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1
Barlow, D. "Stress relief cracking in A533B and A508C1 2 pressure vessel steels." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233221.
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Su, Lan. "Effects of post-harvest treatment and heat stress on the antioxidant properties of wheat." College Park, Md.: University of Maryland, 2006. http://hdl.handle.net/1903/3864.
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Thesis (M.S.) -- University of Maryland, College Park, 2006.<br>Thesis research directed by: Dept. of Nutrition and Food Science. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
3
Hailer, Benjamin Thomas. "Effect of Heat Treatment on Magnetic and Mechanical Properties of an Iron-Cobalt-Vanadium-Niobium Alloy." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/32135.
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Iron-cobalt-vanadium alloys can be processed to have excellent soft magnetic properties for use in high performance power generation applications such as the rotors and stators of aircraft integrated power units. These soft magnetic properties are, however, developed at the expense of mechanical strength and toughness. Small additions of niobium are reported to increase the strength of these Fe-Co-V alloys. This study evaluates the effects of heat treatment on the mechanical and magnetic properties of heavily cold work strip of a 48 wt.% iron-48 wt.% cobalt-2 wt.% vanadium alloy with a 0.3 wt.% addition of niobium.
For heat treatments between 640 and 740°C for 1 hour the tensile and yield strengths and ductility of the alloy were all found to be superior to a similar alloy found in the literature without the addition of Nb and processed in a similar manner. Magnetic permeability, remnant induction, saturation induction, coercivity and core loss were only slightly degraded at all annealing temperatures when compared with the non-niobium containing alloy. All properties were shown to depend primarily on degree of recrystallization of the sample, which was found to fully recrystallize between 720 and 740 °C for 1 hour anneals. No significant change in measured properties were found when annealing time was increased to 2 hours. Full recrystallization was observed for samples annealed for as short of times as 10 minutes at 800 °C.<br>Master of Science
4
Sedighi, Mohammad. "Modelling the influence of manufacturing parameters on variation of residual stresses in quenched parts." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262815.
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Bender, Robert William. "The Effects of Passive Heat Stress on Muscle Fatigue and Intracortical Excitability of the Wrist Flexors." Ohio University Honors Tutorial College / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1307493073.
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Poole, Warren J., B. Raeisinia, X. Wang, and D. J. Lloyd. "A model for predicting the yield stress of AA6111 after multi-step heat treatments." Springer, 2006. http://hdl.handle.net/2429/398.
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A model has been developed to predict the yield stress of the aluminum alloy AA6111
after multi-step heat treatments which involve combinations of ambient temperature
ageing and high temperature artificial ageing. The model framework follows the internal state variable framework where the two principal state variables are i) the volume fraction of clusters which form at ambient temperature and ii) the volume fraction of metastable phases which form during high temperature ageing. The evolution of the these state variables has modeled using a set of coupled differential equations. The mechanical response (the yield stress) is then formulated in terms of the state variables through an appropriate flow stress addition law. To test the model predictions a series of experiments were conducted which examined two scenarios for multi-step heat treatments. In general, good agreement was observed between the model predictions and the experimental results. However, for the case where a short thermal excursion at 250oC was applied immediately after the solution treatment, the results were not satisfactory. This can be understood in terms of the importance of the temperature dependence for the nucleation density of metastable precipitates.
7
Khalil, Heidi F. "Changes in the mechanical behavior of Nitinol following variations of heat treatment duration and temperature." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31852.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.<br>Committee Chair: Gall, Kenneth; Committee Member: McDowell, David; Committee Member: Thadhani, Naresh. Part of the SMARTech Electronic Thesis and Dissertation Collection.
8
Carlson, Mark. "Post-Exercise Responses During Treatment Delays do not Affect the Physiological Responses to Cooling in Cold Water in Hyperthermic Individuals." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24392.
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Victims of exertional heat stroke (EHS) in whom treatment is delayed have higher rates of multi-organ failure and a greater number of fatalities. Death related to EHS is preventable, through immediate treatment via cold-water immersion (CWI). To date little is known about the influence of treatment delays on core cooling following EHS. Thus we sought to examine the effects of treatment delays on cardiovascular and thermal responses prior to, during, and following CWI treatment in individuals with exercise-induced hyperthermia.
Our findings demonstrate that treatment delays resulted in a sustained level of hyperthermia and cardiovascular strain that significantly increased the time an individual is at risk to the potential lethal effects of EHS. Moreover, we report that cold water immersion treatment is powerful enough to overcome the adverse effects of treatment delays and rapidly reduce core temperatures while facilitating the re-establishment of blood pressure towards normal resting levels.
9
Gonzalez-Mendez, Jose Luis. "Prediction of Geometric Distortions and Residual Stresses on Heat Treated Hot Rolled Rings." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1322064630.
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Steffenburg-Nordenström, Joachim. "Process chain simulation of forming, welding and heat treatment of Alloy 718." Licentiate thesis, Högskolan Väst, Forskningsmiljön produktionsteknik(PTW), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-10917.
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Manufacturing of aero engine components requires attention to residual stress and final shape of the product in order to meet high quality product standards.This sets very high demands on involved manufacturing steps to meet design requirements. Simulation of manufacturing processes can therefore be animportant tool to contribute to quality assurance.The focus in this work is on simulation of a manufacturing process chain comprising of sheet metal forming, welding and a stress relief heat treatment.Simulation of sheet metal forming can be used to design a forming tool design that accounts for the material behaviour, e.g. spring back, and avoid problems such as wrinkling, thinning and cracking. Moreover, the simulation can also show how the material is stretched and work hardened. The residual stresses after forming may be of local character or global depending on the shape that is formed. However, the heat affected zone due to welding is located near the weld.The weld also causes large residual stresses with the major component along the weld. It is found that the magnitude of the residual stresses after welding is affected by remaining stresses from the previous sheet metal forming. The final stress relieve treatment will relax these residual stresses caused by e.g. forming and welding. However, this causes additional deformations.The main focus of this study is on how a manufacturing process step affects the subsequent step when manufacturing a component of the nickel-based super alloy 718. The chosen route and geometry is a simplified leading edge of an exhaust case guide vane. The simulations were validated versus experiments. The computed deformations were compared with measurements after each manufacturing step. The overall agreement between experiments and measurement was good. However, not sufficiently accurate considering the required tolerance of the component. It was found from simulations that the residual stresses after each process affects the subsequent step. After a complete manufacturing process chain which ends with a stress relief heat treatment the residual stresses were not negligible. VIII Special experiments were performed for studying the stress relief in order to understand how the stresses evolve through the heat treatment cycle during relaxation. It was found that the stresses were reduced already during the beginning of the heating up sequence due to decreasing Young´s modulus and yield stress with increasing temperature. Relaxation due to creep starts when a certain temperature was reached which gave a permanent stress relief.
11
Naicker, Leebashen. "Influence of heat treatment condition on the stress corrosion cracking properties of low pressure turbine blade steel FV520B." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25377.
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Stress corrosion cracking (SCC) is a corrosion phenomenon which continues to plague the power generating industry especially in low pressure (LP) steam turbine blades operating in the phase transition zone. An investigation has therefore been conducted to examine the effect of heat treatment condition on the microstructure, mechanical properties and SCC properties of one such LP turbine blade material, FV520B, used in the steam turbines of coal-fired power stations in South Africa. The three stage heat treatment cycle of the FV520B turbine blades consists of homogenisation at 1020°C for 30 minutes, solution treatment at 790°C for two hours and precipitation hardening at 545°C for six hours. In this study, the precipitation hardening temperature was varied in the range 430-600°C to investigate how this variation would affect the material and SCC properties. Hardness and tensile testing were performed to obtain mechanical properties while the investigative techniques used to characterise the microstructures were light microscopy, dilatometry, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Stress corrosion susceptibility for the different heat treatment conditions was quantified using U-bend specimens while crack growth rates and threshold stress intensities for SCC (KISCC) were measured using fatigue precracked wedge open loaded (WOL) specimens. Both SCC tests were conducted in a 3.5% NaCl environment maintained at 90°C. XRD results revealed the presence of reverted austenite in the higher tempered specimens due to the precipitation hardening temperature being close to the Ac1 temperature for the material. The presence of reverted austenite was shown to adversely affect mechanical strength and hardness which decreased with increasing precipitation hardening temperature. Light and electron microscopy (SEM and TEM) revealed the presence of Cr-rich precipitates along the prior austenite grain boundaries in all tested heat treatment conditions. The propensity, quantity and size of the Cr-rich precipitates increased as the specimen temper temperature increased. SCC susceptibility was shown to be dependent upon yield strength and decreased as precipitation hardening temperature increased with specimens in the overaged condition showing no cracking after more than 5000 hours in the test environment. WOL testing only produced cracking in the three highest strength specimens after 2000 hours. Crack growth rates and threshold stress intensities were found to be dependent on yield strength and decreased with increasing precipitation hardening temperature. Analysis of fracture surfaces revealed crack propagation along prior austenite grain boundaries in all test heat treatment conditions indicating intergranular stress corrosion cracking (IGSCC) as the dominant cracking mechanism.
12
Norton, Seth J. "Development of a gleeble based test for post weld heat treatment cracking in nickel alloys." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1057177289.
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Kalkanci, Mine. "Phase Transformation And Magnetic Properties Of Multicomponent Heusler Type Alloys." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613660/index.pdf.
