Thin polymeric coatings have been applied to metal surfaces to prevent and/or prolong the onset of fretting corrosion, but the properties that make a polymeric coating effective and the means by which a coating fails are unknown. The purpose of this study was to determine the effect of molecular weight, casting solvent, and amplitude of motion on the life of thin (25 ~m nominal) polystyrene coatings. Narrow molecular weight distribution polystyrene coatings ranging from <Mw>=19,400 to <Mw>=1,460,000 were applied to UNS G10450 steel disks with toluene and MEK as casting solvents. The coatings were fretted against UNS G52100 steel balls at 20 Hz under 22.3 N normal load. Amplitudes of motion ranged from 100 ~m to 500 ~m. Coating life and friction force were measured. Coatings of <Mw>=207,700 showed maximum life at all amplitudes. Friction remained constant for all tests, and increasing amplitude decreased life. Toluene-cast coatings had slightly shorter lives and more coating racks than MEK-cast coatings. Toluene-cast coatings below <Mw>=53,700 cracked severely during solvent removal and were not tested. / Master of Science

Ti-6Al-4V, known for high strength-to-weight ratio and good resistance to corrosion, has been widely used in aerospace, biomedical, and high-performance sports applications. A wide range of physical and mechanical properties of Ti-6Al-4V can be achieved by varying the microstructures via deformation and recrystallization processes. The aim of this thesis is to establish a microstructure-sensitive fatigue analysis approach that can be applied in engineering applications such as fretting fatigue to permit explicit assessment of the influence of microstructure. In this thesis, crystal plasticity constitutive relations are developed to model the cyclic deformation -TiAl has beenabehavior of Ti-6Al-4V. The development of the slip bands within widely reported and has been found to play an important role in deformation and fatigue behaviors of Ti-6Al-4V. The shear enhanced model is used to simulate the formation and evolution of slip bands triggered by planar slip under static or quasi-static loading at room temperature. Fatigue Indicator Parameters (FIPs) are introduced to reflect driving force for the different crack formation mechanisms in Ti-6Al-4V. The cyclic stress-strain behavior and fretting fatigue sensitivity to microstructure and loading parameters in dual phase Ti-6Al-4V are investigated.

<p dir="ltr">Fretting wear occurs when two contacting bodies under load are subjected to small amplitude oscillatory motion. Depending on the applied normal load, displacement amplitude, coefficient of friction and resulting shear force, two types of fretting wear regimes exist – (i) partial slip and (ii) gross slip. At displacement amplitudes higher than gross slip condition, sliding wear regime prevails. Fretting wear becomes dominant in machine components subject to vibrations such as bearings, dovetail joints, etc. whereas sliding wear is observed in brakes, piston-ring applications, etc. The work in this dissertation primarily focuses on characterizing the material response of various machine components subjected to fretting and sliding wear regimes.</p><p dir="ltr">At first, the friction and fretting wear behavior of inlet ring and spring clip components used in land-based gas turbines was investigated at elevated (<a href="" target="_blank">500°C</a>) temperature. In order to achieve this objective, a novel high-temperature fretting wear apparatus was designed and developed to simulate the conditions existing in a gas turbine. The test apparatus was used to investigate fretting wear of atmospheric plasma sprayed (APS) Cr₃C₂-NiCr (25% wt.), high-velocity oxy-fuel (HVOF) sprayed Cr₃C₂-NiCr (25% wt.), HVOF sprayed T-800 and APS sprayed PS400 coated inlet rings against HVOF-sprayed Cr₃C₂-NiCr (25% wt.) coated