Dissertations / Theses on the topic 'Steep site'
To see the other types of publications on this topic, follow the link: Steep site.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Steep site.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Ameen, Noor, and Hassan Safawizadeh. "Visualizing Material on Site for Machines and Humans: A Step toward an Autonomous Construction Site." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-14937.
Full textAbstract:
The construction industry has not seen the same growth in productivity as e.g. the manufacturing- and automobile industry. This is largely due to the ease of implementing automation and robotics in the latter mentioned industries. Now more than before when the urbanization rate is increasing, there is a strong need in increasing the efficiency of the construction industry. That is why the research questions of this thesis work involves finding a complementary solution that will help autonomous construction machines operate in a dynamic construction site. The aim is permeated by two visions. The first one being to have autonomous construction machines collaborating with humans in the most remote places in the world. The second vision is that multiple smaller construction machines is more beneficial. Meaning a few machine breakdowns would not halt the entire construction process. During the research work, using the design research methodology and the innovation process, data showed that a construction site is very dynamic and complex. Having a change in factors such as size of construction site, number of involved stakeholders, location of the construction site, and time phase heavily affects the complexity of the site. Throughout the three case studies there were different characteristics, but there was a pattern. All the mentioned factors played a huge role in what needs expressed by the interviewees. The more complex a site was, the more there was a need to organize the material, personnel and machine flow. Therefore, the final solution is to decentralize the information flow of the construction site. Meaning that all humans, machines and material on site is to communicate its information. The suggested solution is the usage of a tag using GPS and Wi-Fi to communicate location and the necessary information. Thus, when attaching the tag onto a material, the workers and the machine will know of its information. The analogy is that when the implementation of autonomous machines is up to pace, the sites need to be prepared with all the errors and issues that might come with it. Since the autonomous construction machines will be collaborating with humans, it means that the issues expressed today will reappear in the future. Also, since the implementation of autonomy and robotics has been slow for the construction industry, there is a clear need of a complementary solution to speed up the process. By decentralizing the construction site and implementing tags on each interesting point, the once complex and changing construction site, will turn into a fully digitized infrastructure.ME310 2017 Volvo CE
2
Gonzalez, Hernandez Ana. "Site-level resource efficiency analysis." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/284771.
Full textAbstract:
To achieve agreed targets for reducing global carbon emissions, industry must become more resource-efficient. To this end, two viable strategies exist: energy efficiency and material efficiency. Despite their inherent interdependence, industry continues to treat these two strategies as isolated pursuits, providing in the process only a partial insight into the potential of resource efficiency. To resolve this disconnect, this thesis attempts to develop and apply tools that help integrate industrial energy and material efficiency analyses. Three areas of research are explored. The first is concerned with a fundamental component of industrial performance: efficiency benchmarks. No agreed-upon metric exists to measure the efficiency with which the sector trans- forms both energy and materials - that is, how resource-efficient they are. This thesis applies exergy - a well-established method to consolidate energy and materials into a single metric - to a case study of the global steel industry in 2010. Results show that this exergy-based metric provides a suitable proxy to capture the interactions between energy and materials. By comparing energy and material efficiency options on an equal footing, this metric encourages the recovery of material by-products - an intervention excluded from traditional energy efficiency metrics. To realise resource efficiency opportunities, individual industry firms must be able to identify them at actionable time-frames and scopes. Doing this hinges on understanding resources flows through entire systems, the most detailed knowledge of which resides in control data. No academic study was found to exploit control data to construct an integrated picture of resources that is representative of real operations. In the second research area, control data is extracted to track the resource flows and efficiency of a basic oxygen steel-making plant from TataSteel. This second case study highlights the plant's material efficiency options during operations. It does so by building close-to-real-time Sankey diagrams of resource flows (measured in units of exergy) for the entire plant and its constituent processes. Without the support of effective policies the new exergy approach is unlikely to be widely adopted in industry. By collating evidence from interviews and policy documents, the third area explores why the European Union's industrial energy and emissions policies do not incentivise material efficiency. Results suggest several contributing factors, including: the inadequacy of monitored indicators; an imposed policy lock-in; and the lack of a designated industry lobby and high-level political buy-in. Policy interventions are then proposed to help integrate material efficiency into energy and climate agendas. The European Union's limited agency stresses the need for Member States and industry to drive the move to a low-carbon industry in the short-term.
3
Rose, Nathan S. Loehr J. Erik. "Laboratory load tests of side shear for axially loaded piles." Diss., Columbia, Mo. : University of Missouri--Columbia, 2008. http://hdl.handle.net/10355/6286.
Full textAbstract:
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 19, 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. Dr. J. Erik Loehr, Thesis Supervisor. Includes bibliographical references.
4
Baier, Melissa A. Wescott Daniel J. "A biological distance study of Steed-Kisker origins." Diss., Columbia, Mo. : University of Missouri-Columbia, 2009. http://hdl.handle.net/10355/6710.
Full textAbstract:
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. Title from PDF of title page (University of Missouri--Columbia, viewed on March 19, 2010). Thesis advisor: Dr. Daniel Wescott. Includes bibliographical references.
5
Guzda, Mark Richard. "Development of site-specific fatigue truck weights and truck volume." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.18 Mb., p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435844.
Full text
6
Lindh, Johan. "Common language effect size : A valuable step towards a more comprehensible presentation of statistical information?" Thesis, Stockholms universitet, Psykologiska institutionen, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-166438.
Full textAbstract:
To help address the knowledge gap between science and practice this study explores the possible positive benefits of using a more pedagogical effect size estimate when presenting statistical relationships. Traditional presentation has shown limitations with major downsides being that scientific findings are misinterpreted or misunderstood even by professionals. This study explores the possible effects of the non-traditional effect size estimate Common Language Effect Size (CLES) on different training outcomes for HR professionals. This study also explores the possible effect of cognitive system preference on training outcomes. Results show no overall effect of CLES on either training outcomes or cognitive system. A positive effect of CLES on training outcome is found at the subfactor level showing a significant effect. The results can be interpreted that non-traditional effect size estimates have a limited effect on training outcomes. This small but valuable piece to bridge the gap of knowledge is discussed.
7
Lopez, Paul. "In-Situ Structural Evaluation of a Steel-Concrete Composite Floor System." Scholarly Repository, 2007. http://scholarlyrepository.miami.edu/oa_theses/92.
Full textAbstract:
The application of steel joists to floor construction can be traced back more than 100 years to the use of a sheet steel joist in the State of New York Bank Building in 1855. Since that time various forms of joists have been developed and exploited. As a result, two general types of joists are now on the market: a) Solid web joists; b) Open web, or truss type, steel joists. In order to determine the strength, stiffness, and behavior of these structural sections under load, representative open web steel joists have been tested at the University of Miami, School of Nursing Building (building about to be demolished). Using two hydraulic jacks to apply the load at eight different locations along the strip, the assessment of the ultimate structural performance of the floor system to positive moments in correspondence of selected strips was possible. After analyzing the data collected from the sensors through the data acquisition system, it was concluded that the results obtained from the Finite Element model were consistent compared to the results obtained from the experimental approach, helping to understand better the behavior of this structural system. A recommendation for further study is enclosed.
8
Wu, Chun-Hsien. "Microstructure of Flash processed Steel Characterized by Electron Backscatter Diffraction." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/36377.
Full textAbstract:
Flash processing is a new heat treatment process being developed to produce steel with
relatively high strength and ductility. It involves rapidly heating steel sheet or strip to a
temperature in the austenite range and quenching; the entire thermal cycle takes place within
15 seconds. The resulting microstructure is fine and difficult to resolve using standard
metallographic techniques. In this investigation, electron backscatter diffraction was used to
measure the grain size, grain orientations, and phase fractions in AISI 8620 samples flash
processed to a series of different maximum temperatures. The combination of high strength
with moderate ductility obtained by flash processing arises from a refined martensitic
microstructure. The morphology of the microstructure depends upon the maximum
processing temperature; a lower maximum temperature appears to produce a finer prior
austenite grain size and an equiaxed martensite structure whereas a higher maximum
processing temperature yields a more conventional lath martensite morphology.Master of Science
9
Wright, Scott Jason. "In situ molecular analysis using two-step laser mass spectrometry." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/11612.
Full textAbstract:
The work described in this thesis is concerned with the development of laser desorption laser photoionisation mass spectrometry (L2MS) towards spatially resolved analysis of real complex molecular systems. A broad overview of the main elements of the technique is presented. In addition, the experimental procedures and equipment used to carry out this work are described in some detail. Photoionisation mass spectra recorded for a series of azo dyes and porphyrin pigments revealed a marked wavelength dependence in their ionisation and fragmentation channels. The relationship between this behaviour and the known photochemical and photophysical properties of these molecules is discussed. The photochemistry of these molecules has been exploited to aid the differentiation between isomeric species. The selectivity inherent in the L2MS technique has been exploited for in situ studies of a number of real systems. Polymer additives, such as antioxidants and ultraviolet stabilisers, have been successfully detected directly from their host polymer matrices without recourse to extraction, separation or pre-concentration. The technique has been shown to be surface specific, suggesting that the long-term goal of spatially resolved analysis to monitor, for example, additive aggregation and migration to the surface are feasible. In further in situ studies, polycyclic aromatic hydrocarbons, an important class of priority pollutants, adsorbed onto aerosol particulates have been detected. Electrochemically polymerised indoles, known to form conducting films, have also been identified directly from the electrode surface. Finally, current limitations of the L2MS technique are discussed. It is suggested that many of the problems identified are inextricably linked to the laser desorption process. It is shown that energy imparted to neutral molecules during the desorption event can lead to fragmentation. This has implications for both the ionisation of high mass molecules and for quantitative studies. Possible ways of circumventing these problems are discussed. The future outlook for the technique, both for fundamental studies, and as an analytical tool, is also discussed.