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Many Co-based Heusler alloys with the stoichometric composition X2YZ are ideal candidates for the spintronics applications. So, they have been extensively studied theoretically and experimentally. The aim of this work was to investigate the effect heat treatment on phase stability and magnetic properties for quaternary Co2FeSi1-xGax Heusler alloys with varying Si concentration. The Co2FeSi1-xGax alloy samples were prepared by conventional arc melting technique. The structure of Co2FeSi1-xGax bulk alloys were examined by powder x-ray diffraction and differential scanning calorimetry. It was confirmed that Co2FeSi1-xGax alloys display the L21 type structure for all x compositions based on the annealing temperature. The magnetic ordering transition temperature, Tc, was measured by differential scanning calorimetry. It was found that the order-disorder phase transition temperature from the L21 to the B2 structure, T , decreases while the Curie temperature, Tc, increases with increasing x<br>however, the value of these temperatures were not influenced by changing heat treatment process. The magnetic properties of Co2FeSi1-xGax alloy were investigated by using vibrating sample magnetometer. Higher saturation value was obtained at the L21 phase than the value obtained at the B2 phase. It was concluded that the Co2FeSi0.2Ga0.8 alloy was chosen optimum composition for spintronics applications because of its highest Curie temperature and phase stability of L21.
14
Cevik, Gul. "Investigation Of The Effect Of Orientation And Heat Treatment On The Stress Corrosion Cracking Susceptibility Of 7050 Aluminum Alloy." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605220/index.pdf.
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In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking.
The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction.
In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.
15
Seumangal, Nicole. "Influence of the heat treatment procedure on the stress corrosion cracking behaviour of low pressure turbine blade material FV566." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27427.
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Stress corrosion cracking is one of the leading damage mechanisms in low-pressure turbines in the power generation industry; in LP turbine blades it primarily occurs in the last stage blades. The research investigated the influence of tempering temperature on the microstructure, mechanical properties, and stress corrosion cracking properties of 12% chromium FV566 stainless steel, which is used to manufacture LP turbine blades. The standard heat treatment of the steel comprises of austenitising, quenching and double tempering. Austenitising is carried out at 1050°C for one hour - which is sufficiently long to generate a fully austenitic matrix and to dissolve carbon completely. Subsequently, the material is quenched in air. The high level of alloying elements ensures the complete martensitic transformation, with carbon atoms trapped in the matrix and distributed homogeneously. Thereafter, tempering of the material at 580-600°C enhances the ductility and toughness. Tempering replaces the solid solution strengthening of the dissolved carbon with precipitation strengthening by carbides. The final microstructure of the FV566 steel blades is referred to as tempered martensite. van Rooyen showed that for 12% chromium steel tempering at and above 600°C induces passivity of the material against SCC, while tempering of 12% chromium steels at 450-550°C causes sensitisation of the material and the material exhibits intergranular SCC. From such studies, the motivation arises to investigate the impact of heat-treatment parameters - specifically the impact of tempering temperature on the stress corrosion behaviour of the material. The testing methodology comprises heat treatment of FV566 samples at 1050°C for 1 hour, at 350°C for 1 hour, and thereafter tempering for 1 hour at various tempering temperatures. Each stage of heat treatment is followed by air cooling - followed by analysis of the microstructure, mechanical testing and stress corrosion cracking testing of the specimens at the different temper conditions. Stress corrosion testing was divided into two categories. The first set of tests was carried out with U-bend specimens to determine the susceptibility of materials at different heat treatments to SCC, the time taken for SCC to initiate, and the mode of cracking. The second set of tests was conducted to determine the threshold stress intensity, as a function of crack growth rate, for each heat treatment. The SCC failure mechanism observed was intergranular SCC (IGSCC) by anodic dissolution for the 550°C, 560°C, 570°C, 580°C, 590°C, 600°C and 620°C specimens. The material's resistance to SCC improved with increasing tempering temperature. Specimens tempered at 480°C and 550°C were most susceptible to SCC, while specimens tempered at 600°C The material's resistance to SCC improved with increasing tempering temperature. Specimens tempered at 480°C and 550°C were most susceptible to SCC, while specimens tempered at 600°C were immune to SCC in a 4000-hour period. A change in tempering temperature results in a change in the quantity and type of precipitates formed which results in changes in SCC properties of FV566.
16
Littmann, Andrew Edwards. "Use-dependent plasticity of the human central nervous system: the influence of motor learning and whole body heat stress." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/2931.
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The human central nervous system (CNS) is capable of significant architectural and physiological reorganization in response to environmental stimuli. Novel sensorimotor experiences stimulate neuronal networks to modify their intrinsic excitability and spatial connectivity within and between CNS structures. Early learning-induced adaptations in the primary motor cortex are thought to serve as a priming stimulus for long term CNS reorganization underlying long-lasting changes in motor skill. Recent animal and human studies suggest that whole body exercise and core temperature elevation as systemic stressors also recruit activity-dependent processes that prime the motor cortex, cerebellum, and hippocampus to process sensorimotor stimuli from the environment, enhancing overall CNS learning and performance. A primary goal of rehabilitation specialists is to evaluate and design activity-based intervention strategies that induce or enhance beneficial neuroplastic processes across the lifespan. As such, an investgation of the influence of physical, non-pharmacological interventions on cortical excitability, motor learning, and cognitive function provide the central theme of this dissertation.
The first study investigated the effects of a visually-guided motor learning task on motor cortex excitability at rest and during voluntary activation measured via transcranical magnetic stimulation (TMS). Motor learning significantly increased resting cortical excitability that was not accompanied by changes in excitability as a function of voluntary muscle activation. The cortical silent period, a measure of inhibition, increased after learning and was associated with the magnitude of learning at low activation. These findings suggest that separate excitatory and inhibitory mechanisms may influence motor output as a function of learning success. The following studies investigated the influence of systemic whole-body thermal stress on motor cortex excitability, motor learning and cognitive performance. We established the reliability of a novel TMS cortical mapping procedure to study neurophysiological responses after whole-body heat stress. Heat stress significantly potentiated motor cortex excitability, though acute motor learning and cognitive test performance did not differ between subjects receiving heat stress and control subjects. Future research is needed to delineate the potential of whole body heat stress as a therapeutic modality to influence central nervous system plasticity and performance.
17
Galli, Federica. "RIPENING AND POSTHARVEST MANAGEMENT OF PAWPAW FRUIT." UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/507.
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Pawpaw (Asimina triloba (L.) Dunal) has significant potential as a new fruit crop. During ripening, loss of firmness is extremely rapid, and this trait may be the biggest obstacle to the development of a broader market as handling without injury is difficult. Cold storage of pawpaw seems limited to 4 weeks at 4 C. A study of several cultivars with commercial appeal showed that ripening traits such as ethylene production, respiration and loss of firmness were similar in all genotypes, and that no cultivar showed superior responses to cold storage. Cold storage for longer than 4 weeks caused the development of cold injury symptoms such as black discoloration, rapid loss of firmness, impaired respiration, tissue acidification, decrease in antioxidant content, decrease in volatile ester production and development of off-flavor volatile compounds. Overall cold storage injury symptoms observed in pawpaw may be due to oxidative damage linked to the failure of the two major antioxidant systems that could protect against such damage: phenolics and the ascorbateglutamate system. With the aim of enhancing pawpaw low temperature tolerance and prolonging cold storage length, different techniques such as hot air exposure and hot water dips of fruit prior to beginning cold storage, and intermittent warming periods during cold storage, were evaluated. Despite positive results with these techniques for other commodities, all the strategies failed to appreciably alter fruit ripening, loss of firmness or maintain fruit quality during and/or after cold storage.
18
Wong, Pin Sing. "Studies on the pre-treatment of palm oil mill effluent." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/642.
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The feasibility of using hydrochloric acid (HCl), heat, dilution and magnetic stirring for the pre-treatment of palm oil mill Effluent (POME) before the primary anaerobic treatment was investigated in this study. The theoretical background of oily water emulsion which is the characteristic of POME was reviewed. A range of experiments was performed on samples made up of different combinations of the three major components of POME namely, palm oil, solid from decanter and water. The results suggest that the development of a pre-treatment system to remove the 0.5- 1.2% residue oil and 3-4% solid matter from the fresh POME is feasible thus it could improve the efficiency of further downstream POME treatment.Experiments were conducted to examine the rate of oil flotation from the mixtures of different ratios of palm oil and water treated with different concentrations of HCl, and temperatures and magnetic stirring. Similarly, a series of experiments were performed to determine the rate of solid settlement from palm oil-solid mixture, solid-water mixture and palm oil-solid-water mixture of different ratios treated with different concentrations of HCl and different temperatures. The data obtained from the experiments were used to determine the optimum dosage of HCl used and the temperature required for best oil recovery and solid settlement.From the kinetic studies, the models of the kinetic rate of palm oil flotation and solid settlement were derived. A macro kinetic modeling was adapted to the oil flotation while a power model was used for solid settling. The results showed that treatment with 0.5% HCl was sufficient to increase the rate of oil flotation significantly in Palm oil-water mixture. However, the effect was dependent on the oil-water ratio. An increase in temperature gave higher rate of oil flotation but not as great as that of HCl treatment. Dilution was found to be the two other factors that affected the rate of flotation. The solid settling rates in all tested samples were not significantly affected when they were treated with HCl. The rate of solid settlement was found to be temperature dependent. The optimum temperature for the rate of solid sedimentation was found to be in the region of 800C. Similar positive effect was also observed for a more diluted sample of Solid-Palm oil-Water mixture.
19
Akgun, Nevzat. "Effect Of Retrogression And Reaging Heat Treatment On Corrosion Fatigue Crack Growth Behavior Of Aa7050 Alloy." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605332/index.pdf.
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The effect of retrogression and reaging heat treatment on corrosion fatigue crack growth behavior on AA7050 T73651 aluminum alloy is investigated. CT (Compact Tension) specimens are prepared in LS direction for fatigue crack growth tests . Samples are solution heat treated at 477 °<br>C and aged at 120 °<br>C for 24 h (T6 condition). After that, samples are retrogressed at 200 °<br>C for times of 1, 5, 30, 55 and 80 minutes in a circulating oil bath. Then, samples are re-aged at 120 °<br>C for 24 h (T6 condition). Hardness measurements are taken at different retrogression times and at the end of the heat treatment.
