To see the other types of publications on this topic, follow the link: Yield strengt.
Dissertations / Theses on the topic 'Yield strengt'
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 'Yield strengt.'
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
Recman, Lukáš. "Deformační chování nano/mikro vyztuženého PMMA." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2010. http://www.nusl.cz/ntk/nusl-233297.
Full textAbstract:
Práce sleduje vliv velikosti částic na elastický modul a deformační chování za mezí kluzu. Bylo pozorováno, že jak elastická oblast, tak oblast za mezí kluzu ukazuje silnou závislost chování na velikosti částic. Cílem této práce je korelovat experimentální data a teoretické předpoklady které bylo odvozeny pro deformační chování v elastické oblasti a v oblasti za mezí kluzu pro amorfní polymery a konkrétně pro PMMA. Vše je motivováno propojit zatím oddělené oblasti kontinuální mikromechaniky a diskrétní nanomechaniky. Deformační chovaní PMMA plněného nano a mikro plnivem bylo pozorováno v elastické a plastické oblasti. Byl zkoumán vliv velikosti částic na velikost modulu a deformačního zpevnění. Mechanizmus vyztužení je interpretován s použitím teorie imobilizace řetězců, nanočástice mají silný vliv na molekulární dynamiku a kinetiku zapletenin. Mým příspěvkem k tomuto tématu je ukázat výraznou závislost na mechanizmu vyztužení v závislosti na velikosti částic. A to jak pod teplotou skelného přechodu tak nad teplotou skelného přechodu. Ačkoli pro velikost modulu byla publikována značná množství dat, která byla následně i interpretována, vliv částic na deformační zpevnění je poskrovnu. Během elastické deformace je primární struktura materiálu neměnná, jedná se o elastickou deformaci, za mezí kluzu již toto neplatí a primární struktura je zde nevratně poškozena. Bylo ukázáno, že obsah nano částic vede ke zvýšení meze kluzu a vyššímu deformačnímu zpevnění. Tento nárůst deformačního zpevnění je v korelaci s Guth-Gold rovnicí. Je předpokládáno, že nanočástice slouží jako další fyzikální zapleteniny a vedou k fyzikálně více zapletenému systému. Stejný efekt jako v elastické oblast tj. vliv velikosti částic na modul, byla pozorována i během deformačního zpevnění.
2
Shapiro, Nathan. "Optimal fiber yield strength for concrete reinforcement." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38044.
Full text
3
Mullier, Marie Anne. "The strength of agglomerates and their breakage during fluidisation." Thesis, University of Surrey, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293370.
Full text
4
Fraser, Douglas (Douglas H. ). "Triptycene side unit effects on compressive yield strength in polycarbonates." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35071.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (leaf 25).
Polycarbonates have long been studied for their excellent mechanical toughness. Adding side units to polycarbonate could increase physical properties of the polymer. The role of triptycene in polycarbonate was studied by adding a low concentration of triptycene-containing polymer chains, and using compression testing. The triptycene polycarbonate was a blend created from two separate products. Differential Scanning Calorimetry was used to determine if the samples had phase separated. Thermal degradation of the samples was checked for using Thermogravimetric Analysis. Results indicated that triptycene-containing polycarbonates had higher compressive yield strengths than non-triptycene polycarbonates. The polymers were stronger due to the interlocking mechanism and the steric hindrance of the triptycene units. The design of strengthening polymers by adding triptycene units could prove useful to improve high performing polymers, or to give low molecular weight polymers more stability.
by Douglas Fraser.
S.B.
5
Ngan, Alfonso Hing-wan. "The temperature dependence of yield strength in L1 [inferior] 2 compounds." Thesis, University of Birmingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.658066.
Full text
6
Tang, Louis (Ruo Biao). "Plate yield slenderness criteria for structural members fabricated from high strength steels." Queensland University of Technology, 2008. http://eprints.qut.edu.au/20724/.
Full textAbstract:
Increasing demand from flourishing construction markets led to the successful development of high strength steels (HSS). The new structural steel has exceptional high strength, high fracture toughness, long fatigue life, high corrosion resistance, and better weldability making the material attractive for structural design applications in the modern steel buildings and bridges. With their high strength, typically in the range of 500~700 MPa, and reduced weight/dimensions, it frees imaginations of modern designers and opens up new possibilities. Although HSS cost more, this is more than offset by reduced fabrication and erection costs. The advantage of the intrinsic properties of the HSS makes it possible to achieve successful applications in a cost-effective manner. At present, the Australian steel design standard, AS 4100 (SA, 1998), is limited to conventional low strength steels (LSS) with yield stress less than 450 MPa, (i.e. fy . 450 MPa). As a result steel structural members fabricated from HSS in Australia are usually designed according to overseas specifications, such as AISC-LRFD (AISC, 2003) which allows the design for structures fabricated from HSS materials. However, the design provisions of AISC-LRFD were mainly based on experimental and analytical studies on standard LSS. HSS exhibits mechanical properties that are quite different from conventional LSS. On the other hand, the design procedure and approach of the American specifications (AISC, 2003) are unfamiliar with Australian design engineers, which explains why practising engineers in Australia are reluctant to use AISC-LRFD specification in the design of HSS members. Therefore research into the behaviour of HSS members is essential to address this shortcoming. However, since the use of HSS often leads to smaller sections, hence thinner plates, the elastic and inelastic instability of these thin-walled and HSS members become highly critical. Conservatively, the local instabilities of the constituent plate element interactions in the cross-section have been ignored in the current steel practices. Increasing the slenderness of either plate elements within a cross-section leads to a significant reduction in the section capacity of the structural member. Therefore, the interactive effects between flange and web plate elements have to be considered in the strength, stability and deformation studies of HSS members. Furthermore, the current definitions and values of the plate slenderness limits also vary among major steel design codes (AS4100, 1998; AISC, 2003; EN1993, 2003; BS5950, 2000). The main aim of this research project is to investigate the structural behaviour of Ishaped HSS members subjected to local buckling effects in the elastic and inelastic ranges. For this purpose, it will use advanced numerical analyses and laboratory experiments to study the structural behaviour of these HSS members in compression and bending, respectively. The critical review has found that various inconsistencies among the major steel design specifications (AS4100, 1998; AISC, 2003; EN1993, 2003, BS5950, 2000) in the current practice produce conflicting design predictions of section capacities. The experimental measurements of residual stress distributions have confirmed that the ECCS recommendation (1984) is inappropriate for crosssections fabricated from typical HSS materials (i.e. BISPLATE80). The experimental measurements and numerical studies carried out in this project have produced a better understanding of the structural behaviour of HSS members subjected to local instabilities. The study has enabled to provide a series of proposals for proper assessment of plate slenderness limits for structural members made of HSS materials. It may also enable the inclusion of future version of the AS4100 code for HSS materials to be used in the design of steel building and bridge constructions. It is believed that the use of HSS in building and bridge constructions will increase significantly in the very near future, and to fully-facilitate this, the future versions of national and international steel design specifications must include rational and reliable design rules for members made of all steel grades by including the effects of HSS special characteristics and true interactive local buckling behaviour of HSS members. This research project has contributed towards this.
7
Harati, Ebrahim. "Fatigue strength of welds in 800 MPa yield strength steels : Effects of weld toe geometry and residual stress." Licentiate thesis, Högskolan Väst, Avd för tillverkningsprocesser, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-8009.
Full textAbstract:
Nowadays there is a strong demand for lighter vehicles in order to increase the pay load. Through this the specific fuel consumption is decreased, the amount of greenhouse gases is lowered and the transport economy improved. One possibility to optimize the weight is to make the components from high strength steels and join them by welding. Welding is the main joining method for fabrication of a large proportion of all engineering structures. Many components experience fatigue loading during all or part of their life time and welded connections are often the prime location of fatigue failure.Fatigue fracture in welded structures often initiates at the weld toe as aconsequence of large residual stresses and changes in geometry acting as stress concentrators. The objective of this research is to increase the understanding of the factors that control fatigue life in welded components made from very high strength steels with a yield strength of more than 800 MPa. In particular the influences of the local weld toe geometry (weld toe radius and angle) and residual stress on fatigue life have been studied. Residual stresses have been varied by welding with conventional as well as Low Transformation Temperature (LTT) filler materials. The three non-destructive techniques Weld Impression Analysis (WIA), Laser Scanning Profiling (LSP) and Structured Light Projection (SLP) have been applied to evaluate the weld toe geometry.Results suggest that all three methods could be used successfully to measure the weld toe radius and angle, but the obtained data are dependent on the evaluation procedure. WIA seems to be a suitable and economical choice when the aim is just finding the radius. However, SLP is a good method to fast obtain a threedimensional image of the weld profile, which also makes it more suitable for quality control in production. It was also found that the use of LTTconsumables increased fatigue life and that residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welded parts.
8
Larsson, Rikard. "Constitutive Modelling of High Strength Steel." Thesis, Linköping University, Department of Management and Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8157.
Full textAbstract:
This report is a review on aspects of constitutive modelling of high strength steels. Aspects that have been presented are basic crystallography of steel, martensite transformation, thermodynamics and plasticity from a phenomenological point of view. The phenomenon called mechanical twinning is reviewed and the properties of a new material type called TWIP-steel have been briefly presented. Focus has been given on phenomenological models and methods, but an overview over multiscale methods has also been given.
9
Skoufari-Themistou, Leda. "Impact and yield strength behaviour of age-hardening, low-carbon copper-containing steels." Thesis, City University London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319641.
Full text
10
Dominisse, Kyle Richard. "Strength and Stiffness of Weak-Axis Moment End-Plate Connections." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/46194.
Full textAbstract:
Three full-scale experimental tests were conducted to investigate the strength and stiffness of weak-axis moment end-plate connections. Each test consisted of two girders connected to a column web with four-bolt extended moment end-plates. Two tests were conducted with bare steel. One test included a composite concrete slab that confined the top extension of the end-plate.
Finite element models of the tests were created with the commercial software SAP2000. A simplified modeling procedure was developed to overcome the contact problems between the end-plates and column web, and between the bolts and holes in the end-plates and web. The simplified modeling procedure accurately predicted the experimental elastic stiffness, in the form of column web rotations, of the connections.
Yield line theory was used to investigate the plastic strength of the column web. Several yield line patterns were examined. Analytical plastic moment strengths were very conservative when compared to the observed behavior of the column web.
The experimental stiffness of the test with the concrete slab confining the top extension of the end-plate was compared to the stiffness of a similar test without a slab. The slab increased the elastic stiffness of the connection; however, after the concrete began cracking and crushing around the connection, the stiffness was greatly decreased.
Master of Science
11
Gearhart, Gregory P. Jr. "Synthesis Study on Load Capacity of Concrete Slabs without Plans." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522057637077884.
Full text
12
Hankin, G. L. "Radiation-induced evolution of microstructure and mechanical properties of stainless steels." Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/7065.
Full textAbstract:
Radiation-induced changes in microstructures often lead to significant changes in mechanical properties of alloys used in the construction of nuclear reactors. It is desirable to test small specimens to make efficient use of the small volumes available in test and commercial reactor cores and also because small specimens are less affected by the sometimes steep flux gradients experienced in reactor cores and the sometimes large temperature gradients developed in the specimens from gamma heating. (Continues...).
13
Fromm, Bradley S. "Incorporating Grain Size Effects in Taylor Crystal Plasticity." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/1275.
