to understand the influence of the bond coat and the ceramic / bond coat interface on cracking, a wide range of samples with specific morphological and mechanical properties were selected. With this in mind, the bond coat was modified by varying spraying parameters, spraying process and also by post treatments on the bond coat. The link between these interfaces and the associated damages due to laser drilling are presented through 2D and 3D observations, destructive and non-destructive, as well as the study of residual stress modification before and after laser drilling for several thermal barrier coatings systems. For further reducing the interfacial crack, several drilling strategies are considered through the laser peak power variation between the different laser pulses needed to drill through the multi-layer material. The results offer interesting perspectives for improving crack resistance of aeronautical engines parts
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Traore, Yeli. "Influence de la plasticité dans la mesure des contraintes résiduelles par la méthode du contour." Thesis, Reims, 2014. http://www.theses.fr/2014REIMS027.
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La méthode du contour est une technique récente pour la mesure de contraintes résiduelles dans des structures mécaniques. Elle permet d'obtenir un champ de contraintes résiduelles en 2D. Dans la méthode du contour, l'échantillon est découpé en deux parties. Les contraintes résiduelles normales aux faces découpées se détendent, ce qui cause leur déformation. Le profil de déformation des faces coupées est mesuré, puis utilisé pour le calcul de contraintes résiduelles. La méthode du contour est basée sur le principe de superposition élastique. Sa théorie assume que la détente de contraintes résiduelles est entièrement élastique. Cependant, en pratique, la détente élastique de contraintes résiduelles peut être accompagnée d'une détente plastique, ce qui induit des erreurs dans les contraintes mesurées. Ce projet se concentre sur l'étude et le contrôle des erreurs de plasticité dans la méthode du contour. Les résultats de cette recherche fournissent d'importantes informations sur la façon dont les déformations plastiques affectent les résultats de la méthode du contour. Par ailleurs une nouvelle technique de coupe pour l'atténuation des erreurs de plasticité a été développée. Des outils de calcul et des instructions sont proposés pour l'estimation des erreurs de plasticité. Enfin des instructions pour la minimisation des erreurs de plasticité sont proposées et appliquées à la mesure de contraintes résiduelles dans un échantillonThe contour method has emerged as a promising technique for residual stress measurement in relatively large, thick and complex engineering components. The method involves making a cut in the sample of interest, measuring the subsequent relaxed deformation of the cut face and using this profile to back-calculate the original residual stress field by FE modelling. The method is based on the theory of elasticity in that the stress relaxation during test specimen cutting is assumed to be entirely elastic. However, when measuring residual stresses close to the material yield stress, plasticity can occur and affect the measurements.The main aim of this thesis was to develop methods of mitigating and estimating plasticity-induced errors in the contour method. The outcomes of this research provide a valuable insight into how accumulation of plasticity affects the performance of the contour method. A novel cutting strategy that aims at mitigating the plasticity-induced errors has been developed. Furthermore, procedures are developed to estimate the plasticity-induced errors. Finally guidelines are proposed and applied to a case study for mitigating the plasticity-induced errors in the contour method
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Andriuškaitė, Sandra. "Dirvožemio mulčiavimo liekamasis povekis raudonojo burokėlio (Beta vulgaris var. vulgaris) agrofitocenozei." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20120613_114652-48077.
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Magistrantūros studijų baigiamajame darbe pateikiami piktžolių dygimo dinamikos (trumpaamžių, daugiamečių ir vyraujančių rūšių piktžolių) ir burokėlių derlingumo duomenys tiriant įvairių organinių mulčių ir skirtingo storio sluoksnių liekamąjį poveikį.
Darbo objektas – raudonojo burokėlio (Beta vulgaris var. vulgaris) agrofitocenozė.
Darbo metodai: piktžolių daigų skaičiavimui kiekviename laukelyje buvo pažymėtos keturios pastovios aikštelės 0,2 x 0,5 m. Apskaita atlikta kas 10 dienų, nuo gegužės 20 d. iki rugsėjo 30 d. Kiekvienos rūšies piktžolių daigai suskaičiuoti ir išrauti. Piktžolių kiekis perskaičiuotas vnt. m-2. Pagal piktžolių biologinį grupavimą išskirtos trumpaamžės ir daugiametės piktžolės. Nustatytos vyraujančios piktžolių rūšys. Burokėlių derlingumas nustatytas svėrimo metodu. Gautas derlius iš laukelio perskaičiuotas į t ha-1 absoliučiai švarių burokėlių derlių.