Fatigue crack growth tests are performed at as received condition and at different retrogression times with sinusoidal loading of R=0.1 and f=1 in both laboratory air and corrosive environment of 3.5% NaCl solution. The highest fatigue crack growth resistance is observed for 30 min. and 5 min. retrogression for laboratory air and corrosive environment respectively. It is concluded that RRA can successfully be used to improve fatigue performance of this alloy.
20
Руденко, Лідія Федорівна, Лидия Федоровна Руденко, Lidiia Fedorivna Rudenko та К. О. Горбенко. "Возможности закалки инструментальных сталей в магнитном поле". Thesis, Изд-во СумГУ, 2010. http://essuir.sumdu.edu.ua/handle/123456789/6391.
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Dyne, Eric D. "Magnetic Nanoparticle Hyperthermia-Mediated Clearance of Beta-amyloid Plaques: Implications in the Treatment of Alzheimer’s Disease." Kent State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent1618706341759415.
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Ali, Abubeker Yimam. "Understanding the effects of mineralogy, ore texture and microwave power delivery on microwave treatment of ores." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/3988.
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Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010.<br>ENGLISH ABSTRACT: Previous work has shown that microwave heating of mineral ores induces fractures
around grain boundaries due to the differences in absorption of microwaves and the
resulting differential thermal expansion among the various mineral phases in the ore
particles. As a consequence, this reduces the energy required in subsequent grinding
and enhances liberation of valuable minerals. In this study, first, the influences of
different variables on bulk strength reduction of microwave treated ores have been
investigated. Nine different binary ore models were constructed by randomly
disseminating 10 vol.% microwave absorbing minerals in transparent matrices.
Computational simulations of heating, thermal damage and unconfined compressive
strength (UCS) tests on the conceptual binary ores have been undertaken by using
finite-difference modelling techniques. The influence of thermo-mechanical properties
of minerals on strength reduction of microwave treated ores was examined. It was
shown that in general the thermal properties of the microwave absorbing mineral and
the mechanical properties of the transparent matrix have the most significant effect on
the strength reduction. Binary ores containing a microwave absorbing mineral that
has a high thermal expansion coefficient in a strong transparent matrix achieved
higher reductions in strength. The influence of absorbent phase grain size on strength
reduction of ores was also quantified. It was shown that for the same energy inputs
and mineral types, the reductions in strength were much higher in coarse-grained
ores. It has also been shown that for the same mineralogy and treatment condition,
ores with poorly disseminated heated phase achieved much higher strength reduction.
The effect of microwave treatment on the mechanical state of an ore sample was also
examined. It was demonstrated that unconfined compressive strength is less sensitive
to microwave-induced micro-fractures and found to be a poor descriptor of liberation
behaviour.
A new method of characterizing damage in microwave treated ore using a continuum
approach was developed. The method measures the damage around the grain
boundary regions during the heating process. Using the method, it was possible to
elucidate in detail the influences of power density, mineralogy, ore texture on
microwave treatment of ore. It was shown that the amount of grain boundary damage
incurred at a specific power density and energy input is dependent both on the ore mineralogy and its texture. The energy inputs that were required for significant (>
10%) grain boundary damage in the ores range from 0.09 to 7.06 kWh/t depending on
the power density applied, the ore mineralogy and its texture. It was also shown that
for a given mineralogy and ore texture there is a power density level below which no
further increase in grain boundary damage is possible by increasing exposure time.
The effect of pulse repetition frequency on grain boundary damage was also
elucidated using the method. It was found that high pulse repetition frequencies (³ 50
Hz) resulted in an amount of grain boundary damage that was indistinguishable from
that caused by continuous wave operation for a fixed energy input. It has also been
shown that for a fixed microwave energy input the best result would be obtained by
using the lowest possible pulse repetition frequency and highest peak pulse power.
The effect of microwave treatment of ores at different treatment conditions on the
extent of damage and crack pattern was also investigated in detail using bondedparticle
model (BPM). It has been shown that the amount of micro-cracks and also
the cracks pattern in an ore sample after microwave treatment significantly depend on
its mineralogy, microwave treatment condition (power density) and absorbent phase
grain size. It has also been shown that a minimum power density is required to
localize damage around the grain boundary in an ore sample. This minimum power
density was found to strongly depend on the ore mineralogy and its texture.
Initial simulation test work concerning the effect of microwave treatment on liberation
of minerals is also presented. It has been shown that microwave irradiation
considerably changed the fracture pattern of an ore in simulated single particle
crushing. The fracture pattern of the ore treated at high power density (Pd = 0.1 kW
/mm3abs for 1 ms) was along the grain boundary and the absorbent mineral was
intact. In the ore treated at lower power density for the same energy input (Pd = 1
W/mm3abs for 0.1 s) both intergranular and transgranular fractures were observed.
However, in all cases the fracture patterns were preferentially localized around the
grain boundary compared to that of the untreated ore.<br>AFRIKAANSE OPSOMMING: Vorige studies het getoon dat mikrogolfverhitting van mineraalertse tot breuke om die
ertskorrelgrense aanleiding gee, omdat die verskillende mineraalfases in die
ertsdeeltjies die mikrogolwe verskillend absorbeer, en dus ook verskillend uitsit.
Korrelgrensbreuke verminder die vereiste energie vir latere slypwerk, en verhoog die
vrystelling van waardevolle minerale. Hierdie studie het eerstens die uitwerking van
verskillende veranderlikes op die algehele sterktevermindering van
mikrogolfbehandelde ertse ondersoek. Hiervoor is nege verskillende binêre
ertsmodelle vervaardig deur mikrogolfabsorberende minerale met ʼn
volumepersentasie van 10% lukraak in deursigtige matrikse te versprei. Met behulp
van eindigeverskilmodelleringstegnieke is berekeningsimulasies van verhitting,
warmteskade en onbegrensde druksterkte (“unconfined compressive strength”) op die
konseptuele binêre ertse uitgevoer. Die invloed van termomeganiese
mineraaleienskappe op die sterktevermindering van mikrogolfbehandelde ertse is
eerste onder die loep geneem. Daar is bevind dat die warmte-eienskappe van die
mikrogolfabsorberende mineraal, en die meganiese eienskappe van die deursigtige
matriks, die beduidendste uitwerking op sterktevermindering het. Binêre ertse wat ʼn
mikrogolfabsorberende mineraal bevat met ʼn hoë warmte-uitsettingskoëffisiënt in ʼn
sterk deursigtige matriks, het groter sterkteverminderings getoon. Die invloed van
korrelgrootte in die absorbeerfase op die sterktevermindering van ertse is volgende
versyfer. Die studie het getoon dat, op grond van dieselfde energie-insette en
mineraalsoorte, grofkorrelrige ertse groter sterktevermindering ondergaan het.
Eweneens is bewys dat, met dieselfde mineralogie en behandelingsomstandighede,
ertse met ʼn swak verspreide verhittingsfase ook groter sterktevermindering ervaar.
Die uitwerking van mikrogolfbehandeling op die meganiese toestand van ʼn
ertsmonster is boonop ondersoek. Die studie het getoon dat onbegrensde druksterkte
minder gevoelig vir mikrogolfgeïnduseerde mikrobreuke is, en as ʼn swak aanwyser
van vrystellingsgedrag beskou word.
ʼn Nuwe metode om skade by mikrogolfbehandelde ertse te tipeer is gevolglik met
behulp van ʼn kontinuumbenadering ontwikkel. Dié metode meet die skade rondom die
korrelgrens gedurende die verhittingsproses. Deur middel van voormelde metode was
dit dus moontlik om die invloed van kragdigtheid, mineralogie en ertstekstuur op die
mikrogolfbehandeling van erts deeglik te ondersoek. Daar is bevind dat die mate van korrelgrensskade by ʼn bepaalde kragdigtheid en energie-inset, van sowel die
ertsmineralogie as ertstekstuur afhang. Na gelang van die toegepaste kragdigtheid,
die ertsmineralogie en ertstekstuur, het die vereiste energie-insette vir beduidende
(>10%) korrelgrensskade van 0,09 tot 7,06 kWh/t gewissel. Dit het voorts geblyk dat
enige bepaalde mineralogie en ertstekstuur oor ʼn minimum kragdigtheidsvlak beskik,
onder welke vlak geen verlenging in blootstellingstyd enige verdere korrelgrensskade
kan veroorsaak nie. Die uitwerking van pulsherhaalfrekwensie op korrelgrensskade is
ook met behulp van bogenoemde metode verklaar. Die studie het getoon dat, op grond
van ʼn vaste energie-inset, hoë pulsherhaalfrekwensies (≥50 Hz) en gelykgolfwerking
presies dieselfde hoeveelheid korrelgrensskade tot gevolg het.
Volgende is daar met behulp van ʼn gebondedeeltjiemodel (“bonded-particle model”)
noukeurig ondersoek ingestel na die uitwerking van verskillende
mikrogolfbehandelingsomstandighede op die hoeveelheid skade en die kraakpatroon
by ertse. Die studie het getoon dat die hoeveelheid mikrokrake sowel as die
kraakpatroon in ʼn mikrogolfbehandelde ertsmonster in ʼn groot mate van die betrokke
erts se mineralogie, mikrogolfbehandelingsomstandighede (kragdigtheid) en
korrelgrootte in die absorbeerfase afhang. Daar is ook bevind dat ʼn minimum
kragdigtheid nodig is om skade tot die gebied om die korrelgrens te beperk, welke
minimum kragdigtheid oënskynlik grotendeels deur die ertsmineralogie en -tekstuur
bepaal word.