Full textAbstract:
A method to incorporate grain size effects into crystal plasticity is presented. The classical Hall-Petch equation inaccurately predicts the macroscopic yield strength for materials with non-equiaxed grains or materials that contain unequal grain size distributions. These deficiencies can be overcome by incorporating both grain size and orientation characteristics into crystal plasticity theory. Homogenization relationships based on a viscoplastic Taylor-like approach are introduced along with a new function, the grain size and orientation distribution function (GSODF). Estimates of the GSODF for high purity α-titanium are recovered through orientation imaging microscopy coupled with the chord length distribution. A comparison between the new method and the traditional viscoplastic Taylor approach is made by evaluating yield surface plots.
14
Smitchger, Jamin A. "Quantitative Trait Loci Associated with Lodging, Stem Strength, Yield, and Other Important Agronomic Traits in Dry Field Peas." Thesis, Montana State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10607937.
Full textAbstract:
In pea, lodging changes canopy structure, increases disease pressure, reduces yield, and reduces harvest efficiency. In order to discover the quantitative trait loci (QTLs) influencing lodging resistance and other important agronomic traits in pea, a recombinant inbred line (RIL) population was created from a relatively wide cross between the commercial variety Delta and an unnamed pea variety. The RIL population was grown for 6 site-years in Bozeman and Moccasin, MT, USA, and phenotypic data was collected for 22 quantitative morphological traits and seven categorical traits which were thought to be associated with lodging resistance. Genotypic data was derived from genotype by sequencing, microsattelite markers, and cleaved amplified sequence tagged sites.
QTL analysis identified a total of 135 putative QTLs for the 22 traits examined in the study. There were 12 specific regions where 115 QTLs co-located, indicating that as few as 12 genes may be responsible for multiple pleiotropic effects. Ten QTLs were found for lodging resistance. Due to the large amount of phenotypic data collected, the putative mechanism of lodging resistance was determined for each QTL. In nearly every case, lodging resistance was associated with reduced plant height, a change in tendril number, or increased stem strength. This conclusion was supported by mathematical modeling. Branch number, which determines the number of tendrils per plant, was also positively associated with lodging resistance during all site-years, indicating that increasing tendril number also increases lodging resistance.
Yield was controlled by eight QTLs. All QTLs for yield had pleiotropic effects on lodging resistance and yield per plant. Seed size was not correlated with yield, and a model was created which explained why no association between yield and seed size was found.
The pleiotropic effects and utility of the QTLs discovered in this study are discussed. The results of this study further refine the ideotype for pea, and can be used for marker assisted selection in this crop.
15
Tiwari, Shreevant. "Methods for atomistic input into the initial yield and plastic flow criteria for nanocrystalline materials." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53059.
Full textAbstract:
Nanocrystalline (NC) metals and alloys are known to possess superior mechanical properties, e.g., strength, hardness, and wear-resistance, as compared to conventional microcrystalline materials. NC metals are characterized by a mean grain size <100 nm; in this grain size regime, inelastic deformation can occur via a combination of interface-mediated mechanisms viz., grain boundary sliding/migration, and dislocation nucleation from grain boundary sources. Recent studies have suggested that these interface-mediated inelastic deformation mechanisms in fcc metals are influenced by non-glide stresses and interfacial free volume, unlike dislocation glide mechanisms that operate in microcrystalline fcc metals. Further, observations of tension-compression strength asymmetry in NC metals raise the possibility that yield and inelastic flow in these materials may not be adequately described by solely the deviatoric stress. Unfortunately, most literature concerning the mechanical testing of NC metals is limited to uniaxial deformation or nanoindentation techniques, and the multiaxial deformation behavior is often predicted assuming initially isotropic yield and subsequent flow normal to the yield surface.
The primary objective of this thesis is to obtain a better understanding of the nature of inelasticity in NC metals by simulating multiaxial deformation at the atomistic resolution, and developing methods to interpret the results in ways that would be useful from a continuum constitutive modeling viewpoint. First, we have presented a novel, statistical mechanics-based approach to unambiguously resolve the elastic-plastic transition as an avalanche in the proliferation of mobile defects. This approach is applied to nanocrystalline Cu to explore the influence of pressure and multiaxial stress states on the inelastic deformation behavior. The results suggest that initial yield in nanocrystalline Cu under biaxial loading is only weakly anisotropic in the 5 nm grain size regime, and that plastic flow evolves in a direction normal to the von Mises yield surface. However, triaxial deformation simulations reveal a significant effect of the superimposed hydrostatic stress on yielding under shear. These results are analyzed in detail in order to assess the influence of pre-existing internal stresses and interfacial excess volume on the inelastic deformation behavior.
Further, we have studied the effects of imposed hydrostatic pressure on the shear deformation behavior of Cu bicrystals containing symmetric tilt interfaces, as well as Cu nanocrystals of different grain sizes. Most interfaces exhibit an increase in shear strength with imposed compressive hydrostatic pressure. However, for some interfaces, this trend is reversed. Neither the sign nor the magnitude of the pressure-induced elevation in shear strength appears to correlate with interface structure or particular deformation mechanism(s). In Cu nanocrystals, we observe that imposed compressive pressure leads to strengthening under shear deformation, and the effect of imposed pressure on the shear strength becomes stronger with increase in grain size or temperature. Activation parameters for shear deformation have been computed for these nanocrystals, and computed values seem to agree with existing experimental and theoretical estimates. Finally, we have proposed some modifications to conventional isothermal molecular dynamics algorithms, in order to isolate dislocation nucleation events from interfacial sources, and thereby permit explicit computation of the activation parameters for such events.
16
Clark, Justin Lewis. "Dynamic and Quasi-Static Mechanical Properties of Fe-Ni Alloy Honeycomb." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5223.
Full textAbstract:
Several metal honeycombs, termed Linear Cellular Alloys (LCAs), were fabricated via a paste extrusion process and thermal treatment. Two Fe-Ni based alloy compositions were evaluated. Maraging steel and Super Invar were chosen for their compatibility with the process and the wide range of properties they afforded. Cell wall material was characterized and compared to wrought alloy specifications. The bulk alloy was found to compare well with the more conventionally produced wrought product when porosity was taken into account. The presence of extrusion defects and raw material impurities were shown to degrade properties with respect to wrought alloys. The performance of LCAs was investigated for several alloys and cell morphologies. The results showed that out-of-plane properties exceeded model predictions and in-plane properties fell short due to missing cell walls and similar defects. Strength was shown to outperform several existing cellular metals by as much as an order of magnitude in some instances. Energy absorption of these materials was shown to exceed 150 J/cc at strains of 50% for high strength alloys. Finally, the suitability of LCAs as an energetic capsule was investigated. The investigation found that the LCAs added significant static strength and as much as three to five times improvement in the dynamic strength of the system. More importantly, it was shown that the pressures achieved with the LCA capsule were significantly higher than the energetic material could achieve alone. High pressures, approaching 3 GPa, coupled with the fragmentation of the capsule during impact increased the likelihood of initiation and propagation of the energetic reaction. This multi-functional aspect of the LCA makes it a suitable capsule material.
17
Barthélémy, Jean-François. "Approche micromécanique de la rupture et de la fissuration dans les géomatériaux." Marne-la-vallée, ENPC, 2005. https://pastel.archives-ouvertes.fr/pastel-00001296.
Full text
18
Summers, Patrick T. "Microstructure-based Constitutive Models for Residual Mechanical Behavior of Aluminum Alloys after Fire Exposure." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/47678.
Full textAbstract:
Aluminum alloys are increasingly being used in a broad spectrum of applications such as lightweight structures, light rail, bridge decks, marine crafts, and off-shore platforms. The post-fire (residual) integrity of aluminum structures is of particular concern as a severe degradation in mechanical properties may occur without catastrophic failure, even for short duration, low intensity fires. The lack of research characterizing residual mechanical behavior results in an unquantified mechanical state of the structure, potentially requiring excessively conservative repair. This research aims to develop an in-depth understanding of the mechanisms governing the residual aluminum alloys so as to establish a knowledge-base to assist intelligent structural repair.
In this work, the residual mechanical behavior after fire exposure of marine-grade aluminum alloys AA5083-H116 and AA6061-T651 is characterized by extensive mechanical testing. Metallography was performed to identify the as-received and post-fire microstructural state. This extensive characterization was utilized to develop constitutive models for the residual elasto-plastic mechanical behavior of the alloys. The constitutive models were developed as a series of sub-models to predict (i) microstructural evolution, (ii) residual yield strength, and (iii) strain hardening after fire exposure.
The AA5083-H116 constitutive model was developed considering the microstructural processes of recovery and recrystallization. The residual yield strength was calculated considering solid solution, subgrain, and grain strengthening. A recovery model was used to predict subgrain growth and a recrystallization model was used to predict grain nucleation and growth, as well as subgrain annihilation. Strain hardening was predicted using the Kocks-Mecking-Estrin law modified to account for the additional dislocation storage and dynamic recovery of subgrains. The AA6061-T651 constitutive model was developed considering precipitate nucleation, growth, and dissolution. A Kampmann-Wagner numerical model was used to predict precipitate size distribution evolution during elevated temperature exposure. The residual yield strength was calculated using solid solution and precipitate strengthening, considering both shearable and non-shearable precipitates. A modified KME law was used to predict residual strain hardening considering the additional effects of the precipitate-dislocation interactions, focusing on the efficient of dislocation (Orowan) loop storage and recovery about the precipitates. In both cases, the constitutive models were bench-marked against experimental data.Ph. D.
19
Ganaw, Abdelhamed I. "Rheology of grout for preplaced aggregate concrete : investigation on the effect of different materials on the rheology of Portland cement based grouts and their role in the production of preplaced aggregate concrete." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5766.
Full textAbstract:
Preplaced aggregate concrete (PAC) is produced by grouting high workability cement based grouts among the voids of compacted coarse aggregate mass. Because of its low shrinkage, PAC has been used for many repair jobs like; tunnel lines, dams and bridge piers. Moreover, it has been used for underwater construction. Grout has a major effect on the properties of produced PAC and well defined grout controls the properties of resulted PAC. The effect of types and amount of powder materials, admixtures, sand and water content on the properties of fresh and hardened grout for the production of PAC have been investigated. Tests on hardened grout and PAC properties have also been carried out to investigate the most important effects. A correlation between hardened properties of grout and PAC has also been analyzed. Grout rheology using four different gradation sands at two different cement-sand and at different w/c ratios ratios has been identified experimentally; no added chemical admixtures or mineral additives had first employed, then superplasticizer (SP) was added at 2% and 1%, and finally a combination of 1% SP and pulverized fuel ash (Pfa) at 20% of the cement weight was employed for all mixes. Grout tests have included two point workability tests by the Viskomat NT, flow time funnel test, Colcrete flow meter test, and water bleeding test. After that, eighteen grout mixes with high workability were produced using three different sands at three w/c ratios and two c/s ratios with 1% SP and Pfa at 20% of the cement weight were designed. Eighteen hardened grout and PAC then produced and their compressive strength and sorptivity were tested. Grout rheology can be defined by the rheology of cement paste employed and the internal distance between sand particles. The effect of sand surface texture on grout rheology is important at very low internal distances. Fresh grout yield stress is the most important property which gives the same degree of sensitivity for all grouts regardless the material type and content used in the mix. There are strong relations between compressive strength of grout and PAC, but less correlation between them in sorptivity test because of the effect high quantity of coarse aggregate of PAC. Sorptivity of PAC is low comparing with different kinds of concrete suggesting its advantage for underwater construction.
20
Laschke, Erikka. "The importance of material properties on the bendability of Q/QT steels." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103204.
