No / The formation of tribo-layers during machining is very common phenomena, especially when machining `free machining¿ steels. Several kinds of tribo-layers formed in metal cutting processes have been reported, layers of inclusions from the workpiece, oxide layers due to chemical reaction, plastic deformation layers, material transfer layers (MTLs) or built-up layers (BULs). A new tool¿chip contact model is proposed to explain the tribo-layer phenomena, which considers the nature of the shear strain rate distribution in the secondary deformation zone. A shear strain rate distribution in this zone having a shape similar to that found in the preliminary zone is proposed. A cutting interface (CI) is defined and this interface is at different location to the material boundary of tool and chip (MBTC). This difference is a key factor in the formation of the tribo-layer in the secondary deformation zone. This model can be used in improving tool wear prediction and the estimation of tool life.

No description available.

Alloys of titanium are highly preferred materials for their excellent strength to weight ratio but the tribological issues while using them has been posing challenging issues for the tribological analyst, which are still areas of active research. Ti-6Al-4V (Ti64) is the most popular alloy of titanium and our understanding of the fundamental mechanisms of wear and friction of this alloy is still not complete. Previous investigations related to the tribology of these alloys have suggested a synergistic effect of plastic deformation and tribo-oxidation. The present investigation described in this thesis explores the existence of one more mode, namely the formation of a Mechanically Mixed Layer (MML). The thesis examines the effect of these modes one by one and analyses the synergistic effect of these mechanisms, and also the effect of heat generation during sliding. The tribological condition existing have been varied by doing wear experiments using Ti64 pins sliding against alumina and SS316L (controls MML), diameter of pin (expected to control debris entrapment and thus MML formation), tribo-system (horizontal disc Vs vertical disc, which is also expected to control debris entrapment and thus MML formation), environment (ambient and vacuum, expected to control tribo-oxidation) and sliding speed (expected to control interface temperature and thus plastic deformation mechanism and tribo-oxidations). The division of the main chapters has been so made to present the findings spread over Chapters 5-8, with each chapter dealing with specific tribological test conditions. In each chapter, results from the tribological experimentations in the form of wear and friction are presented, together with the characterization methods which throw light into the tribological mechanisms. These characterization methods include Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDAX), X-Ray Diffraction (XRD) and Electron probe micro-analyzer (EPMA). Wherever possible, the debris collected from the experiments have been subjected to morphological and detailed chemical analysis, and a feature which has not been explored much in detail by tribological investigators, but having a promising potential. Experimental results from tribological testing when Ti64 pins slides against two different materials (Alumina and SS316L) in pin-on-disc tribometers under two different environmental conditions (ambient /vacuum) are analyzed. Each set of experiments looks at two different effects - (1) the effect of sliding speed on the tribological behavior while using a pin of a fixed diameter (all other parameters remaining the same) and (2) the effect of using pins of different diameters for a given set of parameters. Three different pin-sizes were employed (2.1 mm. 4.6 mm and 6.6 mm), the normal loads on these pins were changed according to the pin-size used so that all experiments were done at the same contact pressure (2.8 MPa). By performing the experiments against the ceramic disc (alumina) under vacuum conditions, the effect of this plastic deformation is studied in isolation because the possibility of the Tribo Chemical Reaction (TCR) due to oxidation is inhibited and no MML was found to be formed due to poor compatibility of mixing between the metallic pin and the ceramic disc. For the low speeds/strain rates experiments, the effect of plastic deformation as influenced by the adiabatic shear banding is seen to influence wear which progressively changes to temperature induced plastic deformation and wear. The situation is found to be different when we change the environmental conditions from vacuum to ambient for the same tribo-combination. The tests shows a reduction in wear rate with speed, and this is due to the oxide formations due to TCR as confirmed from the SEM/EDAX characterization. In contrast to previous experiments under vacuum, these permit the effect of TCR also to influence the tribological behavior. The scenario changes when the alumina disc is replaced by a metallic one (SS316L) and tests carried out in vacuum, as the MML was found to be formed with this tribo-pair. Because of the mutual affinity of the materials in the tribo-pair, the wear damage is severe in this case and the flash temperatures crossing the phase transition temperature (~880oC) for Ti64 at high speeds. The growth of the β phase with increase in the sliding (temperature) conditions is captured from the XRD spectra of the wear debris. Synergistic effect of all these mechanisms (plastic deformation, MML, and TCR) is permitted by conducting experiments with Ti64 pin against stainless steel and in ambient conditions. A comparison of the tribological response by presenting results when experiments are run over a range of speeds while using different sized pins under ambient conditions (and compared with similar results in vacuum) while using SS316L disc serve to demarcate the differences in the wear modes which are active/inactive depending on the tribological conditions. In addition a study incorporating the effect of frictional heating and its influence on the tribological phenomena is analyzed. Main conclusions from the thesis are: The wear resistance of Ti64 alloy when sliding against SS316L is found to be influenced by Strain Rate Response (SRR), Tribo Oxidation (TO), Mechanically Mixed Layer (MML) and the prevailing heat flux conditions at the contact. The wear rates were found to decrease marginally with sliding speeds (strain rates) up to a certain speed, which is ascribed to reduction in adiabatic shear band intensity with increase in strain rate. Adiabatic Shear Band (ASB), which allows easy crack propagation, intensity reduces as temperature of deformation of Ti64 is increased. From the results it can be confirmed that the propensity for formation of MML depends on compatibility of the disc and the pin material. The contribution due to of entrapment and retention of debris in the contact zone also would influence formation of the MML. The effect of frictional heating plays an influential role as it can affect the factors (TO, ASB, MML) governing the tribological response. The sensitivity to temperature, which is a marked feature of this alloy in undergoing softening, as confirmed by previous researchers, is reflected in the experimental results. Since the main factor that triggers the micro-structural instability is the energy dissipation that accompanies deformation more fundamental research which can improve the thermal transport properties of this alloy, would be the future scope of work of this thesis. Also, the unique composition of the MML which offers high wear resistance under specific operating conditions opens up the possibility of new such alloy formulations, production routes and techniques which should improve the tribological response of this alloy.