Darbo rezultatai. Gausiausiai piktžolės dygo gegužės trečią – 765,6 vnt. m-2 ir birželio pirmą – 270,6 vnt. m-2 dekadas. Vėliau piktžolių dygimas mažėjo visų variantų laukeliuose. Anksčiau įterpti šiaudų, durpių ir žolės mulčiai nežymiai (4,7-6,7 proc.) skatino piktžolių dygimą per visą tyrimų laikotarpį. Nustatytas nevienodas mulčių liekamasis poveikis trumpaamžių piktžolių dygimui. Įterpti durpių ir žolės mulčiai skatino trumpaamžių piktžolių dygimą nuo 5,2 iki 12,6 proc. Paprastosios rietmenės 20 proc. gausiau rasta ankstesniais metais durpių mulčiu mulčiuotuose laukeliuose, smulkiažiedės galinsogos... [toliau žr. visą tekstą]Master degree final research paper provides weed germination dynamics (annual, perennial and predominant weeds sorts) and red beet productivity data when researching residual effect of various organic mulches and different thickness layers. Object of the work – red beet (Beta vulgaris var. vulgaris) crop. Method of the work – to compute weed sprouts each field was divided into four permanent sites 0.2 x 0.5 m. These were observed every 10 days from May 20 till August 30. Each weed species sprouts were counted and torn out. Number of weeds was translated into units. m-2. According to biological grouping of weeds annual and perennial were distinguished. Predominant weed species were established. Red beet productivity was determined by weighting. Received yield from the field was translated into t ha-1 totally useful red beet yield. The results of work. Most of the weeds germinated in the 3rd decade of May – 765.6 weeds number m-2 and 1st decade of June – 270.6 weeds number m-2. Later germination of the weeds decreased in the plots of all treatments. Straw, peat and grass mulches, previously incorporated, moderately (4.7 to 6.7 percent) stimulated weed germination during the entire study period. The different residual effect of mulches was determined for germination of annual weeds. The incorporated peat and grass mulches promoted germination of the annual weeds from 5.2 to 12.6 percent. Echinochloa crus - galli were found thicker by 20 percent in the plots that in previous... [to full text]
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Ben, Afia Souhail. "Influence d'un traitement mécanique de nanocristallisation superficielle (SMAT) sur l'oxydation à hautes températures de l'acier 316L." Thesis, Troyes, 2016. http://www.theses.fr/2016TROY0007/document.
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Ce travail a permis de mettre en évidence l’impact du procédé SMAT (Surface Mechanical Attrition Treatment) sur la résistance à l’oxydation des aciers de type AISI 316L. Cette étude a permis de comparer la composition et la morphologie des couches d’oxydes, la cinétique d'oxydation, les mécanismes de croissance et les contraintes résiduelles sur les surfaces des pièces traitées et oxydées à différentes températures. Ces observations ont montré l’existence d’un effet bénéfique du SMAT sur la résistance à l’oxydation de l’acier 316L pour des hautes températures. En effet, la cinétique d’oxydation des échantillons traités semble être reliée à une croissance préférentielle de chromine dès 700°C. Ceci nous a amenés à conclure que le procédé SMAT utilisé sur le 316L inverse la phase d’oxyde majoritaire, en inhibant la croissance de l’hématite et en favorisant celle de la chromine. Un scénario d’oxydation pour l’acier brut et Smaté a ainsi été proposé et le rôle de la densité des joints de grains introduits par le traitement a été explicité. Pendant ce travail, il a également été proposé un chaînage numérique complet qui prendrait en compte les paramètres du procédé et les propriétés mécaniques du matériau, afin de prévoir les caractéristiques de la nanostructure générée suite au traitement SMAT, en lien possible avec son influence sur l’oxydation à hautes températuresThis work aims at highlighting the impact of the SMA process (Surface Mechanical Attrition Treatment) on the oxidation resistance of steels of type AISI 316L. This study compares the composition and morphology of the oxide layers, the oxidation kinetics, the growth mechanisms and the residual stresses on the surface of treated and oxidized samples at different temperatures. These observations show a beneficial effect of the SMA process on the oxidation resistance of the 316L steel for high temperatures. Indeed, the oxidation kinetics of the treated samples is shown to be related to a preferential growth of chromia starting at 700°C. This led us to conclude that the SMAT used on the 316L reverses the main oxide phase, inhibiting the growth of the hematite and promoting the chromia. An oxidation scenario for untreated and SMATed steel samples is proposed, demonstrating the role of the density of the grain boundaries introduced by the mechanical treatment. During this work, a comprehensive numerical chaining process is proposed. It takes into account the process parameters and mechanical properties of the material, in order to predict the characteristics of the nanostructure generated by SMAT, that could influence the oxidation of this stainless steel at high temperatures
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Villanova, Julie. "Détermination des contraintes résiduelles dans les matériaux céramiques pour SOFC : mesures multi-échelles et influence des cycles d’oxydo-réduction." Thesis, Saint-Etienne, EMSE, 2010. http://www.theses.fr/2010EMSE0587/document.
