Liquid fuel lubricity testing is known to be sensitive to the humidity of the surrounding atmosphere. The effect reported does however not seem to be universal for all diesel types according to available literature. This study was limited to the use of n-hexadecane as base fluid with addition of between 100 - 2000 ppm of palmitic acid (PA) as lubricity enhancer. The fuel spectrum was kept simple to allow a more fundamental approach by limiting the extent of possible chemical reactions. Both wear and seizure load testing were performed. The effect of water on both tests was found to be:  Wear and friction increased with higher soluble water content. Water therefore interferes with the action of the lubricating additive leading to decreased performance.  It is known that hydroxyl groups, from dissociative chemisorption of water, act as active sites for adsorption. It is however postulated that the associative chemisorption and/or physisorption of water interferes by either reducing the active site availability or reducing activity to ligand exchange.  No iron oxyhydroxides (FeOOH) were detected on the wear scars or tracks using Raman spectroscopy. The adsorbed water therefore likely only interact with the surface due to their low concentrations (10 ~ 50 ppm).Liquid fuel lubricity testing is known to be sensitive to the humidity of the surrounding atmosphere. The effect reported does however not seem to be universal for all diesel types according to available literature. This study was limited to the use of n-hexadecane as base fluid with addition of between 100 - 2000 ppm of palmitic acid (PA) as lubricity enhancer. The fuel spectrum was kept simple to allow a more fundamental approach by limiting the extent of possible chemical reactions. Both wear and seizure load testing were performed. The effect of water on both tests was found to be:  Wear and friction increased with higher soluble water content. Water therefore interferes with the action of the lubricating additive leading to decreased performance.  It is known that hydroxyl groups, from dissociative chemisorption of water, act as active sites for adsorption. It is however postulated that the associative chemisorption and/or physisorption of water interferes by either reducing the active site availability or reducing activity to ligand exchange.  No iron oxyhydroxides (FeOOH) were detected on the wear scars or tracks using Raman spectroscopy. The adsorbed water therefore likely only interact with the surface due to their low concentrations (10 ~ 50 ppm). For wear testing the following additional observations were made:  The electric contact resistance (ECR) took longer to increase at higher soluble water content, for all PA concentrations. The equilibrium values attained were also lower, when values were within the measurement range. This again highlights the reduced lubricity performance at higher soluble water content.  Wear scar appearance and colour were uniquely affected at each concentration of PA  Similar trends were observed at 60 °C and 80 °C. At the higher temperature:  Wear scar diameters increased.  Friction coefficients decreased and had less variance.  ECR values were similar, but took longer to increase to a steady value. For seizure load testing the following additional observations were made:  At higher water content, the oscillation-stroke on the test machine used tended to deviate more, before the actual seizure point was reached.  The effects of soluble water were more noticeable at lower PA concentrations. / Dissertation (MEng)--University of Pretoria, 2014. / tm2015 / Chemical Engineering / MEng / Unrestricted

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

Frictional stability and wear resistance are key performance requirements for heavy truck brake linings. Lining-counterface friction affects the rate of vehicle deceleration, but wear also affects stopping characteristics because uneven or high wear can alter the contact geometry of the lining, change the pattern of frictional heat generation, and degrade the response of the braking system. Inertia dynamometer wear tests are commonly conducted in the linings industry, but are expensive and time consuming. It is therefore of interest to seek more convenient, lower-cost test methods that still enable wear rates of various linings to be effectively differentiated. The purposes of the current study were to determine whether the wear of brake lining materials can be measured in shorter-term laboratory tests, and if so, to determine to what extent the relative ranking of several lining materials' wear resistance depends on the method of testing. To investigate these issues, three commercial truck brake lining materials were worn against gray cast iron using three different laboratory-scale wear testing machines. Assessments of wear by gravimetric methods and dimensional changes using the same test apparatus were compared. The three linings ranked in similar order in all three kinds of wear tests, but the relative differences between the wear of one lining and another differed among the test methods. Results are discussed in terms of what test conditions are required to simulate brake lining wear in trucks, and how in situ lining material aging and transfer film formation can affect the wear of brake lining materials. Differences in the entrapment of third-bodies entering the contact had an important influence on the wear results and an additional set of block-on-ring experiments was conducted to demonstrate that effect. Removing wear debris with a wiper pad altered the relative wear ranking of the three materials.