10
Mishani, Siamak. "Investigation of fatigue failure in composite versus steel coiled tube for application in mine site drilling." Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/59665.
Full textAbstract:
Composite coiled tubing could be an economic alternative to the use of steel for exploration drilling due to its potentially greater reliability and higher fatigue life. This PhD study investigated the fatigue life of steel versus composite tubes using both numerical modelling and laboratory scale tests. Results were validated by statistical analysis and confirmed that composite tubing has a higher fatigue life, and potentially opens up a new market place for composite drill pipe.
11
Jarrat, Robert. "Construction in in-situ cast flat slabs using steel fibre reinforced concrete." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/17861.
Full textAbstract:
Thesis (MScEng)--Stellenbosch University, 2011.ENGLISH ABSTRACT: Fibre reinforced concrete (FRC) transforms concrete from a characteristically brittle material to one with a post-crack tensile residual capacity. Its application in industry has varied over the past of which the tensile properties have generally been used in the form of crack mitigation. More recently, the introduction of steel fibres has broadened this scope to structural applications in which the resisting tensile stresses that develop within a steel FRC (SFRC) element can be rather significant. This thesis reviews the existing practices and design models associated with SFRC and the suitability of its implementation as the sole form of reinforcement in in-situ cast flat slab systems. As a material SFRC is dependent on a number of factors which include the fibre type and volume, fibre distributions, element size, as well as the support and applied load conditions. Thus, its performance can be considered rather variable in comparison to conventional concrete should the incorrect practices be implemented. In order to adequately define the material characteristics, it is necessary to use test procedures that accurately reflect on the intended structural application. As a result a number of test procedures have been developed. In addition to this, the post-crack material performance is associated with a non-linear behaviour. This attribute makes the design of structural SFRC elements rather difficult. In an attempt to simplify this, existing design models define stress-strain or stress-crack width relations in which assumptions are made regarding the cross-sectional stress distribution at specified load states. This thesis takes on two parts in defining the suitability of SFRC as the sole form of reinforcement in flat slab systems. The first is a theoretical investigation regarding the micro and macro scale material performance of SFRC, the practices that exist in defining the material properties and its application in structural systems (particularly suspended slab systems), and a breakdown of the existing design models applicable to strain softening deflection hardening SFRC materials. The second part is an experimental program in which the fresh state and hardened state material properties of specified SFRC mix designs defined through flow and beam testing respectively. These properties are then implemented in the design and construction of full scale flexural and punching shear test slabs in an attempt to verify the theory applied. The investigation reveals that the use of SFRC significantly improves the ductility of concrete systems in the post-crack state through fibre crack bridging. This ductility can result in deflection hardening of flat slab systems in which the redistribution of stresses increases the load carrying capacity once cracking has taken place. However, the performance of large scale test specimens is significantly influenced by the construction practices implemented in which the material variability increases as a result of non-uniform fibre distributions. The results indicate that the load prediction models applied have potential to adequately predict the ultimate failure loads of SFRC flat slab systems but however cannot account for possible non-uniform fibre distributions which could result in premature failure of the system.
AFRIKAANSE OPSOMMING: Vesel versterkte beton (VVB) verander beton van die kenmerkende uiters bros material na ‘n material met ‘n residuele post-kraak trekkapasiteit. Die toepassing daarvan in die bedryf het in die verlede gewissel en die trek eienskappe is oor die algemeen gebruik vir kraak vermindering. Meer onlangs het die bekenstelling van staal vesel hierdie omvang verbreed na die strukturele toepassings waar trekspannings wat ‘n VVB element kan weerstaan noemenswaardig kan wees. Hierdie tesis ondersoek bestaande praktyke en ontwerpmodelle met die oog op staalvesel versterkte beton (SVVB) en die geskiktheid van die implementering daarvan as die enigste vorm van bekisting in in-situ gegiete plat blad stelsels. As ‘n materiaal, is SVVB afhanklik van ‘n aantal faktore wat die tipe vesel en volume, vesel verspreiding, element grootte, sowel as die randvoorwaardes tipe aangewende las insluit. As gevolg hiervan, kan die gedrag van SVVB, wat korrek geïmplimenteer word, as redelik varieerbaar beskou word wanneer dit met konvensionele beton vergelyk word. Ten einde die materiaaleienskappe voldoende te definieer, is dit noodsaaklik dat prosedures wat die strukturele toepassing akuraat voorstel, getoets word en daarom is ‘n aantal toets prosedures ontwikkel. Verder het die post-kraak materiaalgedrag ‘n nie-lineêre verband wat struktuurontwerp met SVVB redelik moeilik maak. Om dit te vereenvoudig, definieer bestaande ontwerpmodelle spanning-vervorming of spanning-kraakwydte verhoudings waarin aannames gemaak word ten opsigte van die spanningsverdeling oor ‘n snit, gegewe sekere lastoestande. Hierdie studie bestaan uit twee dele wat die geskiktheid van SVVB as die enigste vorm van bikisting in plat blad stelsels definieer. Die eerste deel bestaan uit ‘n teoretiese ondersoek wat handel oor die mikro- en makro-skaal materiaalgedrag van SVVB, die praktyke wat bestaan om die materiaaleienskappe en toepassing in strukturele sisteme (spesifiek opgelegde blad stelsels) te definieer, en ‘n uiteensetting van die bestaande ontwerpmodelle wat van toepassing is vir defleksie as gevolg van vervormingsversagting wat SVVB material verhard. Die tweede deel bestaan uit ‘n eksperimentele program waarin die materiaaleienskappe van gespesifiseerde SVVB meng-ontwerpe in die vars toestand en in die verharde toestand gedefinieer word deur middel van vloei- en balktoetse onderskeidelik. Hierdie eienskappe word dan toegepas vir die ontwerp en konstruksie van volskaalse buig- en ponsskuif toetsblaaie ten einde die modelle en teorie wat toegepas is, te bevestig. Die ondersoek toon dat die gebruik van SVVB die duktiliteit van beton sisteme noemenswaardig verbeter in die post-kraak toestand deur kraak oorbrugging. Hierdie duktiliteit kan defleksie verharding van plat blad stelsels veroorsaak waarin die herverdeling van spannings, nadat kraking plaasgevind het, die lasdraende kapasiteit verhoog. Die gedrag van die grootskaalse toetsmonsters word egter noemenswaardig beïnvloed deur die konstruksiemetodes wat geïmplementeer word waarin die materialveranderlikheid toeneem as ‘n gevolg van nie-uniforme vesel verdelings. Die resultate dui daarop dat die modelle wat toegepas is om die laste te voorspel, die potensiaal het om die grens falingslas van SVVB plat blad stelsel voldoende te voorspel, maar neem nie moontlike nie-uniforme veselverdelings wat kan lei tot vroeë faling van die stelsel in ag nie.
12
Galles, Daniel Joseph. "Measurement and prediction of distortions during casting of a steel bar." Thesis, University of Iowa, 2013. https://ir.uiowa.edu/etd/4986.
Full textAbstract:
An elasto-visco-plastic deformation model predicts stresses and distortions in a low-carbon steel casting. Features of the model include rate and hardening effects, temperature-dependent properties, and pressure-dependent deformation in the mushy zone. A volume-averaging technique considers the multiple phases during solidification and is used to formulate the conservation equations, which (due to a weak link between temperatures and deformations) are decoupled and solved sequentially using commercial software. Temperature fields are calculated first using MAGMAsoft (MAGMAsoft, MAGMA GmbH, Kackerstrasse 11, 52072 Aachen, Germany) and then exported to a finite element software package, ABAQUS (Abaqus/Standard, Abaqus, Inc., Providence, RI, 2006), which predicts stresses and distortions. In order to simulate the conditions encountered in an industrial casting process, predicted temperatures and distortions are matched with experimental data from in situ casting trials. Preliminary simulations do not agree with the experimental distortions, which suggest that stress-strain data from mechanical tests (from which the mechanical properties were estimated) does not accurately characterize the material behavior of a casting during solidification and cooling. The adjustments needed to match measured and predicted distortions provide valuable insight to the effect a solidified microstructure has on its mechanical properties.
13
Persson, Erik. "Austenite grain growth in bearing steels : An investigation on steel grades 100Cr6 and 100 CRMnMoSi8-4-6." Thesis, KTH, Materialvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-140433.