Full textAbstract:
This master thesis work has been carried out at the company SSAB EMEA in Oxelösund which is a global leader in quenched and tempered high-strength steel. The aim is to examine the importance of the material properties for the bendability of the specific steel grade Weldox. There are many conditions for various applications such as mobile cranes and vehicles that need to be fulfilled in order for the material to be approved, where one main prerequisite is the bendability. It is very important to be able to bend the material without the occurrence of cracks. The purpose of this work has therefore been to investigate and try to find the relationship between the material properties and the critical bending radius. Furthermore has another aim been to find the most suitable treatment process for the composition of this specific steel grade.The work was divided into two parts, where the first part was to examine two equally treated Weldox 960 plates that differed significantly in properties such as bendability and toughness. In the second part seven different plates of the steel grade Weldox 1100 have been investigated where all the plates were treated in various ways. The leveling of the plates was performed in two different ways; either according to the standard leveling or to the property affected leveling (ERIK). The experimental part includes tests such as bending, hardness, toughness, tensile and inclusions measurements.The results have shown that the most significant material properties affecting the bendability are the yield strength and the purity close to the plate surface. Leveling with ERIK as the last treatment step has shown that the toughness of the material can be increased but it does not affect the bendability for these specific steel grades. Other properties such as hardness, ultimate tensile strength and elongation have no major impact on the bendability for this specific composition. The most suitable treatment proved to be tempering at 200°C as the last step in the process chain.
21
Ali, Ghada Abdulbaqi. "Temperature Dependency of the Rheological Properties and Strength of Cemented Paste Backfill That Contains Sodium Silicate." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/41985.
Full textAbstract:
Over the past decades, cemented paste backfill (CPB) has become a common, environmentally friendly method of managing mine wastes (such as tailings). This technology allows up to 60% of the total amount of tailings to be reused and filled in the mine stopes after converting them into cemented material. Beside reducing the environmental risks associated with the traditional disposal of these materials, turning them into cemented material and placing them in the underground mine stopes can also provide secondary support for these stopes in addition to minimizing the risk of ground subsidence in the mine area. CPB is an engineered mixture of tailings, water, and hydraulic binder (such as cement, blast furnace slag, and fly ash) that is mixed in the paste plant and delivered into the mine stopes through a gravity or pumping based transportation system. During the transportation of CPB through the delivery system pipelines, the flowability of CPB depends on the rheology of the transported CPB, which is affected by different factors, such as the transportation time, temperature variation, binder type, and chemical composition of these mixtures. In addition, the performance of CPB, after placing the CPB mixture into the mine stopes, is mainly dependent on the role of the hydraulic binder, as it increases the mechanical strength of the mixture through the process of cement hydration. The mechanical strength is also influenced by different factors, such as time progress, temperature variation, and presence of chemical additives. It has previously been found that fresh CPB transported and/or placed in the mine stopes can be susceptible to temperature variation of different sources, such as the climatic effects, heat generated from the surrounding rocks, and heat generated during the process of cement hydration. Unsuitable flowability of CPB through the delivery system might lead to significant financial losses due to clogging of pipelines with unexpected hardening of CPB during transportation, which will cause delay in work and possible damages to the pipelines. Also, failure of CPB structure in the mine stopes due to inappropriate mechanical strength may cause casualties to the mine workers as well as significant environmental and economic damages. Many researchers studied the rheological properties and/or strength development of CPB under the individual effect of any of the aforementioned factors. Additionally, many researchers have evaluated the coupled effect of some of these factors on the rheology and mechanical strength of CPB material. Hitherto, there are currently no studies that addressed the combined effect of all these conditions on the rheological properties and strength development of CPB. At the first stage of this M.A.Sc. study, a series of experimental tests was conducted on fresh CPB in order to determine the combined effect of time, temperature, binder content, and chemical additives on the rheological properties of CPB. These experiments include rheological properties test (yield stress and viscosity), microstructural analysis (thermal analysis and XRD), chemical analysis (pH and Zeta potential), and monitoring tests (electrical conductivity), which were conducted on 125 CPB samples that were mixed and prepared at different temperatures (2oC, 20oC, 35oC) and cured for different curing time (0 hrs., 0.25 hrs., 1 hr., 2hrs, and 4 hrs.). These samples were prepared with different blends of hydraulic binders (PCI, PCI/Slag, and PCI/FA) and contained different dosages of sodium silicate (0%, 0.1%, 0.3%, and 0.5%). The results obtained show that rheology of CPB increases with the progress of curing time. It also increases with the increase in the initial (mixing and curing) temperature and content of sodium silicate. It was also found that the partial usage of slag and FA reduces the rheological properties. However, CPBs containing PCI/FA as binder have lower rheological properties, and thus better flowability, than those that contain PCI/Slag as binder. At the second stage of this M.A.Sc. study, in order to understand the combined effect of time, temperature and sodium silicate content on the strength development of slag-CPB, unconfined compression (UCS) test, microstructural analysis (thermal analysis and MIP), and monitoring tests (electrical conductivity, suction, and volumetric water content) were conducted on 72 CPB samples that were prepared with PCI-Slag as a binder, cured for different times (1 day, 3 days, 7 days, and 28 days) under different curing temperatures of (2oC, 20oC, 35oC), and contained different dosages of sodium silicate (0%, 0.3% and 0.5%). The results obtained at this stage showed that the strength development of slag-CPB increases with the progress of curing time and temperature. It also increases with the increase in the sodium silicate content. Also, the combined effect of high temperature, high dosage of sodium silicate and longer curing time showed significant enhancement in the mechanical strength of slag-CPB. The findings of this M.A.Sc. research will contribute to cost effective, efficient, and safer design of CPB structures in the mine areas. It will also help in minimizing financial loss associated with unsuitable flowability of CPB transported in the CPB delivery system besides reducing the risks of human loss, and the environmental and economic damages associated with the failure of CPB structures.
22
Bathon, Leander Anton. "Probabilistic Determination of Failure Load Capacity Variations for Lattice Type Structures Based on Yield Strength Variations including Nonlinear Post-Buckling Member Performance." PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/1225.
Full textAbstract:
With the attempt to achieve the optimum in analysis and design, the technological global knowledge base grows more and more. Engineers all over the world continuously modify and innovate existing analysis methods and design procedures to perform the same task more efficiently and with better results. In the field of complex structural analysis many researchers pursue this challenging task. The complexity of a lattice type structure is caused by numerous parameters: the nonlinear member performance of the material, the statistical variation of member load capacities, the highly indeterminate structural composition, etc. In order to achieve a simulation approach which represents the real world problem more accurately, it is necessary to develop technologies which include these parameters in the analysis. One of the new technologies is the first order nonlinear analysis of lattice type structures including the after failure response of individual members. Such an analysis is able to predict the failure behavior of a structural system under ultimate loads more accurately than the traditionally used linear elastic analysis or a classical first order nonlinear analysis. It is an analysis procedure which can more accurately evaluate the limit-state of a structural system. The Probability Based Analysis (PBA) is a new technology. It provides the user with a tool to analyze structural systems based on statistical variations in member capacities. Current analysis techniques have shown that structural failure is sensitive to member capacity. The combination of probability based analysis and the limit-state analysis will give the engineer the capability to establish a failure load distribution based on the limit-state capacity of the structure. This failure load distribution which gives statistical properties such as mean and variance improves the engineering judgment. The mean shows the expected value or the mathematical expectation of the failure load. The variance is a tool to measure the variability of the failure load distribution. Based on a certain load case, a small variance will indicate that a few members cause the tower failure over and over again; the design is unbalanced. A large variance will indicate that many different members caused the tower failure. The failure load distribution helps in comparing and evaluating actual test results versus analytical results by locating an actual test among the possible failure loads of a tower series. Additionally, the failure load distribution allows the engineer to calculate exclusion limits which are a measure of the probability of success, or conversely the probability of failure for a given load condition. The exclusion limit allows engineers to redefine their judgement on safety and usability of transmission towers. Existing transmission towers can be reanalyzed using this PBA and upgraded based on a given exclusion limit for a chosen tower capacity increase according to the elastic analysis from which the tower was designed. New transmission towers can be analyzed based on the actual yield strength data and their nonlinear member performances. Based on this innovative analysis the engineer is able to improve tower design by using a tool which represents the real world behavior of steel transmission towers more accurately. Consequently it will improve structural safety and reduce cost.
23
Ahmed, Ismaila Idowu. "The influence of material factors, including cold work, on the susceptibility of stainless steels to stress corrosion cracking." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/the-influence-of-material-factors-including-cold-work-on-the-susceptibility-of-stainless-steels-to-stress-corrosion-cracking(19937317-f1b4-4dbc-ab0e-3eab3760f716).html.
Full textAbstract:
The main objective of the thesis was to gain better understanding of key parameters associated with Cold Work (CW) and their possible effects on Stress Corrosion Cracking (SCC) susceptibility of Austenitic Stainless Steels (ASS) cold rolled to different degrees. The microstructural characterisation of the cold rolled ASS was carried out using optical microscopy to determine and correlate the average grain size with the level of CW. The assessment of martensite development during the CW was carried out using the neutron diffraction technique. The effects of CW levels and strain paths on the lattice strain evolution during the in-situ loading and on the mechanical failure of cold worked ASS were studied. The electrochemical behaviour of cold rolled ASS was also studied. Finally, The SCC susceptibility of ASS was investigated using the Slow Strain Rate Testing (SSRT) techniques. The post-mortem analyses of the failed samples were carried using the optical and Scanning Electron Microscopy (SEM). The study showed that the average grain size decreases with CW and reaches minimum at 20%CW. The smallest and the largest grain size occurred consistently on the Longitudinal (L) and Short-transverse (S) plane respectively. Evidence of martensite development was only found during the plastic deformation at cryogenic temperature and none was observed at ambient temperature. The study showed that the strength of material increases with the level of CW. The Bauschinger effect occurred when the strain path is reversed and its magnitude is independent on whether the tensile or compressive prestraining comes first or last but rather dependent on the amount of CW. The correlation between the CW levels and the lattice strain evolution during the in-situ loading showed that, the lattice strain increases with prestrain and reaches saturation in the material prestrained to 20%CW.The result of the mechanical failure test showed that, 20% cold rolled material loaded along the L and Transverse (T) directions showed a gradual failure, whilst the material loaded along the S direction exhibited a rapid failure. The SEM micrographs suggest that materials loaded along the L and T direction failed with the characteristic features of pure ductile failure while the specimen loaded along S direction showed mixed features of the ductile and brittle failure. The electrochemical properties of the cold rolled materials are more affected by sample orientation than the levels of CW. The short-transverse plane was observed to be most noble whilst the longitudinal plane was the least noble. The results of the SSRT in the chloride environment showed that the plastic elongation, the ultimate tensile strength and the time to failure decrease as the applied potential increases. The post-mortem analysis of the failed samples with the SEM showed that, the fracture surface contained region of ductile failure characterised by dimples, and region of SCC with secondary cracks along the loading axis. Whilst the cross sectional analysis, showed evidence of predominant transgranular stress corrosion cracks. The study found that SCC susceptibility of the ASS is directly linked to strain heterogeneity and directional anisotropy caused by cold working.
24
Tang, Zhenghua. "Optimising the transformation and yield to ultimate strength ration of Nb-Ti micro-alloyed low carbon line pipe steels through alloy and microstructural control." Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-07212007-110711.
Full text
25
Navarini, Lucas. "Manejo de fungicidas e nitrogênio em trigo e seus efeitos na produtividade e qualidade de grãos." Universidade Federal de Santa Maria, 2010. http://repositorio.ufsm.br/handle/1/3197.