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Les piles à combustible Solid Oxide Fuel Cell sont des systèmes de production d’électricité. Une cellule élémentaire est un multicouche constitué de matériaux céramiques et de métal. Elles sont très sensibles aux contraintes mécaniques générées lors des cycles thermiques et d’oxydo-réduction, limitant leur durée de vie.Ce travail a porté sur la détermination expérimentale des contraintes résiduelles dans des cellules SOFC à anode support en fonction des sollicitations du système. Parallèlement à des mesures in-situ en température, une approche multi-échelles a été développée pour évaluer les hétérogénéités de contraintes dans l’électrolyte liées à la forte anisotropie élastique de la zircone yttriée qui le constitue. Différentes techniques ont été mise en œuvre afin de couvrir les 3 ordres de contraintes. Les mesures à l’échelle macroscopique ont été effectuées par diffraction de rayons X de laboratoire (méthode des sin²(Ψ)). La microdiffraction de rayonnement synchrotron en mode faisceau blanc et monochromatique a permis, après un important travail d’amélioration du protocole de mesure et d’analyse, de déterminer les tenseurs complets de contraintes et déformations grain à grain dans l’électrolyte. Les déformations intra-granulaires ont été évaluées par une technique d’EBSD.Les résultats obtenus ont permis d’analyser les mécanismes principaux qui régissent les évolutions de contraintes dans l’électrolyte. Des hétérogénéités de contraintes entre grains liées à leurs orientations cristallographiques ont été mises en évidence. Au-delà du problème des SOFC, les techniques mises en œuvre ouvrent la voie aux validations expérimentales des modèles mécaniques poly-cristallinsThe Solid Oxide Fuel Cells (SOFC) are high-performance electrochemical devices for energy conversion. A single cell is composed of layers made of different ceramic materials and metal. The mechanical integrity of the cell is a major issue during its lifetime. Damage of the cells is mainly due to the high operating temperature, the “redox” behavior of the anode and the brittleness of the involved materials. In this work, residual stresses in the electrolyte of a planar anode-supported SOFC have been experimentally measured for different treatments of the cell. In situ analysis at various temperatures has been performed. A multi-scale approach has been developed to study the expected strain-stress heterogeneities in the electrolyte due to the strong elastic anisotropy of the involved material (yttria-stabilized zirconia). Different techniques have been used to determinate stresses at the 3 different orders. Macroscopic stresses were studied using the Sin2 method on a laboratory X-ray goniometer. The complete strain and stress tensors of individual grains in the electrolyte have been determinate, after various improvements in the technique, by combining the diffraction of white and monochromatic micro beams produced by synchrotron source. Strain variation into grains has been evaluated using EBSD.This study has identified the main phenomena that control the stresses variation in the electrolyte layer. Stresses heterogeneities from grain to grain have been found and linked to the crystallographic orientation. Beyond SOFC’s considerations, the techniques that have been developed should permit an experimental validation of mechanical modeling to polycrystalline materials
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Desvignes, Marc. "Influence du grenaillage de precontrainte sur la tenue en service de l'acier 35cd4." Paris, ENSAM, 1987. http://www.theses.fr/1987ENAM0011.
