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1
REDDA, BOYNA ROHITH. "IMPACT OF FRICTION TEST SCALE ON BRAKE FRICTION PERFORMANCE." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2051.
Full textAbstract:
It is well known that the friction performance is a system property. The coefficient of friction and its stability, wear rate and the propensity to vibration and noise are always characteristics of a system and it is not easy to predict their performance based on smaller scale friction tests. This paper discusses the relation between performances of different-scale testers and possibility to model the friction performance of real systems in small simpler testers. It addressed the application of “scaling laws,” the application of typically adopted scaling strategies in friction industry and the testing strategies based on understanding of phenomena on the friction surface and in the friction systems. Full scale AKM standard dyno test and small tester (Bruker UMT) are related and the testing strategy is suggested. It is concluded that in spite of the fact that the scaling and simulations do not allow for a perfect prediction of performance (friction is a system property), it is still possible to make educated decisions on the research and development stage, when proper testing strategy on a smaller scale is adopted.
2
Bonfanti, Andrea. "Low-impact friction materials for brake pads." Doctoral thesis, Università degli studi di Trento, 2016. https://hdl.handle.net/11572/369289.
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State-of-the-art friction materials for applications in disc brake systems are constituted by composite materials, specifically formulated to ensure proper friction and wear performances, under the sliding contact conditions of braking events. The bases of typical friction compound formulations usually include 10 to 30 different components bonded with a polymeric binder cross-linked in situ. Main requests to be fulfilled during braking are an adequate friction efficiency and enough mechanical resistance to withstand the torque generated by forces acting on the disc brake. Generally, each component confers distinctive properties to the mixture and their primary function can be classified in the following categories: binders confer mechanical strength to friction material guaranteeing pad compactness during use, abrasives increase friction efficiency and improve compound wear resistance, solid lubricants are responsible for stabilizing friction coefficient and contrasting the build-up effect, reinforcements increase mechanical strength improving wear minimization and stabilization. Furthermore, other modifying components such as fillers and functionalizers are involved which are not directly related to friction efficiency, e.g. cheap materials, pigments, etc. Organic brake pads for disc-brake applications are based on phenolic resin binders, generally it requires three main manufacturing steps: raw material blending, where friction compound components are mixed by blenders. Hot-molding, where blended friction mix is pressed against a metallic support at controlled high pressure (>2kN/cm2), temperature (150-200 °C) and pressing time (3-10 minutes). Brake pads post-curing, to complete the hardening of polymeric binder. This last step for phenolic resin is usually performed in a batch convective oven at temperature above 150 °C for 4-12 h, or alternatively using a continuous process, such as IR in-line tunnel ovens where the process time is 10-15 min, the oven heater temperature is between 500 and 700 °C and brake pad superficial temperature is easily above 300 °C. Such kind of formulations and manufacturing process reflects the generally acknowledged state of the art as regards organic friction materials for passenger cars and light trucks. In this panorama the idea of introducing a completely inorganic binder matrix would represent nowadays an extremely appealing topic in the field considering potential improvements of this alternative approach.
The complete elimination of the organic binder would reduce emission of phenol-formaldehyde hazardous derivatives generated at high-temperature e.g. volatile organic compounds, highly toxic polyaromatic hydrocarbons etc… Nature and toxicity of the organic compounds released at high temperature was investigated on brake pads manufacturing and compared with preliminary studies recently published. Introducing an inorganic hydraulically bonded matrix in place of the traditional organic-based binders would lead to a substantial reduction of the total embodied energy and water of brake pads considering low-temperature manufacturing process and inorganic binders properties. Primary production embodied energy for phenolic resin is estimated in the range of 75 - 83 MJ/kg (cradle to gate), while primary production water usage (embodied water) is in the range of 94 - 282 l/kg. As a matter of comparison, examples of the embodied energy for inorganic binders typically used for concrete construction are: Portland cements 4.9 MJ/kg, fly ash 9.3 MJ/kg, metakaolin 1.4 MJ/kg, silica fume 0.036 1.4 MJ/kg. The embodied water for these raw materials usually is less than 0.048 l/kg. Well-known properties of such peculiar inorganic materials exploiting the hydraulic activity of binders when exposed to water or alkaline environment. The only energy demanding compound was the alkaline solution (e.g. for sodium hydroxide and sodium silicate the embodied energy is respectively of 22MJ/kg and 16 MJ/kg). New brake pad manufacturing process allowed the substitution of commonly implied highly energy-consuming procedures with low-temperatures steps. Friction material components except binders were blended together with conventional plow-blade blender forming a dry friction-mix, then this dry friction-mix is blended with the inorganic binder and water or alkaline activators in a planetary mixer forming a wet friction-mix. Eventually wet friction mix is cold-pressed onto a metal back-plate without the need for further treatments at high temperature. It immediately emerges the energetic benefit connected to the manufacturing process of this inorganic binder-based brake pads. After brake pad production, the behavior of these inorganic materials was compared to traditional phenolic-based friction materials. Brake pads were tested on a full scale automotive brake dynamometer and on a real vehicle (in terms of performance and particle emission) following custom and international standard procedures. The aim of this work was to produce brake pad prototypes with friction material based on an inorganic hydraulic binder at performance comparable to commercial brake pads with organic-matrix based friction materials. The results obtained so far resulted particularly promising and paved the way to further developments of these novel class of friction materials.
3
Bonfanti, Andrea. "Low-impact friction materials for brake pads." Doctoral thesis, University of Trento, 2016. http://eprints-phd.biblio.unitn.it/1808/1/Low-impact_friction_materials_for_brake_pads.pdf.
Full textAbstract:
State-of-the-art friction materials for applications in disc brake systems are constituted by composite materials, specifically formulated to ensure proper friction and wear performances, under the sliding contact conditions of braking events. The bases of typical friction compound formulations usually include 10 to 30 different components bonded with a polymeric binder cross-linked in situ. Main requests to be fulfilled during braking are an adequate friction efficiency and enough mechanical resistance to withstand the torque generated by forces acting on the disc brake. Generally, each component confers distinctive properties to the mixture and their primary function can be classified in the following categories: binders confer mechanical strength to friction material guaranteeing pad compactness during use, abrasives increase friction efficiency and improve compound wear resistance, solid lubricants are responsible for stabilizing friction coefficient and contrasting the build-up effect, reinforcements increase mechanical strength improving wear minimization and stabilization. Furthermore, other modifying components such as fillers and functionalizers are involved which are not directly related to friction efficiency, e.g. cheap materials, pigments, etc. Organic brake pads for disc-brake applications are based on phenolic resin binders, generally it requires three main manufacturing steps: raw material blending, where friction compound components are mixed by blenders. Hot-molding, where blended friction mix is pressed against a metallic support at controlled high pressure (>2kN/cm2), temperature (150-200 °C) and pressing time (3-10 minutes). Brake pads post-curing, to complete the hardening of polymeric binder. This last step for phenolic resin is usually performed in a batch convective oven at temperature above 150 °C for 4-12 h, or alternatively using a continuous process, such as IR in-line tunnel ovens where the process time is 10-15 min, the oven heater temperature is between 500 and 700 °C and brake pad superficial temperature is easily above 300 °C. Such kind of formulations and manufacturing process reflects the generally acknowledged state of the art as regards organic friction materials for passenger cars and light trucks. In this panorama the idea of introducing a completely inorganic binder matrix would represent nowadays an extremely appealing topic in the field considering potential improvements of this alternative approach.
The complete elimination of the organic binder would reduce emission of phenol-formaldehyde hazardous derivatives generated at high-temperature e.g. volatile organic compounds, highly toxic polyaromatic hydrocarbons etc… Nature and toxicity of the organic compounds released at high temperature was investigated on brake pads manufacturing and compared with preliminary studies recently published. Introducing an inorganic hydraulically bonded matrix in place of the traditional organic-based binders would lead to a substantial reduction of the total embodied energy and water of brake pads considering low-temperature manufacturing process and inorganic binders properties. Primary production embodied energy for phenolic resin is estimated in the range of 75 - 83 MJ/kg (cradle to gate), while primary production water usage (embodied water) is in the range of 94 - 282 l/kg. As a matter of comparison, examples of the embodied energy for inorganic binders typically used for concrete construction are: Portland cements 4.9 MJ/kg, fly ash 9.3 MJ/kg, metakaolin 1.4 MJ/kg, silica fume 0.036 1.4 MJ/kg. The embodied water for these raw materials usually is less than 0.048 l/kg. Well-known properties of such peculiar inorganic materials exploiting the hydraulic activity of binders when exposed to water or alkaline environment. The only energy demanding compound was the alkaline solution (e.g. for sodium hydroxide and sodium silicate the embodied energy is respectively of 22MJ/kg and 16 MJ/kg). New brake pad manufacturing process allowed the substitution of commonly implied highly energy-consuming procedures with low-temperatures steps. Friction material components except binders were blended together with conventional plow-blade blender forming a dry friction-mix, then this dry friction-mix is blended with the inorganic binder and water or alkaline activators in a planetary mixer forming a wet friction-mix. Eventually wet friction mix is cold-pressed onto a metal back-plate without the need for further treatments at high temperature. It immediately emerges the energetic benefit connected to the manufacturing process of this inorganic binder-based brake pads. After brake pad production, the behavior of these inorganic materials was compared to traditional phenolic-based friction materials. Brake pads were tested on a full scale automotive brake dynamometer and on a real vehicle (in terms of performance and particle emission) following custom and international standard procedures. The aim of this work was to produce brake pad prototypes with friction material based on an inorganic hydraulic binder at performance comparable to commercial brake pads with organic-matrix based friction materials. The results obtained so far resulted particularly promising and paved the way to further developments of these novel class of friction materials.
4
Nordlund, Erling. "Impact mechanics of friction joints and percussive drills." Doctoral thesis, Luleå tekniska universitet, Geoteknologi, 1986. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16974.
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Impact-loaded conical and cylindrical friction joints are studied theoretically and experimentally. The system considered consists of a long, straight, cylindrical and linearly elastic rod which is impacted axially at one end, and which has a body attached by means of a friction joint at the opposite end. The conditions are such that the wave propagation is 1-D in the rod and can be neglected in the attached body. Slip and energy dissipation due to an impact load are determined. The theoretical results of the impact-loaded conical friction joints exhibit phenomena which sometimes have spectacular appearance. The agreement between theoretical and experimental results is fair. The influence of blow frequency and thrust on the performance of a percussive rock drill is studied theoretically. The drill considered consists of hammer, adapter, rod and bit. Two different rock drills are studied. The first is a simple drill with constant characteristic impedance throughout the drill. The second is a prototype of a high frequency percussive rock drill. The efficiency and the maximum (maximum tensile) and minimum (maximum compressive) stresses are determined. For the simple drill the average efficiency in the range from soft to hard rock is only weakly dependent on the blow frequency up to relatively high blow frequencies but strongly dependent for extremely high blow frequencies. It is also found that the maximum and minimum stresses in the drill in the range from soft to hard rock are only weakly dependent on the blow frequency up to high frequencies but strongly dependent for extremely high frequencies. The maximum stress increases and the minimum stress decreases with thrust.<br>Godkänd; 1986; 20070108 (mlk)
5
Osakue, Edward E. "A study of friction during low-velocity impact." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq54598.pdf.
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Ismail, K. A. "Impact of hard bodies with friction and compliance." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604971.
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The importance of tangential compliance and friction has been realised in order to explain phenomenon of slip reversal at the contact point observed during bounce of sports balls. An impact model that accounts for physical behaviour of the bodies during impact is required in order to accurately calculate motion of the bodies during and after impact, especially to explain the former behaviour. The present analysis incorporates effect of friction at the contact surface and tangential compliance for the contact region using lumped parameter model with discrete compliant elements oriented in the directions normal and tangential to the common tangent plane of impact. Our dynamic collision model that is based on the structure of the bodies accounts for energy losses that are consequences of friction, material hysterisis and rate-dependence dissipation. Experimental work is carried out to study the compliance behaviour of a sports ball. The measurements of static compliance are used to model the compliance of the contact region during impact. An improvement on the linear model is discussed with respect to how this affects the evolution of contact forces. Significant parameters that influence response of a body during bounce have been identified.
7
Pilgrim, Michael. "The impact of differential friction on curve negotiation speed." Thesis, University of Canterbury. Engineering, 2014. http://hdl.handle.net/10092/10276.
