Direct measurements of surface temperatures produced during fretting contact are an unknown area in the discipline of tribology; in addition, the possible effects of such temperatures on the behavior of protective anti-fretting coatings (e.g., polymeric) have never been investigated. An oscillating contact device was designed and built to study fretting contact behavior in tribological processes. The contact geometry consisted of a stationary spherical test specimen loaded against a vibrating sapphire disk driven by an electromagnetic shaker. Surface temperatures generated by frictional heating were measured during fretting contact using an infrared microscope. A photo/video technique was developed to view the fretting contact interface during an experiment and to measure the size and distribution of real area(s) of contact. The effects of size and distribution of the areas on the experimental surface temperatures for polymer-coated steel spheres-on- sapphire were investigated. Archard's theoretical model was also modified to account for multiple contact areas, and the calculated surface temperatures were compared to the experimental results. Polymeric coatings - including polystyrene (PS), polymethylmethacrylate (PMMA), polysulfone (PSO), polyvinylchloride (PVC), and polyvinylidenechloride (PVDC) were studied at a given load (20 N), frequency (150 Hz), amplitude (100 JLm), and film thickness (55 p.m). The surface temperatures generated were generally low and below the glass transition temperatures of the rigid polymers studied. The magnitude of the surface temperatures was found to be particularly dependent on the size and distribution of real area(s) of contact. The most extensive studies were performed using polystyrene coatings. Effects of load, frequency, amplitude, and film thickness on surface temperature rise and the size and distributions of real area of contact were examined. In addition, uncoated steel specimens were studied under various loads and fretting amplitudes. The observed formation of iron oxide at low surface temperature (60°C) tribologica1 experiments was explained in terms of exoelectron emission. There were considerable differences observed in the behavior of polymeric coatings under various fretting conditions. The fretting behavior of the coatings was explained in terms of mechanical and thermo-elastic effects. Thermo-elastic predictions of size distributions of real contact areas (patches) showed good agreement with the observed photo/video studies. A mechanism was proposed for tribological behavior and fretting protection of polystyrene coatings. / Ph. D.

The relative motion between a ball bearing outer race and the bearing's cartridge was investigated. The investigation was part of a larger program, the objective of which is to examine the important parameters influencing fretting corrosion in rolling element bearings. The bearing examined was a 320 size, deep grooved, ABEC 7 ball bearing used in a Navy ship service motor-generator unit. Three axes of acceleration signatures were simultaneously recorded from the outer race and cartridge. These acceleration signatures were Fourier transformed, averaged, and integrated twice to obtain displacement frequency spectrums. Corresponding displacements were vectorially subtracted to produce the relative motion between the outer race and the cartridge. Two load cases (0% and 100% load) and two frequency ranges (15 to 500 Hz and 30 Hz to 10 kHz) are examined. The resulting relative motion spectrums were complex with the bearing's forcing frequencies dominating the spectrums below 250 Hz and rotor imbalance causing the highest spectral component of relative displacement (170 µm). / M.S.

La dégradation par fretting-corrosion des prothèses de hanche cimentées est l’une des principales causes de réintervention chirurgicale. L’étude du fretting-corrosion est effectuée entre un acier inoxydable 316L, matériau utilisé pour les tiges fémorales, et un polymère PMMA, matériau modèle du ciment chirurgical, dans différentes solutions, plus ou moins proches du liquide physiologique.L’étude a d'abord été réalisée à potentiel libre (OCP) pour être proche des conditions in vivo. L’influence des chlorures et le rôle de l’albumine, principale protéine du liquide physiologique, sur la dégradation du 316L et de sa couche passive sont ainsi évalués.Pour pouvoir obtenir des informations sur le courant de corrosion, des essais sont effectués à potentiel imposé. Le potentiel choisi est proche de la valeur de potentiel pendant fretting : E = -400 mV(ECS). Ce potentiel permet d’observer la transition entre courant cathodique et courant anodique en fonction de la force ionique. Lors d’un essai de fretting-corrosion, l’albumine joue le rôle d’inhibiteur de corrosion.La dégradation du 316L par fretting-corrosion est une combinaison entre l’usure corrosive, due au milieu physiologique contenant des chlorures, et l’usure mécanique. Il existe un terme de synergie entre usures corrosive et mécanique. L’influence de la force ionique et de l’albumine sur ce terme de synergie est aussi quantifiée.La forme de la trace d’usure en “W”, caractéristique du fretting-corrosion, est due à un gradient de pH et à un mécanisme de corrosion proche de la corrosion caverneuse. Une étude à pH global imposé a permis d’estimer les valeurs probables de pH dans et à une courte distance de la zone d’usure. / In case of total hip joint cemented prosthesis, one of the most important causes of reintervention is the degradation induced by fretting-corrosion. The study of fretting-corrosion mechanism is conducted between a 316L stainless steel, the same material as the femoral stem, and a polymer PMMA, a model material for bone cement, in several solutions, more or less close to physiological liquid.First, the study was investigated at Open Circuit Potential (OCP), to be close to the in vivo conditions. The influence of chlorides and the role of albumin, the principal protein in the physiological liquid, on the 316L and its passive layer degradation are evaluated.To obtain some information on corrosion current, experiments are investigated at applied potential. The chosen potential is close to the value of the potential during fretting: E = -400 mV(SCE). Besides, this potential is a threshold potential for anodic and cathodic transition of current as a function of ionic strength. One of the key points is the role of albumin as a corrosion inhibitor in the degradation by fretting-corrosion.The 316L degradation by fretting-corrosion is a combination between corrosive wear, due to the physiological liquid which contains chlorides, and mechanical wear. There is a synergy term between corrosive and mechanical wears. The influence of ionic strength and albumin concentration on this synergy term is also quantified.The shape of the worn area in “W”, typical of fretting-corrosion, is due to a pH gradient and a corrosion mechanism close to crevice corrosion. A study where the global pH of the solution is fixed allows estimating values of pH in and at a short distance from the worn area.