Full textAbstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe wheat crop is severely attacked by diseases, which significantly reduce its profitability. The diseases reduce not only productivity but also quality, factor that is essential for the actual economic culture viability. In order to analyze which factors regarding chemical control of foliar diseases are essential to allow bread wheat varieties express the trait, this thesis sought to clarify the interaction between varieties and fungicides in better utilization of nitrogen and its implications for productivity and quality of wheat grains. The two experiments were arranged in a factorial split-plot design in randomized blocks with six replications. The results showed that the fungicides, especially strobilurins, promoted better use of nitrogen in wheat plants. The interactions between the effects provided by fungicides in disease control, and its direct effects on wheat plants physiology, were decisive factors for obtaining high-quality wheat for bread production. The data showed that the increase in nitrogen availability significantly increased the gluten strength. Showing also that, the diseases have committed the remobilization of nitrogen from leaves to grains. Differences were evident between strobilurin and triazole fungicides to control leaf spot and leaf rust, where the epoxiconazole were more effective in the leaf spot complex control, compared to strobilurins. The growth stages of elongation and emission of spikes were critical times for the chemical control of leaf spot. The use of nitrogen in the vegetative stage of wheat increased productivity and its use in the reproductive stages increased the gluten strength. The pyraclostrobin fungicide applied since the seed treatment provided a higher yield and gluten strength.
A cultura do trigo é severamente atacada por doenças, reduzindo significativamente sua rentabilidade. As doenças diminuem não só a produtividade, mas também a qualidade, fator esse imprescindível para a rentabilidade atual da cultura. Com o intuito de determinar os fatores, do ponto de vista do manejo químico de doenças foliares, necessários para obtenção de trigo com qualidade de panificação, esta tese buscou esclarecer a interação entre cultivares e fungicidas na melhor utilização do nitrogênio e suas implicações na produtividade e qualidade de grãos de trigo. Os dois experimentos foram arranjados em esquema fatorial com parcelas subdivididas no delineamento de blocos ao acaso com seis repetições. Os resultados obtidos mostraram que os fungicidas, com destaque para as estrobilurinas, promoveram uma melhor utilização do nitrogênio em plantas de trigo. As interações entre os efeitos proporcionados pelos fungicidas, no controle de doenças, e seus efeitos diretos na fisiologia de plantas de trigo, foram fatores determinantes para obtenção de trigo com alta qualidade de panificação. Os dados mostraram que o aumento na disponibilidade de nitrogênio aumentou significativamente a força de glúten, e que as doenças comprometeram a remobilização do nitrogênio das folhas para os grãos. Ficaram evidentes as diferenças entre estrobilurinas e triazóis no controle de manchas foliares e de ferrugem da folha, onde o epoxiconazol foi mais eficiente no controle do complexo de manchas foliares, enquanto que o controle efetivo da ferrugem da folha do trigo foi proporcionado pelas estrobilurinas. Os estádios fenológicos do elongamento e emissão de espigas foram momentos críticos para o controle químico de manchas foliares. O uso de nitrogênio no período vegetativo do trigo aumentou a produtividade e o seu uso no período reprodutivo aumentou a força de glúten. O fungicida piraclostrobina aplicado desde o tratamento de sementes proporcionou maior produtividade e força de glúten.
26
Heuer, Dennis, Norbert Schwarzer, and Thomas Chudoba. "Contact Mechanics in Dentistry: A systematic investigation of modern composite materials used for fillings." Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200600133.
Full textAbstract:
Nowadays, high demands are made on filling materials in modern dentistry: Durability, Reliability &Aesthetic Requirements
Thus, a group of physicists and an independent practicing dentist investigated 11 different teeth fillings (composite materials) as used in modern
dental practices according to their stability and ability to withstand contact loadings.
27
Theorin, Anders. "Försämrade materialegenskaper i aluminiumkonstruktioner - Liquid Metal Embrittlement inducerat av gallium." Thesis, Försvarshögskolan, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:fhs:diva-6208.
Full textAbstract:
Denna studie undersöker möjligheten att påverka fientliga konstruktioner genom användandet av en effektiv metod, som kan medge en liten risk att upptäckas. Den tänkta påverkan uppnås genom fenomenet Liquid Metal Embrittlement (LME), med vilken höghållfasta metaller kan påverkas så mycket att de kollapsar av sin egenvikt. Uppsatsen studerar LME på ett ofta använt konstruktionsmaterial både civilt som militärt. Ett experiment genomfördes i syfte att undersöka effekterna av LME på en aluminiumlegering, där en aluminiumdetalj exponerades för metallen gallium. Förförsök genomfördes i syfte att undersöka inom vilka tidsförhållanden LME uppstod och experimentets exponeringstider planerades därefter. Efter varje exponeringstid genomfördes ett dragprov för att påvisa en minskad hållfasthet och seghet hos aluminiumet. Resultatet blev en stor minskning av hållfasthet och seghet, där hållfastheten sänktes till 20% av referensvärdet och segheten till 1% av referensvärdet, även om resultatet var spritt.The possibility to damage enemy constructions using an efficient method, which might permit a low risk of detection, is studied in this thesis. This damage is based on the phenomena Liquid Metal Embrittlement (LME) with which high strength metals can be affected so much that they collapse under their own weight. This thesis studies this effect in a material often used for various constructions, both civilian and military. An experiment was conducted in order to evaluate the effects of LME on an aluminium alloy by exposing the aluminium to the metal known as gallium. A pre-experiment was made in order to determine how the time of exposure affected the LME-process and time-periods were decided accordingly. At each of the timeperiods a yield test was conducted in order to measure losses in strength and elasticity of the aluminium. It was shown that a great reduction in strength and elasticity occurred, where the strength was reduced to 20% of the reference sample and elasticity to 1% of the reference sample.
28
Janakiraman, Balasubramanian. "Mechanical property measurement by indentation techniques." Texas A&M University, 2004. http://hdl.handle.net/1969.1/3111.
Full textAbstract:
The mechanical properties of materials are usually evaluated by performing a tensile or
hardness test on the sample. Tensile tests are often time consuming, destructive and need
specially prepared specimens. On the other hand, there is no direct theoretical correlation
between the hardness number and the mechanical properties of a material although
phenomenological relationships do exist. The advantages of indentation techniques are
that they are non-destructive, quick, and can be applied to small material samples and
localized in fashion. Mechanical properties are typically determined from spherical
indentation load-depth curves. This process is again a time consuming one and not
suitable for situations where a quick assessment is required such as in the sheet metal
rolling industry.
In the present study, a novel method of measuring mechanical properties of the material
by multiple spherical indentations is developed. A series of indentations are made on the
substrate with a spherical indenter with different loads. The diameter of the indentation is
related to the load applied to determine the mechanical properties of the material, namely
the yield strength and the work hardening parameters. To determine the diameter of the
indentation quickly, a fiber optic sensing technique is developed. An incident light beam
from a semiconductor laser is coupled back into an optical fiber upon reflection from the
metal surface. By measuring the diffused light power reflected from the metal surface,
the diameter of the indentation is measured.
The spherical indentation technique is difficult for real time mechanical property
measurement of sheet metal in a processing line. Problems arise as the strip is traveling at
2,000 to 4,000 ft/min (10,000 to 20,000 mm/sec) in the processing line. As a first step in
developing a process that could be implemented in a real time processing line, a
preliminary study has been conducted for the prediction of yield strength by laser shock
processing.
29
Dickson, Steven B. "An Investigation of Friction Stir Welding Parameter Effects on Post Weld Mechanical Properties in 7075 AA." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5672.
Full textAbstract:
The effects of weld temperature, travel speed, and backing plate thermal diffusivity on themechanical properties of a weld have been studied. A face centered cubic experiment of designwas completed in which the response variables were yield strength, minimum hardness in the HAZ, and charpy impact toughness. Three models were created from the data gathered usinga stepwise regression in order to see the effects of each parameter. For the yield strength andminimum hardness it was found that only travel speed and backing plate thermal diffusivities werestatistically significant to the properties. The charpy impact toughness saw that all three parameterswere statistically significant to its value. In all three models the travel speed had the greatest affecton the material properties.
30
Lv, Duchao. "A Multi-Scale Simulation Approach to Deformation Mechanism Prediction in Superalloys." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469009668.
Full text
31
Renström, René. "Impact of Metallic Projectiles on a Ceramic Target Surface : Transition Between Interface Defeat and Penetration." Doctoral thesis, Uppsala universitet, Hållfasthetslära, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7264.
Full textAbstract:
The purpose of this thesis is to gain understanding of the load on flat target surfaces produced by projectile impact. Models are proposed from which upper and lower bounds can be derived for the transition be-tween interface defeat and normal penetration. It is shown that the dominating contribution to the normal load is generally provided by the hydrodynamic pressure due to the effect of inertia. In addition it is shown that the contributions from yield strength and compressibility are also significant. For a cylindrical tungsten alloy projectile at an impact velocity representative of to-day’s ordnance velocities, the contributions to the load intensity on the axis of symmetry from yield strength and compressibility are shown to be 15% and 3.4%, respectively, of that of inertia. Impact tests have shown that for conical projectiles transition from interface defeat to penetration occurs at a significantly lower impact velocity than for cylindrical projectiles. In order to better understand the influence of projectile shape, a conical projectile in axi-symmetric impact is studied by use of an analytical model for self-similar flow, and the results obtained are compared to results of numerical simula-tions. It is shown how the maximum load intensity, and the position of the maximum, depends on the apex angle. For an apex angle of 90º, the maximum load intensity is found to be almost three times that pro-duced by a cylindrical projectile with the same impact velocity. This maximum occurs well off the axis of symmetry and is 20% larger than the load intensity at this axis. Both the self-similar model and the nu-merical simulations show that the contribution to the load intensity from compressibility is positive below and negative above an apex angle of around 80º. The contribution of yield strength to the load in-tensity at centre of impact depends only weakly on the apex angle and is therefore similar to that of a cylindrical projectile.
32
Ahmad, Afandi. "Development of Fe-based Superalloys Strengthened by the γ'Phase." Kyoto University, 2020. http://hdl.handle.net/2433/259045.
Full text
33
McAllister, Donald P. "Shearing Mechanisms and Complex Particle Growth in Nickel Superalloy 718." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461079188.
Full text
34
Kocaker, Bahadir Mustafa. "Production Properties Prediction After Forming Process Sequence." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1095512/index.pdf.
Full textAbstract:
Cold metal forming processes have been widely used for manufacturing of their high production rates and increased yield strength after forming process. For the use in service, increased yield strength of the cold-formed products should be known. The new yield strength can be found by several methods. Mechanical tests such as compression or tensile test are direct methods to obtain new yield strength if the product shape is appropriate. Finite element simulations may be another way to get accurate results for new yield strength distribution. Also Vickers hardness number can be used for prediction of yield strengths by available conversion models. The aim of this study is to compare the results of all these methods. During the study two different materials (austenitic stainless steel and carbon steel) cold formed by drawing and extrusion are investigated. FE simulations have been conducted to predict product properties. For this purpose flow curves obtained from compression and tensile tests are used in FE-models based on elasto-plastic, isotropic hardening material. Results show that both materials are highly anisotropic and have much lower yield strength values than found in simulations. Similarly none of the models correlating Vickers hardness numbers and yield strengths are successful since they are designed for an isotropic hardening material. This study basically presents the deviation of a real material behavior from isotropic material behavior.
35
Bouilloud, Randriarimanana Fanomezantsoa M. Michaëlle. "Synthèses et études d'analogues à la matière organique cométaire." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1146/document.