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This thesis considers the impact of differential skid resistance between wheel paths on the speed at
which a vehicle can safely negotiate a curve. Currently the New Zealand Transport Agency undertakes
measurement of the co-efficient of friction on the state highway network by measuring both wheel
paths, but taking the average value to represent the level of skid resistance available. Part of the basis
for this approach is that modern cars have Electronic Stability Control that has historically been
considered to negate the effects of any differential friction.
Aside from straight line braking testing, little research has been done on the impacts of differential
friction on curves. There are however a number of areas of research that can be related to this topic.By PC Crash simulation modeling, this research identifies that there are a number of gaps in our understanding of the relationship between vehicles maneuvering on a curve and the effect of varying skid resistance.
It concludes that taking the average of the two values is not the same as considering them separately and, that as the difference in the co-efficient of friction between the wheel paths increases, the speed at which a vehicle can safely maneuver around a curve decreases. It has also been found that when Electronic Stability Control is used the speed at which the vehicle can safely maneuver around a curve decreases further.
8
Lim, Chwee-Teck. "Effects of compliance and friction on elastic-plastic impact." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/273133.
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Daei, Amir Reza. "IMPACT OF SOLID LUBRICANTS ON FRICTION PERFORMANCE OF ADVANCED AUTOMOTIVE BRAKE MATERIALS." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1900.
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Automotive brake lining materials are complex composites consisting of numerous ingredients allowing for their optimal performance. Different types of carbons have been used in all types of brake pad formulations for more than century. The role of carbon, however, does not seem to be completely understood, since carbon materials possess a wide variety of characteristics and properties and they interact with other ingredients present in the friction process. Carbons/graphites are commonly considered to be solid lubricants but this role is only available at relatively low temperatures and at a sufficient humidity. Since regulations are increasingly limiting Cu content in brake pads and Cu exhibits extremely high thermal conductivity, graphites, being excellent heat conducting materials themselves, are often considered for use when potential Cu replacement options in the low-metallic, non-asbestos organic, hybrid, and ceramic pads are explored. This paper surveys the role of two types of graphites with high thermal conductivity but different mechanical properties and morphology: the so-called i) purified flake graphite (PFG) and the ii) resilient graphitic carbon (RGC). A successful “high-end” commercial low-metallic brake pad was re-formulated (SIU Carbondale) by removing of over 20 wt. % of Cu and replacing it with a cocktail of ingredients including 15 wt. % of these two graphite types. OEM Crown Victoria 1999 mold was used to prepare the pads and they were subjected to the SAE J2430 test and BEEP evaluation using the full-scale automotive brake dynamometer (Link Engineering) and original hardware (rotor and caliper). After friction tests, the surfaces of pads were explored using scanning electron microscopy equipped with the energy dispersive X-ray microanalysis (FEG450 and Inca System) and X-ray diffraction (Rigaku Max-Flash-B). Although the brake pad formulations were otherwise identical and were prepared at the same conditions, the performance of two different low-metallic pads was different. The effectiveness of PFG sample reached value 0.5 and wear of pad was 5.3 g, while the effectiveness was 0.4 and wear detected was 5.9 g in the case of RGC containing sample. Both formulations exhibited extremely good stability of friction during fade section and only low sensitivity to speed variations between 50 and 160 km/h. Surfaces of both pads were covered by a discontinuous (patchy) friction layer which was formed as a consequence of a gentle abrasive mechanisms involved. The different friction levels and different wear of samples were related to the specific character/differences in detected different friction layers. Importantly, the capacity of the PFG to reduce surface oxides is considerably higher when compared to the RGC. It was concluded that the proper understanding of role of individual graphitic forms in particular formulations can be very beneficial when optimizing the performance of brake pads.
10
Wang, Wei. "Simulation of hard projectile impact on friction stir welded plate." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7213.
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A numerical simulation is conducted using LS-DYNA to simulate hard projectile impact on a friction stir welded (FSW) plate. As the hard projectile has a wide range of velocity, mass and shape, when referring to AMC 25.963(e) of CS-25, ―Fuel Tank Access Cover‖, the hard projectile can be defined as 9.5 mm cubic-shaped steel engine debris with an initial impact velocity of 213.4 m/s (700 ft/s). This preliminary study was to evaluate whether the fuel tank adjacent skin panel joined by FSW would pass the regulation. First, the geometry and Johnson-Cook material model of the FSW joint were developed based on previous experimental research and validated by comparison with the tensile test on the FSW specimen. Then the impact on an Aluminium Alloy 2024 (AA 2024) plate without FSW was modelled. The minimum thickness of a homogeneous AA 2024 plate which could withstand the impact from engine debris is 3 mm. Finally the impact on 3 mm thick AA 2024 FSW plate was simulated. The welding induced residual stress was implemented in the plate model. The impact centre was changed from the nugget zone to the thermo-mechanically affected zone, heat-affected zone and base material zone of the FSW joint. Penetration only occurred in the model with impact centre on the nugget zone. Additional simulation indicated that increasing the thickness of the FSW plate to 3.6 mm could prevent the penetration.
11
Mirzababaei, Saereh. "IMPACT OF HUMIDITY ON WEAR AND CREEP GROAN OF AUTOMOTIVE BRAKE FRICTION MATERIALS." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2056.
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In recent decades, significant requirements of changes in composition of brake friction materials in order for faster and more reliable transportation as well as their environmental friendly characterizations attracted attentions. However, the relation between performance and formulation/composition is not clear since friction processes are accompanied by many complex problems such as instability in the coefficient of friction, noise, vibration and wear. Creep-groan is a low frequency vibration which could originate in different part of the system (vehicle). The resulting resonant vibration in the passenger compartment causes discomfort and often leads to complaints of customers and related increase of warranty costs covered by manufacturers. In spite of relatively large amount of publications addressing the creep-groan phenomena, there is not an universal solution addressing the engineering aspects of brake/vehicle design. In addition, Relevance of wear occurring in brake materials increased particularly with relation to the released chemicals and corresponding health and environmental hazards. It is well known that humidity can considerably modify the adhesion of rubbing counterfaces by creating menisci and increasing the contact area. The chemistry, morphology and phase composition of the friction layers (third body) generated on the friction surfaces could play a determining role when amounts of adsorbed water on brake surfaces is concerned. The friction layer is typically a complex mix of numerous materials and, as a rule, contains the agglomerated or sintered nanoparticles. Hence, quantum effects could further modify the adsorption of water. This work addresses the impact of humidity on wear and creep groan of two commercial brake material types: the so called i) "non-asbestos organic" (NAO) and the ii) "semi-metallic" (SM) brake materials rubbed against pearlitic gray cast iron rotors typically used in the passenger vehicles. The friction and wear tests were performed with the Universal Mechanical Tester (UMT) manufactured by Bruker and the wear surfaces/mechanisms were studied by using of scanning electron microscopy, energy dispersive X-ray microanalysis, and optical topography methods. The applied wear testing conditions were designed as a series of particularly designed drag tests and were performed at several different relative humidity levels ranging between 50% and 80%. The major findings confirmed the considerable effect of humidity on wear of brake materials. Both pad types wore noticeably less at increased humidity. This was ascribed to a better capacity to form a protective friction layer. The complex wear mechanisms including abrasive, adhesive, fatigue, and corrosion wear were observed on both material types, irrespectively of humidity levels, and they dependent on the chemistry and phase composition of the friction layer. Humidity also influenced the level of friction.
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Elgizoli, Eshraga Mohamed Elhassan. "Impact of Mild Oxidation on Carbon/Carbon (C/C) Friction Properties." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1649.
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Carbon-Carbon (C/C) composites are dominating materials in aerospace industry, as 90% of its production are used as brake materials in aircraft. C/C composites demonstrate excellent retention of mechanical properties at high temperature where most of conventional materials cannot withstand. The purpose of this study was to oxidize and study impact of oxidation on friction properties and wear rate of three different commercial C/C materials (two-directional of oriented randomly chopped pitch fibers charred in resin, three-directional felt-needled PAN fibers in CVI matrix, and two-directional PAN fibers in CVI matrix. The approach in this study was to measure coefficient of friction (µ) by using Universal Friction Tester (UFT) and to calculate the wear rate by measuring weight and thickness of materials before and after tests. It was shown that oxidation have impact on friction properties of C/C as well as on wear rate, beside other factors as normal load, sliding speed, and temperature that affect friction performance. It is possible to optimize the friction properties of industrial C/C as well as wear rate to improve its performance.
13
Sundar, Sriram. "Impact damping and friction in non-linear mechanical systems with combined rolling-sliding contact." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386245045.
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Larsson, Roland. "Lubrication at impact loading." Licentiate thesis, Luleå tekniska universitet, Maskinelement, 1994. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17267.
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Swarbrick, Arthur L. "Understanding the impact of coatings on the friction performance of carbon fibre ceramic composite brakes." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/15055.
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In the railway industry, and premium luxury and super sports sectors of the automotive industry, traditional cast iron brake discs are gradually being replaced with advanced composites such as carbon fibre reinforced carbon silicon carbide (Cf/C-SiC). These materials offer the ability to operate at higher temperatures, whilst displaying improved friction performance, and vastly reduced wear rates. Their primary benefit comes from being approximately one third of the density of the incumbent material used in the industry, grey cast iron (GCI), a cast iron with a high proportion of graphite flakes formed during solidification. This reduced density means that brake discs manufactured from Cf/C-SiC materials are a highly suitable proposition for a future automotive market, where weight saving in an attempt to meet ever restrictive CO2 emissions is a must. The understanding surrounding the friction mechanisms involved with these new materials has been lacking, until recently, with the majority of the international research focused on the manufacturing methods. Research has shown that friction performance, particularly bedding friction, is highly dependent on the successful formation of a friction transfer film (FTF) at the surface of any disc, comprised from wear debris from both the disc and pad. Prior research carried out at Loughborough University has identified that Cf/C-SiC materials do not readily form such a layer, as might be seen on a GCI equivalent, due to the intrinsically heterogeneous nature of the composite material.
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Hagigat, Michael Kent. "Influence of non classical friction on the rubbing and impact behavior of rotor dynamic systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1057602344.
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Sanderson, Samuel C. "The Effect of Friction Stir Welding Process Parameters on Charpy V-Notch Impact Toughness in HSLA-65." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3745.
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HSLA-65 steel (6.4 mm thick) was friction stir welded at various welding speeds and spindle speeds. Varying weld parameters provided a range of heat inputs. Impact toughness was evaluated as a function of the different weld parameters and corresponding weld heat inputs. Charpy V-Notch (CVN) tests were conducted in parent material and at both the weld nugget centerline and heat-affected zone (HAZ) locations. The upper shelf CVN impact energy of the weld nugget was above that of the base metal for all weld parameters. The upper shelf impact toughness in the HAZ was largely unaffected by changing weld parameters. The nil-ductility transition (NDT) temperature in the weld nugget increased with increasing heat input. The toughness, with respect to the ductile-to-brittle transition, was negatively affected by the increase in heat input. The NDT temperature in the HAZ did not correlate with heat input. The microstructures and microhardness data were examined. Aspects of variation in the impact energy results were identified as the inhomogeneity of the weld microstructure and the placement of the V-notch. Weld nugget microstructures were more inhomogeneous than base metal. Hardness results showed varying values of hardness from the weld crown to the root, transversely across the weld, and longitudinally along the length. Variation due primarily to the inhomogeneity of the weld microstructure is compounded by the location of the V-notch.
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Souilliart, Thibaut. "Usure des tubes GV générée par des impacts répétés contre les supports à jeu." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC035/document.