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La rupture des structures sollicitees mecaniquement s'initient souvent en surface dans les zones en traction. Afin d'augmenter la resistance et la fiabilite des pieces, il est necessaire de durcir la surface et de la mettre en compression par un traitement de grenaillage de precontrainte. Influence des contraintes residuelles de compression sur le comportement en fatigue. Analyse de l'evolution de ces contraintes. Determination de la limite d'elasticite de la couche grenaillee. Prevision des courbes de woehler des pieces grenaillees
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Sarre, Benjamin. "Influence du soudage laser Nd˸YAG sur les propriétés métallurgiques et mécaniques de l'alliage de titane TA6V." Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0019.
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Le soudage est une opération consistant à assembler deux ou plusieurs pièces afin d’assurer la continuité d’une structure. Toutefois, l'opération de soudage n'est pas sans conséquence pour le matériau cible. En effet, l'état métallurgique et mécanique de ce dernier est profondément affecté. Cette étude vise à une meilleure compréhension de l'influence du procédé de soudage sur l'état métallurgique et mécanique de l'alliage de titane TA6V. L'état métallurgique de la liaison soudée a été caractérisé. Ces analyses ont mis en évidence un fort gradient de microstructure entre la zone fondue et le métal de base. Ces évolutions engendrent des contraintes résiduelles. Ces dernières ont été évaluées par le biais de la diffraction des rayons X. Une campagne d'essais a été réalisée à l'ESRF (ligne BM02). Les champs de contraintes ont été comparés aux prédictions d'un modèle de comportement mécanique. Les évolutions de microstructure sont également la source d'un gradient de propriétés mécaniques. Le comportement mécanique des liaisons soudées a été étudié. La zone fondue présente des caractéristiques mécaniques supérieures à celles du métal de base. La rupture intervient au sein de ce dernier, malgré la présence de défauts dans la zone fondue. Les résultats ont été comparés au modèle de Gurson-Tvergaard-Needleman. Le modèle permet de restituer de façon très satisfaisante le comportement mécanique des liaisons soudéesWelding operation consists of assembling two or more pieces to ensure the continuity of a structure. The resulting assembly may withstand mechanical loads. However, the welding operation modifies the state of materials. In other words, the metallurgical and mechanical behaviour of the latter is deeply affected. This work aims to better understand the influence of welding on the metallurgical and mechanical behavior of the Ti-6Al-4V titanium alloy. Comprehensive metallurgical analyses of the welded joint are carried out and reveal a sharp and strong microstructure gradient between the fusion zone and the base metal. Several residual stress fields are quantified by X-ray diffraction analyzes. Those residual stress fields are then compared with finite element simulations of the welding of a Ti-6Al-4V titanium alloy. The simulation are based on a weakly coupled model that accounts for temperature, stresses and phase transformations. The failure behaviour of the welded joint is studied. An overmatch was highlighted with mechanical tests. The fracture finally occurs in the base metal despite the presence of defects in the fusion zone. A Gurson-Tvergaard-Needleman approach is carried on. The mechanical parameters are quantified from mechanical tests on homogeneous samples of base metal and of a representative microstructure of the welded joint, which has been obtained from heat treatments. The model are in good agreement with mechanical tests
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Le, Marion. "Influence des liserés de carbures induits par la nitruration gazeuse sur les mécanismes de fissuration de fatigue de contacts roulants." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0102/document.
