Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 32).

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In the current work, two different coatings, nitrocarburised (CN) and titanium carbonitride (TiCN) on M2 grade high speed tool steel, were prepared by commercial diffusion and physical vapour deposition (PVD) techniques, respectively. Properties of the coating were characterised using a variety of techniques such as Glow-Discharge Optical Emission Spectrometry (GD-OES) and Scanning Electron Microscopy (SEM). Three non-commercial, oil-based lubricants with simplified formulations were used for this study. A tribological test was developed in which two nominally geometrically-identical crossed cylinders slide over each other under selected test conditions. This test was used to evaluate the effectiveness of a pre-applied lubricant film and a surface coating for various conditions of sliding wear. Engineered surface coatings can significantly improve wear resistance of the tool surface but their sliding wear performances strongly depend on the type of coating and lubricant combination used. These coating-lubricant interactions can also have a very strong effect on the useful life of the lubricant in a tribological system. Better performance of lubricants during the sliding wear testing was achieved hen used with the nitrocarburised (CN) coating. To understand the nature of the interactions and their possible effects on the coating-lubricant system, several surface analysis techniques were used. The molecular level investigation of Fourier Transform Infrared Spectroscopy (FTIR) revealed that oxidative degradation occurred in all used oil-based lubricants during the sliding wear test but the degradation behaviour of oil-based lubricants varied with the coating-lubricant system and the wear conditions. The main differences in the carbonyl oxidation region of the FTIR spectra (1900-1600 cm-1) between different coating-lubricant systems may relate to the effective lifetime of the lubricant during the sliding wear test. Secondary Ion Mass Spectrometry (SIMS) depth profiling shows that the CN coating has the highest lubricant absorbability among the tested tool surfaces. Diffusion of chlorine (C1), hydrogen (H) and oxygen (O) into the surface of subsurface of the tool suggested that strong interactions occurred between lubricant and tool surface during the sliding wear test. The possible effects of the interactions on the performance of whole tribological system are also discussed. The study of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) indicated that the envelope of hydrocarbons (CmHn) of oil lubricant in the positive TOF-SIMS spectra shifted to lower mass fragment after the sliding wear testing due to the breakage of long-chain hydrocarbons to short-chain ones during the degradation of lubricant. The shift of the mass fragment range of the hydrocarbon (CmHn) envelope caries with the type of both tool surface and lubricant, again confirming that variation in the performance of the tool-lubricant system relates to the changes in surface chemistry due to tribochemical interactions at the tool-lubricant interface under sliding wear conditions. The sliding wear conditions resulted in changes not only in topography of the tool surface due to mechanical interactions, as outlined in Chapter 5, but also in surface chemistry due to tribochemical interactions, as discussed in Chapters 6 and 7.

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The assessment of the shear strength of soil deposits after the occurrence of large strains is an important issue for geotechnical engineers. One method for doing so, the steady state approach, is based on the assumption that the steady state undrained shear strength is a unique function of the in situ void ratio and effective stress. This method, which has been applied to liquefaction and flow failures, has been criticized because it may overestimate the in situ shear strength. The key to the steady state approach is accurate determination of the relationship between void ratio and effective stress at steady state. This is typically accomplished using conventional isotropically consolidated undrained (ICU) triaxial tests. The triaxial test was developed for measuring peak strengths, which typically occur at small strains, but steady state conditions typically occur at much larger strains. At large strain levels, the suitability of conventional triaxial testing procedures and error corrections is uncertain. The measured response at large strains may be inaccurate due to the influence of various testing errors. Furthermore, the true material response in the test specimen at large strains may not accurately represent in situ material behavior at large strains. This research effort consisted of an experimental and analytical study to examine the validity of steady state undrained shear strength determination using conventional ICU triaxial tests. The analytical study addressed triaxial testing errors and conventional corrections that are applied to test data and their influence on the measured steady state parameters. Finite element analyses were conducted to investigate the influence of variations in restraint at the end platens on stress distributions in the sample and measured stress-strain response. The finite element analyses incorporated axisymmetric interface elements to model the friction characteristics between the end platens and the specimen ends. The experimental study focused on several sands that are susceptible to liquefaction. An interface direct shear test program was conducted in order to evaluate various schemes for reducing end platen friction. ICU triaxial tests were conducted on each material using both conventional and lubricated end platens. / Ph. D.

No description available.