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Ce mémoire présente une étude sur l’usure générée par des impacts glissants obliques faiblement chargés, et plus particulièrement par les impacts répétés entre les tubes de générateur de vapeur et les barres antivibratoires dans les réacteurs à eau pressurisée. L’étude expérimentale de la dynamique des impacts obliques montre une très forte dépendance de leurs caractéristiques à l’angle d’incidence, avec l’existence de deux régimes de frottement distincts, caractérisés par du glissement pendant tout l’impact pour les angles rasants et par une phase de glissement suivi d’une phase d’adhérence pour les angles proches de la normale. Les caractéristiques dynamiques des impacts, telles que le rapport de percussion, la perte d’énergie ou la distance glissée au cours d’un impact, sont exprimées en fonction des paramètres incidents, du coefficient de frottement cinétique et du coefficient de restitution, en étendant les formulations érosives de Brach [1] au cas d’impacts percussifs multi-aspérités faiblement chargés. L’étude de l’usure générée par des impacts obliques en air et en eau à température ambiante montre que celle-ci est reliée linéairement à la perte d’énergie sans période d’incubation, par un coefficient constant en air, et par un coefficient qui dépend fortement de l’angle d’incidence en eau. Les surfaces usées présentent des stries semblables à de fines rayures d’abrasion, sans trace d’adhésion ou de déformation plastique importante, incitant à proposer un scénario d’endommagement fondé sur un enlèvement de matière uniquement généré par des micro-rayures d’abrasion. Deux modèles d’usure par impacts en eau sont formulés, exprimant d’une part le volume usé et d’autre part la profondeur usée en fonction des paramètres incidents des impacts, du coefficient de restitution, du coefficient de frottement cinétique, des caractéristiques géométriques du tube GV et de la BAV et d’un coefficient d’usure constant<br>This thesis presents a study on wear induced by low-loaded sliding impacts in general and on wear induced by repetitive impacts between steam generator tubes and antivibration bars in pressurized water reactors in particular. The experimental study of the impacts dynamics shows that their characteristics strongly depend on the incidence angle. Two friction regimes are observed, characterized by sliding throughout the impact for grazing angles and by the existence of a sliding phase followed by an adhesion phase for the angles close to normal. The dynamic characteristics of the impacts, such as the impulse ratio, the energy loss or the sliding distance during an impact, are expressed as functions of the incident parameters, the kinetic friction coefficient and the restitution coefficient. These expressions extend the erosive formulations of Brach [1] to the case of low-loaded percussive multi-asperities impacts. The study of wear induced by oblique impacts at ambient temperature in air and water environment shows a linear relationship between the wear volume and the energy loss without any incubation period, with a constant proportionality coefficient in air, and with a proportionality coefficient which strongly depends on the incidence angle in water environment. Ridges similar to thin abrasion scratches are observed on the worn surfaces, without any mark of adhesion or significant plastic deformation. Thus, a damage scenario based on micro-scratching abrasion only is proposed. Two impacts wear models in water environment are proposed, which express firstly the worn volume and secondly the maximal worn depth as functions of the impacts incident parameters, the restitution coefficient, the kinetic friction coefficient, the SG tube and AVB geometrical characteristics and a constant wear coefficient
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Eriksson, Johan. "Experimental and numerical studies of nonsmooth mechanical systems : applications of dimension estimation." Licentiate thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-288.
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Freitas, Bruna Brito. "Avaliação da tenacidade da solda de um aço baixa liga C-Mn obtido pelo processo FHPP (Friction Hydro Pillar Processing)." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/118851.
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Os processos de soldagem por atrito apresentam diversas vantagens na união de materiais metálicos. O Friction Hydro Pillar Processing (FHPP) é um processo recente utilizado para fabricação e reparo de estruturas, que surge como uma alternativa à soldagem convencional. As interfaces das soldas FHPP são geralmente as partes mais suscetíveis à falha, devido à concentração de defeitos e microestrutura heterogênea. Por ser uma técnica recente e pouco difundida é importante avaliar as juntas soldadas por esse processo. Diante desse contexto, este trabalho teve como objetivo analisar os resultados macro e microestruturais de um aço C-Mn submetido ao processo FHPP, utilizando-se diferentes parâmetros, e relacioná-los com o perfil de microdureza. Além disso, avaliar a tenacidade ao impacto nas regiões de interface da solda e no material base. Para isso, foram realizados estudos metalográficos e perfis de microdureza Vickers em diferentes regiões das soldas. Complementarmente foram ensaiadas as interfaces das soldas que obtiveram os melhores resultados, através do ensaio Charpy, para avaliação de tenacidade ao impacto. Durante a soldagem foram utilizadas diferentes forças axiais e de recalque, obtendo como resultados variações, principalmente, nas interfaces soldadas. As alterações visualizadas nas interfaces, geraram uma tenacidade ao impacto menor do que a do material base. Esse fato pode ser atribuído, principalmente, porque o material base apresentou uma microestrutura predominantemente ferrítica, enquanto as interfaces soldadas apresentaram microestruturas heterogêneas, com presença de ferrita acicular, ferrita de Widmanstätten, martensita revenida e bainita.<br>Friction welding processes offer several advantages to join metallic materials. Friction Hydro Pillar Processing (FHPP) is a recent process used to manufacture and repair of underwater structure, emerging as an alternative for the conventional welding. FHPP welding interface are generally most susceptible to failure due to its heterogeneous microstructure and defects concentration. As FHPP is a quite recent little known technic, evaluate joints welded by this process is important. In this context, this study objective is to analyze macro and microstructural results of a C-Mn steel welded under different FHPP process parameters, and relate this results to a microhardness profile. Besides that, evaluate welding interface and base material impact toughness. To do that, metallographic analysis and microhardness profiles were done in different regions of the welded joint. In addition welded interfaces with the best results were Charpy tested for impact toughness evaluation. Different axial and forging forces were used, achieving macro and microstructural variations mainly in welded interface as a result. These variations caused interface to have lower impact toughness than base material. It can be explained by the base material mainly ferritic structure, whilst welded interface showed heterogeneous microstructures with acicular ferrite, Widmantätten ferrite, tempered martensite and bainite.
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Bodard, Sébastien. "Expérimentations et approche numérique de la transition combustion-déflagration-détonation dans les milieux pulvérulents initiée par un impact à faible vitesse." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4743/document.
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La présente thèse se concentre tout d'abord à mettre en place des expérimentations de compaction dynamique de poudres.Un montage expérimentale est conçu, testé puis validé. Le but de ce dernier est de générer des ondes de compaction unidimensionnelles et de pouvoir observer le milieu granulaire à l'échelle des grains. Deux types de poudres sont considérés : une poudre de polypropylène et une poudre d'explosif (RDX).Pour cela, des caméras ultra-rapides (50 000 images/s) sont utilisée pour enregistrer les essais. Une technique de corrélation d'image est utilisée pour remonter aux champs de déplacement et de vitesse des grains.Un modèle de compaction multiphasique est implémenté. Les phénomènes de friction grain/paroi sont ajoutés au modèle suite aux observation expérimentale. Une partie du travail a été consacré à l'amélioration de l'équation d'état granulaire et à sa détermination expérimentale.Les résultats numériques sont en bon accord avec les expérimentations, tant que le montage expérimental ne se déforme pas sous l'effet de la pression des grains.De premières expérimentations avec les poudres d'explosifs ont été réalisées. Le montage expérimental nécessite encore certaines améliorations mais il a prouvé son utilité dans l'étude de la transition combustion-déflagration-détonation<br>The first part of the present PhD focuses on the conception and the validation of an experimental set up. The aim of the experiments is to generate one-dimensional compaction waves and to observe the media at the grains scale. Two type of powder are used : polypropylene powder and an explosive powder (RDX).The experimental apparatus uses ultra-fast cameras (50 000 images/s) to record the tests. Image correlation is used to compute the displacement and velocity fields.A multiphasic compaction model is then coded. Grain/wall friction is added as the experimental work underlined its importance. Additional work has been provided concerning the granular equation of state and its experimental determination.Numerical results are in good agreement with the experimenations, as long as the experimental set up is not deformed because of the grains' pressure.A few experiments have been done with explosive powders. The experimental set up still needs some improvement but it proved its usefullness for deflagration to detonation studies
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De, Silva Prashan Roger. "The impact of biofuel ethanol on lubrication and friction in the piston assembly of a gasoline engine." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590275.
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The objective of the research presented in this thesis was to investigate and quantify the impact of biofuel ethanol and the associated water contamination into a commercially available automotive gasoline engine lubricant on the frictional response of piston ring/cylinder liner contacts and the resulting implications for fuel economy under problematic cold-start/warm-up/short-journey driving conditions. Whilst road transport is a major driver of global economic growth, it is also a primary user of fossil fuel based energy and a major emitter of Carbon Dioxide (C02). Therefore, increasingly stringent legislation demanding the use of biofuels in conjunction with conventional fossil fuels has been put in place. Even though biofuels are being blended into conventional gasoline and diesel at varying concentrations, information relating to the impact of these fuels on automotive engine lubrication, friction and fuel economy is scarce. A comprehensive and rigorous laboratory bench-top screening test programme using a reciprocating tribometer and Statistical Experimental Design was developed for the first stage of this investigation. Bespoke engine test programmes were also conducted to identify areas susceptible to ethanol and water dilution on the piston assembly and cylinder liner and to quantify fuel and water dilution into the lubricant present along the cylinder liner wall and in the sump. Tribometer investigations showed that significant reductions in friction resulted when the piston ring/cylinder liner contacts were lubricated with the lubricant-ethanol-water mixtures and the separated phases of these mixtures compared to the formulated lubricant. Temperature measurements on a single cylinder gasoline engine highlighted that lubricant present on the piston skirt, the connecting rod and on the intake side of the cylinder liner was highly susceptible to ethanol and water contamination under cold-start/warm-up conditions. Fuel dilution measurements on the same engine revealed that lubricant present on the upper cylinder liner, at top dead centre, was highly contaminated with ethanol, gasoline and water compared to that present lower down the cylinder, mid-stroke and bottom dead centre, and in the sump. again under cold-start/warm-up conditions.
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Dickson, Steven B. "An Investigation of Friction Stir Welding Parameter Effects on Post Weld Mechanical Properties in 7075 AA." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5672.
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The effects of weld temperature, travel speed, and backing plate thermal diffusivity on themechanical properties of a weld have been studied. A face centered cubic experiment of designwas completed in which the response variables were yield strength, minimum hardness in the HAZ, and charpy impact toughness. Three models were created from the data gathered usinga stepwise regression in order to see the effects of each parameter. For the yield strength andminimum hardness it was found that only travel speed and backing plate thermal diffusivities werestatistically significant to the properties. The charpy impact toughness saw that all three parameterswere statistically significant to its value. In all three models the travel speed had the greatest affecton the material properties.
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Chaudhry, Hina. "Impact of macroeconomic and monetary policy uncertainty shocks on economic growth- an empirical study of Pakistan." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2022. https://ro.ecu.edu.au/theses/2521.
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This study investigates the response of economic growth to macroeconomic and monetary policy uncertainty shocks under different financial conditions using data from Pakistan.
Macroeconomic uncertainty is argued to slow down the recovery of economies after recessions. Further research shows that country’s financial conditions play an important role in the uncertainty – economic growth relationship. Pakistan is an example of critically deteriorating developing economies and has faced significant challenges in economic growth associated with uncertainties in policies. However, there is a lack of in-depth analysis of uncertainty – economic growth relationship when it comes to Pakistan. A review of the sparse literature on Pakistan reveals four key gaps in the literature. First the extant studies suffer methodological biases due to the unavailability of high-frequency data. Second, the critical channel of financial frictions has to date been ignored. Third, the existing literature on Pakistan does not use comprehensive economic uncertainty proxies in their analysis. Fourth, there is no consensus on the best available uncertainty proxies, while there exist some sophisticated economic policy uncertainty indices used in the literature on developed economies.
The critical impact of macroeconomic uncertainty on economic growth and the deteriorating economic conditions in Pakistan motivate this study to address the above gaps in the literature. This is achieved through three key steps. First, along with the established monetary policy uncertainty measure, this study develops a new comprehensive macroeconomic uncertainty variable. Second, the study analyses whether the financial friction in Pakistan affects the impact of uncertainty on economic growth. Third, the study fills the gaps in methodological approaches by using alternative economic growth indicators and monthly data for vector autoregression analysis (VAR). The direction and magnitude of the impact of uncertainty shocks on the economic growth variable are reported through impulse response functions. The contribution of uncertainty shocks in explaining the variation in our macroeconomic indicators is reported through variance decomposition factor analysis. The VAR specifications are then tested for the robustness of Cholesky ordering and the identification of VAR using a Bayesian approach.
The major findings of the study are consistent with the literature and provide empirical evidence of a negative relationship between economic growth and both macroeconomic and monetary policy uncertainties. Additionally, consistent with the literature, this study shows evidence that financial friction exacerbates the negative impact of monetary policy uncertainty on the economic growth of Pakistan. However, contrary to previous research, the study finds that financial friction does not enhance the negative impact of macroeconomic uncertainty.The findings of this study are highly relevant to the regulators, policymakers and investors alike. It provides an empirical understanding of the behaviour of economic growth under uncertain macroeconomic and policy conditions. It also shows that the role of financial conditions cannot be ignored when devising strategies to mitigate the adverse economic impact of monetary policy uncertainty.