There are two main goals of this thesis. Firstly, to improve and develop an existing hot weartester at Karlstad University so that it may test more samples of different sizes. Secondly, totest previously impossible samples and investigate their tribological properties and measurethe coefficient of friction with high reproducibility. The development work on the tribometer wasdone by a prestudy including; Investigating the hot wear tester, idea generation in CAD andcollecting information from the creator and prior users of it. After a few rounds of conceptgeneration and discussion with the supervisor and workshop staff, a new sample holder withdifferent sample adapters was created. Five tests of four different materials were conductedand their friction was measured. The new sample holder was able to solve the mainconcerns with the old design and showed great promise in producing reproducible results,better than any previous versions. The friction of the different TiAlN samples, at roomtemperature, seemed to indicate that there is a certain amount of Al% that maximizes frictionand that there is no simple linear relationship between Al% and coefficient of friction. Finallyit can be concluded that the initial goals of the thesis have been met, and that a newscientific instrument has been created to aid in the further understanding of tribology. / Det finns två huvudsakliga mål med detta examensarbete. För det första, att förbättra ochutveckla en existerande varmnötare på Karlstad Universitet så att den kan testa fler proverav olika storlekar. För det andra, att testa tidigare omöjliga prov och undersöka derastribologiska egenskaper och mäta friktionskoefficienten med hög reproducerbarhet.Utvecklingsarbetet av tribometern skedde via en förstudie som innehöll följande:Undersökning av varmnötaren, idégenerering i CAD och samling av information frånvarmnötarens skapare, samt tidigare användare. Efter några iterationer avkonceptgenerering och diskussioner med handledare och verkstadspersonal så skapadesen ny provhållare med flera olika adaptrar. Fem tester med fyra olika material utfördes ochderas friktion mättes. Den nya provhållaren löste de huvudsakliga problemen med dengamla designen och påvisade goda förhoppningar angående att producera tester med högreproducerbarhet. Markant bättre än tidigare versioner. Friktionsmätningarna från de olikaTiAlN-proverna, vid rumstemperatur, indikerade att det finns en viss mängd Al% sommaximerar friktionen och att det inte finns något linjärt samband mellan Al% ochfriktionskoefficient. Slutligen kan det konstateras att de initiala målen för examensarbetet harblivit uppnådda, och att ett nytt vetenskapligt instrument har blivit skapat för att hjälpa utökaförståelse inom tribologi.