Full textAbstract:
Les comètes présentent un grand intérêt à la fois pour la planétologie et pour l'exobiologie. En effet, ces corps primitifs du fait de leur petite taille et de leurs réservoirs éloignés du soleil, n'ont pas ou que très peu évolué depuis leur formation. L'étude des comètes peut donc permettre de mieux comprendre les processus physico-chimiques ayant eu lieu lors de la formation du Système Solaire. D'autre part, les analyses menées en 1986 dans l'environnement de la comète 1P/Halley ont montré l'existence, dans les grains cométaires d'une phase solide riche en composés organiques. Ainsi, les comètes ont vraisemblablement pu apporter sur la Terre primitive des composés organiques, et favoriser ainsi l'apparition de la Vie. Néanmoins la nature de cette matière organique reste encore très largement méconnue. Ces composés organiques ont vraisemblablement été formés à partir des glaces observées dans le milieu interstellaire et qui sont soumises à différentes sources d'énergie. Les objectifs du travail expérimental mené au cours de cette thèse ont donc été de caractériser les différentes étapes conduisant à la synthèse des composés organiques complexes contenus dans les comètes à partir des glaces interstellaires. En particulier, j'ai étudié i.) la quantification des glaces présentes autour des étoiles naissantes, ii.) les processus de photolyse auxquels elles sont soumises et iii.) la nature des composés organiques qui peuvent être produits durant ces processus. Les observations infrarouges ont permis de détecter de nombreuses molécules en phase condensée autour des étoiles naissantes. Afin de préciser l'abondance de ces molécules, j'ai mesuré les sections efficaces intégrées, aussi appelées forces de bandes, pour huit d'entre elles (H2O, CO, CO2, CH3OH, NH3, CH4, HCOOH and H2CO). En effet, ce paramètre spectroscopique est nécessaire à la quantification des molécules et certaines des valeurs présentes dans la littérature affichaient une grande dispersion. Les nouvelles mesures que j'ai effectuées, basées sur une revue bibliographique exhaustive des masses volumiques et des indices optiques dans le visible, confirment pour certaines molécules (CO2, CO, CH4, NH3) les valeurs utilisées pour déterminer leur abondance. Néanmoins, j'ai pu montrer que les abondances d'autres molécules dans les milieux astrophysiques restent encore très incertaines, en particulier pour CH3OH, H2CO et HCOOH. En phase condensée, la dépendance en longueur d'onde des processus de photolyse est encore très largement négligée. Grâce à l'utilisation de deux lampes VUV, dont l'irradiance spectrale a été préalablement caractérisée, j'ai pu mesurer, dans deux gammes de longueurs d'onde différentes, les rendements quantiques de production de C2H6 et de CO lors de la photolyse de CH4 et CO2. J'ai ainsi pu confirmer que les rendements quantiques dépendent bien de la longueur d'onde de photolyse. L'extrapolation des résultats expérimentaux acquis en laboratoire aux différents milieux astrophysiques nécessite donc une bonne connaissance des spectres VUV mis en jeu. L'objectif final des simulations expérimentales est de prédire la nature de la matière organique cométaire en reproduisant au mieux la chimie pouvant se dérouler dans les glaces interstellaires. Or, le méthane a été détecté en phase condensée dans le milieu interstellaire, mais son influence sur la chimie se déroulant dans des mélanges de glaces contenant les principales molécules interstellaires a été très peu étudiée. J'ai donc soumis un mélange H2O : CH3OH : NH3 : CH4 (10 : 1 : 1 : 2) à une photolyse de 26 heures puis à un chauffage. L'influence du méthane se manifeste par la présence de C2H6 après la photolyse à basse température. Lors du chauffage, le méthane et ses photoproduits semblent se sublimer. Avec ou sans CH4, la chimie à des températures supérieures à 200 K apparaît très similaire. J'en conclu donc que la présence de méthane ne modifie pas notablement la chimie des glaces lors des simulationsComets are very interesting for planetology as well as for exobiology. On one hand, held in the furthest and coldest regions of our solar system and due to their small size, they might not have been altered since their formation. The study of comets should allow a better understanding of the physic-chemical processes occurring during the Solar system formation. On the other hand, the analysis performed in 1986 on the environment of 1P/Halley showed the presence, in the cometary dust, of organic matter. Thus, comets might have brought organics on primitive Earth which might have contributed to the apparition of life. Nevertheless, the nature of these organics is still not well-known. Cometary organics might have been synthesized from the ices detected in interstellar medium which are submitted to different energetic processes. The aims of the experimental work performed during this thesis are to characterize the different steps of the synthesis of complex organic matter contained in comets from the interstellar ices. I studied : i) The quantification of interstellar ices detected around young stellar objects ii) The characterization of the photolysis process to which ices are submitted and iii.) The nature of the organic compounds produced during these processes. Once mixtures and energetic processes are under control, we can make cometary organic analogs. Infrared observations have revealed the presence of several molecules in the solid phase around young stellar objects. To precise their molecular abundances, I have measured the integrated cross sections, also called band strengths, of 8 molecules (H2O, CO, CO2, CH3OH, NH3, CH4, HCOOH and H2CO). Indeed, this spectroscopic parameter is required for the quantification of these molecules and some values presented in literature are scattered. The new measurements performed during this thesis, which are based on a bibliographic review of densities and optical indices in the visible range, confirm the values already used for the quantification of CO2, CO, CH4, NH3. But this work also underlines that abundances of CH3OH, H2CO and HCOOH in interstellar medium are still uncertain. In the solid phase, wavelength dependence of photolysis is often neglected. Thanks to two VUV lamps, for which the spectral irradiances have been characterized, I measured the production quantum yield, in two wavelength ranges, of C2H6 and CO, during photolysis of CH4 and CO2 respectively. Thanks to this study, I point out that quantum yield depends on the photolysis wavelength. Thus, the extrapolation of the experimental results to different astrophysical medium implies a good knowledge of VUV spectra. The final objective of experimental simulations is to foresee the nature of cometary organic matter by reproducing, as realistic as possible, the chemistry occurring in interstellar ices. Methane has been detected in the solid phase in the interstellar medium, but few studies implying methane have been undertaken. Thus, I have photolyzed a mixture composed of H2O: CH3OH: NH3: CH4 (10:1:1:2) during 26 hours at low temperature and then I applied a heating process. The influence of initial methane in the ice chemistry is demonstrated by the presence of its main photoproducts, C2H6, after photolysis. But while increasing temperature, methane and its photoproducts seem to sublimate. Therefore, with or without methane, chemistry occurring at temperature higher than 200K seems to be very similar. I conclude than methane does not have significant influence on ice chemistry
36
Camargo, Severo de Macedo Marcelo. "Élaboration par pulvérisation centrifuge d'alliages Al-Fe-Mo-Si pour applications à haute température : analyse microstructurale et mécanique." Vandoeuvre-les-Nancy, INPL, 1995. http://docnum.univ-lorraine.fr/public/INPL_T_1995_CAMARGO_S_DE_MACEDO_M.pdf.
Full textAbstract:
Certaines parties des aéronefs supersoniques sont soumises à des températures de l'ordre de 150°C pendant les milliers d'heures du fonctionnement de l'appareil. Le choix d'un alliage d'aluminium pour des questions d'allégement de structure se heurte au problème de la faible stabilité thermique des alliages classiques. La solidification rapide a permis d'élaborer industriellement des alliages Al-Fe-V-Si à forte fraction volumique de fins siliciures (caractéristiques mécaniques élevées) stabilisés par la faible diffusivité des éléments de transition dans la matrice. L’objectif de cette étude est d'évaluer le potentiel d'un alliage de cette famille où on a substitué du molybdène au vanadium: selon le rapport Fe/Mo et le traitement thermique on peut maintenir une solution solide sursaturée en molybdène ou faire précipiter en plus du siliciure la phase Al₁₂Mo. Afin d'évaluer les contributions des différents mécanismes de durcissement, un alliage binaire Al-Mo a été préalablement étudié: on note une excellente stabilité thermique mais l'effet durcissant du molybdène est limité par sa faible solubilité. Cinq compositions quaternaires Al-Fe-Mo-Si ont ensuite été étudiées: les caractéristiques mécaniques à froid sont légèrement en dessous de celles des alliages Al-Fe-V-Si du fait d'une fraction volumique inferieure et d'une taille de précipités plus élevée ; en revanche à chaud on note des limites d'élasticité comparables et un creux de ductilité très atténué. La stabilité thermique relative est améliorée par le molybdène
37
Bridges, Robert Leamon. "An Active Study of a Roller Coaster Project in Asia." Digital Commons @ East Tennessee State University, 2010. https://dc.etsu.edu/etd/1670.
Full textAbstract:
A roller coaster manufacturer became aware that improperly heat treated track couplings were sent to a construction site for assembly. Concerns were that suspect couplings might not meet the engineering specifications and could be vulnerable to sudden failure. A testing company in Oak Ridge, TN that specializes in in-situ and laboratory mechanical testing was contacted by the manufacturer for help in this endeavor. The construction company elected to enlist a local testing firm to perform field tests on the components instead of the company in Oak Ridge. The test methods used are incapable of providing quantitative results that could be measured to the engineering specifications, making it unlikely to identify anything but the worst material conditions. This study is an example that the need for accurate analysis is very important. The manufacturer reported that 60 couplings were replaced, but it is presently unknown how many should have been replaced.
38
Tang, Fei. "The Microstructure-Processing-Property Relationships in an Al Matrix Composite System Reinforced by Al-Cu-Fe Alloy Particles." Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/835313-syGDu9/webviewable/.
Full text
39
Machado, Sandro Lemos. "Aplicação de conceitos de elastoplasticidade a solos não saturados." Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/18/18132/tde-24092018-164904/.
Full textAbstract:
Neste trabalho são apresentados resultados de ensaios triaxiais convencionais, de compressão confinada e triaxiais com controle de tensão, realizados em amostras saturadas e com controle de sucção, em corpos de prova indeformados coletados ao longo de um perfil típico de solo da cidade de São Carlos - SP. A partir dos dados obtidos, faz-se um estudo do comportamento de deformação e resistência do solo, em condições não saturadas, ao longo de todo perfil amostrado. Para o solo residual de arenito realiza-se também um estudo das suas principais características de elastoplasticidade, para a condição saturada e para o caso dos ensaios realizados com controle de sucção. Mostra-se que as superfícies de plastificação obtidas para o solo podem ser ajustadas de modo razoável pela superfície de escoamento do Cam-Clay modificado, utilizada nos modelos de Alonso et al. (1990) e Balmaceda et al. (1992). Para esta superfície, o uso de uma lei de fluxo associada conduziu a resultados satisfatórios. Um modelo constitutivo é proposto para representação do comportamento do solo em condições não saturadas. Uma nova superfície de plastificação e uma nova lei de fluxo (não associada) são propostas para o solo, conseguindo-se uma melhor previsão dos pontos de escoamento situados à esquerda da projeção da linha de estados críticos e diminuindo-se os valores dos desvios angulares dos vetores de incrementos de deformação plástica. No modelo constitutivo proposto neste trabalho, a superfície de escoamento LC do solo é obtida levando-se em consideração não somente os valores da pressão de pré-adensamento, mas também os valores de γ(s). Os modelos constitutivos proposto e de Balmaceda et al. (1992) são utilizados na simulação dos ensaios de laboratório, obtendo-se bons resultados. Com o uso dos parâmetros adotados para a simulação dos ensaios de laboratório são realizadas previsões do comportamento de estruturas de fundação em campo, obtendo-se resultados satisfatórios.This thesis deals with the application of elasto-plastic concepts to a typical non saturated soil from São Carlos - SP. The soil profile analysed is composed at is upper part of a sandy soil of coluvium origin and of a residual soil from sandstone at depths larger than 8 m. The water level is at a depth of about 10 m. The experimental work included compression triaxial tests following different stress paths and confined compression tests performed both on saturated and on unsaturated specimens. In the case of the residual soil of sandstone, its main elastoplastic characteristics are studied. It is shown that yield points can be fairly fitted by the yield surface proposed by of Alonso et al. (1990) and Balmaceda et al. (1992), which are an extension of modified Cam-Clay yield surface. In this case, an associated flow law also gave reasonable results in reproducing experimental data. In order to get a better adjustment between experimental and theoretical results, a new constitutive model is proposed using a new yield surface and a non associated flow law. It is shown that this new yield surface can better adjust experimental yield points, mainly those located at left of the critical state line (C.S.L.) and the new flow rule leaded to lower deviation of incremental plastic strain vectors. In the proposed model, the yield surface LC is obtained considering both γ(s) and po experimental values. The proposed and Balmaceda et al. (1992) models were utilised to predict the laboratory soil behaviour, showing good results. The parameters already used to reproduce laboratory tests were also used to model foundation structures built in the soil studied and a fair agreement between experimental and predict results was obtained.