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Chu, Yanyan. "Surface modification to aramid and UHMWPE fabrics to increase inter-yarn friction for improved ballistic performance." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/surface-modification-to-aramid-and-uhmwpe-fabrics-to-increase-interyarn-friction-for-improved-ballistic-performance(d6e35803-9a2c-478a-a96d-a658292f8890).html.
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Manufacturing more reliable and lighter body armour using the fabrics with high-performance fibres is the development trend of ballistic protection device. However,increasing the reliability of the body armour normally needs to increase weight. Thisinvestigation aims to develop better ballistic performance of body armour withoutaffecting weight. Inter-yarn friction in quasi-static state in fabrics constructed for bodyarmour is one of the important factors affecting ballistic performance. This researchfocuses on increasing inter-yarn friction by surface modification methods for superiorballistic protection of woven fabrics. Finite element (FE) simulation is employed toanalyse the effects of inter-yarn friction on ballistic performance theoretically. BothAPPCVD and sol-gel methods are used to achieve the purpose of practically increasinginter-yarn friction. Ballistic experiments are conducted to evaluate ballistic performanceof the fabrics with different levels of inter-yarn friction after treatments. Through both numerical and experimental investigation, it is confirmed that increasinginter-yarn friction in quasi-static state can improve ballistic performance of fabrics. Theoverall energy absorption will be increased with the increase of inter-yarn frictionbecause higher inter-yarn friction generates higher resistance to the projectile, makesfabric structure more stable, leads to more involvement of the secondary yarns andincreases both KE and FDE percentages. Moreover, higher levels of inter-yarn frictionwill flatten the trauma and make the fabric response more globalised owing to the lesstransverse deflection ability. However, over high inter-yarn friction is counterproductivebecause of stress concentration on the primary yarns. For the surface modification, one of the aramid yarns, Twaron® yarn and one of theUHMWPE yarns, Dyneema® yarn, and their fabric products are used as the substrates. SEM analyses are used to characterise the morphology changes. Both FTIR and EDXanalyses are conducted to identify the coated substance. Based on coefficients of friction test and yarn pull-out test, the APPCVD treatment and sol-gel treatment have been proved as two effective ways to increase inter-yarn friction and at the same time the tensile properties of the yarns and the weight are almost unaffected. Moreover, sol-gel treatment has been established as an effective method for improvingballistic performance without significant weight increase, where the energy absorption ofthe Dyneema® fabric can be increased by 6.74%, and the trauma depth can be decreased by16.99% for Twaron® fabric panel and by10.73% for Dyneema® fabric panel.
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Zouabi, Chaïma. "Dynamique d'un contact glissant rugueux-rugueux sous faible charge : expériences et modélisation." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC043/document.
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Résumé Ce travail de thèse concerne le frottement et la dynamique d’un contact glissant entre deux plans secs et rugueux soumis à une faible charge normale. La vibration normale, et le bruit qui en résulte, sont associés à l’excitation induite au cours du glissement par les deux topographies aléatoires des solides en regard. Des mesures expérimentales de l’accélération verticale d’un patin rugueux soumis à son propre poids et en glissement stationnaire sur une piste rugueuse ont permis d’identifier et de caractériser une transition entre deux régimes : un régime de contact ininterrompu entre les solides à basses vitesses et un régime de sauts pour des vitesses plus élevées. Pour ce dernier, la dynamique est gouvernée par de très nombreux impacts entre aspérités que nous avons caractérisés sur le plan statistique (nombre de chocs, durées entre chocs, forces d’impact, etc.). Ces deux régimes conduisent à des comportements en frottement bien distincts. Une des originalités de cette recherche a été de confirmer les scénarios suggérés par les mesures accélérométriques à l’aide d’une mesure haute fréquence des variations temporelles de la résistance électrique de contact au cours du glissement. En améliorant la résolution temporelle des chocs, ces mesures apportent un éclairage dynamique sur la problématique du contact électrique rugueux. Pour interpréter ces résultats expérimentaux, nous avons revisité le modèle standard du Bouncing Ball. Il décrit une bille soumise à la gravité, et rebondissant sur une table animée d’un mouvement vertical aléatoire, représentatif de l’excitation stochastique induite par les topographies de surfaces en glissement. Nous avons introduit pour la première fois dans le modèle un temps de corrélation pour l’excitation aléatoire et montré son influence sur la dynamique des rebonds. Ce temps de corrélation est directement relié aux longueurs de corrélations des surfaces en contact et à la vitesse de glissement. Ce modèle revisité permet in fine une bonne prédiction de la vitesse de transition entre les deux régimes observés expérimentalement<br>This work deals with the friction and dynamics of a sliding contact between two dry and rough surfaces subjected to a low normal load. The normal vibration and the resulting noise are associated with the excitation induced during slip by the random topographies of both solids. Experimental measurements of the vertical acceleration of a rough slider subjected to its own weight and steadily sliding on a rough plate enabled identification and characterization of a transition between two regimes: An uninterrupted contact regime at low speeds and a regime of jumps at higher speeds. For the latter, the dynamics are governed by many impacts between asperities that we have characterized statistically (number of shocks, duration between shocks, impact forces, etc.). These two regimes lead to distinct frictional behaviors. One of the originalities of this research was to confirm the scenarii suggested by the accelerometric measurements through high-frequency monitoring of the temporal evolution of the electrical contact resistance during sliding. By improving the temporal resolution of shocks, these measurements provide a dynamics picture of the problem of rough electrical contact. To interpret these experimental results, we have revisited the standard Bouncing Ball model. It describes a ball subjected to gravity, and bouncing on a table animated by a random vertical motion, representative of the stochastic excitation induced by the topographies of sliding surfaces. We improved the model by introducing a correlation time for the random excitation and showed its influence on the dynamics of the bounces. This correlation time is directly related to the correlation lengths of the surfaces in contact and to the sliding velocity. This revisited model enables a good prediction of the speed at which the transition between the two regimes is observed experimentally
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Punna, Harshitha. "Impact of stiffness and damping capacity using two different rubbers on friction coefficient and noise levels of brake materials." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/theses/2773.
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Friction contact with both external and internal environments can significantly influence its efficiency, which could cause friction instabilities, vibration, and noise. Focusing on the effects that troubles brake pad, rotor, and friction-induced NVH, the main motivation for this study is to understand its drawbacks for some extent in a braking system. By proper study on applied statistics, an experimental design is planned. The design has friction tests that are performed by scaling down real test properties used in dynamometer to scaled-down properties in a subscale tester by using scaling law of physics. The test has two different types of rubbers with different humidity conditions with respect to two different brake pads in a small-scale tester, the Universal Mechanical Tester (UMT). This friction experiment helps in determining how different rubbers impact its stiffness on the coefficient of friction and noise levels, also to evaluate which scenario has the better damping capacity. The effect on the coefficient of friction and noise levels with and without rubbers is also compared. The results are subjected to the Design of Experiments analyses test know the statistical relationship between factors affecting the process and output of that process at different controllable variables namely humidity and temperature.
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Shon, Samuel. "An Experimental Study on the Impact of Various Surface Treatments on Friction, Scuffing, and Wear Characteristics of Lubricated Rolling-Sliding Contacts." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1351629351.
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Lundmark, Jonas. "Rail grinding and its impact on the wear of wheels and rails." Licentiate thesis, Luleå : Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1757/2007/37/index.html.
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Lastakowski, Henri. "Impacts de gouttes sur coussins d'air : surfaces super-hydrophobes, chaudes ou mobiles." Phd thesis, Université Claude Bernard - Lyon I, 2013. http://tel.archives-ouvertes.fr/tel-00991489.
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Cette thèse concerne l'étude de la dynamique d'impacts de gouttes, dans des situations de friction réduite entre le substrat solide et la goutte liquide. Cette diminution de friction s'est faite au moyen d'un film d'air inséré entre le liquide et le solide. Il existe plusieurs stratégies permettant l'existence de ce film d'air : la première est d'utiliser le phénomène de caléfaction, ou effet Leidenfrost : un liquide approché d'une surface chauffée au delà d'une température critique s'évapore suffisamment rapidement pour pouvoir léviter sur sa propre vapeur, et ainsi être isolé de la surface solide. Dans certaines conditions, les surfaces super-hydrophobes micro-texturées permettent au liquide de rester dans un état "fakir", c'est à dire de n'être en contact qu'avec le sommet de micro-piliers, le reste du liquide demeurant au dessus d'un coussin d'air. Enfin, il a également été constaté que l'écoulement d'air engendré par le mouvement d'une surface solide peut induire une force de portance sur une goutte, et ainsi lui permettre de léviter au dessus de cette surface
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Agarwal, Vivek Kumar. "Pounding and impact of base isolated buildings due to earthquakes." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/2217.
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As the cost of land in cities increases, the need to build multistory buildings in close proximity to each other also increases. Sometimes, construction materials, other objects and any projections from a building may also decrease the spacing provided between the buildings. This leads to the problem of pounding of these closely placed buildings when responding to earthquake ground motion. The recent advent of base isolation systems and their use as an efficient earthquake force resisting mechanism has led to their increased use in civil engineering structures. At the same time, building codes that reflect best design practice are also evolving. The movement of these base isolated buildings can also result in building pounding. Since base isolation is itself a relatively new technique, pounding phenomenon in base isolated buildings have not been adequately investigated to date. This study looks at the base isolated response of a single two story building and adjacent two story building systems. Four earthquakes with increasing intensity were used in this study. It was found that it is difficult to anticipate the response of the adjacent buildings due to non- linear behavior of pounding and base isolation. The worst case for pounding was found to occur when a fixed base and base isolated buildings were adjacent to each other.
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PORTOGHESE, LUCA MICHELE. "Essays on macroeconomic impact of heterogeneous banks." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/290981.
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Lo scopo della presente tesi è far luce sul ruolo del mercato interbancario nella trasmissione di shock idiosincratici verso l’economia reale nel suo complesso. Maggiore attenzione è spesa nello studio di shock che nascono dal lato dell’offerta di credito. Il modello utilizzato è composto da un continuo di famiglie identiche e da una massa di imprenditori atomistici. In particolare, gli imprenditori sono di due tipi, uno rischioso e uno sicuro. Abbiamo costruito un modello DSGE che considera un sistema finanziario stilizzato, con un mercato interbancario con due intermediari. Una banca può raccogliere una quantità limitata di depositi dalle famiglie, ed è quindi spinta a raccogliere maggiori risorse sul mercato interbancario. Poiché i tassi di interesse sui prestiti riflettono la rischiosità dei due imprenditori, il tasso più alto dovuto dagli imprenditori rischiosi permette alla banca che prende a prestito sull’interbancario di essere sempre profittevole, permettendo così all’interbancario di verificarsi.<br>In the present paper we aim at shedding some light on the role played by the interbank market in the transmission of idiosyncratic shocks hitting single institutions to the whole system and the real economy. We focus, in particular, on shocks to the supply side of credit. We analyse an economy populated by a continuum of identical households, and a mass of atomistic entrepreneurs. In particular, entrepreneurs are of two types, one risky and one safe. We set up a DSGE model representing a simple economy featuring a stylised financial system, with two intermediaries, and an interbank market. One bank faces an exogeneous constraint on the aggregate amount of deposits it can collect. It can overcome its liquidity constraint by borrowing additional financial resources from the unconstrained bank on the interbank market. Since interest rates on loans reflect the relative riskyness of the two types of entrepreneurs, for each unit of borrowed money, the borrower bank is able to realise higher profits than the lender bank, hence the scope for mutually profitable trade on the interbank market.
The second chapter of my thesis focused on two aspects that have not been already properly inspected, in the contribution offered by economists in the evaluation of economic effects brought by the recent SARS-CoV-19 pandemic. Specifically, as far as we know, the economic models tipically used to study the Corona-virus effects did not take into account i) the possibility to provide workers forced into lockdown with a subsidy, in order to mitigate the economic loss that comes along with the lockdown, and ii) the different levels of people's compliance to the lockdown policy and how to influence it. The aim of this paper is to shed some light on these two aspects. We try to evaluate the effectiveness of a common lockdown policy combined with a subsidy in influencing the behaviour of people in respecting the confinement.