spring clip. The PS400 coated inlet rings demonstrated a significant reduction in friction and wear. A finite element (FE) framework was also developed to simulate fretting wear in HVOF-sprayed Cr₃C₂-NiCr composite cermet coating. The material microstructure was modelled using Voronoi tessellations with a log-normal distribution of grain size. Moreover, the individual material phases in the coating were randomly assigned to resemble the microstructure from an actual SEM micrograph. A damage mechanics based cohesive zone model with grain deletion algorithm was used to simulate debonding of the ceramic carbide phase from the matrix and resulting degradation from repeated fretting cycles. The specific wear rate obtained from the model for the existing material microstructure was benchmarked against experiments. Novel material microstructures were also modeled and demonstrated to show less scatter in wear rate.</p><p dir="ltr">Following, a three-dimensional (3D) continuum damage mechanics (CDM) FE model was developed to investigate the effects of fretting wear on rolling contact fatigue (RCF) of bearing steels. In order to determine the fretting scar geometry, a 3D arbitrary Lagrangian-Eulerian (ALE) adaptive mesh (AM) FE model was developed to simulate fretting wear between two elastic bodies for different initially pristine fretting pressures (0.5, 0.75 and 1 GPa) and friction coefficients (0.15, 0.175 and 0.25) resulting in stick zone to contact width ratios, c/a = 0.35, 0.55 and 0.75. The resulting wear profiles were subjected to various initially pristine RCF pressures (1, 2.2 and 3.4 GPa). The pressure profiles for RCF were determined by moving the contact over the fretted wear profiles in 21 steps. These pressure profiles were then used in the CDM-FE model to predict the RCF life of fretted surfaces. The results indicate that increased fretting pressure leads to more wear on the surface, thereby reducing RCF life. As the RCF pressure increases (P_RCF ≥ 2.2 GPa), the effect of fretting on RCF life decreases for all fretting pressures and c/a values, indicating that life is primarily governed by the RCF pressure. The results from CDM-FE model were used to develop a life equation for evaluating the L₁₀ life of fretted M-50 bearing steel for the range of tested conditions.</p><p dir="ltr">Lastly, the sliding wear characteristics of pitch and poly-acrylonitrile based carbon-carbon (C/C) composites were investigated in air and nitrogen environment by designing and developing a disc brake test rig. It was found that the temperature of the disc, the surrounding environment, the supplied energy flux as well as the type of composite play a critical role in determining whether C/C composites operate in normal wear or dusting wear regime. Further analysis of wear mechanisms revealed interface and matrix cracking with fiber breakage from tests in air environment, whereas in nitrogen environment, particulate and layered debris played a prominent role.</p>

The purpose of this study was to investigate the effects and interactions of lead, frequency, amplitude of slip, humidity, and film thickness of polyvinyl chloride on fretting corrosion. In particular, this study describes the effects of these parameters on the polymer film life and also on the wear of the metal surfaces after metallic contact had occurred. The two levels that were used for each parameter are: load, 15.6 and 31.1 N (3.5 and 7.0 lb); amplitude of slip, 165 and 330 μm (6.5 and 13 mils); frequency of slip, 20 and 40 Hz; humidity of air, 16.6 percent, and 58.4 percent relative humidity; and PVC film thickness, 20 and 37 μm (0.8 and 1.45 mils). The 52100 steel balls were loaded against a 1045 steel disk that was coated with PVC. This configuration was then subjected to a two-level, five-factor experiment comprised of the above levels of conditions. / M.S.