40
Balan, Alexandre. "Modélisation isotherme et anisotherme de la limite d'élasticité précipitation-dépendante de l'Inconel 718." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI003/document.
Full textAbstract:
Ce manuscrit de thèse présente les résultats de travaux concernant les effets des transitoires thermiques sur la précipitation des phases intermétalliques dans le superalliage base nickel Inconel 718® et les conséquences de cette précipitation sur les propriétés mécaniques de cet alliage. Ces travaux se concentrent sur une approche couplée capable de décrire l’évolution de la précipitation de la phase γ'' et ses conséquences sur la limite d’élasticité de l’Inconel 718®. L’état de précipitation est modélisé grâce à l’implémentation des équations de la théorie classique de germination et de croissance, modifiées afin de prendre en compte la géométrie en plaquette des précipités γ''. Ce modèle de précipitation est ensuite validé par des données expérimentales issues de la littérature mais également d’observations au microscope électronique en transmission et d’essais de diffusion de neutrons aux petits angles. La distribution de taille de la phase γ'' ainsi simulée est utilisée comme donnée d’entrée d’un modèle de prédiction de la limite d’élasticité précipitation-dépendant. Ces limites d’élasticité simulées sont enfin comparées à des résultats expérimentaux issus d’essais de traction. Une maquette de soudage a ensuite été réalisée afin de tester le modèle de prévision de limite d’élasticité pour des transitoires thermiques, dans un cas industrielThis thesis manuscript presents the results of work concerning the effects of thermal transients on the precipitation of intermetallic phases in the nickel-based superalloy Inconel 718® and the consequences of this precipitation on the mechanical properties of this alloy. This work focuses on a coupled approach capable of describing the evolution of the precipitation of the γ'' phase and its consequences on the yield strength of the Inconel 718®. The precipitation state is modeled thanks to the implementation of the equations of the classical germination and growth theory, modified to take into account the platelet geometry of the γ'' precipitates. This precipitation model is then validated by experimental data from the literature but also from transmission electron microscope observations and small angle neutron scattering tests. The size distribution of the γ'' phase thus simulated is used as the input data of a model for predicting the precipitation-dependent elasticity limit. These simulated elasticity limits are finally compared with experimental results from tensile tests. A welding model was then made to test the elastic yield prediction model for thermal transients in an industrial case
41
Lee, Jung Hoon. "Local buckling behaviour and design of cold-formed steel compression members at elevated temperatures." Queensland University of Technology, 2004. http://eprints.qut.edu.au/15972/.
Full textAbstract:
The importance of fire safety design has been realised due to the ever increasing loss of properties and lives caused by structural failures during fires. In recognition of the importance of fire safety design, extensive research has been undertaken in the field of fire safety of buildings and structures especially over the last couple of decades. In the same period, the development of fire safety engineering principles has brought significant reduction to the cost of fire protection. However the past fire research on steel structures has been limited to heavier, hot-rolled structural steel members and thus the structural behaviour of light gauge cold-formed steel members under fire conditions is not well understood. Since cold-formed steel structures have been commonly used for numerous applications and their use has increased rapidly in the last decade, the fire safety of cold-formed steel structural members has become an important issue. The current design standards for steel structures have simply included a list of reduction factors for the yield strength and elasticity modulus of hot-rolled steels without any detailed design procedures. It is not known whether these reduction factors are applicable to the commonly used thin, high strength steels in Australia. Further, the local buckling effects dominate the structural behaviour of light gauge cold-formed steel members. Therefore an extensive research program was undertaken at the Queensland University of Technology to investigate the local buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. The first phase of this research program included 189 tensile coupon tests including three steel grades and six thicknesses to obtain the accurate yield strength and elasticity modulus values at elevated temperatures because the deterioration of the mechanical properties is the major parameter in the structural design under fire conditions. The results obtained from the tensile tests were used to predict the ultimate strength of cold-formed steel members. An appropriate stress-strain model was also developed by considering the inelastic mechanical characteristics. The second phase of this research was based on a series of more than 120 laboratory experiments and corresponding numerical analyses on cold-formed steel compression members to investigate the local bucking behaviour of the unstiffened flange elements, stiffened web elements and stiffened web and flange elements at elevated temperatures up to 800°C. The conventional effective design rules were first simply modified considering the reduced mechanical properties obtained from the tensile coupon tests and their adequacy was studied using the experimental and numerical results. It was found that the simply modified effective width design rules were adequate for low strength steel members and yet was not adequate for high strength cold-formed steel members due to the severe reduction of the ultimate strength in the post buckling strength range and the severe reduction ratio of the elasticity modulus to the yield strength at elevated temperatures. Due to the inadequacy of the current design rules, the theoretical, semi-empirical and empirical effective width design rules were developed to accurately predict the ultimate strength of cold-formed steel compression members subject to local buckling effects at elevated temperatures. The accuracy of these new design methods was verified by comparing their predictions with a variety of experimental and numerical results. This thesis presents the details of extensive experimental and numerical studies undertaken in this research program and the results including comparison with simply modified effective width design rules. It also describes the advanced finite element models of cold-formed steel compression members developed in this research including the appropriate mechanical properties, initial imperfections, residual stresses and other significant factors. Finally, it presents the details of the new design methods proposed for the cold-formed steel compression members subject to local buckling effects at elevated temperatures.
42
Mondière, Aurélien. "Contrôle des propriétés mécaniques de l’acier Ferrium® M54® par la maîtrise de sa microstructure au cours du traitement thermique dans l’optique d’applications aéronautiques." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2018. http://www.theses.fr/2018EMAC0006/document.
Full textAbstract:
L’acier Ferrium® M54® présente une composition chimique optimisée, basée sur 40 ans d’évolution et de développement des aciers à durcissement secondaire à précipitation de carbures M2C. Le compromis de propriétés Rm/KIC/KISCC obtenu par la nuance M54® permet d’envisager son utilisation dans les trains d’atterrissage d’avions gros porteurs. Cependant, les premiers essais mécaniques, réalisés par l’utilisateur pour la montée en maturité de la nuance, ont montré une variabilité des propriétés mécaniques suivant le traitement thermique appliqué. Ce travail de thèse s’applique donc à décrire les évolutions microstructurales au cours du traitement thermique de la nuance M54® et les impacts sur les propriétés mécaniques en se concentrant notamment sur le traitement par le froid. Les différentes conditions de mise en solution et de revenu testées ont montré une certaine stabilité de la précipitation au revenu et des propriétés mécaniques qui en découlent. La précipitation a été caractérisée à différentes échelles afin de la comparer avec celle issue des nuances de la même famille. En revanche, selon les conditions de traitement par le froid réalisées, la limite d’élasticité varie de manière significative sans qu’aucun des paramètres liés à la précipitation ne soient modifiés. Le taux d’austénite est en revanche un paramètre déterminant pour la limite d’élasticité et est très sensible aux conditions de traitement par le froid : temps et température entre la trempe à l’huile et le traitement cryogénique et température de traitement cryogénique. Un traitement thermique amélioré a ainsi été proposé pour obtenir un taux d’austénite réduit et constant et limiter ainsi les variations de limite d’élasticitéFerrium® M54® steel presents an optimized composition, based on 40 years of research and development on secondary hardening steels. This alloy exhibits an excellent Rm/KIC/KISCC balance that allows considering its use in landing gears applications of wide-body aircrafts in the future. However, initial mechanical tests performed by the end-user have shown variability in mechanical properties depending on the applied heat treatment. The main goal of this work is to describe the microstructural evolutions of the alloy M54® during heat treatment and their impact on the resulting mechanical properties with a specific focus on the effect of the cryogenic treatment.The different austenitizing and tempering conditions investigated have shown a stability of the tempering precipitation and mechanical properties. This precipitation has been characterized at different scales and compared with other grades of the same family. On the other hand, depending on cryogenic treatment conditions, a significant variation of the mechanical properties and in particular of the yield strength is observed without any modification in the precipitation distribution and volume fraction or size. Austenite content is critical for the yield strength and is very sensitive to the cryogenic treatment conditions: time and temperature before cryogenic treatment and temperature of cryogenic treatment. An improved heat treatment to obtain reduced and constant austenite content is proposed
43
Ouvrard, Blanche. "Matériaux conducteurs à haute limite d’élasticité dans le système Cu-Mg : élaboration, caractérisation et modélisation." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14860/document.
Full textAbstract:
Les alliages conducteurs à haute tenue mécanique sont utilisés dans de nombreux domaines tels que le transport, l’énergie et l’industrie électronique. La demande en ces matériaux est croissante. Les alliages Cu-Be constituent à l’heure actuelle les matériaux conducteurs les plus résistants mais posent un problème de toxicité et de coût. Pour proposer une alternative à ces derniers, nous avons étudié des alliages Cu-Mg hypo-eutectiques. Deux voies de synthèse ont été utilisées afin d’obtenir des composites endogènes possédant une combinaison originale de propriétés structurelles et fonctionnelles : le refroidissement conventionnel et la solidification rapide par melt-spinning. Les microstructures obtenues ont en commun la présence d’agrégats eutectiques et diffèrent principalement par la dimension des paramètres métallurgiques tels que la taille de grains et la distance interlamellaire. Les systèmes présentent des forces motrices de transformation de phases importantes conduisant à une précipitation au cours d’un maintien thermique. L’investigation des propriétés mécaniques et électriques des alliages Cu-Mg montre que ces dernières égalent celles des alliages Cu-Be. En complément de l’approche expérimentale, nous avons adapté deux modèles : un modèle thermocinétique pour décrire l’évolution temporelle de la microstructure qui a lieu à haute température et un modèle mécanique permettant de rationaliser l'influence des paramètres microstructuraux sur les propriétés mécaniques et électriquesCopper-based high strength conductive alloys are used in a myriad of applications such as transport, energy and electronic industries. The demand for these materials is booming. The strongest conductive alloy is based on the Cu-Be system which has the disadvantage of toxicity and cost. In an attempt to find an alternative to these, we have developed hypoeutectic Cu-Mg alloys. Two synthesis routes were applied to produce endogenous compounds with a unique combination of structural and functional properties: the conventional cooling and the rapid solidification by melt-spinning. The obtained microstructures share the presence of eutectic aggregates and differ mainly by the size of the metallurgical parameters such as grain size and interlamellar distance. The two systems provide high driving forces for phase transformations leading to precipitation during aging. The investigation of the mechanical and electrical properties of Cu-Mg alloys shows that they are equal to those of the Cu-Be alloys. In addition to experimental approach, we have adapted two models: a thermo-kinetic one to describe time evolution of the microstructure which takes place at high temperature and a mechanical one to rationalize the influence of microstructural parameters on mechanical and electrical properties
44
Ranawaka, Thanuja. "Distortional buckling behaviour of cold-formed steel compression members at elevated temperatures." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16417/.