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Yuan, Fuping. "PLATE IMPACT EXPERIMENTS TO INVESTIGATE DYNAMIC SLIP, DEFORMATION AND FAILURE OF MATERIALS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1193161550.
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De, Feo Modestino. "Impact du vieillissement de l'additif MoDTC sur ses propriétés tribologiques pour les contacts acier-acier et DLC-acier." Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0054/document.
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La législation européenne sur les émissions des véhicules devient de plus en plus sévère et ceci afin de minimiser l'impact sur l'environnement de la pollution occasionnée par les moteurs à combustion interne. La réduction des pertes par frottement et une plus faible consommation du carburant représentent différents aspects sur lesquels il est possible d’intervenir dans ce sens. Pour diminuer les pertes par frottement, plusieurs approches ont été utilisées, soit au niveau du design des pièces mécaniques, soit au niveau de l’optimisation du lubrifiant pour un contact considéré. Le dithiocarbamate de molybdène (MoDTC) est l’un des additifs modificateur de frottement permettant d’atteindre les plus faibles coefficients de frottement pour un contact acier/acier lubrifié en régime limite. La molécule se décompose dans le contact à des températures et des pressions élevées, en formant des feuillets lamellaires de MoS2 sur les surfaces frottantes. Cependant, il est nécessaire d'optimiser la durée de vie de ces additifs, en empêchant leurs appauvrissements ou dégradations prématurés dans le lubrifiant. Il a été montré, en effet, que les performances du MoDTC sont sensibles au temps de fonctionnement du moteur et sont donc liées à sa dégradation. L'objectif principal de cette thèse était donc de mieux comprendre le comportement tribologique (frottement et usure) d’une huile de base contenant du MoDTC en fonction de la dégradation du lubrifiant pour des contacts acier/acier et DLC/acier. L’approche utilisée pour mieux comprendre le comportement du MoDTC lorsqu'il est soumis à une dégradation thermo-oxydative consiste à combiner des expériences tribologiques, à des caractérisations de surface (XPS, FIB / TEM / EDX, Raman, SEM) et à des caractérisations chimiques des huiles (chromatographie en phase liquide, spectroscopie de masse, FT-IR). Un lien direct et cohérent entre la composition du tribofilm et la voie de décomposition chimique de l'additif MoDTC proposée a été mise en évidence. Les additifs modernes sont conçus pour être utilisés sur des surfaces à base de fer. Il est donc essentiel d'optimiser simultanément les lubrifiants et les revêtements pour améliorer leurs performances. Dans cette thèse, un modèle d'usure du revêtement DLC hydrogéné lubrifié en présence de MoDTC a été proposé. Nous avons établi à l’aide de plusieurs techniques, que l’usure est due principalement à la formation de carbure de molybdène présent dans le tribofilm formé à la surface de l’acier<br>European legislation on vehicle emissions continues to become more severe to minimize the impact of Internal Combustion Engines (ICE) on the environment. One area of significant concern in this respect is the reduction of friction losses resulting in reduced emissions and as well as higher fuel efficiency and lower fuel consumption. To decrease these losses, several approaches have been made particularly at design of mechanical parts stage and at experimental level to optimize lubricant components. A great contribution to solve the problem can be given by the optimization of the additives package blended into the engine lubricants. The molybdenum dithiocarbamate (MoDTC) is the additive showing the best tribological performance by acting as friction modifier. It decomposes under high temperatures and pressure, forming layered structures on the engine surfaces. However, the use of effective friction reducing additives to achieve low boundary friction coefficient is not enough to have great engine fuel efficiency. In addition, in fact, it is needed also to maximize their durability, preventing premature consumption or depletion of these additives. It has been shown, in fact, that the friction reduction performance of MoDTC is sensitive to engine operating time and that is related to the degradation of MoDTC itself. In the first part of my thesis we tried to get a good comprehension of the chemical mechanisms of MoDTC ageing and to study the impact on the tribological properties. The chemical bulk oil characterization of MoDTC blended into the base oil when subjected to thermo-oxidative degradation allowed to propose a new hypothetical chemical pathway followed by the friction modifier molecules during the ageing process. At the same time, these findings were linked to the impact of the MoDTC degradation on its tribological properties. As reported in literature, another MoDTC drawback is its strong antagonism with DLC coating. In fact, when DLC-involving contacts are lubricated by MoDTC-containing base oil, a catastrophic DLC wear is produced. For this reason, in the second part of the project a multi-techniques approach has been adopted to get a better understanding of this wear mechanism. The combination of all the findings allowed to propose for the first time a new wear mechanism based on the formation of molybdenum carbide species inside the contact. A strong chemical interaction between the molybdenum-based species formed on the steel counter-body and the carbon of the DLC material has been supposed, leading to the formation of MoC species. All the results found are discussed to clarify the correlation between degradation time, tribological performance and tribofilm characterizations in both steel/steel and DLC/steel contact
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Haddouni, Mounia. "Algorithmes de résolution de la dynamique du contact avec impact et frottement." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI022/document.
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La simulation des systèmes multicorps avec une dynamique non régulière trouve ses applications dans différents domaines comme l'aéronautique, l'automobile, le ferroviaire, la robotique, la réalité virtuelle et même l'industrie horlogère. Ces industries ont de plus en plus d'exigences sur la rapidité ainsi que la précision des méthodes utilisées pour calculer la dynamique. Par conséquent, la recherche dans le domaine de la mécanique non régulière est très active et a pour objectif constant de proposer des algorithmes plus robustes et plus rapides pour calculer la dynamique ainsi que de développer de meilleurs modèles pour le contact avec ou sans frottement. Les méthodes proposées doivent en plus bien gérer les sauts dans la vitesse et l'accélération des systèmes, ces sauts résultent de phénomènes tels que l'impact et le frottement. Dans ce manuscrit, quelques méthodes d'intégration d'équations différentielles algébriques d'index 3, 2 et 1 sont testées sur plusieurs mécanismes industriels avec contraintes unilatérales et bilatérales. Ces méthodes sont ensuite comparées sur la base de la satisfaction des contraintes bilatérales, de l'efficacité numérique et de leur capacité à gérer une dynamique raide. Cette étude a aussi permis d'apporter une réponse claire sur le choix de la méthode d'intégration pour un système mécanique connaissant ses caractéristiques (nombre de contacts, présence de contraintes bilatérales, dynamique raide...). La deuxième partie de ce travail traite certains problèmes qui sont fréquemment rencontrés dans la simulation des systèmes multicorps, notamment: le phénomène d'accumulation des impacts, la résolution du frottement, ainsi que la gestion des sauts qui peuvent être provoqués par la présence de singularités géométriques. Calculer la dynamique dans ces cas est particulièrement difficile dans le cadre des schémas event-driven. La solution proposée est un schéma d'intégration mixte "event-driven/time-stepping" dont le but est d'utiliser les avantages de chacune des familles d'intégration (event-driven et time-stepping). Notre algorithme est ensuite testé sur de nombreux exemples<br>The applications of the nonsmooth multibody systems field cover several fields including aeronautics, automotive, robotics, railway, virtual reality and watch industry to cite a few. These industrial applications have ever more stringent requirements on both accuracy and speed of the numerical methods used for the computation of the dynamics. As a consequence, the research in the nonsmooth mechanics domain is very active, to provide better integration methods for the resolution of the equations of motions and to develop better models for the contact problems with and without friction. Since the nonsmooth mechanics framework allows for jumps in the velocity and in the acceleration of the mechanical systems, the resulting algorithms have to handle such non-smoothness. In this PhD, several numerical schemes for the resolution of index-3, index-2 and index-1 DAEs are compared on industrial benchmarks with bilateral and unilateral constraints. The aim is to improve the efficiency of the Ansys Rigid Body solver which is based on an event-driven integration strategy. Points of comparison include the enforcement of the bilateral constraints, time efficiency and handling the stiff dynamics. This study also aimed at having a clear idea on the choice of the most suitable integration method for a given mechanical system knowing its characteristics (number of contacts, presence of bilateral constraints, stiff dynamics...). The second part discusses several issues that frequently occur in the simulation of multibody systems, namely, the problem of accumulation of impacts, the resolution of friction and handling the jumps resulting from the presence of some geometrical singularities. Dealing with such issues is very difficult, especially in the framework of event-driven schemes. In order to handle these problems, a mixed event-driven/time-stepping scheme is developed which takes advantage of both integration families (event-driven and time-stepping). Several examples are used to validate our methodology
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Walters, Andrew John Charles. "Inter-war, inter-service friction on the North-West Frontier of India and its impact on the development and application of RAF doctrine." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7681/.
Full textAbstract:
India’s North-West Frontier was the one area where the British Raj could suffer a knockout blow from either external Russian invasion or internal revolt. Frontier defence was amongst the greatest burdens during India’s inter-War financial austerity. Despite the RAF’s operational and financial efficacy in 1920s Iraq, air control was never implemented on the Frontier and air power’s potential was never fully exploited. Instead, aircraft were employed to enhance the Army’s traditional battlefield capabilities, resulting in efficient tactical co-ordination during the 1930s Waziristan campaign - the RAF’s most operationally-active pre-War theatre. To address why air power was constrained on the Frontier, the Thesis examines the inter-War relationship between the Armies of India and the RAF and its impact on the development and application of RAF doctrine. It concludes that the conservatively-natured Indian Armies were slow to recognise the conceptual shift required to fully exploit air power. This entrenchment was reinforced by inter-Service rivalry and the threat of aircraft replacing land forces with a concomitant loss of political standing. The enduring high-level internecine conflict resulted in the squandering of both resources and the opportunity to test independent, ‘strategic’ air power theory prior to WWII. Its legacy impacted on Army-RAF relations into WWII.
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Zhou, Jonathan, and n/a. "The friction in China-Japan trade co-operation (1979-1985) : a case study on the impact of the different developments of two Confucian societies." University of Canberra. Management, 1989. http://erl.canberra.edu.au./public/adt-AUC20061112.122349.
Full textAbstract:
After a long period of isolation, China embarked on an open
door policy in 1978. Keen to modernize her economy and
improve her living standards, China sought to intensify her
economic relations with Japan, one of her closest neighbours
and one of the most advanced and dynamic economies in the
world.
An air of optimism marked the signing of the Japan-China
Long Term Trade Protocol in 1978. China was confident that
this agreement would launch her into the path of modernization
in a relatively short period of time. This process of
intensification of economic links with Japan, however, was not
without difficulties. Over the years between 1979 and 1985,
the Chinese failed to fulfil key obligations of the agreement
including the non-payment for service received and the
permiting of, severe shortfalls in the supply of agreed goods.
The execution of the agreement was beset with problems. The
agreement from which both sides had hoped to reap
substantial economic benefits did not bear fruit; instead friction
developed, which had ensued with disastrous consequences
for both sides.
What was the root cause of this friction? Was it the
consequence of the incompatibility of the economic systems,
one communist and the other capitalist? Or was the failure the
result of political factors? Or could it be a much deeper reason
relating to inherent socio-cultural factors which affected the
decision-making processes in each of the countries?
This thesis seeks to examine closely the root cause of the
Chinese-Japanese trade friction. The writer argues that while
different ideologies and political systems contributed to the
problem, the dominant reason has socio-cultural origins, which
have to do with the way the Chinese and Japanese societies
evolved historically. Although both societies had Confucian
ethical underpinnings of their social systems, they began to
develop their own distinct characteristics. This coloured their
world views and had a major impact in the way each society
evolved its management practices. The Chinese rejection of
some key aspects of Confucianism and its acceptance of Qinstyle
authoritarianism, as subsequently modified by Sino-
Marxist principles, produced an organisational framework and
set of practices that did not prepare China to meet the
demands of economic modernisation. This had adversely
effected China's abilities to manage its trade relations with the
economically advanced Japan.
Section One of this thesis, which includes Chapters 1 and 2,
outlines the framework of Chinese-Japanese trade cooperation
beginning in the late 1970's. Chapter 1. seeks to give
an overview of the rationale behind China's new open-door
policy and its expectations of trade co-operation with Japan. It
outlines the nature of trade co-operation including the structure
of China-Japan trade. Chapter 2. proceeds to discuss the
ensuing difficulties and the responses of the Chinese and
Japanese governments. The writer then discusses the
subsequent actions taken by the two governments to revive the
co-operation that had gone wrong. An analysis of the faults of
both governments that led to the disastrous consequences is
then made.