Die studie bevat ook die resultate van aanvangsimulasietoetse oor die uitwerking van
mikrogolfbehandeling op mineraalvrystelling. Die toetse het getoon dat
mikrogolfbestraling ʼn beduidende verandering tot gevolg het in die ertsbreekpatroon
met gesimuleerde enkeldeeltjievergruising. Die breekpatroon van die erts wat by hoë
kragdigtheid (Pd = 0,1 kW/mm3abs vir 1 ms) behandel is, het ál langs die korrelgrens
gestrek, terwyl die absorberende mineraal nog ongeskonde was. In die erts wat by
laer kragdigtheid dog dieselfde energie-inset behandel is (Pd = 1 W/mm3abs vir 0,1
s), is sowel tussenkorrel- as oorkorrelbreuke opgemerk. In teenstelling met die
onbehandelde erts, was die breekpatrone by die behandelde erts egter in alle gevalle
steeds merendeels rondom die korrelgrens geleë.
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Lukawska, Anna Beata. "THERMAL PROPERTIES OF MAGNETIC NANOPARTICLES IN EXTERNAL AC MAGNETIC FIELD." Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1401441820.
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Liu, Jie [Verfasser], Norbert [Akademischer Betreuer] Huber, and Mathias [Akademischer Betreuer] Göken. "Phase transformations and stress evolution during laser beam welding and post heat treatment of TiAl-alloys / Jie Liu. Betreuer: Norbert Huber ; Mathias Göken." Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2015. http://d-nb.info/1073611051/34.
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Воробйов, Сергій Ігорович, Сергей Игоревич Воробьев, Serhii Ihorovych Vorobiov та ін. "Вплив орієнтації мультишарів на основі Co та Gd у зовнішньому магнітному полі на їх магнітні властивості". Thesis, Сумський державний університет, 2015. http://essuir.sumdu.edu.ua/handle/123456789/40798.
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На сучасному етапі розвитку магнітоелектроніки велика увага дослідників приділяється вивченню впливу різних фізичних полів на стабільність робочих характеристик матеріалів чутливих елементів датчиків магнітного поля. Дана робота присвячена встановленню загальних закономірностей впливу температури термообробки на магнітні властивості мультишарів на основі Со і Gd при зміні їх
орієнтації у зовнішньому магнітному полі.
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Dai, Tao Dai. "Effect of Postweld Heat Treatment on the Properties of Steel Clad with Alloy 625 for Petrochemical Applications." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523572474171801.
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Banerjee, Sayanti. "Effect of Chemistry on the Transformation of Austenite to Martensite for Intercritically Austempered Ductile Iron." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/19258.
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Intercritically austempered ductile iron (IADI) with a matrix microstructure of ferrite plus metastable austenite has an excellent combination of strength and toughness. The high strength and good ductility of this material is due to the transformation of metastable austenite to martensite during deformation. In the present study, the transformation of austenite to martensite for intercritically austempered ductile irons of varying alloy chemistry (varying amounts of nickel and/or manganese) were examined using in-situ neutron diffraction under strain-controlled loading at VULCAN at the Spallation Neutron Source at Oak Ridge National Laboratory (ORNL). Both diffraction and tensile data were collected and synced using the VDRIVE software (a proprietary ORNL software package). The single peak fit method was employed in the analysis of the diffraction data. <br /><br />In this thesis, the stress and strain for the start of the transformation of metastable austenite to martensite were determined. The development of residual stresses during deformation and the elastic diffraction constants for both the ferrite and austenite phases were also determined. The material was characterized using optical microscopy, backscattered imaging in the scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy.<br /><br>Master of Science
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Malmberg, Andreas. "The influence of carbonitriding on hardness, retained austenite and residual stress in 52100 steel." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173804.
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High rolling contact fatigue parts are vital for the long service life of fuel pumps. Cummins Fuel Systems are currently using an M2 tool steel for one of the most important roller bearing application in their pumps, namely the cam follower. The future design of the cam follower is a pin-less tappet roller. The wear and fatigue properties of the roller is vital to ensure reliability of the fuel system. M2 tool steel is an expensive material and becomes even more so if diamond like coating (DLC) is needed to decrease the friction coefficients. To cut costs of the fuel pump it might be possible to replace the M2 tool steel with 52100 steel (100Cr6). Competitive methods have proven that carbonitrided 52100 can reach excellent wear and fatigue properties making it a candidate to replace M2 tool steel. How the properties of hardness, toughness and compressive residual stresses are developed in 52100 and how they affect the fatigue and wear resistance has been researched from the literature. A big part of this project was to do an extensive analysis of a roller bearing that was believed to have gone through one of these competitive methods that produce excellent wear and fatigue resistance. The analysis was done with background to the knowledge gathered from the literature. Finally process trials were set up to carbonitride 52100 steel samples. The trials were done to develop a better understanding of how adding carbon together with nitrogen to the surface of 52100 steel will influence the metallurgical parameters that results in good wear and fatigue resistance. From this analysis Cummins hope to create a process recipe that can be used for carbonitriding the cam follower and maybe other components in their fuel systems.
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Ornek, Cem. "Performance characterisation of duplex stainless steel in nuclear waste storage environment." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/performance-characterisation-of-duplex-stainless-steel-in-nuclear-waste-storage-environment(4db73e9b-c87c-40a6-9778-0b823b1c499f).html.
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The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.
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Simsir, Caner. "3d Finite Element Simulation Of Steel Quenching In Order To Determine The Microstructure And Residual Stresses." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609412/index.pdf.
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In the course of thermal treatments, materials are usually subjected to continuous heating and cooling cycles during which microstructural evolution and mechanical interactions occur simultaneously at different length and time scales. Modeling of these processes necessitates dealing with inherent complexities such as large material property variations, complex couplings and boundary conditions, coupled heat and mass transfer mechanisms and phase transformations. In this study, a mathematical framework based on finite element method (FEM) capable of predicting temperature history, evolution of phases and internal stresses during heat treatment of metals and alloys was developed. The model was integrated into the commercial FEA software MSC.Marc®<br>by user subroutines. The accuracy of the model was verified by simulating the quenching of eccentrically drilled steel cylinders. Simulation results were justified via SEM observations and XRD residual stress measurements. According to the results, the model can effectively predict the trends in the distribution of microstructure and residual stresses with a remarkable accuracy.
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Klement, Jan. "Výpočtová analýza napjatosti turbinové lopatky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229982.
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This diploma thesis continues to the Ing. Damborský work and deals with strain-stress and dynamic analysis of the steam turbine blade. This blade is part of the last row of low pressure level of steam turbine. Computational analysis has been performed in first part using FEM. After that follows a modal analysis for the blade without residual stress as well as for the blade affected by heat treatment. Main goal is to obtain whether the state of stress is in the crack initiation area is influenced by thermal treatment. This problem was solved by computational simulation in commercial software Ansys 11.0.
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Chiqueti, Cleber Michel. "Estudo das distorções em aços AISI 5160 e AISI 6150 com variação da temperatura e da agitação do meio de resfriamento." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18150/tde-13012011-150331/.
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A distorção em tratamento térmico é a maior causa dos problemas na indústria. Existem vários parâmetros que compõem esse fenômeno. Com o avanço da tecnologia, a medição de algumas variáveis intrínsecas ao fenômeno da distorção se tornou possível, auxiliando no melhor conhecimento do processo o que resulta na diminuição do retrabalho e sucata na indústria. A concretização de melhoria em processos produtivos já é uma realidade; que se tornou possível com a diminuição dos limites de padronização e com processos de produção bem definidos e simplificados. Estudos localizados em determinados produtos específicos, bem como os seus meios de resfriamentos estão em constante evolução, tornando possível a troca de informação e tecnologia, auxiliando na diminuição dos desperdícios e contribuindo para a mitigação dos impactos ambientais. Esse trabalho visa estudar as distorções produzidas em aços AISI 5160 e AISI 6150, com corpos de prova sensíveis a distorção, variando alguns fatores como, mudança em três níveis de temperatura e em três níveis de agitação em óleo mineral convencional; os quais fazem parte do processo produtivo na indústria. Variando as temperaturas do meio de resfriamento e a agitação do banho, é possível determinar com o auxílio estatístico, metalográfico, das curvas de resfriamento e das curvas das taxas de resfriamento quais são as variáveis que tem influência na distorção. Esses resultados mostraram que a agitação e a temperatura do meio líquido de resfriamento são parâmetros imprescindíveis de controle para uma uniformidade da têmpera para a obtenção das características desejáveis.<br>The heat treatment distortion is the biggest cause of problems at companies. There are many parameters which cause this phenomenon. Studies in specific products, as well as in the quenchants are always progressing what became possible the dissemination of information and also the technology, helping to decreasing of waste and to improve environment. With the technology improvement, distortion phenomenon has become well known, resulting in better control of variables decreasing scrap metal and rework. However, this subject still needs to be investigated. In his context, this work studies the distortion phenomenon in two different steels (AISI 5160 and AISI 6150) under variable conditions of the cooling. Mineral oil quenchant in three bath temperatures and three agitation levels were used in this work. Changing those parameters it was possible to determinate which conditions would promote worst results in terms of distortion. Statistics studies, cooling curves analysis and metallographic observation offered support for the obtained conclusion.
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Alexandre, édina Serpa. "Avaliação da influência da temperatura e ponto de orvalho no recozimento final de aços elétricos semiprocessados e totalmente processados." Universidade do Estado de Santa Catarina, 2010. http://tede.udesc.br/handle/handle/1774.