Full textAbstract:
In recent times, light gauge cold-formed steel sections have been used extensively in residential, industrial and commercial buildings as primary load bearing structural components. This is because cold-formed steel sections have a very high strength to weight ratio compared with thicker hot-rolled steel sections, and their manufacturing process is simple and cost-effective. However, these members are susceptible to various buckling modes including local and distortional buckling and their ultimate strength behaviour is governed by these buckling modes. Fire safety design of building structures has received greater attention in recent times due to continuing loss of properties and lives during fires. Hence, there is a need to fully evaluate the performance of light gauge cold-formed steel structures under fire conditions. Past fire research has focused heavily on heavier, hot-rolled steel members. The buckling behaviour of light gauge cold-formed steel members under fire conditions is not well understood. The buckling effects associated with thin steels are significant and have to be taken into account in fire safety design. Therefore, a research project based on extensive experimental and numerical studies was undertaken at the Queensland University of Technology to investigate the distortional buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. As the first phase of this research program more than 115 tensile coupon tests of light gauge cold-formed steels including two steel grades and five thicknesses were conducted at elevated temperatures. Accurate mechanical properties including the yield strength, elasticity modulus and stress-strain curves were all determined at elevated temperatures since the deterioration of the mechanical properties is one of the major parameters in the structural design under fire conditions. An appropriate stress-strain model was also developed by considering the inelastic characteristics. The results obtained from the tensile coupon tests were then used to predict the ultimate strength of cold-formed steel compression members. In the second phase of this research more than 170 laboratory experiments were undertaken to investigate the distortional buckling behaviour of light gauge coldformed steel compression members at ambient and elevated temperatures. Two types of cross sections were selected with various thicknesses (nominal thicknesses are 0.6, 0.8, and 0.95 mm) and both low and high strength steels (G250 and G550 steels with minimum yield strengths of 250 and 550 MPa). The experiments were conducted at six different temperatures in the range of 20 to 800°C. A finite element model of the tested compression members was then developed and validated with the help of experimental results. The degradation of mechanical properties with increasing temperatures was included in finite element analyses. An extensive series of parametric analyses was undertaken using the validated finite element model to investigate the effect of all the influential parameters such as section geometry, steel thickness and grade, mechanical properties and temperature. The resulting large data base of ultimate loads of compression members subject to distortional buckling was then used to review the adequacy of the current design rules at ambient temperature. The current design rules were reasonably accurate in general, but in order to improve the accuracy further, this research has developed new design equations to determine the ultimate loads of compression members at ambient temperature. The developed equation was then simply modified by including the relevant mechanical properties at elevated temperatures. It was found that this simple modification based on reduced mechanical properties gave reasonable results, but not at higher temperatures. Therefore, they were further modified to obtain a more accurate design equation at elevated temperatures. The accuracy of new design rules was then verified by comparing their predictions with the results obtained from the parametric study. This thesis presents a description of the experimental and numerical studies undertaken in this research and the results including comparison with simply modified current design rules. It describes the laboratory experiments at ambient and elevated temperatures. It also describes the finite element models of cold-formed steel compression members developed in this research that included the appropriate mechanical properties, initial geometric imperfections and residual stresses. Finally, it presents the details of the new design equations proposed for the light gauge coldformed steel compression members subjected to distortional buckling effects at elevated temperatures.
45
Silva, Neto Miguel Arcangelo da. "Constribui??o t?cnica de um sistema de emuls?o inversa a base de ?leos vegetais para fluidos de perfura??o." Universidade Federal do Rio Grande do Norte, 2002. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15775.
Full textAbstract:
Made available in DSpace on 2014-12-17T15:01:19Z (GMT). No. of bitstreams: 1
MiguelASN.pdf: 491289 bytes, checksum: be60500500779f6a3fd87b90108feb8c (MD5)
Previous issue date: 2002-09-27The developments in formulating drilling fluids to apply in petroleum fields are based on new technologies and environmental challenges, where the technical performance of a developed drilling fluid is used to produce a minimum environmental impact, showing great economy in costs. It is well known that the potential use of oil-based drilling fluids is limited because these fluids when discharged in the sea do not disperse as much as water-based ones and may form waterproof films in the seabed, having a profound effect on plants and animals living in this environment. The current works have been made in investigating fluids called pseudofluids, which are synthetic ester-based, n-paraffin-based and other fluids formed from inverse emulsion. In this research the principal parameters involved in inverse emulsion process were studied, in laboratory scale, using esters as main component. Others commercial drilling fluids were used as comparative samples, as well as samples from laboratory and field where these drilling fluids are being applied. Concentrations of emulsifier and organophilic clay, which are viscosity donor, were varied to verify the influence of these parameters, in different oil/water ratios (55/45, 60/40, 65/35, 70/30, and 75/25). The salt concentration (NaCl) is an indicative parameter of stability and activity of an esterbased fluid. In this research the salt concentration was varied in 10,000, 20,000, and 50,000 ppm of NaCl. Some rheological properties of the produced fluids were studied, such as: initial gel, plastic viscosity, yield point, and apparent viscosity. Through the obtained rheological measures, the existence of two systems could be verified: fluid and flocculated. It could be noticed that the systems were influenced, directly, by the oil/water ratio and emulsifier, organophilic clay and NaCl concentrations. This study showed the viability to use an ester obtained from a regional vegetable product baba?u coconut oil to obtain an efficient and environmental safe drilling fluid
O desenvolvimento atual e futuro, em campos de petr?leo, baseia-se em novas tecnologias e desafios ao meio ambiente, onde se utiliza principalmente a performance t?cnica de um fluido de perfura??o que produza o m?nimo impacto ambiental, mostrando ainda, uma ?tima economia nos custos desses desenvolvimentos. Sabe-se que o potencial de continuidade de fluidos de perfura??o a base de ?leo est? limitado e, por conseguinte, o avan?o ambiental tem sido na investiga??o de fluidos chamados pseudo-fluidos, ou seja, fluidos sint?ticos base ?ster, ?ster, n-parafina e outros fluidos de emuls?o inversa, os quais est?o em estudo. Neste trabalho estudou-se em n?vel de laborat?rio as principais vari?veis envolvidas no processo de emuls?o inversa usando ?steres como componente principal, utilizando-se amostras comparativas de outros fabricantes, como tamb?m amostras provenientes de laborat?rio e de campo onde est?o sendo utilizados estes fluidos de perfura??o. As concentra??es de emulsificante ou argila organof?lica, que ? doadora de viscosidade, foram variadas para verificar a influ?ncia destes par?metros a diferentes raz?es ?leo/?gua (55/45, 60/40, 65/35, 70/30 e 75/25), mantendo-se constante os demais componentes do fluido. A concentra??o do sal, que ? um par?metro indicador de estabilidade e da atividade em fluido a base ?ster, foi variada em 10.000, 20.000 e 50.000 ppm de NaCl. Algumas propriedades reol?gicas dos fluidos assim produzidos foram estudadas, tais como: gel inicial, viscosidade pl?stica, limite de escoamento e viscosidade aparente. A partir das medidas reol?gicas obtidas, p?de-se verificar a exist?ncia de dois sistemas: fluido e floculado. P?de-se perceber que os resultados obtidos foram influenciados diretamente pela raz?o ?leo/?gua e pelas concentra??es do emulsificante, da argila organof?lica e do NaCl. Este estudo consolidou importantes conhecimentos que abrir?o portas para o sucesso de novas pesquisas, tornando-se fundamental a viabiliza??o de coloc?-lo posteriormente no mercado de trabalho do Brasil
46
Nabi, Brahim. "Nouveaux alliages Fe-Co magnétiques pour l’aéronautique, à microstructure partiellement recristallisée et à texture fortement orientée." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112018/document.
Full textAbstract:
Les propriétés magnétiques et mécaniques des alliages Fe-49%Co-2%V et Fe-27%Co, utilisés respectivement dans les générateurs et les transformateurs électriques de l’aéronef, ont été étudiées en fonction des traitements thermiques. Concernant le Fe-49%Co-2%V, les résultats expérimentaux ont montré que les propriétés magnétiques et mécaniques dépendent de la distance entre les interfaces qui séparent les cristallites présents dans la microstructure et ceci quel que soit le taux de recristallisation. Le champ coercitif dépend linéairement de l’inverse de la distance entre ces interfaces et la limite d’élasticité suit une loi de Hall et Petch modifiée pour tenir compte des sous-joints. De plus, une relation linéaire entre la contrainte de friction de la loi de Hall et Petch avec le taux d’ordre à grande distance mesuré par diffraction de neutrons a été établie. Finalement, en s’appuyant sur l’expérience, une loi polynomiale de degré deux reliant les pertes magnétiques et la limite d’élasticité a été proposée. Concernant l’alliage Fe-27%Co, un suivi de l’évolution de la composante de Goss {011}<100> pendant le processus de fabrication a été réalisé. Cette composante est recherchée car favorable pour les propriétés magnétiques. Il a été trouvé que l’origine de cette texture est intimement liée au cisaillement développé lors du laminage à chaud. De plus, le développement de la texture {111}<112> de déformation à froid a été étudié. Le système de glissement {110}<111>, majoritairement activé, a été mis en évidence via un couplage d’analyses EBSD et de simulations VPSC. Au cours de la déformation plastique, les composantes de Goss et Cube tournée ({001}<110>) tournent afin de positionner leur plan {110} pour le glissement facile. Ces rotations, respectivement de 35° et 55° autour de la direction transverse, permettent de former la composante {111}<112>Magnetic and mechanical properties of Fe-49%Co-2%V and Fe-27%Co alloys, used in electric generators and transformers of the aircraft, have been investigated as a function of heat treatments. As regards to Fe-49%Co-2%V alloy, experimental results have shown that the magnetic and mechanical properties depend on the boundary spacing, which separate the microstructure crystallites, whatever the recrystallized fraction. The coercivity depends linearly on the inverse of the boundary spacing and the yield strength follows a modified Hall Petch relationship by taking into account the sub-grain size. Moreover, a linear relationship between the frictional stress and the long range order degree measured by neutron diffraction has been established. Finally, based on the experiment, a square polynomial degree relationship between the magnetic losses and the yield stress has been proposed. As respect to the Fe-27%Co alloy, the evolution of the {011}<100> Goss component during the manufacturing process has been investigated. This sought component is favorable for the magnetic properties of the sheet. It has been found that the origin of this texture is related to its development by shearing during hot rolling. Moreover, the development of the {111}<112> cold deformation texture was studied. It has been established by coupling EBSD analysis and simulation based on VPSC model that the {110}<111> system is the predominant active slip system during the plastic deformation. During the deformation, the Goss and the rotated Cube ({001}<110>) components, rotate of 35° and 55° respectively with regard to the transverse direction. That happens in order to place the active slip plane {110} in the favorable position for gliding to develop the {111}<112> component
47
Gueguin, Maxime. "Approche par une méthode d’homogénéisation du comportement des ouvrages en sols renforcés par colonnes ou tranchées." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1062/document.