Section Two, which includes Chapters 3 and 4, seeks to
examine the fundamental causes of the friction in the trade
relations between the two countries. The writer examines the
role played by socio-cultural factors and how they affected the
decision-making processes in both countries. In particular,
Chapter 3. analyses the role of feudalism in China as modified
by the emergence of the centralized bureaucracy which
characterize the Qin dynasty (221 to 207 BC). The impact of
the anti-merchantilism, which was the direct consequence of
Qin-style bureaucracy, and the question of the destruction of
the urban middle class by the bureaucracy are highlighted.
The writer argues that the absence of the urban middle class is
one of the fundamental reasons why China is unable to
produce an economically-progressive, capitalist-oriented
society. This led to a state of economic backwardness.
Chapter 4. contrasts the Chinese situation with Japan, by
analysing the ideological underpinning of Japanese society. It
outlines the various reform movements in Japan that led to the
development of a society that is economically dynamic . A
modern state has emerged in Japan in contrast to the
emergence of a backward society in China. The writer also
discusses the influence of Japanese Confucian values in the
development of this modern state. This was to have a
significant impact on Japanese management philosophy and
practices.
The last Section, which includes Chapter 5, 6, and 7,
discusses the lessons to be learnt from the trade friction
betwen the two countries. In particular, Chapter 5. analyses
the vastly different approaches taken by the Chinese in
contrast to the Japanese. The Chinese decision-making
process which is characterized by chaos, inefficiency and
bureaucratic bungling is contrasted with the Japanese style.
The latter's approach is systematic, well thought out and
meticulously planned. The Japanese, however, failed to take
into account the vastly different operating environment in their
dealings with China. Chinese behavioural responses were a
variable that the Japanese were unprepared to deal with. This
resulted in chaos in the strategic management of the trade
relations between the two countries. Notwithstanding this
friction, however, both China and Japan realize that they must
proceed with their trade relations and minimize whatever
frictions emerged over time. The last part of the thesis, Chapter
6. outlines the possible approaches that both sides can adopt
in their dealings with each other. An approach with Lindblom's
"muddling through" perspective is recommended by the writer.
Chapter 7 contains the conclusion drawn from this study.
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Grégoire, Isaac. "Analyse du coefficient de frottement sur les contacts lubrifiés et impact sur le grippage : Application aux transmissions par engrenages aéronautiques." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI100.
Full textAbstract:
Le développement de nouvelles technologies permettant d’obtenir des procédés de fabrication novateurs, de même que l’utilisation de nouveaux matériaux et lubrifiants, ont rendu possible une amélioration globale de l’efficacité des systèmes mécaniques et la résolution de nombreuses défaillances. Néanmoins, certains types de détérioration comme le grippage restent difficiles à appréhender car ils résultent de nombreux paramètres connexes tels que le régime de lubrification, la température du contact et le coefficient de frottement. Le grippage est un phénomène qui apparait de manière brutale et qui se caractérise par des arrachements et des transferts de matières entre les surfaces en contact pouvant aller jusqu’à la destruction complète du système. Ce dernier est généralement associé à une mauvaise dissipation des calories entrainant des températures de contact élevées. De nombreux critères basés sur la dissipation d’énergie dans le contact ont été établis sans pour autant que l’un d’eux ne soit unanimement reconnu par la communauté scientifique. La première partie de cette étude a consisté à caractériser le comportement en frottement d’un couple matériau-lubrifiant grâce à l’utilisation d’une machine bi-disque. En parallèle, une modélisation thermique de ce banc d’essais a été réalisée en utilisant la méthode des réseaux thermiques. Les corrélations entre les formules analytiques et les mesures expérimentales ont permis d’aboutir à l’établissement d’une loi de frottement liant conditions de contact et température de masse des éprouvettes. Il a aussi pu être démontré que la température de masse des disques pouvait être considérablement différente de la température d’injection du lubrifiant en fonction des conditions opératoires. Ce résultat permet une analyse nouvelle des critères de grippage dont la plupart assimilent la température des éprouvettes à celle d’injection du lubrifiant. Malgré cela, les différents essais de grippage réalisés montrent que l’unique considération de la température de contact pour établir un critère de grippage s’avère insuffisante<br>The development of new technologies, which allow innovative manufacturing processes, as well as the use of new materials and lubricants have led to an overall improvement of mechanical systems efficiency and reliability. However some failures, like scuffing, remain difficult to understand since they depend on many related parameters such as the lubrication regime, the contact temperature and the friction coefficient. Scuffing is a critical damage that appears suddenly and which is characterised by local welds and scratches between the sliding surfaces. It can lead to complete destruction of the mechanical system. This phenomenon is in general related to poor heat dissipation and overheating resulting in high contact temperature. Numerous studies were conducted in order to establish a scuffing criterion based on energetic approach. But none of them is unanimously recognized by the scientific community. The first part of this study consisted in characterizing the frictional behaviour of a given couple of lubricant and material thanks to the use of a twin-disc machine. In a second part, a thermal modelling of this test bench has been realised using the thermal network methodology. Correlations between analytical formulas and experimental measurements allowed to establish a friction law relating contact conditions and disc bulk temperature. It has also been demonstrated that the disc bulk temperature could be considerably different from the lubricant injection temperature depending on the operating conditions. This result allows a new interpretation of existing scuffing criteria, which for most of them consider the disc temperature to equal the oil temperature. Despite this analysis, the scuffing experiments performed reveal that accounting solely for the contact temperature is not sufficient to establish a reliable scuffing criterion
39
Frýza, Josef. "Elastohydrodynamic Film Study under Impact Loading and Lateral Vibrations." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-371778.
Full textAbstract:
Disertační práce se zabývá chováním a odezvou elastohydrodynamického (EHD) mazacího filmu za neustálených provozních podmínek. V úvodní části práce jsou shrnuty poznatky z oblasti EHD mazání; od jeho historie, přes základní mechanismy mazání a používané experimentální metody, až po nedávno publikované studie zaměřené na transientní podmínky. Hlavním cílem práce bylo experimentálně objasnit vliv provozních parametrů a reologických vlastností maziv na chování mazacího filmu v bodovém kontaktu při jeho nárazovém zatěžování a vystavení příčným vibracím. Za tímto účelem byla vyvinuta laboratorní zařízení umožňující měření rozložení mazacího filmu a tření za kontrolovaných nestacionárních podmínek. Experimenty odhalili zásadní roli přibližovacích a zatěžovacích rychlostí na formování stlačených mazacích filmů při nárazovém zatěžování. Výsledky byly srovnávány s nedávným teoretickým řešením. Bylo ukázáno na jeho nedostatky, jež byly následně odstraněny implementací empirických vztahů zohledňujících reologii maziv. V případě příčných vibrací byly nalezeny hranice selhání mazacího filmu a určeny vztahy popisující vliv příčných vibrací na centrální tloušťku filmu a její fluktuace jednotně pro všechny maziva. Závěrečná část práce poskytuje nový pohled na reologii maziv pomocí inovativního přístupu měření třecích reakcí maziva současně ve dvou směrech kontaktu za podmínek příčných vibrací. Tyto původní výsledky rozšiřují pochopení mechanizmů EHD mazání a mohou být použity k dokonalejším návrhům strojů, a vylepšit tak jejich účinnost, spolehlivost a životnost.
40
Raffai, Peter. "Modeling the Impact of Piston Rings on Oil Consumption of Internal Combustion Engines." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-316144.
Full textAbstract:
V rámci této práce byl vyvinut komplexní simulační nástroj, vycházející z výpočtového modelování fyzikálních a chemických dějů, který je doplněn vhodnými matematickými postupy. Výsledný software je schopen stanovit ztrátový výkon sady pístních kroužků pomocí účinků klíčových mechanismů a jejich vzájemné interakce při standardním provozu pístních kroužků. Simulační výstupy byly navrženy v souladu se zájmy průmyslové praxe, např. určení objemového toku plynů pístní skupinou, ztrátové výkony vlivem tření a spotřeba oleje, která je ovlivněna sadou pístních kroužků. Při vývoji simulačního modelu byly technické experimenty vykonány na tříválcovém zážehovém motoru za účelem získání vstupních dat a ověření výsledků. Možnosti navrženého simulačního nástroje jsou na tomto motoru dále demonstrovány v podobě parametrických studií, využitelných zejména při návrhovém procesu. Cílem dizertační práce bylo zaplnit mezeru ve výzkumné oblasti simulačních nástrojů, které mohou účinně propojit výpočtové modelování třecích ztrát a současně i spotřeby oleje, a podpořit tak výrobce pístních kroužků a vývojová oddělení spalovacích motorů.
41
Ponthus, Nicolas. "Contact sec glisssant sous faible charge : de la topographie des surfaces à la dynamique des solides de l'interface." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC021/document.
Full textAbstract:
Cette thèse porte sur la dynamique, normale à l'interface, d'un contact sec en glissement stationnaire entre deux surfaces de topographies aléatoires, soumis à une faible charge normale. Dans ce contexte, le mouvement d'un patin sous son propre poids a été étudié expérimentalement. Des mesures par vibrométrie laser du déplacement et de la vitesse normale du patin ont confirmé que, lorsque la vitesse de glissement augmente, le patin transite entre un régime où le contact est permanent vers un régime dynamique où il subit décollements, chocs et rebonds.À basse vitesse, le mouvement normal résulte d'un filtrage géométrique des topographies. Les caractéristiques statistiques et spectrales de ce mouvement ont pu être décrites. Les influences de la rugosité, de la longueur de corrélation, de la largeur de bande du spectre de rugosité et de l'aire apparente de contact ont été identifiées et analysées. Ces résultats ont pu être reproduits par des modèles numériques, mais aussi analytiques en adaptant la théorie des valeurs extrêmes. Des modèles de type Bouncing Ball, dont l'excitation est supposée donnée par le processus de filtrage géométrique, ont également été mis en place. Ils reproduisent une large gamme d'observations en régime dynamique, de la transition aux vibro-impacts.Pour tester certaines hypothèses des modèles mis en place, un patin multi-voies original a été développé et a permis d'accéder à la localisation spatiale des micro-contacts transitoires entre surfaces antagonistes. On observe que les micro-contacts sont gouvernés par une longueur caractéristique à basse vitesse de glissement et par un temps caractéristique à haute vitesse. Les rotations du patin deviennent importantes à haute vitesse, modifiant la répartition des micro-contacts à la surface du patin<br>This PhD thesis addresses the issue of the dynamics, normal to the interface, of a dry steady-sliding contact between two random topographies under weak normal load. In this context, the motion of a slider under its own weight has been studied experimentally. Measurements, using a laser vibrometer, of the normal displacement and velocity of the slider confirm the existence of a transition, as the sliding speed increases, from a regime of permanent contact to a regime of lift-offs, shocks and rebounds.At low speed, the normal motion is due to a geometrical filtering of the topographies, the statistical and spectral properties of which have been described. The roles of the roughness, including its spectral breadth and correlation length, and of the apparent contact area have been identified and analyzed. Those results have been reproduced not only using numerical models, but also using analytical ones based on the extreme value theory. Bouncing-Ball-like models, the excitation of which is assumed to be given by the geometrical filtering, have also been implemented and match with a broad range of experimental observations in dynamical regime, from the transition to vibro-impacts.To test some of the hypothesis of the models, a new experimental multi-channel slider has been designed and has enabled access to the spatial localization of the transient micro-contacts between the antagonists surfaces. It has been shown that micro-contacts are governed by a characteristic length at low sliding speed and by a characteristic time at high speed. The rotational motion of the slider also increases with sliding speed, changing the micro-contact distribution along the surface of the slider
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Herschberg, Basualdo Rafael. "Modeling the Diffusion of Interstitial Impurities and their Impact on the Ageing of Ferritic Steels." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS443/document.