A major challenge in tire research, is tire wear modeling. There are too many factors affecting tire wear, and part of those factors are difficult to be accurately expressed in physics and math. The objective of this research is to develop a machine learning based rubber sample wear model, and find the correlation between sample wear and tire wear. To develop this model, accurate and diverse wear data is necessary. The Dynamic Friction Tester (DFT) was designed and built for this purpose. This test machine has made it possible to collect accurate rubber sample wear data which has been validated under different conditions. Wear tests under diverse test conditions were conducted, and the test data were used to train machine learned based wear models with different algorithms, such as Neural Networks and Support Vector Machines. With test-proved wear behavior classification as additional input, and feature selection, performance of the trained rubber sample wear model has been further improved. To correlate rubber sample wear and tire wear, a set of correlation functions were developed and proposed. By validating the correlation functions using tire wear test data collected on roads, this research contributes a fast and economical approach to predict tire wear. / Doctor of Philosophy / Tire wear is closely related to the life time of tire, and excessive wear of tire can results in serious accidents. Since 1950s, research have been done to predict tire wear using experiments and empirical relations. These approaches are expensive, time consuming, and highly restricted to certain conditions. The objectives of this research is to develop a statistic based rubber sample wear model, and find the correlation between rubber sample wear and tire wear. To develop the statistic based rubber sample wear model, a test machine, named Dynamic Friction Tester (DFT) was designed and built to collect rubber sample wear data. The final rubber sample wear model is trained by wear data under 600 different test conditions. A set of mathematical equations were proposed to correlate rubber sample wear and tire wear. These equations were validated by actual tire wear data collected from lab and public roads. In combination of the statistic based rubber sample wear model and mathematical relation between rubber sample wear and tire wear, this research contributes a flexible, economical, and fast method to predict tire wear.

During normal walking, the relative motion of the human knee involves flexion/extension, anterior/posterior sliding, and medial/lateral rotation. As well, the knee experiences a complex, dynamic loading curve with a peak of up to seven times body weight. However, most wear testing machines that have been used to evaluate total knee replacement materials are unidirectional and/or apply only static force. This thesis presents an alternate wear testing device capable of simulating the most prevalent motions of the knee, and applying physiologically-correct loading to the material interface. By incorporating a CoCr disc, an UHMWPE block, stepping motors, pneumatic components, computer control, and linear tables in an x-y configuration, the device is capable of quickly screening new and alternative materials to UHMWPE before evaluating them on a much more expensive knee simulator. In addition, flexibility of the device allows programming of many different motion and loading configurations permitting materials testing under only certain circumstances, or evaluating the effects on wear of specific motions. Design rationale, development, validation, and future recommendations are presented. / Master of Science

The cervical spine must provide structural support for the head, allow large range of motion and protect both the spinal cord and branching nerves. There are two types of spinal joints: the intervertebral discs which are flexible connections and the facets, which are articulating synovial joints. Both types degenerate with age. Current surgical treatments include spinal fusion and articulating disc replacement implants. If both disc and facet joints are degenerated, fusion is the only option. In spinal fusion, the disc is removed and the adjacent vertebrae are fused which causes abnormally high stress levels in adjacent discs. In disc replacement, an articulating device is inserted to restore intervertebral motion and mimic healthy spinal kinematics. Disc arthroplasty does not significantly increase adjacent level stress but the lack of rotational constraint causes increased facet contact pressures. Thus, there is a need for a cervical total level arthroplasty system (CTLAS) that has a disc implant specifically designed to preserve the facet joints and implants for facet arthroplasty that can act independently or in-unison with the disc replacement. The conceptual design of a CTLAS implant system was proposed that would replace the disc and the facet joints. To facilitate medical imaging, PEEK (polyetheretherkeytone) was selected as the structural and bearing material. In the present thesis, multi-station pin-on-plate wear testing was initiated for pairs of unfilled (OPT) and carbon-fiber-reinforced (CFR) PEEK. Wear is important in arthroplasty implant design because wear particles can cause osteolysis leading to loosening. A variety of experiments were performed to investigate the effects of load, contact geometry and lubricant composition on wear. CFR PEEK was found to have much lower and more predictable wear than OPT PEEK in the present experiments. The wear of OPT PEEK pairs showed sensitivity to lubricant protein concentration. The coefficient of friction during testing was found to be quite high (up to 0.5), which might have clinical implications. Also, some subsurface fatigue was found, exposing carbon fibers of CFR PEEK. This remains a concern for its long-term application. Further wear testing is recommended using actual implants in a spine wear simulator.