Full textAbstract:
Ce travail s'inscrit dans le contexte des techniques de renforcement des sols, permettant d'améliorer les performances mécaniques de terrains de qualité médiocre. Parmi ces techniques, l'utilisation d'inclusions souples prenant la forme de colonnes ou de tranchées croisées connaît une diffusion croissante. Même si les aspects relatifs à leur procédé de construction sont aujourd'hui bien maîtrisés, les méthodes de dimensionnement de ces ouvrages en sols renforcés restent à améliorer. Dans cette thèse, nous proposons d'utiliser la méthode d'homogénéisation afin d'analyser le comportement global des ouvrages en sols renforcés, dans le cadre de la théorie de l'élasticité (propriétés de rigidité) aussi bien que dans celle du calcul à la rupture (propriétés de résistance). Tenant compte de la périodicité géométrique des différentes configurations de renforcement, nous déterminons le comportement des sols renforcés tout d'abord au niveau local puis à l'échelle de l'ouvrage. Pour évaluer les capacités de résistance des ouvrages en sols renforcés, les approches statique et cinématique du calcul à la rupture sont mises en œuvre analytiquement ou numériquement selon la nature du matériau de renforcement utilisé. Par des formulations numériques innovantes adaptées à cette théorie, nous parvenons notamment à évaluer les domaines de résistance macroscopiques des sols renforcés par colonnes ou tranchées croisées, qui peuvent ensuite être pris en compte dans le comportement à la rupture des ouvrages en sols renforcés. Deux exemples d'application de cette procédure, relatifs au problème de capacité portante d'une semelle de fondation reposant sur un sol renforcé d'une part et à l'analyse de la stabilité d'un remblai d'autre part, sont effectuésThis work takes place in the context of soil reinforcement techniques, aimed at improving the mechanical performances of poor quality grounds. Among these techniques, the use of soft inclusions taking the form of columns or cross trenches has known important developments. Even if the aspects relative to their construction process are presently well mastered, the design methods of such reinforced soil structures still remain to be greatly improved. The present work advocates the use of the homogenization method for assessing the global behavior of reinforced soil structures, both in the context of linear elasticity (stiffness properties) and in the framework of yield design (strength properties). Taking into account the geometrical periodicity of the various reinforcement configurations, we thus determine the behavior of the reinforced soils first locally and then at the global scale. To assess the strength capacities of reinforced soil structures, the static and kinematic approaches of the yield design theory are performed analytically or numerically depending on the kind of reinforcing material which is used. Adopting innovative numerical formulations dedicated to this theory, we can notably evaluate the macroscopic strength domains of column as well as cross trench reinforced soils which can then be introduced in the yield design of reinforced soil structures. Two illustrative applications of this procedure are performed relating to the bearing capacity problem of a reinforced soil shallow foundation on the one hand, the stability analysis of an embankment on the other hand
48
Heva, Yasintha Bandula. "Behaviour and design of cold-formed steel compression members at elevated termperatures." Queensland University of Technology, 2009. http://eprints.qut.edu.au/29310/.
Full textAbstract:
Cold-formed steel members have been widely used in residential, industrial and commercial buildings as primary load bearing structural elements and non-load bearing structural elements (partitions) due to their advantages such as higher strength to weight ratio over the other structural materials such as hot-rolled steel, timber and concrete. Cold-formed steel members are often made from thin steel sheets and hence they are more susceptible to various buckling modes. Generally short columns are susceptible to local or distortional buckling while long columns to flexural or flexural-torsional buckling. Fire safety design of building structures is an essential requirement as fire events can cause loss of property and lives. Therefore it is essential to understand the fire performance of light gauge cold-formed steel structures under fire conditions. The buckling behaviour of cold-formed steel compression members under fire conditions is not well investigated yet and hence there is a lack of knowledge on the fire performance of cold-formed steel compression members. Current cold-formed steel design standards do not provide adequate design guidelines for the fire design of cold-formed steel compression members. Therefore a research project based on extensive experimental and numerical studies was undertaken at the Queensland University of Technology to investigate the buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. As the first phase of this research, a detailed review was undertaken on the mechanical properties of light gauge cold-formed steels at elevated temperatures and the most reliable predictive models for mechanical properties and stress-strain models based on detailed experimental investigations were identified. Their accuracy was verified experimentally by carrying out a series of tensile coupon tests at ambient and elevated temperatures. As the second phase of this research, local buckling behaviour was investigated based on the experimental and numerical investigations at ambient and elevated temperatures. First a series of 91 local buckling tests was carried out at ambient and elevated temperatures on lipped and unlipped channels made of G250-0.95, G550-0.95, G250-1.95 and G450-1.90 cold-formed steels. Suitable finite element models were then developed to simulate the experimental conditions. These models were converted to ideal finite element models to undertake detailed parametric study. Finally all the ultimate load capacity results for local buckling were compared with the available design methods based on AS/NZS 4600, BS 5950 Part 5, Eurocode 3 Part 1.2 and the direct strength method (DSM), and suitable recommendations were made for the fire design of cold-formed steel compression members subject to local buckling. As the third phase of this research, flexural-torsional buckling behaviour was investigated experimentally and numerically. Two series of 39 flexural-torsional buckling tests were undertaken at ambient and elevated temperatures. The first series consisted 2800 mm long columns of G550-0.95, G250-1.95 and G450-1.90 cold-formed steel lipped channel columns while the second series contained 1800 mm long lipped channel columns of the same steel thickness and strength grades. All the experimental tests were simulated using a suitable finite element model, and the same model was used in a detailed parametric study following validation. Based on the comparison of results from the experimental and parametric studies with the available design methods, suitable design recommendations were made. This thesis presents a detailed description of the experimental and numerical studies undertaken on the mechanical properties and the local and flexural-torsional bucking behaviour of cold-formed steel compression member at ambient and elevated temperatures. It also describes the currently available ambient temperature design methods and their accuracy when used for fire design with appropriately reduced mechanical properties at elevated temperatures. Available fire design methods are also included and their accuracy in predicting the ultimate load capacity at elevated temperatures was investigated. This research has shown that the current ambient temperature design methods are capable of predicting the local and flexural-torsional buckling capacities of cold-formed steel compression members at elevated temperatures with the use of reduced mechanical properties. However, the elevated temperature design method in Eurocode 3 Part 1.2 is overly conservative and hence unsuitable, particularly in the case of flexural-torsional buckling at elevated temperatures.
49
Larsson, Markus, and Johan Kullander. "Utbytets och malningens inverkan på NSSC-massans egenskaper." Thesis, Karlstad University, Faculty of Technology and Science, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-5208.
Full textAbstract:
Neutralsulfitkokning av björk möjliggör ett högt utbyte av hemicellulosa, vilket bidrar positivt till flutingens egenskaper och minskar vedkostnaden. Neutralsulfitkoket ska avbrytas när delignifieringen nått tillräckligt långt för att veden ska kunna defibreras skonsamt med en rimlig energiinsats, men innan nedbrytningen av hemicellulosa hunnit accelerera. Syftet med detta examensarbete var att undersöka utbytets och malningens inverkan på NSSC-massans egenskaper.
En laboratoriestudie genomfördes där massan kokades till olika utbyten och maldes vid olika insatser. Resultatet av den studien användes sedan för att ställa om kokaren och raffinörerna på lämpligt sätt vid fabriksförsöken. Massaprover togs ut efter det andra kvarnsteget och skickades för analys. De mest väsentliga egenskaperna för fluting testades genom CCT (Corrugated Crush Test), CMT (Concora Medium Test) och SCT (Short Span Compression test) men övriga konventionella egenskaper testades likväl. En avgörande egenskap för fluting är också dess krypstyvhet som undersöktes på laboratorie genom isokrona kryptester. För att få en djupare förståelse för NSSC-massans egenskaper samt kokningens och malningens inverkan på dessa utfördes även fiberkaraktärisering.
Resultatet visar att styrkan på NSSC-massan kan påverkas genom att variera både utbytet och effekten i raffinörerna. För att åstadkomma en signifikant styrkeökning krävs ett lågt utbyte tillsammans med en hög effekt i raffinörerna. Kraftiga ändringar av dessa parametrar leder dessvärre till att papperets egenskaper förändras i den grad att körbarheten på maskin kan påverkas. Studien visar även att fluting som uppfyller dagens riktvärden kan framställas kostnadseffektivt genom ett högt utbyte i kokaren och en hög insats i raffinörerna. Samtidigt erhålls då en ljusare massa, vilket kan vara betydande i vissa fall. Krypmätningarna visar samtidigt att malningen i positiv bemärkelse påverkar krypstyvheten medan utbytets inverkan är mer svårtolkat. Ett allt för högt utbyte verkar dock vara negativt ur krypstyvhetssynpunkt.
Neutral sulphite cooking of birch enables a high yield of hemicelluloses. This contributes positively to the properties of the flute, reduces the amount of wood needed and hence the cost. The neutral sulphite cook is to be terminated when the delignification has gone sufficiently far so that the wood can be refined mercifully with a reasonable energy input, but before the delignification has gone so far that the degradation of hemicelluloses has started to accelerate. The objective with this thesis was to examine how yield and refining affects the properties of the NSSC pulp.
A laboratory study was performed where the pulp was cooked to different yields and then beaten with different energy inputs. The results from this study were then used to determine how to set the boiler and the refiners appropriately in the paper mill trials. Pulp samples were collected after the second refiner and were then sent for analysis. The most important properties for flute were tested through CCT (Corrugated Crush Test), CMT (Concora Medium Test) and SCT (Short Span Compression test). More conventional properties were tested as well. Another important property for flute, the creep resistance, was tested in the laboratory through isochronous creep tests. To get a deeper understanding of the properties of NSSC-pulp, along with the effects of cooking and refining, fiber characterization was also performed.The results indicate that it is possible to affect the strength properties on the NSSC pulp by varying both the yield and the energy input in the refiners. To accomplish a large increase in strength, a relatively low yield is needed, along with increased refining. Large changes of those parameters may unfortunately lead to changes in paper properties in such a way that the runability on the paper machine is affected.
The results also indicate that it is possible to manufacture flute in a more cost efficient way by lowering the H-factor in the boiler while increasing the degree of refining, still keeping the strength properties above the critical values.A pulp with a higher brightness is also acquired when running the mill this way, which can be important in some aspects. The creep studies indicate that increased refining has a positive effect on the creep resistance. It is harder to make conclusions about the impact of yield, but it seems as though all too high yields affects the creep resistance negatively.
50
Michalčíková, Magdaléna. "Vývoj injektážních směsí pro dodatečné těsnění sypaných hrází." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227206.
Full textAbstract:
Seal of sand or gravel by chemical injection is known and used for a long time. Chemical grouting are however expensive and sometimes the use of cement does not lead to desire effects. So it is trying to find new materials and methodologies injection arrangement works. To achieve savings of chemical products are added to a mixture clay and cement. Clay-cement grouting mix are used not only in order that they are better quality, but also because in this way proposed mixtures have a tendency to penetrate better into incoherent sediments that need additional sealant of chemical injection. For further possible reductions of economic terms the mixture is trying to replace the classic clay. As a suitable substitute for classic clay is to a certain extent the use of secondary raw materials. Above all it is fly ash. As a part of my thesis I deal with the appropriateness use of these materials and examining their properties in the mixture. It was found that by using fly ash were improving consistency of the fresh mixture, reducing the amount of water-cement ratio and reduce shrinkage of the mixture. On the other hand, by using fly ash has been increasing decantation, permeability atc. In the next stage of my work was examined the influence of the quality of cement, lime and liquefaction in the mixture. The aim of thesis is to propose the optimal injection mixture for additional sealing earth dams.