Full textAbstract:
An investigation of austenite grain growth of two bearing steel grades; 100Cr6 and100CrMnMoSi8-4-6 is performed. Austenitization treatments were performed between 860°C and 1200 °C for 5 minutes to 5 hours and the grain size was determined for each sample.Grain boundary etching was carried out using a water based, picric-acid etchant. Generally,100CrMnMoSi8-4-6 was harder to etch than 100Cr6. Therefore, a precipitation heattreatment was performed in order to facilitate etching of prior austenite grain boundaries in100CrMnMoSi8-4-6. The precipitation treatment was found to be effective. However, theprecipitation heat treatment was not suitable for 100Cr6 as the grain size increased duringthe precipitation heat treatment.Light optical microscope equipped with a camera was utilized to take micrographs for grainsize evaluation. Jeffries' standard procedure according to ASTM E112-96 was used tomeasure the grain size. The results shows that the austenite grain size increases withtemperature and time as expected. The experimental data was fitted to a well-known graingrowth model. The model only worked for the temperatures investigated and could not bemade to fit different temperatures.Local grain size variation was studied and its influence on fatigue properties was evaluated.The result showed that variation in local grain size can significantly alter the fatigueproperties. The findings are only theoretical and have not been tested practically.Two different spheroidization heat treatments and one homogenization heat treatmentwere performed. Both spheroidization heat treatments investigated exhibited similar grainsize. The homogenization heat treatment reduced the local grain size variation.Homogenization treatment prior to the spheroidization treatments did not increase ordecrease the grain size. The long heating, holding and cooling times in the secondspheroidization heat treatment is probably the reason for the lack of grain refinementcompared to the first spheroidization heat treatment. The grains had time to grow to theinitial austenite grain size during each cycle.
14
Davut, Kemal. "Characterization Of Steel Microstructures By Magnetic Barekhausen Noise Technique." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12608103/index.pdf.
Full textAbstract:
This aim of this thesis is to examine the possibility of using Magnetic Barkhausen Noise (MBN) technique in characterizing the microstructures of quenched and tempered low alloy steels as well as annealed low carbon steels. To determine the average grain size by MBN, SAE 1010 steel consisting of dominantly ferrite was used. The specimens were slowly cooled in the furnace after austenitizing at different time and temperature variations. By metallographic examination the average ferrite grain size of specimens was determined. The magnetic parameters were measured by a commercial MBN system. With increasing ferrite grain size, the magnetic Barkhausen jumps caused by the microstructure were decreased due to the reduction in grain boundary density per unit volume. A clear relationship has been observed between average grain size and the magnetic Barkhausen noise signals. SAE 4140, 5140 and 1040 steels were used to characterize the microstructures of quenched and tempered specimens. After austenitizing and quenching identically, the specimens were tempered at various temperatures between 200oC and 600oC. Formation of the desired microstructures was ensured by metallographic examinations and hardness measurements. The results show that as tempering temperature increases the Barkhausen activity increases due to the enhancement of domain wall displacement with softening of the martensite. It has been shown that MBN is a powerful tool for evaluating the microstructures of martensitic and annealed steels.
15
Coupar, Matthew S. "The strength and ductility of the steel moment connection with reinforced side plates /." Available to subscribers only, 2005. http://proquest.umi.com/pqdweb?did=1079666011&sid=5&Fmt=2&clientId=1509&RQT=309&VName=PQD.
Full text
16
Schilling, Sibylle. "Liquid in situ analytical TEM : technique development and applications to austenitic stainless steel." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/liquid-in-situ-analytical-tem-technique-development-and-applications-to-austenitic-stainless-steel(fd490551-7d7a-4b2e-9b1f-917b5f8165b3).html.
Full textAbstract:
Environmentally-assisted cracking (EAC) phenomena affect the in-service behaviour of austenitic stainless steels in nuclear power plants. EAC includes such degradation phenomena as Stress Corrosion Cracking (SCC) and Corrosion Fatigue (CF). Factors affecting EAC include the material type, microstructure, environment, and stress. This is an important degradation issue for both current and Gen III+ light water reactors, particularly as nuclear power plant lifetimes are extended ( > 60 years). Thus, it is important to understand the behaviour of the alloys used in light water reactors, and phenomena such as SCC to avoid failures. Although there is no agreement on the mechanism(s) of SCC, the importance of localized electrochemical reactions at the material surface is widely recognised. Considerable research has been performed on SCC and CF crack growth, but the initiation phenomena are not fully understood. In this project, novel in situ analytical TEM techniques have been developed and applied to explore localised reactions in Type 304 austenitic stainless steel. In situ transmission electron microscopy has become an increasingly important and dynamic research area in materials science with the advent of unique microscope platforms and a range of specialized in situ specimen holders. In metals research, the ability to image and perform X-ray energy dispersive spectroscopy (XED) analyses of metals in liquids are particularly important for detailed study of the metal-environment interactions with specific microstructural features. To further facilitate such studies a special hybrid specimen preparation technique involving electropolishing and FIB extraction has been developed in this thesis to enable metal specimens to be examined in the liquid cell TEM specimen holder using both distilled H2O and H2SO4 solutions. Furthermore, a novel electrode configuration has been designed to permit the localized electrochemical measurement of electron-transparent specimens in the TEM. These novel approaches have been benchmarked by extensive ex situ experiments, including both conventional electrochemical measurements and microcell measurements. The results are discussed in terms of validation of in situ test data as well as the role of the electron beam in the experiments. In situ liquid cell TEM experiments have also explored the localized dissolution of MnS inclusions in H2O, and correlated the behaviour with ex situ experiments. Based on the research performed in this thesis, in situ liquid cell and in situ electrochemical cell experiments can be used to study nanoscale reactions pertaining to corrosion and localized dissolution leading to "precursor" events for subsequent EAC phenomena.
17
Aborass, Marwa A. EL-Mehde. "Effect of diamond-like carbon coating on implant drill wear during implant site preparation." University of the Western Cape, 2017. http://hdl.handle.net/11394/6306.
Full textAbstract:
Magister Chirurgiae DentiumDental implants are artificial fixtures that are surgically inserted into the jaws to replace missing teeth. The success of dental implant treatment is dependent on achieving successful osseointegration (Branemark et al. 2001). Drills used for implant site preparation are made of different materials such as stainless steel (SS), zirconia and ceramic. Most of them do not have sufficient cutting efficiency and wear resistance (Oliveira et al. 2012). Recently diamond-like carbon coating (DLC) has been added as a drill coating to increase the cutting efficiency, increase wear resistance and drill hardness (Batista Mends et al. 2014).
18
Ekström, Simon. "Musikaliskt lärande : Musikers syn på sitt musikaliska lärande." Thesis, Kungl. Musikhögskolan, Institutionen för musik, pedagogik och samhälle, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kmh:diva-1754.
Full textAbstract:
Syftet med detta arbete har varit att undersöka hur musiker inom den afroamerikanska musiktraditionen ser på sitt musikaliska lärande. Deltagarna har haft olika musikaliska bakgrunder så som låtskrivare, frilansmusiker och instrumentallärare. Undersökningen tar sin teoretiska utgångspunkt ur ett kulturpsykologsikt perspektiv där synen på lärande ses som en process som utvecklas mellan individer i en lokalt rådande kultur. Informanterna har i undersökning fått prova att spela lap steel och dobro i fyra olika stämningar som därefter avslutats med en intervju. Vid dessa tillfällen har deltagarna reflekterat och delat med sig av sina åsikter och erfarenheter som berör deras musikaliska lärande.Resultatet av undersökningen pressenteras i tre kategorier som jag i detta arbete kallar för, det speltekniska perspektivet, gehöret och det visuella lärandet samt det musikaliska uttrycket. Dessa tre kategorier återspeglar vilka parametrar informanterna intagit och redogjort för när de reflekterat över sitt musikaliska lärande. Undersökning visar i detta på en nyansrikedom som berör musikaliskt lärande där både likheter och olikheter bland de medverkande informanterna redovisas.
19
Rattakham, Krittin. "Mechanism of Cathodic Prevention of Carbon Steel in Concrete." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6630.
Full textAbstract:
In this work, I aim to clarify the mechanism that allows steel to attain higher chloride threshold as it is cathodically polarized. Specifically, I seek to provide empirical information on whether an intrinsic (predominantly interfacial effects of polarization) or an extrinsic (predominantly concentration changes due to polarization) mechanism may be dominant in the beneficial effect of polarization. I carried out this experiment with 12 identical concrete specimens, each with a cast-in steel plate, constantly exposed them to high-chloride environment. The specimens were divided into 4 triplicates and polarized at 4 different level from OCP, -200, -300 to -400 mVSCE
The specimens were closely monitored for signs of corrosion. When corrosion was detected in a specimen, it was demolished to gain access to steel-concrete interface. Measurements of pH using a novel procedure and chloride ion concentration were done on the interface using an adapted in-situ pH measurement and a Florida Department of Transportation procedure respectively. The pH and chloride ion concentrations obtained in this study favor to some extent a dominant intrinsic mechanism interpretation, while the evidence in support of a dominant extrinsic mechanism interpretation remains elusive.
20
Wang, Wenbo. "Failure Analysis of High Nickel Alloy Steel Seal Ring Used in Turbomachinery." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6635.
Full textAbstract:
The system of upper high nickel alloying steel seal ring and lower high nickel alloying steel seal ring, installed in the grooves of turbine, can extend out and fit with the wall of valve cage, resulting in forming a good seal under the pressure. In the project, the failure steel seal ring is considered. This situation had threatened the safety of the whole steam turbine system. The purpose of this study is to identify the failure cause of the steel seal ring used in nuclear steam turbines. New high nickel steel alloy seal ring was compared with the failed seal ring. The dimensions of macroscopic ring with clearly plastic deformation were measured using calipers. Surface morphology of ring was observed by optical microscopy through metallographic analysis. There is a lot of precipitation in the grain boundaries of used seal ring, along with smaller grain size than the new seal ring. To explore the composition of precipitation, scanning electron microscopy (SEM) with energy-dispersive spectrometer (EDS) were used. The results indicated that the concentration of titanium (Ti) and molybdenum (Mo) was higher in the precipitation of used seal ring. At the same time, the hardness and elastic modulus of used seal ring were reduced, measured by nanoindentation test. In-situ SEM tensile testing were used to record and analyze the generation of crack source and crack development under applied load. The reasons of the seal ring failure can be answered because of these experimental results at both macroscopic and microscopic scales.