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Previous issue date: 2010-12-07<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Semi-processed electrical steels require annealing after processing in the motors manufactures to improve motors efficiency by reducing losses and increasing permeability. Annealing in fully processed electrical steel is performed to relax the residual stress and promote recovery or recrystallization of distorted parts. Commercial samples from different steels with different chemical compositions were selected to evaluate the influence of final annealing heat treatment temperature and dew point on the magnetic properties, the carbon content and grain size increase. Were performed with annealing atmosphere without steam and with dew point of 5, 10, 20 and 25°C at temperatures of 760 and 790°C. Magnetic losses, relative permeability, carbon content, grain size and mechanical properties measurements were made in addition to the evaluation of the microstructure to determine this influence. It was observed in the semi-processed steel with 300 ppm carbon content, which with dew point increase the carbon content reduce the grain size increase and improve magnetic properties. In the other steels studied, reducing the dew point improved the magnetic properties, but the atmosphere without steam has improved only fully processed steel with 2% silicon. It was found that in fully processed steels the best results were obtained with annealing temperature of 790°C.<br>Aços elétricos semiprocessados necessitam de recozimento após a sua manufatura para melhorar o rendimento dos motores com a redução das perdas magnéticas e aumento da permeabilidade. os aços totalmente processados o recozimento é realizado para relaxar as tensões residuais e promover a recuperação ou recristalização das partes deformadas. Amostras comerciais de diferentes aços com variadas composições químicas foram selecionadas para avaliar a influência do ponto de orvalho e temperatura de recozimento final nas propriedades magnéticas, no teor de carbono e no aumento do tamanho de grão. Foram realizados recozimentos com atmosfera sem vapor e com ponto de orvalho de 5, 10, 20 e 25°C, nas temperaturas de 760 e 790°C. Medições de perdas magnéticas, permeabilidade, teor de carbono, tamanho de grão e propriedades mecânicas, além da avaliação da microestrutura, foram efetuados para determinar esta influência. Foi verificado no aço com 300 ppm de carbono, que com aumento do ponto de orvalho reduziu o teor de carbono, aumentou o tamanho de grão e melhorou as propriedades magnéticas. Nos demais aços estudados, a redução do ponto de orvalho melhorou as propriedades magnéticas, porém com ausência de umidade somente houve melhora no aço totalmente processado com 2% de silício. Foi verificado ainda que nos aços totalmente processados os melhores resultados foram obtidos com a temperatura de recozimento de 790°C.
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Epalle, Thibaut. "Suivi de l'état viable non cultivable de souches de Legionella pneumophila soumises à différents stress (thermique ou chloré) : Evaluation de leur pouvoir pathogène." Thesis, Saint-Etienne, 2015. http://www.theses.fr/2015STET001T/document.
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Legionella pneumophila, l’agent responsable de la légionellose est transmissible à l’Homme par les aérosols environnementaux et infecte les macrophages pulmonaires. Après l’exposition à différents stress L. pneumophila est capable de d’entrer dans un état Viable Non Cultivable (VBNC) qui semble être une stratégie de survie. L’objectif de nos travaux était d’étudier l’état VBNC de différentes souches de L. pneumophila après des traitements thermique et chimique et d’évaluer le pouvoir infectieux des formes VBNC envers les macrophages et les cellules épithéliales alvéolaires. Nous avons étudié les profils physiologiques de L. pneumophila de trois souches différentes. Les résultats montrent que pour chaque souche 3 populations peuvent être identifiées, les légionelles viables cultivables, les VBNC et les bactéries mortes. Lorsque soumises aux stress, chaque souche possède un profil physiologique propre et la présence ou non de bactéries VBNC était dépendante du traitement appliqué et de la souche utilisée. La deuxième partie fut relative à l’étude des traitements thermiques de 70°C pendant 30 min et des chocs au dioxyde de chlore de 4, 6 et 7 mg/L pendant 60 min à température ambiante sur ces VBNC. Aucune légionelle VBNC n’est capable de se développer au sein des cellules et aucune croissance sur milieu BCYE n’a été observée après co-culture. La suite de notre étude a été d’étudier le comportement, envers les macrophages, de L. pneumophila revivifiées après culture sur amibes. Les résultats montrent que les légionelles VBNC induites par choc thermique et revivifiées par co-culture sur Acanthamoeba polyphaga sont capables d’infecter de nouveau les macrophages. En conclusion, ces résultats suggèrent que: (i) les formes VBNC de L. pneumophila ne sont pas spontanément infectieuses pour les macrophages et les cellules épithéliales alvéolaires in vitro et (ii) elles peuvent devenir pathogènes pour les cellules humaines après revivification préalable sur A. polyphaga<br>Legionella pneumophila, the causative agent of legionellosis is transmitted to human through aerosols from environmental sources and invades lung’s macrophages. It also can replicate within various protozoan species in environmental reservoirs. Following exposures to various stresses, L. pneumophila enters a Viable Non Cultivable state (VBNC) which is likely to be a survival strategy. The objective of our work was to study the VBNC forms of several strains of L. pneumophila serogroup 1 obtained after thermal and chemical treatments and to evaluate the infectivity of these VBNC forms against macrophages and alveolar epithelial cells. First we studied the physiological patterns of the three different strains (Philadelphia GFP 008, 044 clinical and environmental RNN). For all strains we observed the presence of VBNC bacteria in the native (non stressed) state. The results show that for each strain, three populations of Legionella can be identified: viable and culturable, VBNC and dead cells. Once submitted to the various stresses, we observed that each strain had its own physiological pattern and the presence (or not) of VBNC bacteria was dependent on the applied treatment and the strain used. The second part was related to the study of the pathogenicity of these VBNC forms against macrophages or epithelial cells. The study focused on heat shock treatment at 70°C for 30 min and chlorine dioxide treatment at 4, 6 and 7 mg/L for 60 min at room temperature. The results show that no Legionella VBNC forms were able to grow within the cells and no growth on BCYE medium was observed after co-culture. Then we investigated the behavior of L. pneumophila resuscitated after culture on ameba within macrophages. The results shows that Legionella VBNC induced by heat shock treatment and resuscitated by Acanthamoeba polyphaga co-culture are able to infect macrophages. In conclusion, these results suggest that: (i) the VBNC forms of L. pneumophila are not infectious for macrophages and alveolar epithelial cells in vitro and; (ii) they can be pathogenic for human cells after revivification by an amoeba (A. polyphaga)
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Debuigne, Marc. "Modélisation thermomécanique des traitements de durcissement superficiel en phase solide par laser CO2 continu : application et validation dans le cas de l'alliage de titane TI-6AL-4V." Châtenay-Malabry, Ecole centrale de Paris, 1988. http://www.theses.fr/1988ECAP0052.
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Mise en évidence des possibilités de simulation des phénomènes thermiques et mécaniques tridimensionnels induits par un traitement de surface par laser et de détermination des contraintes résiduelles et des déformations dans les pièces traitées.
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Felippe, Douglas Marquezin. "Comparação entre os processos de tratamentos térmicos convencional e por indução de rolamentos do aço DIN 100Cr6." Universidade Presbiteriana Mackenzie, 2010. http://tede.mackenzie.br/jspui/handle/tede/2746.
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Previous issue date: 2010-02-23<br>Fundo Mackenzie de Pesquisa<br>Heat treatment processes are related to control heating and quenching with the aim of improving physical properties, such as: hardness, abrasion resistance, toughness, among others. During the heat treatment process, the quenching media are of great importance steps, because it extracts heat from the part with the achieve of obtaining specification properties. However, the hardening process causes undesired distortion that can be related to the permanent residual stress in the parts, generated during quenching. Some conventional hardening heat treatments do not have the control of the position during quenching, this control is usually applied in induction heat treatment, improving the homogeneity of heat
exchange in the quenching process, suggesting lower distortion. The induction process can be a sustainable one, because the heating is applied just in the part. This survey compared both metallurgical and mechanical properties between two heat treatment processes of DIN 100Cr6 steel bearings: conventional and induction. With the result of this survey, it is intended, to change the conventional heat treatment process for the induction process in bearing manufacturing, with the objective of reducing the typical out-of-roundness from the conventional heat treatment process, and a reduction the bearing manufactured costs.<br>A têmpera compreende operações de aquecimento e resfriamento controlado, que objetivam melhorias nas propriedades físicas como dureza, resistência à abrasão, tenacidade entre outras. Durante o processo de têmpera, o meio de resfriamento é uma das etapas mais críticas, pois extrai calor da peça com o objetivo de obter as propriedades desejadas. Porém, o processo de têmpera gera deformações não desejadas, que podem estar relacionadas às tensões residuais que ficam permanentes na peça, introduzidas durante o resfriamento. Alguns tratamentos térmicos de têmpera convencional não têm controle da posição da peça durante o resfriamento. Este controle é normalmente utilizado em processos de têmpera por indução, melhorando a homogeneidade da extração de calor durante o resfriamento, sugerindo menores índices de deformação. O processo por indução pode ser considerado sustentável, pois o aquecimento é localizado apenas no componente. Este trabalho comparou as propriedades metalúrgicas e mecânicas entre dois processos de têmpera de rolamentos do aço DIN 100Cr6: convencional e por indução. Como resultado deste trabalho, pode-se substituir o tratamento térmico com aquecimento convencional pelo tratamento térmico com aquecimento por indução para a manufatura de rolamento, com objetivo de redução da deformação de ovalização característica do processo de tratamento térmico convencional.
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Taheri, Andani Mohsen. "Modeling, Simulation, Additive Manufacturing, and Experimental Evaluation of Solid and Porous NiTi." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438888243.
