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This thesis describes a series of fretting fatigue experiments carried out under closely controlled conditions of partial slip. These experiments confirm the existence of a size effect whereby the fretting fatigue life of an aluminium alloy is shown to vary with contact size. The configuration chosen, of cylindrical fretting pads contacting a plane specimen is amenable to classical stress analysis and the surface tractions between the contacting bodies are derived. The effects of tension in the specimen, finite specimen thickness, differing elastic constants, and surface roughness are all investigated and incorporated into the analysis where appropriate. A technique is then developed to calculate stress intensity factors for plane cracks growing under the contact load at an arbitrary angle to the free surface. The analysis is then applied to the experimental results and three possible explanations for the size effect are proposed, based on statistical effects, crack arrest, and crack initiation. These are examined in the light of the experimental evidence and it is proposed that the variation of fatigue life with contact size is due to an increase in the amount of fretting damage above a threshold level for crack initiation. A composite parameter is chosen to characterise the severity of fretting conditions and this is shown to describe the experimental results accurately. Finally, the use of this parameter in design calculations is discussed.

In modular hip implants, micro-motion, which leads to fretting corrosion at the head/neck and neck/stem interfaces, has been identified as a major cause of early revision in hip implants, particularly those with heads larger than 32mm. It has been found that the type of fluid used to simulate the fretting corrosion of biomedical materials is crucial for the reliability of laboratory tests. Therefore, to properly understand and effectively design against fretting corrosion damage in modular hips, there is the need to replicate the human body environment as closely as possible during in-vitro testing and validation. In this work, corrosion behavior of CoCrMo in 0.14 M NaCl, phosphate buffered saline (PBS) and clinically relevant simulated body fluid (sbf) is carried out. Also, fretting corrosion studies of the CoCrMo alloy in a clinically relevant novel simulated body fluid (sbf) environment is studied. The presence of phosphate ions in PBS accounted for the higher corrosion rate when compared with 0.14 M NaCl and sbf environment. Despite the low and comparable corrosion rates in 0.14 M NaCl and sbf, the nature of the protective passive film formed in sbf shows the suitability of the novel sbf for future corrosion and fretting corrosion analysis. Finally, the influence of micro-motion at the modular head/neck and neck/stem interfaces on the concentration of metallic ions that goes into the synovial fluid and surrounding tissues is reported.

Thesis (M. Sc.)--University of Alberta, 2010. / Title from pdf file main screen (viewed on July 15, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Materials Engineering, Department of Chemical and Materials Engineering, University of Alberta. Includes bibliographical references.

Electrical connectors are widely utilized for signal communications in automotive electronic systems whose performance is related to the reliability of the entire system. Electrical connectors are frequently affected by the engine vibration, resulting in fretting damages on electrical connector. In this thesis, the main propose is to find a signal analysis method to predict the fretting damages on fuel pump connector induced by engine vibration. The data of the fuel pump connector is studied from a vibration test of the four-cylinder engine and the dominating frequencies are used in the fretting test to verify the analysis method. The fretting damage is identified through visual inspection by microscope. The model of the connector is built in COMSOL to explain the fretting on the contact surfaces. The results present the signal analysis method can be directly used to predict the risk of fretting damages during the engine vibration. Some significant frequencies are pointed out as guidelines for future tests and optimization.

Fretting of solvent cast polyimide coatings was investigated in a ball-on-flat geometry as a function of relative humidity. Polyimides were synthesized from benzophenone tetracarboxylic dianhydride (BTDA) and bisanline (Bis P), 6-fluoro bis dian hydride (6FDA) and Bis P, and pyromellitic dianhydride (PMDA) and bis A phenyl phosphine oxide (BAPPO). Coating life - the time for the steel ball to wear through the coating - shortened with increasing humidity. Iron oxides or other reaction products from 52100 ball generated at high humidity acted as abrasives and accelerated the wear of the coatings. Variation of coating life among the three polyimides was attributed to the residual stress, which developed upon cooling from the annealing temperature due to the mismatch of thermal expansion coefficients between the polymer and the metal substrate. Calculated from elasticity theory, the normal stress dropped shortly after the start of the test, remained relatively constant, and increased toward the end. This variation correlated with the wear rate and accounted for the non-linear increase of coating life with coating thickness. Sub-surface shear stress and surface tensile stress predicted well, respectively, the debonded shape and the inter-crack spacing of Hertzian cracks. / Ph. D.

A fundamental study was conducted to analyze the friction and degradation mechanisms of thin rubber coatings used as fretting corrosion inhibitors. Two elastomers, polyurethane and styreneethylene-butylene (SEBS), were investigated. The mechanisms of wear were studied by analyzing wear scars with optical microscopy. Friction mechanisms were investigated using friction forcedisplacement hysteresis loops and friction force variation with test frequency, fretting amplitude and fIlm thickness. Lastly, coating life variation with these three parameters was studied and explained through a simplified fatigue mechanics approach. / Master of Science

M.S.

The purpose of this study was to evaluate the effect of film thickness on a polystyrene coating used to prevent fretting corrosion in a steel-on-steel system. The polystyrene coating was applied to a 1045 steel disk and fretted against a 52100 steel ball. Two sets of experiments were employed. The first set evaluated film life by using seven different film thicknesses ranging from 7.9 to 52 um. The results from this set of experiments indicated that a drastic increase in film life occurred for coatings thicker than 40 pm. The other set of experiments was used to study how fretting damage progressed with time and how it was affected by film thickness. For this purpose two film thicknesses, 38 and 52 μm, were used. The results from these experiments led to the speculation that stress and temperature conditions were different in the 38 and 52 μm films. These differences resulted in a milder fretting regime, and therefore longer life, in the thicker film. Optical and scanning electron microscopy and computer graphics were used to study in detail the fretting interface. The fretting mechanisms were explained in terms of mechanical, chemical, tribochemical, and tribophysical effects. / Master of Science

A statistical analysis was conducted to investigate the effect of applied load and relative humidity of the atmosphere on the durability and coefficient of friction of five polymer coatings used to protect against fretting corrosion. Chlorine and non-chlorine containing polymers were used in this research to see if the large humidity effect seen in a previous study with polyvinyl chloride is strictly a chlorine related phenomenon. The five polymers used were polyvinyl chloride, polyvinylidene chloride, polystyrene, and two siloxane modified polyimides. Disks made of 1045 steel were coated with thin polymeric films and fretted against a 52100 steel ball. Three levels of load were used: 11.12, 22.25, and 44.5 N, and the two levels of relative humidity were less than 10% and between 45 and 55%. Amplitude of oscillation was 330 μm peak to peak, frequency of oscillation was 40 Hz, and the coating thickness was 25 μm. Statistically significant variables and interactions are identified, and reasons for their significance are discussed. Increasing the humidity had no consistent effect on the ending coefficient of friction between the polymer film and the oscillating ball, increasing the load decreased the coefficient of friction, and either increasing the humidity or load decreased the life of the coating during fretting. The extent of this reduction in life depends on the polymer. The relative humidity of the environment affected the coating life of only one of the chlorine-containing polymers. Humidity was also shown to affect the coating life of two polymers that do not contain chlorine. / Master of Science