The main reason of the seal ring failure is a combination of long-term stress and elevated temperature during turbine operation. Complex work environment caused recrystallization and recovery, resulting in grain refinement and secondary phase precipitation. Further embodiment, recrystallization and recovery caused the elastic modulus and hardness of used seal ring decrease. Moreover, a lot of secondary phase precipitates appeared at grain boundaries during use. The appearance of secondary phase precipitates become the weakest part of used seal ring. The applied load lead to seal ring failure from the formation of microvoids to microvoids aggregated becoming microcracks until to the appearance of cracks at macroscopic scale. These changes of microscopic structure ultimately reflected in critical plastic deformation of used seal ring.
21
Miyata, Edwin S. "An investigation of the monocable system for cable yarding of small, low-value trees on steep, difficult sites /." Thesis, Connect to this title online; UW restricted, 1991. http://hdl.handle.net/1773/7061.
Full text
22
Hansen, Kristoffer Werner. "Phase Transformation Study of X70 Steel by EBSD during In Situ Heating and Quenching." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18909.
Full textAbstract:
Arctic steels, like the API X70 steel explored in this master thesis, are developed to withstand very low temperatures, with a ductile/brittle transition temperature below −60◦C. However, during welding, brittle phases like martensite-austenite (M-A) islands may form in the heat affected zone (HAZ). In this master thesis in situ heat treatment and quenching experiments have been combined with electron backscatter diffraction (EBSD) inside a field emission scanning electron microscope in order to simulate a second weld cycle simulation. In conjunction with this a quenching device has been designed with respect to an existing hot stage.Inside the SEM, it was found difficult to recreate the characteristic microstructure of API X70 steel from a traditional second cycle thermal weld simulation. This was probably due to the slow heating rate and the excessive high temperature holding time. The developed quenching device was based on gas quenching and produced a steel sample cooling time from 600◦C to 400◦C, ∆t6/4, of approximately 6.5 seconds in every experiment. As a result of the gas quenching substantial amounts of oxide contamination, covered the sample surface following the experiments. This contamination layer produced artifacts, such as unreasonable amounts of austenite in the EBSD phase maps.Despite the quenching, islands of austenite (FCC) observed at elevated temperatures transformed into a low strain BCC structure. Some austenite islands showed a memory- effect during phase transformation, while others adapted the orientation of the surround- ing structure. No retained austenite was observed in the API X70 steel after the in situ gas quenching, probably due to insufficient cooling rates.
23
Ghahari, Seyed Majid. "In situ synchrotron x-ray characterisation and modelling of pitting corrosion of stainless steel." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3269/.
Full textAbstract:
Pit propagation in stainless steels under electrochemical control was investigated using in situ synchrotron X-ray microtomography, which was used to confirm that the lacy covers commonly found for pits in stainless steels grow through perforation of the metal surface by upward growth of rapidly dissolving lobes from the main pit. In situ synchrotron X-ray radiography has been used to observe the evolution of 2D pits growing at the edge of stainless steel foils under electrochemical control in chloride solutions. Pit growth shape, kinetics and stability under current and potential control at various bulk chloride concentrations have been studied. It was found that the pit depth tends to grow under diffusion control, whereas lateral development is influenced by solution conductivity. The impact of the perforated cover on the pit growth and stability was examined and its formation was found to be similar to the observations from 3D by X-ray microtomography. A method for extracting the key dissolution kinetic parameters from radiographs has been developed. The local anodic current density along the boundary of a pit was directly measured from the rate of advance of the pit into the metal. Then the local metal ion concentration and potential drop inside the pit cavity was back-calculated using transport equations and the requirement to maintain charge neutrality, establishing the relationship between local current density, interfacial potential and metal ion concentration in the solution. The predictive model for pit propagation in stainless steel developed by Laycock and co-workers was examined, its sensitivity to key growth parameters was evaluated, and a modified version of the model was developed based on the kinetic parameters extracted from the radiographic measurements.
24
van, Niekerk Cornelis Janse. "In-situ alloying of AISI 410L martensitic stainless steel with nitrogen during laser cladding." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61341.
Full textAbstract:
The feasibility of in-situ alloying of AISI 410L martensitic stainless steel with nitrogen during Nd-YAG laser cladding was investigated with the aim of achieving a nitrogen content of at least 0.08 wt% and fully martensitic microstructures in the final clad deposit. Two in-situ nitrogen alloying techniques were studied.
In the first set of experiments, the absorption of nitrogen from nitrogen-rich gas atmospheres was studied. Laser cladding with commercially available AISI 410L powder was performed using nitrogen-rich shielding and carrier gas. A marginal increase in deposit nitrogen content was observed, with the clad deposit displaying low hardness and mostly ferritic microstructures. Poor nitrogen absorption from nitrogen-containing atmospheres during Nd-YAG laser cladding is generally attributed to the short thermal cycle and to suppression of plasma formation above the weld pool.
In the remaining experiments, Si3N4 powder was investigated as an alternative source for nitrogen during cladding. The addition of Si3N4 to the AISI 410L powder feed resulted in clad microstructures consisted of columnar -ferrite grains with martensite on the grain boundaries, higher hardness and an increase in deposit nitrogen content (to a maximum of 0.064 wt% nitrogen). Higher nitrogen contents in the clad deposit, however, significantly increased the volume percentage porosity in the clad layer. This prompted an investigation into the feasibility of raising the nitrogen solubility of the alloy through additions of manganese and nickel to the powder feed.
Thermodynamic modelling revealed that the addition of manganese to AISI 410L powder increases the nitrogen solubility limit due to its negative interaction parameter with nitrogen. The addition of up to 3.5 wt% manganese to AISI 410L powder containing Si3N4 significantly increased the nitrogen solubility in the deposit. A martensitic microstructure with 0.12 wt% nitrogen and a peak hardness of 410 HV was achieved without any adverse increase in porosity in the clad layer. The clad nitrogen content easily exceeded the minimum requirement of 0.08 wt%.
High nickel concentrations in AISI 410L stainless steel expand the austenite phase field at the expense of -ferrite and alter the solidification mode from ferritic to austenitic-ferritic. The addition of up to 5.5 wt% nickel, or combinations of nickel and manganese, to the nitrogen-alloyed AISI 410L powder feed raised the deposit nitrogen content, but not to the same extent as those deposits alloyed with manganese only. Since more austenite is present on cooling in nickel-alloyed AISI 410L deposits, less nitrogen is rejected to the liquid phase on solidification, resulting in higher nitrogen contents and less porosity in the room temperature microstructures.
The amount of dilution during single-track laser cladding is mainly influenced by the specific energy per unit mass delivered by the laser beam. The clad height is strongly influenced by the powder deposition rate, whereas the bead width is influenced by the wettability of the deposits during laser cladding. During multi-track cladding, the observed percentage porosity is a function of the aspect ratio of the individual beads making up the clad layer, the deposition rate and the clad height. High deposition rates result in thicker layers, increasing the distance that N2 gas bubbles have to travel to escape to the atmosphere, while a high aspect ratio favours interbead porosity. The results suggest that in-situ nitrogen alloying during laser cladding should preferably be performed at low deposition rates to ensure higher clad nitrogen contents and hardness, lower clad heights, less dilution and less porosity.Dissertation (MEng)--University of Pretoria, 2016.
Materials Science and Metallurgical Engineering
MEng
Unrestricted
25
Collins, Sunniva Refsnes. "Forging effects on manganese sulfide inclusions as fatigue initiation sites in AISI 4140 steel." Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1057696631.
Full text
26
Zhu, Yong. "Retrofitting of reinforced concrete coupling beams by bolted side steel plates for strength and deformability." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36434048.
Full text
27
Zhu, Yong, and 朱勇. "Retrofitting of reinforced concrete coupling beams by bolted side steel plates for strength and deformability." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36434048.
Full text
28
Gopalan, Sowmya. "Estimating Columnar Grain Size in Steel-Weld Images using Image Processing Techniques." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1250621610.
Full text
29
Barke, Derek Woolrich 1975. "An in situ test for stress corrosion damage and tension in bolts." Monash University, Dept. of Mechanical Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/7686.
Full text
30
Dubois, André. "Essai de compression-translation : Contribution à l'identification des lois de comportement surfaciques et volumiques." Valenciennes, 1995. https://ged.uphf.fr/nuxeo/site/esupversions/b97e143c-6fb6-44cc-83c8-e34fc7845c1e.
Full textAbstract:
La caractérisation du comportement surfacique des pièces en acier revêtues est étudiée à l'aide du test de compression-translation. Au cours du test un indenteur vient en contact avec l'ébauche jusqu'à une pénétration donnée (phase de compression), puis crée une zone plastique localisée à la surface de contact en glissant le long de celle-ci (phase de translation). L'identification fiable des lois de frottement repose sur une reproduction fidèle des conditions de contact et de frottement ainsi que sur une connaissance précise du comportement volumique au voisinage de la zone de contact. Une première étude par la méthode des éléments finis du test est alors menée et conduit à la détermination optimale de la géométrie et de la pénétration de l'indenteur ; l'essai reproduit alors des pressions de contact et des déformations plastiques équivalentes représentatives des conditions de contact réelles. Une seconde étude est ensuite proposée confrontant résultats expérimentaux et numériques de la phase de compression. Une procédure itérative minimisant l'erreur commise entre ces différents résultats conduit à la détermination du comportement volumique au voisinage de la surface de l'ébauche. Enfin, une analyse mécanique associée a des modèles numériques de la phase de translation autorise l'identification des lois de frottement linéaires et non linéaires. Cette stratégie est appliquée à des ébauches cylindriques en acier 1522 recuit revêtues de phosphate de zinc et de produits non polluants à base de dépôts de sels minéraux
31
Boåsen, Magnus. "Modeling framework for ageing of low alloy steel." Licentiate thesis, KTH, Hållfasthetslära (Inst.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-246036.