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Ramosoeu, Makhabo Khabiso Ellen. "Characterisation and static behaviour of the DMLS Ti-6AI-4V for Bio-medical applications." Thesis, Bloemfontein: Central University of Technology, Free State, 2015. http://hdl.handle.net/11462/275.
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Thesis (M. Tech. (Engineering: Mechanical)) -- Central University of Technology, Free State,<br>The Centre for Rapid Prototyping and Manufacturing (CRPM) at the Central University of Technology, Free State (CUT) manufactures implants using Electro Optical Systems (EOS) titanium Ti-6Al-4V alloy powder (further referred to as EOS Ti64 powder) by means of Direct Metal Laser Sintering (DMLS) process on the EOSINT M 270 machine. For this reason, there is a need to characterise and acquire knowledge of the basic properties of direct metal laser sintered EOS titanium Ti-6Al-4V alloy samples (further referred to as DMLS Ti64 samples) under static tensile loading in order to provide the CRPM with engineering design data. The first objective of this Master’s study is to acquire the characteristics of EOS Ti64 powder in order to ascertain its suitability in the DMLS process. Secondly, the study aims to assess tensile properties and elastic constants of DMLS Ti64 samples produced from the set process parameters of EOSINT M 270 machine. Thirdly, it is to investigate microstructures of DMLS Ti64 samples subjected to different heat treatment techniques which will eventually assist in the determination of a suitable heat treatment technique that will yield higher ductility. Finally, the study aims to validate the static behaviour of DMLS Ti64 samples subjected to the static tensile loading up to a yield point in order to determine failure due to yielding.
The samples were manufactured at CRPM Bloemfontein. The metallographic examinations, heat treatment and the determination of mechanical properties were done at the CSIR in Pretoria. Optical Microscope (OM) and Scanning Electron Microscope (SEM) were used to determine microstructures of DMLS Ti64 samples while Energy Dispersive X-Ray (EDX) analyses were performed using SEM. The samples were heat treated at temperatures of 700, 1000 and 1100°C respectively, and subsequently either cooled with the furnace, air or were water quenched. The mechanical property tests included tensile, hardness and determination of elastic constants. The static behaviour of DMLS Ti64 samples under static tensile load up to a yield point was predicted and verified using ABAQUSTM Finite Element Analysis (FEA). The stress-strain curves from ABAQUSTM were interpreted using MDSolid program. The point of interest was Von Mises yield stress at 0.2% offset, in order to determine failure due to yielding.
EOS Ti64 powder particles were spherical in shape and the alpha and alpha+beta phases were identified. As-laser sintered samples possess a very fine and uniform alpha case with islands of martensitic plates; samples were brittle and showed low levels of ductility with an average elongation of 2.6% and an area reduction of 3.51%. Ultrasonic test results showed that DMLS Ti64 samples have Young’s modulus of 115 GPa, Shear modulus of 43 GP, a bulk modulus of 109 GPa and Poisson’s ratio of 0,323 while the density was 4.4 g/cm3. Slow cooling of DMLS Ti64 samples from 1000 and 1100oC resulted in a microstructure constituted more by the alpha phase of lower hardness than those from 700oC and as-laser sintered samples. High hardness was obtained by water quenching. The water quenched samples showed martensitic transformation and high hardness when compared to furnace cooled samples. Beta annealing tailored a microstructure of as-laser sintered samples into a lamellar structure with different lath sizes as per cooling rate. Beta annealing improved ductility levels up to 12.67% elongation for samples furnace cooled for 4 hours and even higher to 18.11% for samples furnace cooled for 34 hours, while area reduction increased to 25.94% and 33.39%, respectively. Beta annealing conversely reduced yield strength by 19.89% and ultimate tensile strength was reduced by 23.66%.
The calculated maximum Von Mises stresses found were similar to the FEA interpreted results. The average percentage error, without the stress concentration factor, was approximately 8.29%; with the stress concentration factor included, it was 0.07%. The small reaction forces induced in both x-axis and z-axis contributed to this error of 0.07% between the calculations and ABAQUSTM FEA results. Samples that were not heat treated fell outside the Von Mises criterion and failed due to yielding. This justified the brittleness found in the tensile test results where elongation and area reduction were 2.6% and 3.51% respectively. However, all samples that were heat treated fell within the Von Mises criterion.
The objectives of this study were achieved; the mechanical properties were similar to those of standard specification for wrought annealed Ti-6Al-4V alloy for surgical implant applications and EOS GmbH manufacturer’s material data sheet. DMLS Ti64 samples must be beta annealed in order to attain higher levels of ductility. A recommendation was made to further investigate the effect of heat treatment on the other mechanical properties. Furthermore, detailed results of basic properties of DMLS Ti64 samples are provided in the appendices in chart format and were written on a CD disc.
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Boufoussi, M'Barek. "Modélisation thermique, métallurgique et mécanique du traitement thermique superficiel par faisceau laser." Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL046N.
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Cette étude porte sur la modélisation du traitement thermique superficiel par faisceau laser. Au cours de son traitement le matériau subit des évolutions de température et de microstructure qui génèrent des déformations et des contraintes internes dans la pièce traitée. Elle comporte d'une part une étude de l'influence des paramètres du procédé sur les profils des contraintes résiduelles. Le calcul thermique-métallurgique-mécanique est appliqué au traitement thermique superficiel de plaques en acier xc42 et 55c1. La genèse des contraintes internes et des déformations permanentes au cours du traitement a été analysée. Le calcul permet de prévoir de façon satisfaisante la géométrie, les distributions de dureté et de contraintes résiduelles de la zone affectée thermiquement. L'étude de l'influence des paramètres du procédé sur les profils de contraintes résiduelles montre que les variations admissibles de ces paramètres, conduisent a des contraintes résiduelles en surface qui restent relativement faibles par rapport a la limite d'élasticité du matériau. Ce fait est attribué principalement aux vitesses de refroidissement mises en jeu dans le traitement laser qui sont limitées par la conduction dans le matériau. Une simulation numérique a permis de montrer qu'un traitement laser avec un refroidissement additionnel de la pièce traitée, permet d'augmenter notablement le niveau de contraintes résiduelles de compression dans la zone traitée
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Nguyen, Thanh Manh. "Effets des contraintes environnementales (densité en hôtes et stress thermiques) sur quelques traits d'histoire de vie des mâles d'anisopteromalus calandrae." Thesis, Tours, 2013. http://www.theses.fr/2013TOUR4055/document.
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Chez les parasitoïdes, le succès reproducteur n’est pas seulement de permettre une perpétuation de l’espèce il est aussi très important pour la lutte biologique contre les insectes nuisibles. Donc, il est essentiel que la population se développe durablement et produise des descendants fertiles. Au cours de leur vie, à cause de leur petite taille, les parasitoides doivent faire face aux contraintes écologiques (biotiques et abiotiques) qui peuvent agir directement ou indirectement sur l’individu, impliquant des changements morphologiques, physiologiques ou comportementaux qui, à leur tour, affectent la survie et notamment le succès reproducteur d’individus. L’objectif général de cette thèse était de mieux comprendre les conséquences des contraintes écologiques sur la reproduction à partir d’un ectoparasitoide Anisopteromalus calandrae. Nos résultats montrent que la décision de ponte des femelles parasitoïdes est liée à la densité en hôtes qui affecte à la fois la taille des individus et leur fitness avec comme conséquence une augmentation du nombre de mâles dans la descendance. D’autre part, le stress thermique appliqué soit au stade nymphal ou adulte cause des effets négatifs sur la survie et une diminution du stock de spermatozoïdes est également observée<br>In parasitoids wasps, reproductive success not only perpetuation of the species, it is also a very important factor for biological control against pests, since it is essential that the population grows and sustainably produce fertile offsprings. During their lives, because of their small size, parasitoids face ecological constraints (both biotic and abiotic) that may affect directly or indirectly the individuals, involving changes in their morphology, physiology or behavior, which in turn, affect the survival and reproductive success. The overall objective of this thesis was to better understand the consequences of the ecological constraints on reproduction in the ectoparasitoid wasp Anisopteromalus calandrae. Our results show that the parasitoid females’ decision to lay eggs is related to the host density that affects both the offspring’s size and fitness, consequently increasing the number of males in the offspring. On the other hand, the thermal stress applied to the pupae or adults had negative effects on survival and decreased the quantity of sperm. Moreover, stressed males are less successful competitors
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Aubry, Cécile. "Modélisation et étude expérimentale des cinétiques de revenu/autorevenu d'aciers trempés : prévision des contraintes résiduelles de trempe dans un acier cémenté en incluant l'autorevenu." Vandoeuvre-les-Nancy, INPL, 1998. http://www.theses.fr/1998INPL030N.
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La prévision quantitative des contraintes résiduelles de traitement thermique nécessite la modélisation et le calcul des champs de température, des transformations de phases et de l'évolution des contraintes et des déformations au cours du traitement. Si de nombreux travaux portent sur le traitement de trempe, l'incidence de l'autorevenu et du revenu de la structure trempée a été peu étudiée. Le but de ce travail est d'analyser les conséquences de l'autorevenu de la martensite sur la genèse des contraintes internes lors de la trempe de pièces cémentées. Nous avons développé un modèle de calcul des cinétiques de transformations de phases au cours du revenu et de l'autorevenu, basé sur la connaissance des cinétiques isothermes (diagrammes TTT de revenu). Le revenu est décrit par trois transformations : la précipitation des carbures de transition, la décomposition de l'austénite résiduelle et la transformation des carbures de transition en cémentite. L’autorevenu est associé uniquement à la précipitation des carbures de transition. Une validation expérimentale de ce modèle est décrite dans le cas de l'acier 70MC5. Elle a consisté à établir expérimentalement, par dilatométrie et résistivimétrie, un diagramme de transformations au chauffage continu, à en déduire le diagramme TTT de revenu. Nous avons ensuite comparé les cinétiques et les courbes dilatométriques expérimentales et calculées pour différentes conditions de chauffage. Ce modèle métallurgique a été intégré dans le modèle de prévision des contraintes résiduelles de traitement thermique déjà développé au laboratoire. Nous avons de plus pris en compte les variations de densité provoquées par l'autorevenu de la martensite. Le calcul complet a été appliqué au cas de cylindres d'acier 27MC5 cémentés et trempés dans différents fluides (huile à 50°C, huile à 160°C, gaz (azote)) afin d'obtenir différents niveaux d'autorevenu de la martensite. Du point de vue expérimental, nous analysons les différences entre ces traitements, en comparant les évolutions de température, les résultats métallurgiques (microstructures, duretés, teneurs en austénite résiduelle) et les résultats mécaniques (profils de contraintes résiduelles). La genèse des contraintes internes est analysée à l'aide de la simulation numérique, en relation avec la chronologie des différentes transformations de phases. L’effet de l'autorevenu est précis. La comparaison entre résultats expérimentaux et numériques fait ensuite l'objet d'une discussion.