A tribo Ingeae Benth. compreende 36 gêneros, destes 24 são endêmicos do Novo Mundo, de 935 a 966 espécies, que se difundem nas regiões tropicais, subtropicais e temperadas. Para o Brasil são estimados 16 gêneros, 302 espécies, 10 subespécies e 46 variedades. O presente estudo objetivou contribuir para o conhecimento da diversidade de espécie dessa tribo na Floresta Nacional de Caxiuanã. Foram reconhecidos sete gêneros, 27 espécies, uma subespécie e duas variedades. O gênero mais representativo foi Inga Mill. com 17 espécies distribuídas em sete seções: Inga seção Bourgonia (/. alba (Sw.) Willd., I. hrachyrhachis Harms, I. cylindrica (Vell.) Mart., /. laurina (Sw.) Willd. e 1. microcalyx Spruce ex Benth.); Inga seção Inga (/. edulis Mart.); Inga seção Leptinga (/. gracilifoliã Ducke, I. paraensis Ducke e I. ohidensis Ducke); Inga seção Longiflorae (/. grandiflora Ducke, I. longiflora Spruce ex Benth., I. micradenia Spruce ex Benth. e I. ruhiginosa (Rich.) DC.); Inga seção Multijugae (/. thihaudiana DC. subsp. thihaudiana); Inga seção Pseudinga (/. capitata Desv. e I. stipidares DC.) e Inga seção Tetragonae (/. macrophylla Humb. & Bonpl. ex Wilk). Em seguida vem Abarema Pittier, que está representado por três espécies (A. jupunba (Willd.) Britton & Killip, A. mataybifolia (Sand.) Bameby & J. W. Grimes e Abarema sp.); Calliandra Benth. com duas espécies (C. surinamensis Benth. e Calliandra sp.); Zygia P. Browne com duas espécies e uma variedade (Z racemosa (Ducke) Barneby & J. W. Grimes e Zygia latifolia (L.) Fawc. & Rendle var. lasiopus (Benth.) Barneby & J. W. Grimes); Enterolobium Mart. {E. schomburgkii (Benth.) Benth.); Hydrochorea Barneby & J. W. Grimes (H. corymbosa (Rich.) Barneby & J. W. Girmes) e Macrosamanea Britton & Rose ex Britton & Killip (M pubiramea (Steud.) Bameby & J. W. Grimes var. pubiramea). São apresentas chaves de identificação, descrições e ilustrações dos táxons, além de dados adicionais sobre distribuição geográfica, comentários e fenologia.

M. Tech. Metallurgical Engineering. / StudIes the tribocorrosion behaviour of copper-nickel-titanium shape memory composite reinforced by zirconia,synthesized through powder metallurgy process. The research aims to achieve the following objectives: 1. Study the tribocorrosion mechanisms of the composites in NaCl solution (typical human body fluid). 2. Investigate the tribocorrosion mechanisms of the composites in other environments typical of some engineering applications.The proposed study on incorporating zirconia into the matrix NiTiCu through powder metallurgical process and investigations of the phenomenon of joint wear-corrosion synergism occurring in sodium chloride considered typical of human body system and sulphuric acid environment typical of wide range engineering applications is therefore very novel. It is therefore aimed that information on the tribocorrosion behaviour of NiTiCu as well as with zirconia incorporation will form basis for typical compositional formulation approaches for improved bio-tribocorrosion improvement in biomedical applications and actuators used in other engineering applications.