Full textAbstract:
Ageing of low alloy steel in nuclear applications commonly takes the form as a hardening and an embrittlement of the material. This is due to the evolution of the microstructure during irradiation and at purely thermal conditions, as a combination or separate. Irradiation introduces evenly distributed solute clusters, while thermal ageing has been shown to yield a more inhomogeneous distribution. These clusters affect the dislocation motion within the material and results in a hardening and in more severe cases of ageing, also a decreased work hardening slope due to plastic strain localization into bands/channels. Embrittlement corresponds to decreased fracture toughness due to microstructural changes resulting from ageing. The thesis presents a possible framework for modeling of ageing effects in low alloy steels.In Paper I, a strain gradient plasticity framework is applied in order to capture length scale effects. The constitutive length scale is assumed to be related to the dislocation mean free path and the changes this undergoes during plastic deformation. Several evolution laws for the length scale were developed and implemented in a FEM-code considering 2D plane strain. This was used to solve a test problem of pure bending in order to investigate the effects of the length scale evolution. As all length scale evolution laws considered in this study results in a decreasing length scale; this leads to a loss of non-locality which causes an overall softening at cases where the strain gradient is dominating the solution. The results are in tentative agreement with phenomena of strain localization that is occurring in highly irradiated materials.In Paper II, the scalar stress measure for cleavage fracture is developed and generalized, here called the effective normal stress measure. This is used in a non-local weakest link model which is applied to two datasets from the literature in order to study the effects of the effective normal stress measure, as well as new experiments considering four-point bending of specimens containing a semi-elliptical surface crack. The model is shown to reproduce the failure probability of all considered datasets, i.e. well capable of transferring toughness information between different geometries.Åldring av låglegerade stål i kärntekniska användningsområden framträder typiskt som ett hårdnande och en försprödning av materialet. Detta på grund av utvecklingen av mikrostrukturen under bestrålning och under rent termiska förhållanden. Bestrålning introducerar jämt fördelade kluster av legeringsämnen. Termisk åldring har däremot visats ge upphov till en mer ojämn fördelning. Klustren hämmar dislokationsrörelsen i materialet och ger därigenom upphov till en ökning av materialets sträckgräns, vid en mer påtaglig åldring det även leda till ett sänkt arbetshårdnande på grund av lokalisering av plastisk töjning i s.k. kanaler/band. Försprödning är en sänkning av materialets brottseghet som en följd av de mikrostrukturella förändringar som sker vid åldring. Arbetet som presenteras i den här avhandlingen har gjorts i syfte till att ta fram ett möjligt ramverk för modellering av låglegerade stål.I Artikel I, används en töjningsgradientbaserad plasticitetsteori för att kunna fånga längdskalebeteenden. Längdskalan i teorin antas vara relaterad till dislokationernas medelfria väg och den förändring den genomgår vid plastisk deformation. Flera utvecklingslagar för längdskalan har analyserats och implementerats i en finita element kod för 2D plan deformation. Denna implementering har använts för att lösa ett testproblem bestående av ren böjning med syfte att undersöka effekterna av utvecklingen hos längdskalan. Alla de utvecklingslagar som presenteras i artikeln ger en minskande längdskala, vilket leder till vad som valt att kallas förlust av icke-lokalitet. Fenomenet leder till ett övergripande mjuknande vid fall där den plastiska töjningsgradienten har stor inverkan på lösningen. Resultaten är i preliminär överenstämmelse med de typer av lokalisering av plastisk töjning som observerats i starkt bestrålade material.I Artikel II utvecklas ett generaliserat spänningsmått i syfte att beskriva klyvbrott, här benämnt effektivt normalspänningsmått. Detta har använts i samband med en icke-lokal svagaste länk modell, som har applicerats på två experimentella studier från den öppna litteraturen i syfte att studera effekterna av det effektiva normalspänningsmåttet. Utöver detta presenteras även nya experiment på ytspruckna provstavar under fyrpunktsböj. I artikeln visas att modellen återskapar sannolikheten för brott för alla undersökta experimentuppställningar, d.v.s. modellen visas vara väl duglig för att överföra brottseghet mellan geometrier.
QC 20190312
32
Gibbs, Parker Kenneth. "Strain Path Effect on Austenite Transformation and Ductility in TBF 1180 Steel." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7127.
Full textAbstract:
TBF 1180 steel was studied under various conditions focusing on the correlation of ductility and amount of retained austenite. Samples were prepared from sheet stock and then strained using limiting dome height tooling (LDH), a standard uniaxial test frame, and a tensile stage for use in an electron microscope. The steel was observed in plane, biaxial, and uniaxial strain to determine its effect on retained austenite transformation and ultimately, ductility. Retained austenite was observed using a scanning electron microscope (SEM) equipped with an electron backscatter detector (EBSD) to distinguish the different phases present. Initial austenite levels were around 5% by volume and was quickly reduced as the sample was strained. The biaxial samples were the slowest to transform, having about 2.5% austenite at .05 effective strain, which allowed the specimen to reach an effective strain of .3 with 1.1% austenite remaining. In contrast, the plane strain samples had the fastest rate of transformation having only 1.2% austenite at .05 effective strain and .7% austenite at a final effective strain of .18. Both forms of uniaxial, (in-situ and ex-situ), were near identical, as expected, and exhibited an austenite transformation curve between that of the plane and biaxial curves. The uniaxial austenite level at .05 strain was 2.1% and was able to reach about .15 strain with a final austenite percentage around 1%. It was concluded that the biaxial strain path had the greatest ductility due in part to its slower austenite transformation rate while plane and uniaxial strain paths were not as ductile with their faster austenite transformation rates.
33
Korkut, Ahmet Esat. "A Practical Optimum Design Of Steel Structures With Scatter Search Method And Sap2000." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615682/index.pdf.
Full textAbstract:
In the literature, a large number of metaheuristic search techniques have been proposed up to present time and some of those have been used in structural optimization. Scatter search is one of those techniques which has proved to be effective when solving combinatorial and nonlinear optimization problems such as scheduling, routing, financial product design and other problem areas. Scatter search is an evolutionary method that uses strategies based on a composite decision rules and search diversification and intensification for generating new trial points. Broodly speaking, this thesis is concerned with the use and application of scatter search technique in structural optimization. A newly developed optimization algorithm called modified scatter search is modified which is computerized in a software called SOP2012. The software SOP2012 is integrated with well-known structural analysis software SAP2000 using application programming interface for size optimum design of steel structures. Numerical studies are carried out using a test suite consisting of five real size design examples taken from the literature. In these examples, various steel truss and frame structures are designed for minimum weight according to design limitations imposed by AISC-ASD (Allowable Stress Design Code of American Institute of Steel Construction). The results reveal that the modified scatter search technique is very effective optimization technique for truss structures, yet its performance can be assessed ordinary for frame structures.
34
Nelson, Daniel R. "Transesterification and Recovery of Intracellular Lipids Using a Single Step Reactive Extraction." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/642.
Full textAbstract:
A single-step, extractive reaction for extraction of lipids such as biodiesel components, omega-3 fatty acids, or other triglycerides from microbial cells was examined. Conventional methods for lipid extraction use toxic solvents, and require multiple steps and long processing times. When the goal is to produce fatty acid methyl esters or FAMEs, the extracted lipids are subjected to a separate transesterification reaction with simple alcohols in the presence of an acid or base catalyst. A simplified, single-step reactive extraction method can be applied that combines the sequential extraction followed by transesterification using acidified alcohols - a process known as in situ transesterification. It was hypothesized that the in situ transesterification could be scaled-up for industrial processing by a systematic understanding of fundamental reaction parameters including temperature, catalyst concentration, and biomass/solvent ratios. The hypothesis was tested using a marine fungus, Schizochytrium limacinum SR21. Growth of SR21 resulted in biomass yields of 0.3g-biomass/g-glycerol and accumulated high amounts of palmitic acid (C16:0, 0.255g-FAME/g-biomass), docosahexaenoic acid (DHA, C22:6, 0.185g-FAME/g-biomass), myristic acid (C14:0) (0.017g-FAME/g-biomass), and pentadecanoic acid (C15:0, 0.012g-FAME/g-biomass). The bulk phase separation characteristics of the FAMEs were evaluated at high biomass concentrations. Recyclability of the acidified methanol in the system was also tested. A significant finding was that automatic phase separation of the FAMEs could be achieved. When FAME concentration reaches critical solubility, 22.7mg-FAME ml-1 methanol, all remaining FAMEs automatically phase separate. After FAME separation, the remaining methanol was recycled and used in subsequent in situ reactions. Upon recycling, greater than 85% of product extraction and recovery was achieved. The kinetics of the transesterification reaction was evaluated under various acid and biomass/solvent conditions. Based on the fundamental reaction mechanism governing the in situ transesterification, a theoretic model was derived to predict the conversion of TAGs into FAMEs. Kinetic parameters were estimated by fitting the experimental data and the resulting model. The model derived closely resembled the observations in this study. Through understanding of the fundamental reaction kinetics and limitations during processing, a new, reliable, and cost-effective system for large scale lipid production can be developed for microbial biomass including oleaginous algae, fungi, and yeast.