La dégénérescence articulaire sévère de la hanche est une pathologie fréquente et son traitement ultime est le remplacement prothétique. L’arthroplastie la plus répandue au monde est la prothèse totale de hanche (PTH) avec un couple de frottement métal-sur-polyéthylène (MPE). Cependant ce type d’intervention présente une longévité limitée à cause de l’usure de PE et ne convient pas aux patients actifs souffrant de coxarthrose sévère tôt dans leur vie. Afin de palier à ce problème, une nouvelle génération de surfaces de frottement métal-sur-métal (MM) est actuellement employée. Ces surfaces de frottement sont utilisées en PTH avec tête de 28 mm, en resurfaçage (RH) et avec la PTH à tête de grand diamètre. Alors qu’il y a beaucoup d’évidence à l’égard du bon fonctionnement des implants PTH 28 mm et du RH, les données quant aux performances in vivo des PTH MM à grand diamètre manquent. Malgré cela, ces implants sont utilisés à grande échelle. Dans un premier temps, l’objectif de ce travail de recherche était d’évaluer l’effet et de comparer les taux d’ions chrome (Cr) et cobalt (Co) chez des sujets porteurs de PTH MM à grand diamètre à ceux de 64 porteurs de RH, tous deux possédant des surfaces de frottement aux propriétés tribologiques identiques. Dans un deuxième temps, nous avons comparé les taux ioniques (Cr, Co et titane (Ti)) entre quatre PTH MM à grand diamètre provenant de fabricants différents (Zimmer, DePuy, Smith & Nephew et Biomet). Les mesures d’ions étaient effectuées dans le sang entier dans un laboratoire indépendant par la technique de spectrophotométrie de masse à haute résolution HR-ICP-MS, pour l’ensemble de ce travail de recherche. Les deux comparaisons ont démontré le rôle crucial joué par la modularité au niveau de la jonction tête-col des PTH MM à grand diamètre. En effet, des écarts considérables dans les concentrations ioniques de Co ont été retrouvés entre les RH et PTH Durom ayant un couple de frottement identique, ainsi qu’entre les 4 différents designs de PTH MM à grand diamètre comparés entre eux. La PTH MM à grand diamètre Durom était la moins favorable alors que celle de Biomet était la plus performante. Nos observations démontrent que des sources inattendues comme la jonction tête-col de certains implants PTH MM à grand diamètre peuvent contribuer au relargage ionique systémique. Une meilleure compréhension de ce phénomène est indispensable avant l’utilisation clinque de nouveaux implants de ce type. / The treatment for advanced degenerative hip disease consists in replacing the native joint with artificial implants. This is a very common procedure and the type of arthroplasty most practiced worldwide is metal-on-polyethylene (MOPE) total hip replacement (THR). However, this type of bearing has limited lifespan and is not adapted for active patients struggling with hip osteoarthritis early in their lives. In order to increase implant longevity, new generation, metal-on–metal (MOM) bearing surfaces is used nowadays in this particular population. These MOM bearings are used in 28 mm THR, in resurfacing hip arthroplasty (RH) and in large diameter head THR. Although consistent results have been obtained with the 28 mm THR and RH, large diameter head THR are increasingly used despite lack of scientific data about their performances. The main purpose of our first paper was to compare chromium (Cr) and cobalt (Co) concentrations among patients implanted with large diameter head THR and with RH. In this case, both bearing surfaces presented identical tribological properties. In the second paper, we compared performances in terms of ion release (Cr, Co and titanium (Ti)) from four different manufacturers of large diameter head THR systems (Zimmer, DePuy, Smith & Nephew and Biomet). Whole blood was used for all samples and ion measurements were conducted by an independent laboratory in a blinded fashion, using high-resolution inductive coupled plasma mass spectrophotometry (HR-ICP-MS). Both papers have emphasized the crucial role played by modularity at the head-neck junction in metal ion release from large diameter THR MOM bearings. In fact, significant differences were found in Co ion concentration between large head THR and HRA as well as among the different designs of large head THRs. Briefly, the Durom large head THR system was the least favorable implant while the Biomet large head THR system showed the best results. Our results prove that systemic ion release might origin from surprising sources such as modularity at the head-neck junction in patients implanted with certain large head MOM THR systems. A better comprehension of head-neck junction biomechanics is necessary before clinical use of such new devices.