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La nitruration gazeuse est utilisée par les fabricants d’engrenages pour traiter la surface des dentures. En effet, l’augmentation de la dureté et l’introduction de contraintes résiduelles de compression contribuent à retarder voire inhiber l’initiation et la propagation des fissures superficielles de fatigue de contact. Cependant la majorité des aciers alliés présentent des réseaux de précipités de carbures dans la couche nitrurée. Ceux-ci ont la particularité de se retrouver aux joints de grains relativement parallèles à la surface, ce qui leurs ont attribué les surnoms de «liserés de carbures». Associés à une phase dure et fragile, ces carbures constituent des zones d’hétérogénéités. Par ailleurs, la norme pour la qualité des matériaux d’engrenages autorise une large gamme de tailles de grains, conduisant à diverses microstructures pour les couches nitrurées des aciers alliés. En effet, la morphologie des réseaux de carbures après nitruration dépend entre autres de la taille de grain de l’acier. De par le manque de travaux sur l’impact réel de ces précipités sur la fatigue de contact, la présente étude propose des analyses d’essais. Les essais consistent à reproduire de l’écaillage initié en surface sur des éprouvettes dont les couches nitrurées, issues d’un seul traitement thermochimique, présentent les mêmes propriétés mécaniques (dureté et contraintes résiduelles) mais différentes propriétés microstructurales (tailles de grains et morphologies de carbures). Les analyses ont permis de proposer des mécanismes d’initiation de micro-fissures induites en proche surface sous les conditions d’essai appliquées. Les sites d’initiation dépendent de la taille de grain de l’acier et peuvent en particulier s’établir au niveau des carbures intergranulaires. L’étude des réseaux de fissures couplée à l’analyse des contraintes résiduelles a permis d’établir des scénarii de propagation des fissures dans les couches nitrurées. Sous les conditions de contact appliquées, l’apparition de déformation plastique entraîne, par accommodation des variations de volume, la relaxation des contraintes résiduelles compressives initialement présentes dans le matériau, aux profondeurs les moins sollicitées. Ces contraintes étant moins compressives, elles libèrent les micro-fissures déjà présentes en proche surface. Dès lors, la propagation au travers des carbures qui s’apparentent à des sites privilégiés pour la croissance des fissures en cours de fatigue est possible. En particulier, ces précipités entraînent les fissures vers le cœur lorsqu’ils sont en forte densité dans les couches nitrurées, tandis que l’endommagement reste superficiel lorsque l’éloignement entre les précipités est trop important. Enfin, la continuité et la longueur des carbures augmentent localement la vitesse de propagation des fissures. Ceci se traduit par l’apparition plus rapide de l’écaillage initié en surface pour les couches nitrurées de microstructures grossièresGas nitriding is a thermochemical surface treatment widely used by gear manufacturers to improve the rolling contact fatigue endurance of their components. Indeed, increasing the hardness and introducing compressive residual stresses to the geartooth surfaces inhibit or delay crack initiation and propagation. However, most of the alloyed steel nitrided layers show the presence of intergranular carbide networks. The precipitation of these carbides specifically occurs at parallel grain boundaries during the treatment and, being a carbon-rich phase, they are associated to tough and fragile heterogeneities. Besides, standards for gear material quality recommend a broad range of steel grain sizes which lead to various possible microstructures on gear components after nitriding. Indeed, the intergranular carbide network morphology depends on the steel grain size. Since there is no evidence regarding the real effect of the carbides on rolling contact fatigue, this work presents experimental investigations carried out on a twin-disc machine. The tests consist in reproducing surface-initiated pitting on specimens whose nitrided layers, obtained by a unique thermochemical surface treatment, display similar mechanical properties (hardness and compressive residual stresses) but different microstructures (grain sizes and carbide network morphologies). The first analysis resulted in suggesting the micro-crack nucleation mechanisms. In this study, the test conditions were chosen to induce these micro-cracks near the disc surfaces. For a given contact stress field, nucleation sites depend on the steel grain size and can take place at intergranular carbides. Investigations of crack networks led on cross sections and 3D observations by means of high energy X-ray computed tomography, coupled with compressive residual stress evolution analysis, help the authors proposing the rolling contact fatigue crack propagation scenarios in nitrided layers. When contact shear stresses locally exceed the material micro-yield shear stress limit, micro-deformations arise and add compressive residual stresses to the treated layers. To accommodate these volume variations the compressive residual stresses, initially induced by nitriding, release at depths where contact stresses are lower. The pre-existing residual stresses being less compressive, micro-cracks near the surface can propagate through the carbides that act as preferential crack growth sites. When the nitrided layers display high carbide density, the intergranular precipitates drag the cracks toward the core, whereas rolling contact fatigue failures are limited to the near surface when the distance between the precipitates is too important. Finally, the length and the continuity of the carbides, linked to the steel grain size, locally increase the crack propagation speed. This gives rise to a lower endurance to surface-initiated pitting in coarse microstructures
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LIMA, NELSON B. de. "Influencia da textura em medidas de tensao residual." reponame:Repositório Institucional do IPEN, 1991. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10293.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Lobos, Cristian Marcelo Villegas. "Modelos log-Birnbaum-Saunders mistos." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/45/45133/tde-05112010-114755/.