35
Engelberg, Dirk Lars. "Grain boundary engineering for intergranular stress corrosion resistance in austenitic stainless steel." Thesis, University of Manchester, 2006. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:207805.
Full textAbstract:
Austenitic stainless steels are frequently used for engineering applications in aggressive environments. Typical sources of component failures are associated with localized attack at grain boundaries, such as intergranular corrosion and stress corrosion cracking. To prevent premature failures, structural integrity assessments are carried out, with the aim of predicting the maximum likelihood of cracking that may develop. For accurate predictions it is of great importance to know the interaction of parameters involved in life-determining processes. This PhD thesis investigates the effect of microstructure and stress on intergranular stress corrosion cracking in Type 302 / Type 304 austenitic stainless steels. High-resolution X-ray tomography has been successfully applied to examine, for the first time in 3-dimensions, in-situ, the interaction between microstructure and crack propagation. The development and subsequent failure of crack bridging ligaments has been observed and correlated with regions of ductile tearing persistent on the fracture surface. These ductile regions were consistent with the morphology of low-energy, twin-type grain boundaries, and are believed to possess the capability of shielding the crack tip. Following this observation, a new grain bridging model has been developed, in order to quantify the effect of static stress and crack bridging on the maximum likely crack length. The model was compared and evaluated with in the literature available percolation-like models. Intergranular stress corrosion tests in tetrathionate solutions have been designed and carried out to validate the new model. The assessment comprised,(i) a thorough examination of the microstructure and analysis parameters employed,(ii) the determination of the degree of sensitisation with subsequent crack path investigations,(iii) the identification of a suitable test system with associated grain boundary susceptibility criteria,(iv) the application of Grain Boundary Engineering (GBE) for microstructure control,(v) statistical crack length assessments of calibrated IGSCC test specimens. The results of these tests showed that the new model successfully predicts the magnitude of stress and the effect of grain boundary engineering on the maximum crack lengths.
36
Guérin, Jean-Dominique. "Analyse des essais de compression et de traction des aciers après solidification in situ et des essais d'indentation des aciers phosphatés." Valenciennes, 1993. https://ged.uphf.fr/nuxeo/site/esupversions/b769f69b-4777-454d-94ad-c3bac6b6fab1.
Full textAbstract:
La mise en forme à chaud et à froid des aciers est étudiée avec deux types d'expérimentations : les essais à hautes températures des aciers juste après leur solidification et les essais à température ambiante des aciers phosphates. Le premier type d'expérimentation consiste à mener un essai de compression ou de traction à vitesse de traverse constante sur des éprouvettes, cylindriques pour l'essai de compression et axisymétriques à entaille circulaire pour l'essai de traction, en acier solidifie in situ. Il s'agit a partir des données expérimentales de caractériser le comportement de l'acier solidifie in situ teste. Une procédure d'essai est donc proposée et des modélisations analytiques permettent, d'une part, de déterminer le comportement élasto-thermo-viscoplastique de l'acier solidifie et, d'autre part, d'évaluer les contraintes et déformations caractéristiques dans les zones de l'éprouvette d'essai propices a l'apparition de criques. La comparaison des résultats obtenus analytiquement et par éléments finis, pour des essais de référence sur deux types d'acier, montre que les analyses proposées sont suffisamment précises pour identifier efficacement le comportement de l'acier solidifie situ. Le deuxième type d'expérimentation consiste à mener un essai d'indentation rotation sur une éprouvette cylindrique revêtue d'une ou plusieurs couches de frottement en phosphate ou stéarate de zinc. La spécificité du contact indenteur éprouvette durant la phase d'indentation de l'essai requiert une modélisation adéquate pour étudier le comportement de l'éprouvette sous la zone de contact. Un modèle par éléments finis local au contact est donc construit et des calculs sont menés pour des cas typiques de revêtements phosphates. Ce modèle par éléments finis s'avère apte à déterminer efficacement les répartitions de contraintes et de déformations dans l'éprouvette et il est ainsi opérationnel pour prédire l'efficacité du revêtement sans procéder à l'expérimentation.
37
Cramer, Jeffrey Grant. "Strain Path Effect on Austenite Transformation and Ductility in Q&P 1180 Steel." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6650.
Full textAbstract:
The ductility of Q&P 1180 steel was studied with regard to retained austenite transformation under different strain paths. Specimens were tested in uniaxial tension in a standard test frame as well as in situ in the scanning electron microscope (SEM). Then digital image correlation (DIC) was used to compute the effective strain at the level of the individual phases in the microstructure. Stretching experiments were also performed using limiting dome height (LDH) tooling, where specimens were strained in both biaxial and plane strain tension. The experiments were done incrementally, for each strain path, and the retained austenite at each level of strain was measured using electron backscatter diffraction (EBSD). Retained austenite levels in the uniaxial tension case dropped from an initial measured level of about 8% to about 2% during an initial strain increment of 0.02, but then stabilized as the specimen was strained to 0.1. In the plane strain and biaxial tension cases retained austenite also dropped significantly during an initial strain increment of about 0.04, but then continued to decrease as the specimens were strained to failure. Biaxial tension, in particular, was the most effective strain path for transforming retained austenite to martensite, resulting in a final volume fraction of 0.3% at an effective strain of 0.3. Retained austenite in the plane-strain tension case dropped at a faster rate than in the biaxial tension case, but finished at about 1% at a strain of 0.1. The greatest limit strains were seen in the biaxial tension case, which may be partly explained by the more effective conversion of retained austenite than was seen in the uniaxial tension case.
38
Shrestha, Alina. "Fatigue Testing and Data Analysis of Welded Steel Cruciform Joints." ScholarWorks@UNO, 2013. http://scholarworks.uno.edu/td/1670.
Full textAbstract:
In this study, ABS Publication 115, “Guidance on Fatigue Assessment of Offshore Structures” is briefly reviewed. Emphasis is on the S-N curves based fatigue assessment approach of non-tubular joints, and both size and environment effects are also considered. Further, fatigue tests are performed to study the fatigue strength of load-carrying and non-load-carrying steel cruciform joints that represent typical joint types in marine structures. The experimental results are then compared against ABS fatigue assessment methods, based on nominal stress approach, which demonstrates a need for better fatigue evaluation parameter. A good fatigue parameter by definition should be consistent and should correlate the S-N data well. The equivalent structural stress parameter is introduced to investigate the fatigue behavior of welded joints using the traction based structural stress approach on finite element models of specimens, and representing the data as a single Master S-N curve.
39
Jones, Benjamin S. "The Other Side of the Fence." VCU Scholars Compass, 2006. http://scholarscompass.vcu.edu/etd/843.
Full textAbstract:
I pull from what I see in my urban surroundings. There is always a sense of dread fused with optimism that prevails. Is it beautiful? Fragments of low-riders and tricked-out cars become symbols of desire and the glowing red lens of a stop light becomes a Cyclops poised to defend his garden. Candy-coated, blooming, dripping and seductively slick confronts you with the obvious warning: STOP! You could be next
The grass really is greener on The Other Side of the Fence. At least until winter comes.
40
Silveira, João Ricardo Filipini da. "Modelamento do efeito do tamanho de grão sobre o campo coercivo de aços elétricos." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-26082011-140213/.
Full textAbstract:
Chapas de aço elétrico (0,7% Si e 0,3% Al) foram laminadas a diferentes graus de deformação e recozidas (760º C, 2h) de modo a obter diferentes tamanhos de grão por recristalização. Um outro conjunto de chapas do mesmo material foi recozido a tempos e temperaturas diferentes de modo a obter tamanho de grão variado por crescimento de grão. Os tamanhos de grão foram medidos pelo método dos interceptos e os parâmetros da distribuições de tamanho de grão determinados por um método semi-analítico que se baseia na medição das áreas individuais de cada grão na micrografia. A partir do ensaio quase-estático de histerese magnética no quadro de Epstein obtiveram-se os campos coercivos de cada amostra, a diferentes induções máximas (0,6 0,8 1,0 1,2 1,4 e 1,5T). Notou-se que o conjunto dos dados se enquadra com menos de 4% de desvio médio absoluto uma lei fenomenológica do tipo: Hc aBmax^c /TG bBmax^d Na qual Hc é o campo coercivo, TG é o tamanho de grão, Bmax é a indução máxima do ensaio de histerese e a, b, c e d são os parâmetros de ajuste. A partir da inserção do efeito do campo desmagnetizante no contorno de grão no modelo físico de Mager obteve-se uma boa estimativa para os valores dos parâmetros independentes da indução a e b, além de propor um significado físico para os mesmos. Com a integração dos modelos Mager e Preisach, determinou-se uma equação diferente para o ajuste dos dados, a qual oferece um valor aproximado de c. Para que o modelo físico explique completamente a relação fenomenológica resta ainda elucidar o parâmetro d.Electrical steel sheets (0,7% Si and 0,3% Al) were cold-rolled and annealed (760º C, 2h) in order to obtain different grain sizes through recrystallization. Another set of sheets from the same material were annealed at different temperatures and time-frames, so as to produce different grain sizes through grain growth. Grain size was measured through the intercept method and grain size distribution parameters were determined via a semi-analytical method based on measurement of individual grain areas upon micrographs. From quasistatic hysteresis measurements in an Epstein frame, the coercive field of each sample was determined at various maximum induction values (0,6 0,8 1,0 1,2 1,4 e 1,5T). The data set fits with less than 4% average deviation a phenomenological law of the type: Hc aBmax^c /TG bBmax^d In which Hc is the coercive field, TG is the grain size, Bmax is the maximum induction value and a, b, c and d are the fitting parameters. By introducing the grain boundary demagnetizing field effect on Magers physical model, a good estimate of the values of a and b was obtained, as well as a reasonable explanation to their physical meaning. Integrating Mager and Preisach models, a different equation for the data was obtained, which offered an approximate value of c. In order for physical models do fully explain the phenomenological equation, there is still need to understand the parameter d.