La dégradation par fretting-corrosion des prothèses de hanche cimentées est l'une des principales causes de réintervention chirurgicale. L'étude du fretting-corrosion est effectuée entre un acier inoxydable 316L, matériau utilisé pour les tiges fémorales, et un polymère PMMA, matériau modèle du ciment chirurgical, dans différentes solutions, plus ou moins proches du liquide physiologique.L'étude a d'abord été réalisée à potentiel libre (OCP) pour être proche des conditions in vivo. L'influence des chlorures et le rôle de l'albumine, principale protéine du liquide physiologique, sur la dégradation du 316L et de sa couche passive sont ainsi évalués.Pour pouvoir obtenir des informations sur le courant de corrosion, des essais sont effectués à potentiel imposé. Le potentiel choisi est proche de la valeur de potentiel pendant fretting : E = -400 mV(ECS). Ce potentiel permet d'observer la transition entre courant cathodique et courant anodique en fonction de la force ionique. Lors d'un essai de fretting-corrosion, l'albumine joue le rôle d'inhibiteur de corrosion.La dégradation du 316L par fretting-corrosion est une combinaison entre l'usure corrosive, due au milieu physiologique contenant des chlorures, et l'usure mécanique. Il existe un terme de synergie entre usures corrosive et mécanique. L'influence de la force ionique et de l'albumine sur ce terme de synergie est aussi quantifiée.La forme de la trace d'usure en "W", caractéristique du fretting-corrosion, est due à un gradient de pH et à un mécanisme de corrosion proche de la corrosion caverneuse. Une étude à pH global imposé a permis d'estimer les valeurs probables de pH dans et à une courte distance de la zone d'usure.

Fretting phenomenon occurs when two bodies in contact undergo small repetitive relative motion such that the localized surface and subsurface material properties are altered leading to damage or failures. Fretting conditions are obtained by controlling externally applied parameters such as load, frequency of displacement, displacement amplitude. Material properties which influence fretting behavior include hardness, ductility, hardening behavior. External parameters like surface roughness, temperature also play a role in deciding the extent of damage. Based on fretting conditions and specimen geometry, various fretting modes can be classified. Rotational fretting is one such damage mode, observed in industrial applications such as cable ropes under tension used for support in construction industry and variable stator vanes (VSVs) in compressors of turbines. In spite of industrial and engineering relevance, rotational fretting has received little attention. In the present work, rotational fretting of self-mated AISI 4340 material pair was studied, with the objective of characterizing subsurface damage induced by fretting. AISI 4340 (EN 24) is a low alloy martensitic steel with an excellent combination of strength, ductility and toughness. It is widely used in high strength cyclic loading applications like gears, bearings, automobile pistons and aircraft landing gears as well as in low corrosion, high strength offshore applications. It can be readily machined and surface hardened which makes it useful for wear related applications. A novel rotational fretting test set up, capable of operating under various test loads, frequencies, displacement amplitudes and temperatures was used to perform experiments. Specimens were subjected to a combination of normal load and rotational displacement and caused to mutually contact on non-conformal curved surfaces which simulate a bearing or bushing geometry. Fretting results were primarily determined by the frictional torque versus angular displacement plots. The running condition response was linked to the fretting material response regime. Surface and subsurface characterization studies of fretted regions were conducted using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). TEM studies revealed varying levels of fretting induced plastic deformation within the fretted contact zone. Good correlation with available literature relating to formation of dislocation cells and presence of high dislocation density in the fretting damaged regions was established. Although quantifying the dislocation density as a damage indicator is a challenge, it is proposed that a microstructural feature based approach has the potential to be developed into a useful tool for life assessment and life prediction studies.