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O objetivo principal deste trabalho é introduzir os modelos log-Birnbaum-Saunders mistos (log-BS mistos) e estender os resultados para os modelos log-Birnbaum-Saunders t-Student mistos (log-BS-t mistos). Os modelos log-BS são bastante conhecidos desde o trabalho de Rieck e Nedelman (1991) e particularmente receberam uma grande atenção nos últimos 10 anos com vários trabalhos publicados em periódicos internacionais. Contudo, o enfoque desses trabalhos tem sido em modelos log-BS ou log-BS generalizados com efeitos fixos, não havendo muita atenção para modelos com efeitos aleatórios. Inicialmente, apresentamos no trabalho uma revisão das distribuições Birnbaum-Saunders e Birnbaum-Saunders generalizada (BSG) e em seguida discutimos os modelos log-BS e log-BS-t com efeitos fixos, para os quais revisamos alguns resultados de estimação e diagnóstico. Os modelos log-BS mistos são então apresentados precedidos de uma revisão dos métodos de quadratura de Gauss Hermite (QGH). Embora a estimação dos parâmetros nos modelos log-BS mistos seja efetuada através do procedimento Proc NLMIXED do SAS (Littell et al, 1996), aplicamos o método de quadratura não adaptativa a fim de obtermos aproximações para o logaritmo da função de verossimilhança do modelo log-BS de intercepto aleatório. Com essas aproximações derivamos as funções escore e a matriz hessiana, além das curvaturas normais de influência local (Cook, 1986) para alguns esquemas de perturbação usuais. Os mesmos procedimentos são aplicados para os modelos log-BS-t de intercepto aleatório. Discussões sobre a predição dos efeitos aleatórios, teste para o componente de variância dos modelos com intercepto aleatório e análises de resíduos são também apresentados. Finalmente, comparamos os ajustes de modelos log-BS e log-BS mistos a um conjunto de dados reais. Métodos de diagnóstico são utilizados na comparação dos modelos ajustados.The aim of this work is to introduce the log-Birnbaum-Saunders mixed models (log-BS mixed models) and to extend the results to log-Birnbaum-Saunders Student-t mixed models (log-BS-t mixed models). The log-BS models are well-known since the work by Rieck and Nedelman (1991) and particularly have received great attention in the last 10 years with various published papers in international journals. However, the emphasis given in such works has been in fixed-effects models with few attention given to random-effects models. Firstly, we present in this work a review on Birnbaum-Saunders and generalized Birnbaum-Saunders distributions and so we discuss log-BS and log-BS-t fixed-effects models for which some results on estimation and diagnostic are presented. Then, we introduce the log-BS mixed models preceded by a review on Gauss-Hermite quadrature. Although the parameter estimation of the marginal log-BS and log-BS-t mixed models are performed in the procedure NLMIXED of SAS (Littell et al., 1996), we apply the quadrature methods in order to obtain approximations for the likelihood function of the log-BS and log-BS-t random intercept models. These approximations are used to derive the respective score functions, observed information matrices as well as the normal curvature of local influence (Cook, 1986) under some usual perturbation schemes. Discussions on the prediction of the random effects, variance component tests and residual analysis are also given. Finally, we compare the fits of log-BS and log-BS-t mixed models to a real data set. Diagnostic methods are used in the comparisons.
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Plunkett, Richard. "Assessment of residual composite properties as influenced by thermal mechanical aging." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-11072008-063142/.
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Santana, Tiago Viana Flor de. "Modelo linear beta Weibull generalizado: propriedades, estimação, diagnóstico e aplicações." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/11/11134/tde-29112016-150708/.