The usage of titanium alloys in many industries has increased significantly over the years due to their superior properties. However, they are extremely difficult to machine because of their distinctive characteristics such as their high temperature strength, low thermal conductivity, and high chemical affinity for tool materials. Hence, despite their increased usage, they are still expensive to machine when compared to other metals. The current research aims to address the machinability issues of titanium alloys by developing novel compositions of a new generation of self-adaptive Physical Vapor Deposition (PVD) coatings that function by forming beneficial tribo-films through their interaction with the environment. These tribo-films form during cutting and provide enhanced lubricity, hardness, strength, and thermal barrier characteristics to the cutting tool. It was found that during Ti6Al4V machining, significant BUE and crater wear formation occurs; however, one is dominant over the other depending on the cutting conditions. Therefore, the coatings investigated were designed by taking into consideration the dominant tool wear mechanisms and the complex tribological phenomena that occur in the cutting zone. The current research investigated monolayer TiB2 and CrN self-adaptive PVD coatings for the rough (cutting speed - 45 m/min, feed -0.15 mm/rev, and depth of cut – 2 mm) and finish (cutting speed - 150 m/min, feed -0.1225 mm/rev, and depth of cut – 0.25 mm) turning of Ti6Al4V alloy. Detailed experimental studies were performed to study the effectiveness of the coatings during machining. Micro-mechanical characteristics of the coatings were also studied to understand how coating properties affect the coatings performance in machining and tribo-film formation. The results obtained show that both the TiB2 and CrN coatings significantly improve tool performance during the rough turning of Ti6Al4V alloy compared to the current industrial standard, which is due to certain micro-mechanical coating properties and the beneficial tribo-films formed. A coating of CrN coating was found to increase tool life during finish turning. It was also established that for machining applications where intensive adhesive interaction occurs at the tool-chip interface, coatings with lower hardness values perform significantly better than harder ones. / Thesis / Doctor of Philosophy (PhD) / Titanium alloys are increasingly becoming the material of choice for many industrial applications due to their superior properties. However, they are very difficult to machine since they have high chemical affinity towards tool materials, low thermal conductivity, and high temperature strength. These properties cause rapid failure of the tool. The objective of the current research is to address machinability issues during Ti6Al4V machining and improve tool performance. One effective strategy to minimize tool wear is to apply self-adaptive PVD tool coatings that can form beneficial tribo-films through their interaction with the environment and provide enhanced lubricity, hardness, strength, and thermal barrier characteristics to the cutting tool. In the current research, two self-adaptive PVD coatings were developed that offset the dominant tool wear mechanisms prevalent during the rough and finish turning of Ti6Al4V alloy and reduced the tool wear rate by more than 60% compared to the current industrial standard.

no / The interface tribo-layer (ITL) in an automotive brake friction pair is a layer of material created from transfer films, wear particles, and surface transformations between the rotor and stator. Its presence in a brake friction interface has been proven, e.g. by the existence of a temperature ‘jump’ across the friction interface. In this paper two static transient heat transfer models which force one dimensional heat flow, have been used to investigate the ITL behaviour and obtain an equivalent thermal conductance value. The ITL equivalent thermal conductance value is important as it reduces computational requirements and software restrictions encountered in the physical model of the ITL. This approach is developed into a more realistic two-dimensional coupled temperature-displacement model using commercial FEA software (ABAQUS). A newly developed relationship that utilises the contact pressure, real contact area, and the ITL equivalent thermal conductance, has been used to estimate the effective thermal conductance at the friction interface. Subsequently the effective thermal conductance relationship is combined with the 2-D coupled temperaturedisplacement model. The combination of this relationship with the 2D FE model provides a new method of heat partition prediction in brake friction pairs. Heat partition at a brake friction interface is confirmed to be neither uniform nor constant with time. / IMechE / The full text will not be made available in Bradford Scholars due to the publisher's copyright policies.

På grund av det rådande miljöhotet så bör fokus för forskning och utveckling i ämnet riktas åt att utnyttja så många förnybara energikällor som möjligt, samt även optimera dessa för största möjliga energiupptagning. Vind, vatten och solljus är välkända och väl utformade källor för energi. Huruvida vatten i form av regn kan utnyttjas och dess potential kommer studeras i det här arbetet. Materialval och konstruktionslösningar står i centrum för arbetet. Vidare så studeras dess bakgrunder för utvinningsmetoderna och dess grundläggande principer tas upp för att skapa en bättre förståelse för möjligheterna att utnyttja tekniken. Fortsättningsvis så har rådande potentiella användningsområden och kommande utmaningar diskuterats utförligt. / Because of the prevailing environmental threat, focus for research and development in the subject should aim towards taking advantage of as many renewable energy sources as possible aswell as optimizing them to convert as much energy as possible. All renewable energy must be utilized, but above all, also optimized. Wind, water and sunlight are well-known and well-designed sources of energy. Whether water in the form of rain can be utilized and its potential as a sustainable commercial method will be studied in this paper. Material selection and design solutions are at the heart of the work. Furthermore, its backgrounds for the extraction methods are studied and its basic principles are addressed to create a better understanding of the possibilities of utilizing the technology. Moreover, the current potential uses and future challenges have been discussed in detail.