41
Berthelot, Mathieu. "Extension PI de porphyrinespar couplage oxydant C-N intramoléculaire." Thesis, Bourgogne Franche-Comté, 2019. https://nuxeo.u-bourgogne.fr/nuxeo/site/esupversions/bdbabe4e-fa90-4cfa-8143-b07e530e3f78.
Full textAbstract:
L’extension π de porphyrines a été réalisée par couplage oxydant C-N intramoléculaire entre un fragment pyridinyle périphérique et le cœur porphyrinique. Les précurseurs à fusionner ont été synthétisés au départ de la 5,15-bis(p-tolyl)porphyrine et de la 5,15-bis(p-tolyl)-10-phénylporphyrine. Celles-ci ont été fonctionnalisées par réactions de substitution nucléophile aromatique en position(s) meso ou de couplage croisé au palladium(0) en position β-pyrrolique permettant d’introduire la 2-mercaptopyridine et la 8-hydroxyquinoline. Le couplage de la 2-picoline sur la 5,15-bis(p-tolyl)-10-phénylporphyrine a également été réalisé par réaction entre l’organolithien correspondant et la porphyrine. Afin de comparer l’influence du métal présent dans la cavité interne de la porphyrine sur la réaction de fusion C-N, les précurseurs ont été métallés au nickel(II) et au zinc(II). L'analyse par voltamétrie cyclique des complexes synthétisés a permis de mettre en évidence une différence de réactivité marquée selon la nature du métal inséré. Les conditions d’oxydation chimique et électrochimique permettant le couplage C-N du fragment pyridinyle sur la porphyrine ont été établies et adaptées à la substitution et à la métallation du macrocycle. Les propriétés électrochimiques, spectroscopiques et structurales des porphyrines fusionnées ont été analysées et comparées à leurs précurseurs respectifsΠ-extension of porphyrins has been performed via intramolecular oxidative C-N coupling of peripheral pyridinyl fragment(s) with the porphyrin core. These fusion reactions lead to the formation of C-N bond(s) between the substituent(s) and the porphyrin. The precursors were functionnalized with 2-mercaptopyridine, 8-hydoxyquinoline and 2-picoline at their meso or β-pyrrolic positions via aromatic nucleophlic substitution, cross-coupling reaction or reaction of the macrocycle with organolithium reagents. Voltametric analyses revealed some marked differences on the reactivity of the porphyrins depending on their substitution pattern and metalation (nickel(II) or zinc(II)). Chemical and electrochemical conditions were established to perform the intramolecular oxidative coupling and adapted depending on the substitution and metalation. The electrochemical, spectroscopic and structural properties of the fused products were analysed and compared to their respective precursors
42
Myeong-Heom, Park. "Effect of Grain Size on Mechanical Properties of Dual Phase Steel Composed of Ferrite and Martensite." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225592.
Full text
43
Halim, Amalia Yunita. "Investigation of the impact of nitrate injection to control sourcing problem in oil reservoir : benefit and side effects on steel materials." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/1035.
Full textAbstract:
The successful control of reservoir souring by nitrate injection has been well documented in the literature. Recent interest has centred on how nitrate application can increase the corrosion risk in pipelines and metal equipment. This study was conducted to observe the impact of nitrate reducing bacteria (NRB) and sulphate reducing bacteria (SRB) on the extent of corrosion on UNS S31603 and ASTM-A572-50 carbon steel, two commonly used materials in the oil and gas industry. The bacteria used in this experimental study were indigenous bacteria, isolated from the crude oil and production water samples of an oil field off the northwest of Western Australia. The NRB were isolated using nitrate broth, targeting nitrate reducers while SRB were isolated using Starkey media, targeting lactate utilizing bacteria (Desulfotomaculum and Desulfovibrio). In this study, a mixture of corrosive production water which contains a high level of chloride (21000 mg/L) supplemented with 10% (v/v) crude oil was used as the testing solution. The crude oil was taken into account because in the oil field it serves as the carbon source for the bacterial growth and it may also influence the corrosion behaviour of any steel material. However, this study has limited its scope to observe the impact of SRB and NRB using electrochemical techniques in a closed batch culture system without any water/nutrient renewal.The basic experimental design for the two materials investigated, UNS S31603 and the ASTM-A572-50 carbon steel were similar. The experiments were conducted at 50°C in electrochemical cells containing 10% (v/v) crude oil in 700mL production water and purged with filter-sterilized nitrogen to keep the oxygen level as low as possible. Each of the two materials were evaluated under four different conditions: (1) control cell (no bacteria), (2) NRB inoculated cell, (3) SRB inoculated cell, and (4) mixed bacteria (NRB+SRB) inoculated cell. A small amount of 5 mM NaNO3, was added as the growth nutrient for the bacteria. The open circuit potential (Ecorr) of the corrosion coupons, and the redox potential (Eh) of the solution were monitored throughout the experiments. Additionally, the microbial populations were counted by Most Probable Number (MPN) method and direct counting method using a Helber Counting Chamber Z30000. A production water analytical analysis (nitrate, nitrite, sulphate and sulphide) was conducted before and after the experiment.However, the exposure time in the corrosive media and the electrochemical analysis were different for each of the two materials tested. The immersion time for the UNS S31603 was 28 days and at the end of the immersion period, Linear Polarization Resistance (LPR) and Cyclic Polarization Scan (CPS) were carried out to determine the uniform and localized corrosion behaviour, respectively. The immersion time for the ASTM-A572-50 carbon steel was 21 days; LPR and electrochemical impedance spectroscopy (EIS) were conducted at an interval of every five days to monitor the biofilm formation, corrosion product formation and corrosion rate changes.The results for both UNS S31603 and ASTM-A572-50 carbon steel demonstrated that: (1) The addition of nitrate, promoted the growth of NRB and suppressed the growth of SRB, hence H2S production can be eliminated; (2) The NRB was able to oxidize the sulphide and also maintain a redox potential of above -100 mV, a level which inhibits the growth of SRB; (3) An increase in Ecorr was observed in the presence and absence of bacteria.The results from the UNS S31603 investigation show that: (1) NRB forms patchy biofilms on the UNS S31603 surfaces that weaken steel passivity and decrease its Critical Pitting Potential (CPP) to a greater extent than SRB after 28 days, (2) On the contrary, the corrosion rate of the UNS S31603 in the SRB inoculated cell is higher than the corrosion rate of the coupons in the NRB inoculated cell. This can be due to the formation of metastable pits as observed in the non-polarized corrosion coupon of the SRB inoculated cell after 28 days. (3) In order to study the effect of immersion time on the NRB and mixed bacteria (NRB+SRB), additional tests were conducted in the same manner for a short period of seven days of exposure. The results show that the CPP for the corrosion coupons in both the NRB inoculated cell and the mixed bacteria inoculated cell is higher than the corrosion coupons in the control cell. Therefore, it is postulated that, in this particular corrosive biochemical environment (high chloride level), the NRB and the mixed bacteria (NRB+SRB), may give beneficial protection to UNS S31603 for a short immersion time, and may give detrimental effects in longer exposure times.The results from ASTM-A572-50 carbon steel investigation show that: (1) the EIS technique can be used to monitor the formation of biofilm and/or corrosion products layers on the steel surface, (2) LPR, EIS and weight loss results show that in the tested corrosive environment, the presence of bacteria give lower rate of corrosion of ASTM-A572-50 carbon steel coupons compared to the corrosion coupons in the control cell. This indicates the corrosion inhibition activity of bacteria in this particular environment. (3) However, in the presence of bacteria, localized corrosion is inevitable as pits may form underneath bacterial biofilm.In general, it is important to examine the corrosion impact of nitrate application on case by case basis because it is a complex mechanism and cannot be simply predicted based on electrochemical techniques alone. Further work is required to understand the biological materials that were produced by NRB, especially in the presence of other bacteria, which in a real situation in an oil reservoir may not only be SRB. Such studies can aid in understanding the fundamentals of the biochemistry of nitrate injection, thus resulting in important information for the process and design of field applications.
44
Siafakas, Dimitrios. "On deoxidation practice and grain size of austenitic manganese steel." Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Material och tillverkning – Gjutning, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-37788.