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Neste trabalho dois novos modelos estatísticos de regressão são propostos, com estrutura muito semelhante aos Modelos Lineares Generalizados (MLG) porém, admitindo as distribuições Weibull exponenciada (WE) e beta Weibull (BW) para o componente aleatório as quais não pertencem a família exponencial como é requerido em MLG. Os novos modelos trazem uma nova abordagem para as distribuições admitidas em modelos de regressão e estende o MLG para além da família exponencial. Os modelos, nomeados por Modelo Linear Weibull Exponeciada Generalizado (MLWEG) e Modelo Linear Beta Weibull Generalizado (MLBWG), possuem como caso particular o modelo Exponencial, pertencente a família de MLG, além de outros modelos que os MLGs não contemplam como, por exemplo: Weibull, WE, Exponencial Exponenciado (EE) entre outros. Além da função taxa de falha (ftf) constante da distribuição Exponencial, os novos modelos ajustam também formas monótonas e não monótonas da ftf. Quando se admite função de ligação logarítmica obtém-se o mesmo modelo de locação e escala, muito utilizado em análise de sobrevivência, sem a necessidade de transformação da variável resposta simplificando a modelagem e permitindo maior compreensão da influência das covariáveis na resposta. Método de estudo de observações influentes foi construído baseado na metodologia de influência local sobre três esquemas de perturbações: perturbação da verossimilhança, da variável resposta e das covariáveis e a análise de resíduo foi proposta a partir da função quantílica. Por fim, dois conjuntos de dados reais foram utilizados para ilustrar a aplicabilidade dos modelos propostos e seus resultados discutidos.In this work two new statistical regression models are proposed, with very similar structure to Generalized Linear Models (GLM) but, assuming the exponentiated Weibull (EW) and beta Weibull (BW) distributions for the random component which do not belong to the exponential family as required in GLM. The new models bring a new approach to the distribution accepted in regression models and extend the GLM beyond of the exponential family. The models, named by Generalized Exponentiated Weibull Linear Model (GEWLM) and Generalized Beta Weibull Linear Model (GBWLM) have as a particular case the Exponential model, belonging to the family of GLM, and other models that GLMs do not include, for example : Weibull, EW, Exponentiated Exponential (EE) among others. Besides the failure rate function (frf) constant of Exponential distribution, the new models also model monotonous and not monotonous forms of frf. When it accepts logarithmic link function obtains the same location and scale model, widely used in the analysis of survival without the need to transform the response variable simplifying the modeling and allowing greater understanding of the inuence of covariates on the response. Study of inuential observations method was built based on the methodology of the local inuence on three perturbations schemes: perturbation of the likelihood of the response variable and the covariates and residual analysis was proposed from the quantile function. Finally, two sets of real data are used to illustrate the applicability of the models proposed and results discussed.
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Blomgren, Axel. "Influence of logging residues on MeHg accumulation in soil." Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-234263.
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Forestry has been found to increase the accumulation of methyl mercury (MeHg), a highly neurotoxic compound, in forest soils. However, little is known about how forestry influences catchment processes that governs the mercury (Hg) methylation process. Logging residues are used in harvested catchments in stick roads to reduce soil disturbances caused by forestry machinery. Logging residues left on site after harvest have been suggested to act as a source of high-quality organic matter that stimulates the activity of the microorganisms that carry out the methylation of Hg. In addition, logging residues might influence the activity and abundance of methylating bacteria by reducing the temperature fluctuations in soils below residues and by increasing the soil moisture content. To evaluate the impact of logging residues on the accumulation of MeHg, an experimental field study was carried out in three sites, one in Uppland and two in Västerbotten. The concentration of MeHg was compared between soils covered with residues and soils without residues, and between the lower and upper parts residue piles. Logging residues were not found to influence the levels of MeHg in soils. However, an increased accumulation of MeHg was found in the lower part of residue piles. The accumulation of MeHg in the lower parts was accompanied by a reduced temperature amplitude and an increased water content compared to the upper part of the piles. The increased formation of MeHg might have been mediated by an