Made available in DSpace on 2016-07-27T14:22:12Z (GMT). No. of bitstreams: 1 Nivia Claudia Santos Leite.pdf: 3117405 bytes, checksum: 86d58d006057b599e44fd25441307d9c (MD5) Previous issue date: 2010-04-12 / In this study, we researched the meaning of being an adolescent for ten members of the urban tribe named emotional hardcore (EMO) in the municipality of Goiânia, in the state of Goiás, Brazil. We intended to grasp the senses and the meanings that adolescents belonging to the EMO tribe attribute to adolescence and the emotional dimensions that are present in their relationships with themselves, their peers, their families, their schools, and society. This research aimed at offering a contribution to social psychology, broadening the knowledge about adolescence from the perspective of social historical psychology in relation to the singularity of the individual and the social subjectivity in which the study participants are inserted. This study was carried out based on social historical psychology and on Vigotski, its main representative, who used the dialectical materialism as a philosophy, theory, and method. We employed qualitative research using the methodological proposal of triangulation procedure: simple observation, interviews, and focus groups. Participants were ten adolescents, ranging from 15 to 17 years old, five of each sex, members of the EMO tribe. In this study, we gave these adolescents the chance of being heard, which opened the possibility of understanding them as significant individuals, who have things to say, to do, to think about, who are aware of what is going on around them, and who reflect the events of human life, revealing how they are constituted and how they constitute themselves based on their social relationships. Therefore, at first, the analysis of the senses and meanings that emerged during this research revealed that adolescence means a time to make a mess, passage and transition, pressure, conflicts, uncertainties, loneliness, as well as a time for discoveries and challenges; in a second moment, it showed that the participants correlated adolescence with their spaces in the EMO tribe, in their families, and in their schools, also allowing us to grasp both the senses and meanings of sexuality and prejudice experienced by the adolescents belonging to the EMO tribe. / Este trabalho resultou de pesquisa acerca do significado de ser adolescente para dez integrantes da tribo urbana emotional hardcore (EMO) na cidade de Goiânia, GO. Pretendeuse apreender os sentidos e os significados que adolescentes pertencentes à tribo EMO atribuem à adolescência e as dimensões emocionais que se fazem presentes em sua relação consigo mesmos, com seus pares, suas famílias, suas escolas e a sociedade. A pesquisa objetivou oferecer uma contribuição para o campo da psicologia social, ampliando o conhecimento acerca da adolescência na perspectiva da psicologia sociohistórica, em relação tanto à singularidade do sujeito quanto à subjetividade social em que os participantes deste estudo estão inseridos. Esta pesquisa foi conduzida pautando-se na psicologia sociohistórica e tendo como seu principal representante Vigotski, que se apropriou do materialismo dialético como filosofia, teoria e método. Trabalhou-se com pesquisa qualitativa utilizando como abordagem a proposta metodológica da triangulação de procedimentos: observação simples, entrevistas e grupos focais. Participaram desta pesquisa dez adolescentes, com idades entre 15 e 17 anos, sendo cinco de cada sexo, todos pertencentes à tribo EMO. Neste estudo, deu-se voz a esses adolescentes, possibilitando compreendê-los como indivíduos significantes, que têm o que dizer, fazer, pensar, sentir, que têm consciência do que está acontecendo e que refletem os eventos da vida humana, revelando como são constituídos e se constituem com base em suas relações sociais. Portanto, em um primeiro momento, a análise dos sentidos e significados emergentes da pesquisa revelou a adolescência significada como tempo de bagunça, passagem e transição, cobranças, conflitos, incertezas e solidão, bem como de descobertas e desafios; já em um segundo momento, mostrou que estes sujeitos relacionaram a adolescência aos seus espaços dentro da própria tribo, na família e na escola, também tendo possibilitado a apreensão dos sentidos e significados sobre a sexualidade e os preconceitos vividos pelos adolescentes pertencentes à tribo EMO.