Contact fatigue damages resulting either from static or dynamic contact are of interest for understanding the failure modes and mechanisms leading to improvement of the components’ performances in tribological applications. The objective of this research was to ascertain how and to what extent the counterface materials, loading conditions, contact configuration, lubrication, and the environment affect the failure behaviours of material under static and dynamic contact fatigue loading. An experimental ball-on-flat test configuration was employed for both static and dynamic contact fatigue testing. In house designed test rig was used to study static cyclic loading contact fatigue behaviours of brittle polymethylmethacrylate (PMMA) in contact with balls made of different materials, i.e. Si3N4, steel, aluminium, bronze and PMMA in dry and oil-lubricated conditions. A modified four ball test machine was used to study dynamic rolling contact fatigue behaviours of thermally sprayed molybdenum and titanium coatings in contact with steel balls in dry and seawater conditions. The static contact fatigue and the dynamic contact fatigue test results revealed that counterface material, loading magnitude, lubricant and the environment play a vital role in controlling failure modes and the extent of damage. In static contact fatigue, adhesive strength of the interface was the key factor controlling damage of the PMMA plate in both dry and oil-lubricated conditions. In dry conditions, three failure modes, i.e. adhesive wear, ring cracks, and radial cracks controlled the damage of PMMA to a different degree for each combination of materials. Whereas, the damage of each combination in oil-lubricated conditions was affected by the extent of three failure modes, i.e. adhesive wear, radial cracks and abrasive wear. In dynamic contact fatigue tests, adhesive wear and inter-lamellar cracking were the major failure modes controlling damage of molybdenum coating and titanium coating in dry contact conditions while abrasive wear, corrosion and lubrication controlled damage processes in seawater conditions.

As características tribológicas do poli-éter-éter-cetona (PEEK) contendo de 0% a 40% de fibra de carbono, sob deslizamento em ambiente lubrificado com óleo, foram estudadas para diferentes acabamentos superficiais da contrapeça. Os quatro acabamentos escolhidos, comumente usados na indústria automobilística, foram o torneamento, a retífica, o brunimento e o polimento. O sistema de teste usado foi o tri-pino-disco, com o pino em PEEK e a contrapeça em aço, sendo totalmente imersos no óleo ATF Dexron VI. Alguns parâmetros de teste foram mantidos constantes como a pressão aparente de 2 MPa, a velocidade linear de deslizamento de 2 m/s e a temperatura do óleo em 85°C. Analisou-se o efeito do tempo de deslizamento na taxa de desgaste e no atrito para o PEEK com 30% de fibra de carbono contra disco acabado por torneamento, estudou-se o efeito do acabamento do disco no atrito e desgaste do PEEK natural e do PEEK com 30% de fibra de carbono, avaliou-se o efeito da adição da fibra de carbono na taxa de desgaste e atrito em acabamento torneado e foi definido o regime de lubrificação para os acabamentos de polimento e torneamento para o PEEK natural e para os acabamentos de polimento, brunimento, retífica e torneamento para o PEEK com 30% de fibra de carbono nas condições de 2 MPa e 2 m/s. Constatou-se que o regime permanente de desgaste ocorreu a partir de 60 minutos após a estabilização da taxa de desgaste e coeficiente de atrito. O atrito e o desgaste do PEEK e seus compósitos se mostraram sensíveis ao acabamento da contrapeça, pois este foi o principal fator que definiu os regimes de lubrificação. Nas condições de teste supracitadas o polimento operou em regime hidrodinâmico, o torneamento e a retífica em regime limítrofe, e o brunimento em regime misto. Foi levantada a curva de Stribeck para o PEEK com 30% de fibra de carbono deslizando contra o disco com acabamento de brunimento para a faixa de pressão de 1 MPa a 14 MPa. Nestas condições foram observados os três principais regimes de lubrificação, tornando possível gerar um mapa que relaciona o regime de lubrificação com pressão, velocidade e coeficiente de atrito. / The sliding tribological properties of poly-ether-ether-ketone (PEEK) containing from 0 to 40% of carbon fiber were studied within oil lubricated environment for different surface finishing of the counterpart. Four different finishing processes commonly used in the automotive industry were chosen for this study: turning, grinding, honing and polishing. The test system used was three pin-on-disc with pins made of PEEK and counterpart made of steel, they were fully immersed in the Dexron VI ATF oil. Some test parameters were held constant as the apparent pressure of 2 MPa, the linear velocity of 2 m/s and the oil temperature at 85 °C. It was analyzed the effect of the sliding time on friction and wear of PEEK with 30% of carbon fiber on turning disk, studied the effect of disc finishing on friction and wear of natural PEEK and PEEK with 30% of carbon fiber, evaluated the effect of carbon fiber on wear rate and friction for turning counterbody finishing and the lubrication regime was for polishing and turning finishes for natural PEEK and polishing, honing, grinding and turning for PEEK with 30% of carbon fiber under 2 MPa and 2 m/s. It was found that steady state of wear occurred from 60 minutes of test after wear rate and friction coefficient stabilization. The friction and wear of PEEK and its composites were sensitive to the counterbody finishing; it was the main factor which defined the lubrication regimes. In the above test conditions polishing operated in hydrodynamic regime, turning and grinding on boundary condition and honing in mixed regime. The Stribeck curve was raised for PEEK with 30% carbon fiber by sliding against the honing finishing disk under 1 MPa to 14 MPa of apparent pressure range. Under these conditions the three main lubrication regimes were observed and it was possible to create a map that relates lubrication regime with pressure, speed and coefficient of friction.

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Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Michael D. Bryant. Vita. Includes bibliographical references.