increased water content in the lower part of the residue piles, possibly by increasing the abundance and activity of Hgmethylating microorganisms due to suboxic/anoxic conditions within biofilms around decomposing needles. The dissolved organic matter composition in soil water differed in soils below residues compared to without residues, but the organic matter signature in soil water under residues was not found to be compliant with an elevated mercury methylation rate. As MeHg accumulated in the lower part of residue piles could become mobilized and transferred to surface water, the suitability of using logging residues in stick roads depends on the location within the catchment. The removal of logging residues could prevent the potential mobilization of MeHg from residue piles. Though, as soil disturbances may cause an increased Hg methylation rate and mediate MeHg export to surface waters, other form of protection, e.g. logging mats, should be used if logging residues are not used to protect soils.Mänsklig aktivitet har lett till förhöjda halter av kvicksilver (Hg) i atmosfären. Genom långväga transport och deposition har detta orsakat förhöjda halter i svensk natur. Den huvudsakliga exponeringsvägen av Hg för människan sker genom konsumtion av fisk. Halterna av Hg i svensk insjöfisk överstiger EU:s gränsvärden för god kemisk status samt Världshälsoorganisationens riktlinjer för konsumtion i majoriteten av svenska vatten. Ackumuleringen av Hg i biota sker främst i form av metylkvicksilver (MeHg) som är starkt neurotoxiskt. Avverkning av skog tros bidra till en ökad bildning av MeHg i skogsmark genom att skapa miljöer som gynnar etableringen och aktiviteten av de mikroorganismer som omvandlar icke-organiskt kvicksilver (Hg(II)) till organiskt kvicksilver (MeHg). Dessutom kan skogsbruk bidra till en ökad export av MeHg till följd av ändrade hydrologiska förhållanden samt markskador. En ökad bildning av MeHg är oönskad då mobilisering sedermera kan ske till vattendrag där MeHg kan ackumuleras i akvatisk biota. Dock är kunskapen om hur skogsbruk påverkar specifika processer som är av betydelse för metyleringen av Hg begränsad. Inom skogsbruk används avverkningsrester, bestående av till exempel grenar och toppar, i rishögar för att skydda marken mot körskador. Avverkningsrester som lämnas kvar på området efter avverkning tros bidra till en ökad metylering genom att utgöra en källa av högkvalitativt organiskt material vilket kan stimulera bakteriell aktivitet. Dessutom kan avverkningsrester bidra till en ökad metylering av Hg genom att minska temperaturfluktuationerna i mark täckt med ris samt öka markens vattenhalt, vilket kan bidra till en ökad etablering samt att stimulera aktiviteten av Hg-metylerande mikroorganismer. För att utvärdera effekten av avverkningsrester på ackumuleringen av MeHg genomfördes en experimentell fältstudie där koncentrationen av MeHg jämfördes i mark täckt med ris och mark utan ris. Dessutom undersöktes huruvida en ökad metylering kan ske i den nedre delen av riset, vilket skulle kunna möjliggöras av bakterier i biofilmer kring ris under nedbrytning. Koncentrationen MeHg var högre i den nedre delen av rishögarna jämfört med den övre delen. I den nedre delen av riset var temperaturfluktuationerna lägre och vattenhalten högre än i den övre delen av riset. Ackumuleringen av MeHg kan ha skett via biofilmer i de nedre delarna av riset, där tillgången till hög kvalitativt organiskt material samt mer syrefria förhållanden kan ha gynnat etableringen och aktiviteten av de bakterier som utför metyleringen av Hg. Däremot hade typen av marktäcke, dvs mark täckt med ris och mark utan ris, inte någon påverkan på metyleringen av Hg. Karaktären av organiskt material i markvatten skiljde sig mellan typ av marktäcke, men visar inte på att avverkningsrester utgör en källa av högkvalitativt organiskt material. Vattenhalten i mark under rishögar skiljde sig inte jämfört med mark utan ris, men temperaturen var lägre med mindre variation i mark under rishögar. Därmed visar resultatet på att avverkningsrester kan bidra till en ökad bildning av MeHg. En potentiell mobilisering av MeHg som bildats i rishögarna skulle därför kunna bidra till en ökad export av MeHg från avverkade områden. Användningen av avverkningsrester, för att skydda marken vid körning med skogsmaskiner, anses ändå vara fördelaktig för att minimera utläckage av MeHg. Körskador kan skapa stående vattensamlingar där MeHg kan bildas samt kompaktera mark och skapa snabba ytliga flödesvägar i området. Däremot tyder resultatet på att användningen bör ske med hänsyn till att förhindra eventuell transport av MeHg till vattendrag. Ifall avverkningsrester inte används för att motverka markskador bör ett substitut användas, exempelvis stock-mattor, då körskador kan bidra till en ökad metylering och mobilisering av MeHg. Dock saknas kunskap om eventuell mobilisering av MeHg från rishögar till vattendrag och detta bör utvärderas i framtida studier.
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