Ce travail s'inscrit dans la problématique de la dégradation des prothèses de hanche cimentées par fretting corrosion. L'endommagement de l'acier inoxydable 316L, alliage constituant la tige fémorale, par frottement contre du polyméthacrylate de méthyle (PMMA), composé modèle du ciment chirurgical, a été particulièrement étudié. Deux types d'expériences ont été envisagées : à sec et en solution de Ringer voisine, par sa teneur en chlorures, de la composition du liquide physiologique. Dans un premier temps, à partir des conditions expérimentales choisies de déplacement et de force normale, la carte de fretting a été tracée pour le contact 316L/PMMA permettant de fixer des conditions reproductibles de glissement total pour un déplacement sinusoïdal de demi-amplitude égale à 40 μm et des forces normales comprises entre 42,5 N et 170 N. Ensuite, l'étude, à sec, du fretting entre l'acier inoxydable et du PMMA a permis de quantifier le volume d'usure du PMMA, seul matériau à se dégrader, en fonction de l'énergie dissipée. Le phénomène de stick-slip a été nettement mis en évidence lors du glissement et augmente en fonction de la force normale de contact. Grâce à la transparence du PMMA, la production et l'évolution des débris ont pu être isolées et commentées en cours de fretting. De plus, les analyses infrarouges des débris de PMMA, à la surface de l'acier inoxydable, ont amené des informations sur le changement de configuration au cours du processus de dégradation. En solution de Ringer, milieu corrosif, l'acier inoxydable se dégrade d'une manière très significative pendant le fretting contre du PMMA et du ciment chirurgical. Au cours du processus de dissolution à potentiel libre, la réaction de réduction des ions oxoniums semble s'ajouter à la réduction du dioxygène. L'acier inoxydable 316L présente une forme particulière d'usure en ‘W'. Un effet de crevasse permet de proposer un mécanisme d'endommagement assisté par le fretting. De plus, l'énergie dissipée varie en fonction du potentiel imposé. Une analyse des courants a montré l'existence d'une réaction cathodique supplémentaire. Enfin, les expériences effectuées à l'air ambiant et en solution de Ringer ont fourni des données quantitatives d'usure du PMMA et du 316L.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: David. L. McDowell; Committee Member: Min Zhou; Committee Member: Naresh N. Thadhani; Committee Member: Rami M. Haj-Ali; Committee Member: Richard W. Neu.

Experimental and theoretical analyses have been conducted upon electrical connector contacts under low frequency fretting conditions. The phenomena of "fretting" -relative micromovements in the components parts of an electrical contact - is known to take a major role in the degeneration of electrical contacts. Low frequency fretting is of particular interest and is typically caused by thermal differential expansion of the component parts due to temperature changes in the environment or the device itself. This thesis begins with a survey of possible failure mechanisms of the contact system. These are analysed and classified into three groups of chemical, physical, and mechanical degradation mechanisms. Fretting has been classified under the mechanical mechanism of degradation but is reported to exacerbate other degradation mechanisms resulting in the phenomena of "fretting corrosion". Developments in contact technology are then surveyed with the emphasis of this study on lubrication of the contact system. A novel fretting simulation apparatus has been developed to study the degradation mechanisms upon the contact system resulting from low frequency micromovements. The study includes investigations on the simulation apparatus of the contact system under different conditions. Particular! y emphasis is given to contacts under the conditions of electrical load and lubrication. Novel trends in the contact performance are reported with respect to electrical contact resistance, corrosion and wear of the contact interface. It is shown that electrically loading or lubricating the contact system has dramatic effects upon the contact performance. Chemical, physical and mechanical mechanisms at the contact interface are presented to explain the contact behaviour under several conditions of low frequency fretting. A "Two Process Model" is proposed which summarises the interaction of these different mechanisms. This model consists of two processes in balance - contact cleaning and contact degradation processes - which either increases or reduces the electrical area of contact. A theoretical computer simulation model is proposed for evaluating contact resistance behaviour of a fretting contact system under several conditions, particularly conditions of electrically loaded and lubricated conditions. Chemical, physical and mechanical mechanisms and their interact are simulated in the model using the Monte Carlo technique.

The purpose of this study is to determine whether chlorinated polymers such as polyvinylchloride (PVC) and polyvinylidenechloride (PVDC) degrade in a fretting interface. Polymer coated 52100 steel balls are fretted against a polished 1045 steel plate for 30 minutes in air and nitrogen at 25-30 percent and greater than 95 percent relative humidity. ESCA analysis is used to determine interface chemistry and help conclude that the color formation observed in the polymer coating is due to polymer degradation. Additional tests of thermally stabilized PVC on a steel plate supported this theory and aided in understanding the polymers performance in the interface. Experiments with the “pure” PVC on a glass plate showed that iron at the interface can initiate and catalyzes the polymer degradation. The effects of the different atmospheres, as well as the effect of humidity is also presented. / M.S.

A fundamental study was conducted to investigate the ability of thin polymeric coatings to prevent metallic contact and fretting corrosion in steel-on-steel systems. Ten polymer types were chosen for study: polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE), polyimide (PI), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), low-density polyethylene (LOPE), high-density polyethylene (HDPE), polysulfone (PSO) and polystyrene (PS). These polymers were applied as thin films to a steel disk which was in turn fretted by a normally-loaded steel sphere. The experimental investigation consisted of two phases. In the first phase, the lives of the ten polymer types were evaluated over a range of normal loads from 11.1 to 44.5 N. In the second phase, optical and electron microscopy were used to document the fretting process at the sphere-film interface as a function of time. / Master of Science