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Nous modélisons la diffusion des atomes interstitiels (C et O) dans des solutions solides (Fe-Cr et Nb-V) et comparons nos résultats aux données expérimentales disponibles dans la littérature. Un ensemble d’énergies de liaisons entre interstitiels et solutés substitutionnels, et de barrières de migration des interstitiels, ont d’abord été calculés en utilisant la théorie de la fonctionnelle de la densité. Des modèles d’interactions de paires ont ensuite été ajustés sur ces données pour calculer les barrières de migration dans n’importe quel environnement chimique local. Ces modèles de paires sont enfin intégrés dans des simulations Monte Carlo cinétiques, afin de modéliser des expériences de diffusion de traceur et de frottement interne. Dans les alliages Fe-Cr-C, les simulations prévoient la formation d’un pic de Snoek unique, dans tout le domaine de composition entre le fer pur et le chrome pur. La barrière de migration moyenne du carbone, donnée par la température de ce pic, augmente progressivement avec la teneur en chrome, l’augmentation étant très faible en dessous de 6% de Cr. Dans les alliages riches en Cr, la barrière de migration moyenne obtenue lors d’une simulation de diffusion de traceur est plus grande que celle obtenue lors d’une simulation de frottement interne. Nous en concluons que la barrière mesurée lors d’une expérience de diffusion de traceur est fortement affectée par le piégeage du carbone dans des environnements riches en fer, qui limite la diffusion à grande distance ; alors que la barrière mesurée par friction interne, qui ne nécessite qu’une diffusion à courte distance, est principalement contrôlée par les barrières de migration des configurations les plus probables. Dans les alliages Nb-V-O dilués, les simulations font apparaitre un pic de Snoek à haute température lorsque la concentration en oxygène est plus faible que celle en vanadium. Quand la concentration en oxygène devient plus importante, un deuxième pic apparait à plus basse température, tandis que le premier pic se déplace vers des températures plus petites. Nous en concluons que le pic à haute température correspond à des paires V-O, et que celui à basse température correspond à la diffusion de l’oxygène dans le niobium pur. Les simulations sont utilisées pour tester le modèle de Koiwa, dans la limite de l’alliage ternaire infiniment dilué. Les deux approches sont en bon accord et nous montrons que la position du pic à haute température n’est pas reliée à une fréquence de saut unique, mais à une fonction complexe de plusieurs fréquences de sauts. Nous présentons enfin les résultats d’une étude préliminaire sur l’effet du carbone sur les cinétiques de séparation de phases dans les alliages fer-chrome irradiés. Nous montrons que la forte attraction entre atomes de carbone et défauts d’irradiation (auto-interstitiels et surtout lacunes) peut dans certaines conditions limiter l’accélération de la précipitation du chrome habituellement provoquée par l’irradiation<br>The diffusion of interstitial atoms (C and O) in bcc solid solutions (Fe-Cr and Nb-V) is modelled and compared to experimental data. A set of binding energies and migration barriers for the direct interstitial diffusion mechanism in different local chemical environments are first calculated using Density Functional Theory. Two different pair interaction models are developed in order to reproduce these data and predict the migration barriers in all possible environments. The diffusion models are then implemented in a kinetic Monte Carlo method to simulate tracer diffusion experiments, using a standard procedure, and internal friction experiments, using a novel method. In the Fe-Cr-C systems our internal friction simulations show a unique Snoek peak in the whole concentration range, between pure iron and pure chromium. The average migration enthalpy for C diffusion in Fe-Cr alloys is found to increase progressively with the Cr concentration, with a small rate below 6 %Cr. In Cr-rich alloys, the effective migration barrier for C diffusion is found to be larger in tracer diffusion than in the internal friction simulations. We conclude that the effective migration barrier extracted from tracer diffusion is closely related to trapping effects of C atoms in Fe-rich local environments, whereas the migration barrier associated with internal friction is mainly controlled by the spectrum of migration barriers of the most frequent configurations, as it is clearly shown in the Cr-rich domain. In the dilute Nb-V-O alloys, we find a high temperature Snoek peak when the concentration of oxygen is lower than the vanadium content. But when the oxygen concentration is higher, we see the appearance of a second peak but at a lower temperature and a shift of the first peak to lower temperatures. We conclude that the high temperature peaks correspond to the oxygen-vanadium pairs, and the low temperature peak corresponds to the oxygen Snoek peak in pure Nb. We also use our model in order to validate the Koiwa model in infinitely dilute ternary alloys. Both approaches are in good agreement and we observe that the high temperature peak cannot be directly related to a single jump frequency but to a complex function of them. We also show preliminary results on the effect of C in the precipitation of the Fe-Cr phase separation under irradiation. We observee that a strong attraction between carbon atoms and point defects (vacancies and self-interstitials) might be able to slow down the acceleration of the α’ precipitation
43
Charles, Alexandre. "Dynamique des systèmes de solides rigides avec impacts et frottement." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4738/document.
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Avec en perspective l’application à la robotique ou à l’étude des milieux granulaires, nous discutons la formulation des problèmes de contacts avec frottement en dynamique et pour les systèmes constitués de solides rigides. L’approche usuelle est event driven et ne permet pas d’écrire de manière systématique un problème d’évolution. Ceci a motivé l’émergence d’une nouvelle approche dans le cas sans frottement que nous généralisons au cas avec frottement. Suivant le point de vue de Lagrange sur l’équation de la dynamique, nous mettons en exergue l’usage systématique des puissances virtuelles et de la dualité. Ce parti-pris suggère de mettre l’accent sur l’effort généralisé de réaction dans la formulation et non sur les forces de réactions locales dans le monde réel, comme il est usuel. Ce point de vue permet d’échapper à des pathologies connues sous le nom de paradoxe de Painlevé<br>In the view of robotics or granular media mechanics, we question the statement of the dynamical evolution problem for multibody systems with contacts and friction. The usual approach is event driven and does not allow to state an evolution problem in a systematic way. This matter of fact gave rise to a new approach in the frictionless case we generalize to the case with friction. Sticking to the point of view of Lagrange on the equation of the dynamics, we emphasize the systematic use of virtual powers and duality. This bias suggests to put emphasis on generalized reaction forces in the statement of the evolution problem and not on local reaction forces of the real world, as it is usual in practice. This point of view allows to escape from pathologies known as Painlevé paradox
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Touret, Thomas. "Health Monitoring : Impact thermique d’un défaut dans une transmission par engrenages - application aéronautique." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI041.
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Le Health monitoring (maintenance préventive conditionnelle) appliqué aux transmissions par engrenages et basé sur des mesures dynamiques et/ou acoustiques est une méthodologie en plein développement. Cependant, cette technologie peut se heurter à des difficultés d’analyse des signaux pour identifier les défaillances. C’est pourquoi une autre approche de Health monitoring peut être envisagée, cette fois-ci basée sur des mesures thermiques. Le niveau de température des systèmes mécaniques est imposé par leur efficacité énergétique et leur environnement. Ainsi une dégradation des composants mécaniques peut se traduire par une diminution du rendement et donc une augmentation de la température du composant touché. L’étude s’est donc portée sur l’évaluation de la capacité d’une approche thermique à permettre la détection de défauts mais aussi le diagnostic et le pronostic des composants mécaniques. Une étude bibliographique a pu montrer que l’analyse thermique est effectivement une approche viable pour détecter les défaillances dans les transmissions mécaniques. Un nombre relativement important d’études s’est déjà intéressé à ce sujet. Cependant cette investigation a aussi montré que les études existantes étaient rarement en mesure de diagnostiquer ou pronostiquer l’état des transmissions mécaniques du fait d’un manque de modèle associé. La réalisation d’un modèle utilisant la méthode des réseaux thermiques a permis de montrer que les variations de pertes entrainent des variations localisées de températures. Le modèle a aussi permis de montrer que les variations de températures étaient directement proportionnelles aux variations de pertes observées. Ces deux observations suggèrent que les mesures thermiques doivent permettre de réaliser respectivement le diagnostic et le pronostic des transmissions mécaniques. L’utilisation de machines bi-disques, qui simulent les conditions de contact des engrenages, a permis de mettre en évidence un lien direct entre la présence de défauts, en l’occurrence le micropitting, et l’augmentation du coefficient de frottement des surfaces lubrifiées. Cette série d’essais suggère aussi que les engrenages des transmissions mécaniques pourraient voir leur rendement impacté par la présence de défauts. Finalement l’utilisation d’un banc FZG a permis de réaliser des essais de caractérisations des pertes et des températures à plusieurs niveaux de développement du micropitting sur les dentures. Ces essais ont permis de montrer que les températures d’une transmission mécanique sont directement impactées par les variations de pertes. Les variations des températures se sont avérées cohérentes avec celles issues du modèle numérique élaboré. Au final, ces résultats montrent que l’étude des températures est un moyen viable de diagnostiquer l’état de transmissions mécaniques<br>Health monitoring applied to gear units and based on dynamic or acoustic measurements is a growing technology. It is especially true in the present industrial context that tends to increase constrains on any mechanical systems. Nevertheless, this technology faces great difficulties regarding signal treatments and failure identifications. Thus, another health monitoring approach based on temperature measurements is considered. Enclosed gear drive temperatures are imposed by their efficiency and their environment. Therefore, any component damage can lead to efficiency degradation and so a local temperature increase. The proposed study aims to evaluate the capability of temperature measurements to detect, diagnose and estimate the remaining life expectancy of any mechanical component. A bibliographic study shows that temperature analysis is a valid approach to detect failure in mechanical systems. Indeed, a substantial number of studies deal with this subject. But, these studies are rarely able to diagnose or estimate remaining life expectancy as they are lacking of a comprehensive thermal model. Considering this observation, a model based on the thermal network approach was developed to simulate the energetic behavior of a given gear unit. It shows that any variation in mechanical system efficiency results in localized temperature increase. It also reveals that the simulated temperature variation is proportional to the power loss one. Those two observations suggest that temperature measurements could be a relevant approach. Experimental investigations were conducted with twin-disc machines to replicate gear mesh contact conditions. This study shows that a defect such as micropitting has a direct impact on friction coefficient for a lubricated contact. The relationship between friction increase and defect number appears to be proportional. These experiments suggest that the efficiency of geared mechanical systems could be directly impacted with such failures. Finally, an FZG test rig was used to experimentally characterize the effect of micropitting on power losses and temperatures. Tests indicate that there is a direct relationship between efficiency and temperatures. Furthermore, efficiency variations are numerically linked to gear surface features and micropitting magnitude evolutions observed during tests. Temperature variation appears to be consistent with the ones obtained with the thermal model. In fine these results show that temperature measurements are a valuable approach to diagnose and estimate the remaining life expectancy of a geared mechanical system
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Bilarev, Todor. "Feedback Effects in Stochastic Control Problems with Liquidity Frictions." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19592.
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In dieser Arbeit untersuchen wir mathematische Modelle für Finanzmärkte mit einem großen Händler, dessen Handelsaktivitäten transienten Einfluss auf die Preise der Anlagen haben.
Zuerst beschäftigen wir uns mit der Frage, wie die Handelserlöse des großen Händlers definiert werden sollen. Wir identifizieren die Erlöse zunächst für absolutstetige Strategien als nichtlineares Integral, in welchem sowohl der Integrand als der Integrator von der Strategie abhängen.
Unserere Hauptbeiträge sind hier die Identifizierung der Skorokhod M1 Topologie als geeigneter Topologue auf dem Raum aller Strategien sowie die stetige Erweiterung der Definition für die Handelserlöse von absolutstetigen auf cadlag Kontrollstrategien.
Weiter lösen wir ein Liquidierungsproblem in einem multiplikativen Modell mit Preiseinfluss, in dem die Liquidität stochastisch ist. Die optimale Strategie wird beschrieben durch die Lokalzeit für Reflektion einer Diffusion an einer nicht-konstanten Grenze. Um die HJB-Variationsungleichung zu lösen und Optimalität zu beweisen, wenden wir probabilistische Argumente und Methoden aus der Variationsrechnung an, darunter Laplace-Transformierte von Lokalzeiten für Reflektion an elastischen Grenzen.
In der zweiten Hälfte der Arbeit untersuchen wir die Absicherung (Hedging) für Optionen. Der minimale Superhedging-Preis ist die Viskositätslösung einer semi-linearen partiellen Differenzialgleichung, deren Nichtlinearität von dem transienten Preiseinfluss abhängt.
Schließlich erweitern wir unsere Analyse auf Hedging-Probleme in Märkten mit mehreren riskanten Anlagen. Stabilitätsargumente führen zu strukturellen Bedingungen, welche für ein arbitragefreies Modell mit wechselseitigem Preis-Impakt gelten müssen. Zudem ermöglichen es jene Bedingungen, die Erlöse für allgemeine Strategien unendlicher Variation in stetiger Weise zu definieren. Als Anwendung lösen wir das Superhedging-Problem in einem additiven Preis-Impakt-Modell mit mehreren Anlagen.<br>In this thesis we study mathematical models of financial markets with a large trader (price impact models) whose actions have transient impact on the risky asset prices.