Full textAbstract:
The exceptional wear resistance and work hardenability, place Hadfield steel as one of themost important materials for manufacturing cast components used in the mining, crashing,drilling, and excavation industries. In all metallic alloys used for component casting, themechanical properties are highly influenced by the microstructure of the material. Castcomponents with finer microstructural characteristics are known to present bettermechanical properties and reduced risk of defects when compared with components witha coarser microstructure. A reduced grain size in Hadfield steel can increase the strengthof the material up to 30% and reduce the risk of porosity formation during solidification.The practice of adding selected compounds or alloying elements in a metal melt to modifyand refine the microstructure is called inoculation. It is currently one of the trendingmethods utilized in light-metal alloys and cast-iron components production but has not,yet, gained adequate acceptance in the steel casting industry because researchers have notbeen able to find proper inoculants.The main objective of this work is to investigate the qualitative and quantitativecharacteristics of the by-products of deoxidation of Hadfield steel that remain in thematerial after solidification and their positive or negative effect on the coarseness of thefinal as-cast microstructure. This type of research can help to identify the type of particlesor alloying elements that are most effective for refining the microstructure of austeniticsteels and pave the way for developing new or improving conventional deoxidation andinoculation processes that will, in turn, result in the improvement of the properties of thecomponent.The precipitation of particles and the as-cast grain size are studied in aluminum andtitanium deoxidized Hadfield steel samples acquired under pilot scale experimentalconditions. In the first part of this work, the qualitative and quantitative characteristics ofparticles such as type, morphology, composition amount and size are identified. Thesequence of precipitation is established. A model for predicting particle size and growth isdeveloped. The experimental results are compared against thermodynamic equilibriumcalculations and the precipitation mechanisms for each type of particles are described. Inthe second part, the as-cast grain size of samples with varying deoxidation treatments ismeasured. Then, the grain-size is correlated with certain particle characteristic and theparticles are ranked according to their ability to refine the microstructure. The particledisregistry with austenite is calculated and compared to the experimentally acquiredranking.Hadfieldstålen exceptionella slitstyrkan och deformationshårdnande har gjort dessa till ettav de viktigaste materialen för tillverkning av gjutna komponenter som används inomgruv-, kross-, borr-och gruvindustrin. I alla metallegeringar som används för tillverkningav gjutna komponenter styrs de mekaniska egenskaperna av materialets mikrostruktur.Gjutna komponenter med fin mikrostruktur presentera bättre mekaniska egenskaper ochminskad risk för defekter jämfört med komponenter med grov mikrostruktur. En minskadkornstorlek i Hadfieldstål kan öka materialets hållfasthet upp till 30% och minska riskenför porositetsbildning vid stelning.Tillsatsning av spårämnen eller legeringselement i en metallsmälta för att modifiera ochförbättra mikrostrukturen kallas ympning. Denna metod används i lättmetaller och vidtillverkning av gjutjärnskomponenter, men har ännu inte fått acceptans i stålindustrineftersom forskningen inte har funnit effektiva kärnbildare att användas som ympmedel.Huvudsyftet med detta arbete är att undersöka kvalitativa och kvantitativa egenskaper hosde desoxideringsprodukter som skapas under tillverkningen av Hadfield stål och hur deunder och efter stelning påverkar mikrostrukturens grovlek. Arbetet syftar till att identifierapartikeltyper och legeringselement som är effektiva för att förfina den austenitiskamikrostrukturen och bana väg för utveckling nya och förbättra desoxiderings- ochympningsprocesser som i sin tur kommer att resultera i en förbättring av den gjutnakomponentens egenskaper.Partiklarnas utskiljning och materialet resulterande kornstorlek studerades i aluminiumochtitan-desoxidiserade Hadfieldstål, tillverkade i pilotskala. Den första delen av dettaarbete var att identifiera kvalitativa och kvantitativa egenskaper hosdesoxidationspartiklar, som typ, morfologi, sammansättning och storlek.Utskiljningssekvensen fastställdes. En modell för att förutsäga partikelstorlek och derastillväxt utvecklades. De experimentella resultaten jämfördes med termodynamiskajämviktberäkningar och utskiljningen för varje typ av partikel beskrevs. I den andra delenstuderades kornstorleken och hur denna varierade desoxideringsbehandlingen. Därefterkorrelerades kornstorleken med partikeltyp och dess karaktäristika och rangordnades efterderas förmåga att förfina mikrostrukturen. Partiklarnas kristallografiska missanpassningmot austenitens kristallstruktur beräknades och jämfördes med experimentellt fastställdarangordningen.
InDeGrainS I
45
Babinský, Tomáš. "Rekrystalizace automatové oceli studované technikou in-situ SEM/EBSD." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378404.
Full textAbstract:
Placing recrystallization annealing in a manufacturing proces is often necessary in order to restore plasticity of worked blanks right before working products to its final shape. For better understanding of processes which are taking place in a material during annealing the use of in-situ techniques is favorable. Such observations enable us to watch changes in the materiál in real time at the original spot. Observations at grain-level are ideally made with scanning electron microscope – SEM by electron back-scattered diffraction – EBSD. The technique makes watching nucleation, growth and potential coarsening of recrystallized grains possible. Special construction of a tensile stage allows us to watch changes of a sample during tensile tests which can be used in observing influence of MnS inclusions on plasticity of free-cutting steels. Materials studied in this work are commonly used free-cutting steel 11SMnPb30 and its lead-free alternative 11SMnBi30.
46
Shahedipour, Fatemeh. "Diamond synthesis on steel substrates using magneto-active plasma chemical vapor deposition with novel in situ FTIR spectroscopy characterization /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9901278.
Full text
47
Hirsch, Michael Robert. "Fretting behavior of AISI 301 stainless steel sheet in full hard condition." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24759.
Full text
48
Safara, Nosar Nima. "Modeling the Microstructure Evolution During and After Hot Working in Martensitic Steel." Licentiate thesis, Högskolan Dalarna, Institutionen för information och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-287278.
Full textAbstract:
In this study, the goal is to predict the microstructure evolution during and after the hot working of a martensitic stainless steel with 13% chromium using a physically-based model in the form of a MATLAB toolbox. This model is based on dislocation density theory and consists of coupled sets of evolution equations for dislocation, vacancies, recovery, recrystallization, and grain growth. The focus in this work is on the flow stress calculation and the effect of second phase particles on the strengthening mechanisms in the material at elevated temperatures. Recovery and recrystallization are also studied for this alloy during deformation and following stress relaxation. The experimental part of this work was performed with a Gleeble thermo-mechanical simulator over the temperature range of 850 to 1200°C. Samples were investigated later by a light optical microscope (LOM) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS). Hardness test and phase isolation were also performed on the samples and the results are compared with the modeling results. The model can satisfactorily predict the grain growth, recovery, recrystallization, and flow stress for this alloy. Further investigation on the second phase particles showed that the measured mean size of carbides has a good agreement with what is obtained from the model and the hardness values. On the other hand, the modeled volume fraction of the carbides followed a slightly different trend comparing to hardness values, and phase isolation results at temperatures higher than 1000°C. Additionally, the Ms temperature and fraction of the martensite phase are calculated for quenched samples where the results are following the measured hardness values. Finally, the Zener-Hollomon parameter (Z) and its relation to the flow stress and the activation energy for deformation are defined. The dynamic recrystallization (DRX) kinetic is modeled and the fraction DRX was calculated at various temperatures and strain rates for this alloy.I denna studie är målet att förutsäga mikrostrukturutvecklingen under och efter varmbearbetning i ett martensitiskt rostfritt stål med 13 % krom med hjälp av en fysisk baserad modell i form av en MATLAB verktygslåda. Denna modell är baserad på en teori för dislokationstäthet och bestårav kopplade uppsättningar av evolutionsekvationer för dislokation, vakanser, återhämtning, rekristallisation och kornstillväxt. Fokus i detta arbete är beräkning av flytespänningen och effekten av sekundärfaspartiklar på härdningsmekanismerna i materialet vid höga temperaturer. Återhämtning och rekristallisation studeras också för denna legering under deformation och efter spänningsrelaxation. Den experimentella delen av detta arbete utfördes med en Gleeble termomekanisk simulator inom temperaturområdet 850 till 1200°C. Proverna undersöktes senare med ett ljust optiskt mikroskop (LOM) och svepelektronmikroskop(SEM) utrustad med energidispersiv spektroskopi (EDS). Hårdhetstest och fasisolering utfördes också på proverna och resultaten jämförs med modelleringsresultaten. Modellen på ett tillfredsställande sätt kan förutsäga korntillväxt, återhämtning, rekristallisation och flytspänningen för denna legering. Vidare undersökning av partiklarna i sekundärfasen visade att den uppmätta medelstorleken för karbider har bra överensstämmelse med vad som erhålls från modellen och hårdhetsvärdena. Den modellerade volymfraktionen av karbiderna följde en något annorlunda trend vid temperaturerna högre än 1000°C jämfört med hårdhetsvärden och fasisoleringsresultat. Dessutom beräknas Ms temperaturen och fraktionen av martensitfasen för släckta prover där resultaten följer de uppmätta hårdhetsvärdena. Slutligen definieras Zener-Hollomon-parametern (Z) och dess förhållande till flytspänningen och aktiveringsenergin för deformation. Den kinetiska dynamiska rekristallisation (DRX) modelleras och fraktionen DRX beräknades vidolika temperaturer och töjningshastigheter för denna legering.
49
Sakai, Akira, Ken Sugimoto, Takeo Yamamoto, Masahisa Okada, Hiroya Ikeda, Yukio Yasuda, and Shigeaki Zaima. "Reduction of threading dislocation density in SiGe layers on Si (001) using a two-step strain–relaxation procedure." American Institute of Physics, 2001. http://hdl.handle.net/2237/6996.
Full text
50
Mao, Wenqi. "Deformation mechanism of metastable austenitic steel with TRIP effect and associated kinetics of deformation induced martensitic transformation." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263657.
Full text