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Lúcio, João Gilberto. "Estudo do processo de dobramento a frio de grampo para feixe de mola." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-29072014-141801/.
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O aço SAE 1552 modificado é um desenvolvimento recente da família do aço carbono manganês ligado ao silício, sendo utilizado para confecção de grampo U que tem como finalidade prender o feixe de molas no eixo do veículo. A somatória das fases de produção dessa matéria prima introduz os limites de resistência mecânica final necessária para atender a classe de resistência normativa. A peça produzida com esse aço tem alcançado crescimento de utilização na indústria automotiva devido à mesma apresentar propriedades mecânicas que atendem a requisitos normativos de classe de resistência e com vantagem de evitar tratamento térmico na fase de confecção do grampo e sendo esse processo realizado a frio em todas as suas fases. O objetivo desse trabalho foi estudar falha de grampo na etapa do processo de dobramento em forma de U e aplicar ensaios como: programa de simulação de tratamento térmico Stecal 3.0, ultrassom, fadiga, teste de cela e análise de fratura para solucionar essas falhas. Também foi realizado ensaios para prever fraturas catastróficas como: elementos finitos através de programa de computador Abaqus, ensaio de extensometria, tenacidade a fratura e medições de tensões residuais através de técnica de difração de raios-x. Foi concluído através dos resultados dos estudos de microestrutura resultante de tratamento térmico da matéria prima que o processo com resfriamento controlado em esteira é mais adequado para a produção do aço para confecção de grampo. O ensaio de ultrassom antes e após ensaio de fadiga possibilitou dimensionar o crescimento da profundidade da trinca em cotovelo de grampo e através de elementos finitos e extensometria associado com mecânica da fratura foi possível conhecer as tensões em ponto de estudo e entender o motivo de não ocorrer falha catastrófica. O ensaio de difração de raios-x permitiu o entendimento das tensões residuais introduzidas na peça de estudo.<br>SAE 1552 steel modified is a recent development of manganese carbon steel group linked to silicon, which is used to manufacture u-bolt that aims to fix leaf spring at vehicle axle in the back part. The sum of production stages of this raw material introduces the final mechanical resistance limits to meet class rules resistance. The piece produced with this steel has achieved growth of use in the automotive industry due to the mechanical properties it presents, which meet regulatory requirements for strength class and the advantage of avoiding heat treatment during manufacturing of the u-bolt and all the phases of this process are carried out in cold. This work aims to study the u-bolt failure during the folding process in the form of U and apply tests such as heat treatment simulation -Stecal 3.0, ultrasonic test, fatigue test, cell testing and analysis of crack. Other tests have been carried out to predict catastrophic fractures such as: finite element through computer program called Abaqus, extensometry testing, toughness testing for fracture and residual stress measurement by X ray diffraction technique. Results of heat treatment studies, by microstructure analysis, allowed choosing appropriate process for steel production. Ultrasonic testing before and after fatigue testing enabled to measure growth of crack depth on u-bolt elbow, and through finite element and extensometry testing associated with Mechanical of Fracture it was possible to know the stress concentrated at a point and to understand why catastrophic failure did not occur. Residual stress understanding has provided overall vision of u-bolt studied and contributed to have precision in measurement at inner and outer part of the u-bolt elbow.
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Bortoleto, Eleir Mundim. "Modelamento numérico-computacional das transformações de fase nos tratamentos térmicos de aços." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-20102010-154444/.
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Neste trabalho, propõe-se um modelo numérico-computacional representativo dos processos de tratamento térmico, que seja uma ferramenta eficiente e forneça meios para um entendimento efetivo do mecanismo de geração de tensões residuais durante a têmpera de aços. Foram investigados os fenômenos térmicos, mecânicos e de transformação de fase observados na têmpera, bem como o acoplamento entre esses três fenômenos. O modelo utiliza o Método dos Elementos Finitos (MEF) e o programa ABAQUS®, além de rotinas numéricas em FORTRAN responsáveis pela resolução do problema termo-mecânico-microestrutural acoplado. A utilização de sub-rotinas, que implementam uma alteração na formulação (matemática e numérica) do programa de Elementos Finitos, permite incluir no modelo as informações presentes em uma curva CRC (curva de resfriamento contínuo) do aço SAE 4140, implementando o cálculo de deformações da peça simulada de modo incremental e cumulativo. Os resultados mostram que a utilização das sub-rotinas desenvolvidas neste trabalho permitiu implementar, conjuntamente com o programa ABAQUS®, o cálculo das frações volumétricas, durezas, distorções e tensões que surgem em um tratamento térmico de têmpera, simulando as transformações martensítica, perlítica, bainítica e ferrítica. Os resultados dos modelos foram equivalentes aos relatados pela literatura, principalmente no que se refere às durezas e tensões associadas a cada transformação de fase. Em particular, os resultados indicam que a transformação martensítica está sempre associada à formação de tensões compressivas. Ensaios experimentais foram realizados a fim de validar os modelos computacionais propostos, utilizando-se um teste Jominy adaptado e instrumentado, de modo a permitir a amostragem da variação de temperaturas no material. Ensaios metalográficos permitiram correlacionar as frações volumétricas transformadas durante a têmpera do corpo de prova Jominy aos valores calculados pelo modelo numérico acoplado.<br>The objective of this work is to analyze residual strains and stresses and volumetric expansion due to phase transformations that occur during quenching of a steel body, as well as to predict these phase transformations. The coupled thermo-mechanical-phase transformation problem was analyzed, specifically in terms of the quenching process. Different computational models were presented, based on the finite element software ABAQUS® and on the use of FORTRAN subroutines. The continuous-cooling-transformation (CCT) diagrams of SAE 4140 steel are represented differently in each model, depending on the transformed phases and correspondent volumetric expansion. These subroutines include information from the CCT diagrams of SAE 4140 into a FORTRAN code. The subroutine calculates all the microstructures resulting from quenching (ferrite, pearlite, bainite, and martensite), depending on cooling rate. The numerical analysis conducted in this work provided results in terms of the temperature and stresses developed during quenching. The properties determined in this work are hardness, yield strength, volumetric fraction and distortion. Hardness has been predicted by the use of analytical equations. The finite element analyses were able to explain and reproduce phenomena observed during quenching of a steel cylinder. In particular, numerical results indicated that martensite formation is always related to a compressive stress field. The results of the models are in qualitative agreement with data provided by literature, particularly, in relation to the stresses originated by each different phase transformation during quenching process. Experimental testing was conducted, based on the analysis of the quenching of a Jominy probe, in order to validate the computational model developed in this work.
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Tuel, Alain. "Caracterisation de la structure de silices de precipitation par resonance magnetique nucleaire de solide et de leur morphologie." Paris 6, 1987. http://www.theses.fr/1987PA066653.
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Etude par rmn en phase solide et par analyses d'images de microscopie electronique. Evaluation du pourcentage des differentes especes, de la densite en hydroxyles et de leur evolution en fonction d'un traitement thermique determine. Etude de la structure geometrique des surfaces apres griffage de petites molecules (diols et alcools). Proposition d'un modele ou la surface des silices de precipitation est constitue d'une couche tres desorganisee d'epaisseur donnee. Caracterisation des projections bidimensionnelles des agregats de silice par des exposants fractals, a partir des micrographies electroniques
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Lados, Diana Aida. "Fatigue crack growth mechanisms in Al-Si-Mg alloys." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0204104-125758.
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Thesis (Ph. D.)--Worcester Polytechnic Institute.<br>Keywords: Microstructure; Elastic-Plastic Fracture Mechanics; Crack closure; A356; J-integral; Conventionally cast and SSM Al-Si-Mg alloys; Residual stress; Heat treatment; Fatigue crack growth mechanisms; Threshold stress intensity factor; Plastic zone; Paris law; Fracture toughness; Roughness. Includes bibliographical references.
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Kang, Nan. "Élaboration "in-situ" par mélanges de poudres de composites à matrice métallique au cours du processus de fabrication additive." Thesis, Belfort-Montbéliard, 2016. http://www.theses.fr/2016BELF0305/document.