At first, we study the question of how to define the large trader's proceeds from trading. To extend the proceeds functional to general controls, we ask for stability in the following sense: nearby trading activities should lead to nearby proceeds. Our main contribution in this part is to identify a suitable topology on the space of controls, namely the Skorokhod M1 topology, and to obtain the continuous extension of the proceeds functional for general cadlag controls. Secondly, we solve the optimal liquidation problem in a multiplicative price impact model where liquidity is stochastic. The optimal control is obtained as the reflection local time of a diffusion process reflected at a non-constant free boundary. To solve the HJB variational inequality and prove optimality, we need a combination of probabilistic arguments and calculus of variations methods, involving Laplace transforms of inverse local times for diffusions reflected at elastic boundaries.
In the second half of the thesis we study the hedging problem for a large trader. We solve the problem of superhedging for European contingent claims in a multiplicative impact model using techniques from the theory of stochastic target problems. The minimal superhedging price is identified as the unique viscosity solution of a semi-linear pde, whose nonlinearity is governed by the transient nature of price impact.
Finally, we extend our consideration to multi-asset models. Requiring stability leads to strong structural conditions that arbitrage-free models with cross-impact should satisfy. These conditions turn out to be crucial for identifying the proceeds functional for a general class of strategies. As an application, the problem of superhedging with cross-impact in additive price impact models is solved.
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Nenad, Grahovac. "Анализа дисипације енергије у проблемима судара два или више тела". Phd thesis, Univerzitet u Novom Sadu, Fakultet tehničkih nauka u Novom Sadu, 2011. http://dx.doi.org/10.2298/NS20111208GRAHOVAC.
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Анализиран је судар два тела као и дисипација енергије укључена кроз механизам сувог трења моделираног неглатком вишевредносном функцијом и кроз деформацију вискоеластичног штапа чији модел укључује фракционе изводе. Проблем судара два тела је приказан у форми Кошијевог проблема који припада класи неглатких вишевредносних диференцијалних једначина произвољног реалногреда. Кошијев проблем је решен нумеричким поступком заснованим на Тарнеровом алгоритму. Испитано је кретање система и дисипација енергије за разне вредности улазних параметара. Показано је да се уведене методе могу применити и на проблем судара три тела.<br>Analiziran je sudar dva tela kao i disipacija energije uključena kroz mehanizam suvog trenja modeliranog neglatkom viševrednosnom funkcijom i kroz deformaciju viskoelastičnog štapa čiji model uključuje frakcione izvode. Problem sudara dva tela je prikazan u formi Košijevog problema koji pripada klasi neglatkih viševrednosnih diferencijalnih jednačina proizvoljnog realnogreda. Košijev problem je rešen numeričkim postupkom zasnovanim na Tarnerovom algoritmu. Ispitano je kretanje sistema i disipacija energije za razne vrednosti ulaznih parametara. Pokazano je da se uvedene metode mogu primeniti i na problem sudara tri tela.<br> Impact of two bodies was analyzed as well as energy dissipation, which was included through dry friction phenomena modelled by a set-valued function, and through deformation of a viscoelastic rod modelled by fractional derivatives. The impact problem was presented in the form of the Cauchy problem that belongs to a class of set-valued fractional differential equations. The Cauchy problem was solved by the numerical procedure based on Turner’s algorithm. Behaviour and energy dissipation of the system was investigated for different values of input parameters. It was shown that suggested procedure can be applied on the problem of impact of three bodies.
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Cederqvist, Wilma, and Cecilia Linhatte. "Lastkapacitet hos murar byggda med C3Cblocksystem® : Påkörningslaster och oavsiktlig stöt." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104829.
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Världen har de senaste åren upplevt flera terrorattentat där fordon har använts som vapen för att orsaka skador i folkmassor. Fotgängare kan vara i en utsatt miljö på gångstråk och skydd i form av betonghinder kan användas för att stoppa oönskad trafik på gågator. C3C Engineering AB tillverkar betongblock som antingen kan användas som enskilda element eller byggas ihop likt lego för att skapa murar och barriärer. Betongblocken kan således även användas som skyddsbarriärer vid pågående vägarbeten, för tillfälliga konstruktioner på exempelvis återvinningscentraler eller som stödmurar. C3C tillverkar i så stor utsträckning som möjligt betongblocken av restbetong som blivit över vid gjutning av andra typer av element. Syftet med denna studie var att undersöka betongblocks lastkapacitet med avseende på påkörningslaster från personbilar, lastbilar och gaffeltruckar. Betongblocket var av typen C3Cblock® 1688 med dimensionerna 800 mm x 800 mm x 1600 mm och tillverkades i betongkvalité C20/25. Arbetet undersökte hur olika förstärkningar såsom ingjutna gängstänger samt kontreforer kunde öka blockens kapacitet. Även hur blockens underlag påverkar lastkapaciteten med avseende på glidning undersöktes. Påkörningslaster är dynamiska laster. I detta arbete behandlades samtliga dynamiska laster med hjälp av statiskt ekvivalenta laster. Lastkapaciteten hos blocken med avseende på stjälpning, glidning, dymlingsverkan, skjuvkapacitet i styrkonsoler och moment- och tvärkraftskapacitet jämfördes med rekommenderade värden för påkörningslaster från Eurokod 1 och EKS6. För exceptionella lastfall kan blocken tillåtas att gå sönder, glida eller stjälpa eftersom deras huvudsakliga syfte är att stoppa trafik och skydda människor på gator eller arbetsplatser utmed trafikerade vägar. Beräkningar utfördes med hjälp av MathCad och Excel för att ta fram ett beräkningsdokument samt en tabell med lastkapacitet för samtliga lastfall som undersökts. Resultat från beräkningar för stjälpning och glidning jämfördes med underlag som C3C tillhandahöll. Beräkningar gjordes för enskilda block samt för olika murar med olika utföranden där bland annat höjden på muren och vilken sida av blocken som lasten angrep var parametrar som varierade. Resultatet visade att lastens angreppshöjd hade stor inverkan på murens kapacitet. Lastbilar och gaffeltruckar har högre angreppshöjd än personbilar. För de höga angreppshöjderna kommer stjälpning av muren att bli dimensionerande, jämfört med låga angreppshöjder där glidning inträffar först. Blocken kan tillåtas att gå sönder och därmed är moment- och tvärkraftskapacitet av sekundär betydelse. Styrkonsolernas skjuvkapacitet var stor och kommer därför inte vara dimensionerande. På grund av avgränsningar studerades endast en typ av betongblock. Ingen hänsyn togs till andra laster såsom vind eller snö som även de kommer att påverka en murs kapacitet. Det krävs därför vidare studier för att undersöka hur dessa laster samt hur olika dimensioner påverkar lastkapaciteten hos enskilda block eller murar. Försök kan med fördel utföras för att validera de teoretiska lasterna som beräknats i detta arbete.<br>Due to an increasing number of acts of terror where vehicles are used as a form of weapon a need to protect pedestrians has arisen. In this study the load capacity of interlocking concrete blocks with a rectangular cross section was examined based on various deformations and collapses. The concrete blocks could be used as protection against collisions such as terrorist attacks with vehicles as well as a barrier between work zones and close by traffic. The purpose of the study was to determine the load capacity in the event of a collision with a car, truck or forklift for different types of walls as well as for single blocks. The concrete blocks in the walls have both been built as Lego as well as stacked parallel on top of each other. The work is based on calculations. The results have been checked against existing documents from C3C Engineering AB. Using MathCad and Excel a document for calculations has been designed. The result from the calculations shows that walls will slide when a load acts at a low height in relation to the ground. The wall will overturn when the load acts at a higher distance from the ground.
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Svahn, Fredrik. "Low-cost control of discontinuous systems including impacts and friction." Licentiate thesis, Stockholm : Farkost och flyg, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4581.
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Abia, Sonny D. "Application of Reliability Analysis to Highway Design Problems: Superelevation (e) Design, Left Turn Bay Design-Safety Evaluation and Effect of Variation of Peak Hour Volumes on Intersection Signal Delay Performance." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/447.
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This research has three parts. Part 1: The Policy on Geometric Design of Highways and Street provides 5 methods of superelevation (e) distribution. Many states use methods 2 and 5 for low speed, urban and rural high-speed facilities. Method 5 aims to address speed variations; but is complicated, computationally intractable and may violate design consistency. Design recommendation by NCHRP439 accounts for speed variation, tractable; but is cumbersome along with irregular/step-wise design curves. New reliability based e distribution method is developed that addresses the speed variation; which is simple in determining and evaluating acceptable required e rates. At 95% level of reliability, the e rate obtained is lower than that from current practice resulting in cost savings. Part 2: Current practice/research does not address safety issue of the left-turn-bay at high degree of saturation (x). Left-Turn-Bay distance has three components: clearance, breaking to a stop and queue. The variation in the queue length reduces clearance and breaking distance resulting in unsafe breaking. Failure = clearance plus breaking distance < demand. The reliability of the left-turn-bay defined as the availability of the three components for left-turning vehicles to complete clearance and breaking maneuver safely; measured as increase in the deceleration rate over limit of 11.2ft/s2, safety index and probability of failure. Results show that at 95% reliability, current design practice fails when x exceeds 50%. Part 3: Current practice uses mean traffic volumes (Vd) as input for traffic signal control at roadway intersections. Variations in traffic flows affect the performance of intersection measured by the delay per vehicle traversing the intersection in seconds. Peak hour factor (PHF), the hourly volume divided by the peak 15-min flow rate within the peak hour is adopted by Highway Capacity Manual (HCM) to control surge. HCM suggests PHF design value of 0.92 for urban and 0.88 for rural areas. Fixed PHF may lead to increase in delay. Effects of variation of peak hour volumes on intersection signal delays are examined with large data. A new model is developed for PHF and Vd and used in signal timing to minimize intersection delay. The results show that the assumption of Poisson distribution for Vd is not reliable; delay reduction of 6.2 seconds per vehicle is achieved. Annual savings in travel time, fuel consumption and emissions cost is estimated in billions of dollars.
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Bouattour, Fatma. "Impact of financial Frictions on international Trade in Brazil and emerging Countries." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLED009/document.
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Ce travail a pour but d’approfondir l’analyse des effets des contraintes de financement sur le commerce international, en portant une attention particulière aux pays BRICS, notamment le Brésil. Cette thèse comporte trois chapitres. Le premier chapitre évalue la vulnérabilité financière des secteurs manufacturiers brésiliens dans les années 2000, en se basant sur le travail de Rajan et Zingales (1998). Ce chapitre souligne l’importance du développement financier et des crédits publics dans l’allocation intersectorielle du capital au Brésil. Le deuxième chapitre étudie les effets des contraintes financières sur les exportations des firmes brésiliennes, dans le cadre théorique de firmes hétérogènes (Manova, 2013). Il s’agit de repenser le lien entre la taille et les performances d’exportation, en présence de contraintes financières au niveau sectoriel. Ce chapitre montre l’importance des difficultés d’accès au crédit au Brésil dans l’explication des performances d’exportation. Le troisième chapitre étudie les effets du développement financier sur les exportations vers les BRICS, avec un intérêt particulier pour les effets de la crise financière de 2008. Ce chapitre confirme l’importance du développement financier comme source d’avantage comparatif dans les secteurs dépendants de la finance externe. Cet avantage lié au développement financier perd de son importance pendant la crise. Les résultats confirment l’importance du canal financier de transmission de la crise<br>This thesis aims at deepening the analysis of the effects of financial constraints on international trade performances, with a focus on the BRICS countries, notably Brazil. This thesis includes three chapters. The first chapter aims at evaluating the level of financial vulnerability of Brazilian manufacturing sectors in the 2000s, based on the work of Rajan and Zingales (1998). This chapter stresses the importance of the financial development and of public credits in causing the inter-sectoral capital misallocation. The second chapter focuses on the link between financial constraints and the performances of Brazilian exporters, in a framework of heterogeneous firms as in Manova (2013). Specifically, I revisit the link between firm size and firm exports by focusing on the financial constraints at sector-level. Findings emphasize the importance of problems of access to credit in Brazil, in explaining Brazilian firms’ export performances. The third chapter analyzes the effects of financial development in exporting countries on their exports to BRICS countries, with a focus on the recent financial crisis effects. Results confirm the role of financial development as a source of comparative advantage in sectors with high reliance on external finance. The positive effect related to financial development is lessened during the crisis. This confirms the importance of the trade finance transmission channel of the crisis