Fretting is a serious concern in many industrial components, specifically, in nuclear industry for the safe and reliable operation of the component/system. Till date, a lot of efforts has already been made to understand the basic mechanics and mechanism involved in fretting, but still limited understanding on the following domains exists, (i) No standard experimental set up and procedures exists which could quantify the entire fretting domain. (ii) Limited data available for the designer under controlled environment conditions. (iii) Limited work in correlating fretting damage with the mechanical responses, specifically, for the materials with good adhesion properties. (iv) Limited work to understand the nucleation/initiation of cracks under fretting condition and, the effect of loading on crack propagation. (v) Displacement and shear force distribution at the contact interface accounting the failure mechanism. The whole efforts in this thesis are focused on the above points and, are investigated in detail. Further, studies are focused to simulate fretting conditions in a Fast Breeder Reactor (FBR). Reactor core components are exposed to sodium environment, which is a low oxygen environment. Experiments under liquid sodium are difficult and as a first step, the tests were done under vacuum condition to simulate condition in sodium environment. Stainless steel (SS316L) is a reactor core component material used in FBRs. Chromium carbide coatings are already qualified based on the performance criteria for friction coefficients, wear rates and galling resistance, but are not evaluated under fretting conditions. Thus, stainless steel and chromium carbide coatings are investigated in detail. In this thesis, mechanics and mechanisms involved in the degradation processes for self-mated stainless steel under fretting conditions are examined in detail. Further, chromium carbide with 25% nickel chrome binder coatings using plasma spray and high-velocity oxy-fuel (HVOF) processes on stainless steel are also investigated. The choices of the coating processes have been made such that the substrate must be maintained in a particular metallurgical condition. The effect of normal load, displacement amplitude, environment conditions, surface roughness, and stress field are critically examined. Stainless steel (SS) is often used in the nuclear industry because of its excellent mechanical properties under high temperature and irradiation environment, but on the other hand, SS is characterized as having relatively poor wear and galling resistance. In nuclear power plants (NPPs), different components move relative to each other, due to differential thermal expansion or flow-induced vibration or during loading and unloading events, and such conditions can be categorized under fretting. The objective of the present work is to understand the mechanics and mechanisms of nuclear grade material (NGM), specifically for sodium-cooled NPPs, under fretting conditions. The first-of-a-kind fretting machine has been designed and developed to simulate fretting condition in both, air and vacuum. The test in vacuum simulates conditions under sodium environment. The major challenge in the design of a fretting machine is to achieve low displacement amplitude, as low as 1µm, between the contact surfaces under constant normal load. The hydraulic actuated machine works under displacement controlled mode, for any frequency between 4Hz and 120Hz, under high vacuum of 10–5mbar and for temperatures up to 873K. A unique feature of the machine is the design of flexural member which provides not only high axial stiffness but also flexibility in the lateral direction. A robust control system with an efficient data acquisition system adds to the reliability of the system. Contact conditions prevailing at the interface were identified on the basis of variation of coefficient of friction (COF) with number of cycles, running condition fretting loops, and total energy dissipation at the contact interface. Gross sliding conditions have been observed under normal load of 70N and 250N and displacement amplitude in the range of 50µm to 200µm, except for normal load of 250N and displacement amplitude of 50µm. The tests were conducted under both ambient and vacuum environment. Higher value of COF observed for self-mated SS, compared to SS versus coated surface, has been attributed to the existence of strong adhesion prevailing at the contact interface. Running condition fretting loops were correlated with damage observed from the scar profile and the micrographs. In addition to elliptical and quadratic loops, triple loops were also identified. The existence of strong adhesion results in an increase of shear force, whereas subsequent drop in shear force is due to third body formation at the contact interface. Higher magnification micrograph reveals fatigue striations at the contact edge, while the fracture features were observed in the central region. The surface morphological features of the material under seizure conditions, which have been observed under a normal load of 250N and displacement amplitude of 50µm, shows large scale cracking on one side of the pin and the flat. Micrographs at higher magnification of the cracked surface just adjacent to the contact interface shows formation of slip bands within the grains, whereas the central region reveals shear fracture. Coated surfaces shows major surface degradation mainly in the form of fracture and spalling of the coatings. Energy dispersive spectroscopy (EDS) shows the occurrences of material transfer between the contacting surfaces. Frictionally constrained conditions have also been investigated at high normal load of 600N and for