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La micro fusion laser d'un lit de poudre (SLM) permet la réalisation de pièces complexes avec des microstructuresfines. Cette technologie présente de nombreux avantages mais se heurte encore à une faible disponibilité des poudres d'alliages. En SLM, la pièce est d'abord conçue par CAO (conception assistée par ordinateur), puis construite couche par couche avec un faisceau laser commandé par un ordinateur. Dans ce cadre, le travail effectué dans cette thèse a consisté à étudier et à développer une nouvelle méthode pour réaliser des pièces en alliages et en composites à partir de mélanges de poudres élémentaires, ouvrant ainsi la voie à une grande variété de compositions.Au niveau expérimental le choix s'est porté sur le système aluminium-silicium avec différentes teneurs en silicium (12, 18 et 50% en poids). L'effet de l'ajout d'un champ magnétique statique a aussi été proposé comme un outil supplémentaire de contrôle de la microstructure.Dans le processus de fabrication de pièces par SLM la puissance du laser et la vitesse de balayage déterminent au premier chef la densité, la microstructure, la composition des phases et les propriétés mécaniques du produit. Une analyse systématique de l'effet de ces paramètres sur l'alliage Al - Si fabriqué par SLM à partir de mélanges de poudres est présentée. Des alliages ont été ainsi obtenus pour plusieurs domaines de composition visés correspondant à des applications pratiques (structures légères, système tribologique, emballage électronique, ...).Les microstructures fines obtenues grâce à la solidification rapide des matériaux fondus conduit à des propriétés quise comparent de façon favorable à celles obtenues avec les techniques classiques d'élaboration et de mise en oeuvre<br>As a new manufacturing technology, Selective laser melting (SLM) has a large potential in the manufacturing of complex parts with ultrafine microstructure.Selective laser melting has many significant advantages over traditional manufacturing methods but still faces a low availability of powder materials. With SLM, the part is firstly designed via 3D computer-aided design (CAD)), then built layer-by-layer with a high energy computer-controlled laser beam The work done in this study was therefore aiming at developing a new way to obtain alloys and composites directly from elemental powder mixtures with a large composition flexibility.Experimentally the choice was made of the aluminum-silicon system with several silicon contents (12, 18, 50 wt. %).Adding a static magnetic field was also considered as an additional way to control the microstructure. When parts are manufactured by SLM, laser power and scanning speed are the main parameters determining the density, microstructure, phase composition and mechanical properties. A systematic analysis of the role of these parameter on the manufacturing of Al - Si alloys by SLM from mixtures of powders was therefore conducted. Al - Si alloys with a very fine microstructure were thus obtained for several composition ranges corresponding to practical applications (lightweight structures, high wear resistance alloys, electronic packaging material, ...). The properties of the materials obtained in this way, according to the performed characterizations, compares favorably with those obtained via the conventional production technologies
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Febvay, Laura. "Étude par spectroscopie de résonance magnétique nucléaire (RMN) des modifications physico-chimiques provoquées par des traitements thermiques (« torréfactions ») de graines du caféier Coffea arabica L." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLA033.
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Le traitement thermique (« torréfaction ») des graines de Coffea arabica L. détermine leur composition chimique et, de ce fait, la composition et les propriétés organoleptiques de la boisson qui en est issue (« café »). Dans cette étude, nous avons utilisé plusieurs techniques de spectroscopie de résonance magnétique nucléaire quantitative (q RMN) pour explorer les phénomènes qui ont lieu au cours de la torréfaction et de l’extraction en phase aqueuse des grains de café broyés. Des plans d'expériences ont été mis en œuvre, afin d’examiner l’influence de paramètres clés des torréfactions et, in fine, d'identifier les mécanismes des phénomènes que ces traitements provoquent. Contrairement aux études antérieures, nous avons appliqué des barèmes de torréfaction représentatifs des pratiques industrielles. Nous avons établi que les paramètres de commande et de contrôle utilisés par l’industrie ne suffisaient pas à caractériser les diverses torréfactions. Puis, par des analyses chimiométriques, nous avons identifié les composés dont les concentrations varient avec les cinétiques considérées. Des traitements thermiques plus poussés ont aussi été effectués afin (1) d'établir des corrélations entre ces composés et des changements de couleur et de pH et (2) d'identifier les mécanismes réactionnels qui interviennent au cours des torréfactions<br>The heat treatment (“roasting”) of Coffea arabica L. seeds determines their chemical composition and, as a result, the composition and organoleptic properties of the resulting beverage ("coffee"). In this study, we used several quantitative nuclear magnetic resonance (q NMR) spectroscopy techniques to explore the phenomena that occur during roasting and extraction of coffee beans in the aqueous phase. Experimental designs were implemented to examine the influence of key roasting parameters and, ultimately, to identify the mechanisms of the phenomena that these treatments cause. Unlike previous studies, we applied roasting kinetics that are in line with industry standards. We determined that the parameters used by the industry were not sufficient to characterize the various roasts. Then we used chemometrics in order to identify markers, i.e. compounds whose concentrations vary with the kinetics involved. More extensive heat treatments were also carried out to (1) establish correlations between these compounds and changes in colour and pH and (2) identify the reaction mechanisms that occur during roasting
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Cochet-Muchy, Didier. "Elaboration par solidification rapide et caractérisation de nouveaux matériaux magnétiques durs." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0094.
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Effets microstructuraux de l'oxygene dans l'alliage pour aimant permanent nd#1#5fe#7#7b#8 a l'etat brut de fonderie et apres traitement l'oxydation a l'air. Analyse des microstructures de rubans nd#1#5fe#7#7b#8 trempes des vitesses croissantes a partir du liquide, ainsi que celles de rubans cristallises depuis l'etat amorphe. Correlation entre microstructure et proprietes magnetiques. Etude de rubans microcristallises d'alliages a matrice sm(fe, ti)#1#2 obtenus par solidification rapide suivie de differents traitements thermiques provoquant la cristallisation de phases secondaires
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Xiang, Ziyin. "Enhancing low-frequency induction heating effect of ferromagnetic composites : Toward medical applications." Thesis, Lyon, 2021. http://www.theses.fr/2021LYSEI022.
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Les composites ferromagnétiques, matrices polymères renforcées de particules ferromagnétiques présentent un potentiel intéressant dans de nombreuses applications médicales. Dans cette thèse, nous nous concentrons particulièrement autour du Chauffage par Induction Basse Fréquence (CIBF) de cathéters ferromagnétiques, une méthode alternative pour l'ablation des varices. L'effet CIBF apparaît dès lors que le composite est exposé à un champ magnétique alternatif. Ce phénomène est principalement dû aux courants de Foucault dits "microscopiques" générés par les mouvements des parois des domaines magnétiques. En introduisant le cathéter à travers la varice endommagée et en l'excitant par un champ magnétique basse fréquence, haute amplitude, il est concevable d'atteindre une température suffisamment élevée pour guérir correctement la zone endommagée sans perturber les zones saines environnantes. Par comparaison aux traitements existants, la méthode CIBF est précise, économique et simple. En transférant la chaleur sans conduction, l'encombrement du cathéter est réduit et le procédé semble applicable même pour des veines très sinueuses. Des composites ferromagnétiques de différentes formes et fractions volumiques ont été fabriqués et testés grâce à un dispositif expérimental dédié. Différents paramètres (fréquence, pourcentage de particules…) ont été analysés afin d’établir la combinaison présentant la meilleure réponse thermique. Les propriétés physiques (perméabilité, conductivités électrique et thermique) ont également été caractérisées. Un modèle Comsol® combinant comportement ferromagnétique et thermique a été conçu afin d’améliorer la compréhension des phénomènes. Pour améliorer la conversion, des échantillons anisotropes ont été développés en imposant un champ magnétique statique dans la phase de solidification. Finalement, une imprimante 3D de type extrusion a été utilisée pour imprimer des échantillons de formes proches de celle d’un cathéter. Des spécimens isotropes et anisotropes ont été imprimés. Les réponses CIBF distinctes et marquées entre les différentes directions testées chez les échantillons anisotropes ouvrent la voie à d’autres applications médicales comme le suivi électromagnétique (navigation chirurgicale)<br>Ferromagnetic composites, polymer matrix mixed with ferromagnetic particles show good potential in medical applications. In this thesis, we especially focus on the Low Frequency Induction Heating (LFIH) of ferromagnetic catheters as an alternative process for varicose veins ablation. The LFIH effect appears as soon as the composite is exposed to an alternating magnetic field. This phenomenon is mainly due to the so-called "microscopic" eddy currents generated by the magnetic domain wall motions. By inserting the catheter through a damaged varicose vein, and exciting it with a low frequency, high amplitude magnetic field, it is conceivable to reach a temperature high enough to properly heal the damaged area without injuring the surrounding healthy ones. Compared to the existing treatments, the LFIH method is accurate, cost competitive and simple. By transferring heat in a non-conductive way, the catheter bulkiness is reduced and the method is applicable even in tortuous veins. Ferromagnetic composites with different shapes and particle volume fractions were built and tested in a specific experimental bench. Different parameters (frequency, particle fraction …) were analyzed to reach the best thermal answer. The physical properties (permeability, electrical and thermal conductivities) were also characterized. A Comsol® model combining ferromagnetic behavior and thermal transfer properties was designed to improve the understanding of the phenomena. For a better efficiency, specimens with anisotropic magnetic behaviors were built by curing them under the influence of a static magnetic field. Finally, a commercial extrusion-type 3D printer was used to print samples with catheter shapes. Isotropic and anisotropic specimens were built. Interesting LFIH behavior were observed and for the later ones directional answers potentially interesting in alternative medical applications like the electromagnetic tracking (surgery navigation)
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Bouhouch, Lahoussine. "Élaboration des couches d'alliages NI-FE par voie électrolytique : Études électrique, magnétique et structurale." Nancy 1, 1988. http://www.theses.fr/1988NAN10089.
Full textAbstract:
Mécanismes, caractéristiques et facteurs influant le dépôt électrolytique. Techniques d'élaboration et de dosage du fer dans les alliages NI-FE déposés. Influence des conditions opératoires sur la nature et composition des alliages élaborés. Étude des propriétés électriques magnétiques et de l'influence des traitements thermiques sur la structure des alliages