displacement amplitude in the range of 25µm to 200µm. Constant shear force with number of cycles and dependence of friction force on displacement amplitude were observed as the typical characteristics of frictionally constrained bodies. Two distinct regions, viz. center stick region and annular micro slip region, indicate the existence of partial slip regimes. Junction growth due to plastic flow of the material resulted in an increase of real area of contact at the contact interface. It is believed that the cyclic variation in the contact area, under cyclic tangential loading, may have given rise to micro slip in the annular region, and finally resulted in two distinguishable regions. It has been observed that the occurrence of micro slip in the annular region resulted in the material transfer from flat to pin surface, as evident from EDS responses. Damage in the form of circumferential cracks has also been observed in the annular region, whereas the center region shows features of shear fracture. Detail micro structural studies have been carried out for two extreme conditions, viz., gross sliding and seizure conditions. The conditions were identified mainly based on shear force variation with number of cycles and running condition fretting loops. Subsurface damage under both conditions has been compared based on the severity of plastic deformation and the orientation of subsurface cracks. Severity of plastic deformation has been quantified based on hardness variation along depth. A steep gradient of hardness indicates that the damage is very much confined in the region just beneath the contact interface. Gross sliding condition at the contact interface resulted in the propagation of subsurface cracks parallel to the surface, whereas under seizure condition the cracks were found inclined at an angle between 450 and 540 to the surface. Further, severe plastic deformations under seizure condition have resulted in the formation of shear bands and were found oriented in the direction of macroscopically imposed plastic flow. Influence of initial surface roughness on wear damage has also been quantified based on energy wear coefficient. Higher energy wear coefficient has been found for machined pin under sliding condition, whereas, under seizure condition polished pin shows higher energy wear coefficient. A computer code has been developed for the evaluation of surface and subsurface stress field, under both partial slip and gross sliding condition. Cattaneo and Mindlin approach has been adopted to model the partial slip condition. Energy based approach has been adopted for the quantification of damage observed under both contact conditions. Shear strain energy density and normalized strain energy release rate have been evaluated at the surface and in the subsurface region. Effect of contact conditions and the influence of coefficient of friction on stress field have been studied in detail. Analysis results shows that gross sliding results in higher tensile stress at the trailing edge, as compared to the stress induced under partial slip condition. Further, it has been observed that higher shear strain energy density at the surface and in subsurface region controls the nucleation of damage under both partial slip and gross sliding conditions. A criterion for the no growth of subsurface cracks has been discussed based on the distribution of stress intensity factor and normalized strain energy release rate as a function of crack size. It has been observed that subsurface cracks can grow up to significant depth depending on the crack propagator energy. The availability of crack propagator energy depends on coefficient of friction and contact conditions prevailing at the contact interface. The analytical results were found in good agreement with experimental observations. Non-linear analyses have been carried out using finite element analysis to evaluate stress and strain fields, assuming the existence of fully stick condition at the contact interface. Fully stick condition simulates the contact condition under strong adhesion. The analysis investigates the effect of shear or tangential loading on pressure distribution, contact radius, energy dissipation, and damage mechanism involved under elastic-plastic deformation. The accumulation of equivalent plastic strain in each cycle is believed to be responsible for ductile fracture. It has been observed that both cyclic plasticity and ratcheting are involved in the damage mechanism. Ratcheting has been observed as the governing damage mode under cyclic tangential loading condition. In contrast to this, due to limited ductility or brittle nature of coated surfaces, stress based criteria governs the damage. Continuous micro slip model has been developed to evaluate the displacement field and shear force distribution for partial slip and gross sliding condition. Further, the studies have been carried out to study the influence of relative tangential modulus of the contacting bodies on displacement field and shear force distribution. Plane strain and axisymmetric elastic elements are considered in the modeling while the interfacial layer has been modeled as an elastic-plastic layer. The model gives the shear force distribution at the contact interface and subsequently subsurface stress field can be estimated, once the tangential stiffness of the contact interface layer is known. The value of tangential modulus can be estimated either from numerical analysis or from experiments. Further, the study shows that as the relative tangential modulus of an interfacial layer increases, the shear force becomes more intense in the stick-slip transition region making this location more prone for damage nucleation.