The cervical spine must provide structural support for the head, allow large range of motion and protect both the spinal cord and branching nerves. There are two types of spinal joints: the intervertebral discs which are flexible connections and the facets, which are articulating synovial joints. Both types degenerate with age. Current surgical treatments include spinal fusion and articulating disc replacement implants. If both disc and facet joints are degenerated, fusion is the only option. In spinal fusion, the disc is removed and the adjacent vertebrae are fused which causes abnormally high stress levels in adjacent discs. In disc replacement, an articulating device is inserted to restore intervertebral motion and mimic healthy spinal kinematics. Disc arthroplasty does not significantly increase adjacent level stress but the lack of rotational constraint causes increased facet contact pressures. Thus, there is a need for a cervical total level arthroplasty system (CTLAS) that has a disc implant specifically designed to preserve the facet joints and implants for facet arthroplasty that can act independently or in-unison with the disc replacement. The conceptual design of a CTLAS implant system was proposed that would replace the disc and the facet joints. To facilitate medical imaging, PEEK (polyetheretherkeytone) was selected as the structural and bearing material. In the present thesis, multi-station pin-on-plate wear testing was initiated for pairs of unfilled (OPT) and carbon-fiber-reinforced (CFR) PEEK. Wear is important in arthroplasty implant design because wear particles can cause osteolysis leading to loosening. A variety of experiments were performed to investigate the effects of load, contact geometry and lubricant composition on wear. CFR PEEK was found to have much lower and more predictable wear than OPT PEEK in the present experiments. The wear of OPT PEEK pairs showed sensitivity to lubricant protein concentration. The coefficient of friction during testing was found to be quite high (up to 0.5), which might have clinical implications. Also, some subsurface fatigue was found, exposing carbon fibers of CFR PEEK. This remains a concern for its long-term application. Further wear testing is recommended using actual implants in a spine wear simulator.

In the thesis lubrication and wear at metal/HDPE contacts was addressed. In particular this type of contact occurs in artificial joint replacements. Wear of HDPE was recognized as a major factor limiting device performance. In the thesis, fully implicit fully coupled numerical approach was developed to simulate lubrication and wear. Approach allows solving stationary and transient problems for rough surfaces in a wide range of parameters. Wear coefficients were estimated from experimental data. Wear particles formed in wear process were investigated. Particles were found to be approximately 100 nm in diameter and spherical in shape. Considering theoretical solutions, it was concluded that debris may play a role of third-body abrasive wear particles. In the summary section, some discussion was provided on the topic of theoretical modeling of friction and wear and recommendations for future research were formulated.

Wear and friction are among the major problems faced in several industries such as mining industry. This creates challenges to select better materials with good wear behavior in order to improve the service life of the components. In the present project, three steel wire grades OH 70, OH 75 and OH 101 have been heat treated by quenching and partitioning heat treatment and tested using three wear testing methods. The wear tests performed were a pin-on-disc test, dry-pot test and slurry pot-test, and the results were compared with the conventional quenched and tempered steel. Tensile tests, hardness, impact Charpy tests, scanning electron microscope, optical microscope, X-ray diffraction and magnetic measurements were applied to characterize mechanical properties and microstructure of the steels before wear tests. The results showed that the quenched and partitioned steels with considerable amount of retained austenite had higher ductility and good impact toughness than the quenched and tempered steels. After the pin on disc tests, OH 75 grade showed the highest wear resistance, while the lowest wear resistance was obtained by OH 70 grade. The damage mechanisms identified after pin-on-disc were abrasion and oxidative wear. During erosive wear, almost no measurable wear was recorded under the dry pot conditions, while the slurry pot test owned significant wear mass loss. The main modes of the worn surfaces after erosive tests were ploughing and cutting. In addition, cracks were also observed.

Wear is a commonly occurring degradation mechanism for materials and components in the rock drilling industry. The wear can occur by either abrasion or adhesive wear. Further corrosion and presence of water or other lubricating fluids with or without particles may influence the behavior. Which mechanism, or mechanisms, and under which conditions it occurs, as well as the relative wear rate is dependent on the actual operating conditions for the component. In the present study, commonly available and general test methods for wear on high-alloy carbon steel has been analyzed. The project has been carried out through literature reviews and study visits at the tribology laboratory at KTH and at the Angstroms laboratory at Uppsala University. The present study indicates that it is difficult to suggest a feasible test method that is possible to use for all different situations of the wear that may occur. A test adapted to the actual situation is required to achieve a proper wear rate comparable to the wear rate in a real application.  According to the requirements from Ovako AB, a test that is general, cost effective and can be used when developing steel with higher wear-resistance, following wear testing methods has been compared: a pin-on-disk apparatus, a dry/wet sand/rubber wheel, a dry/wet sand/steel wheel, a tumbling mill, a particle erosion rig, a solid particle impingement using gas jets and a grinding machine. The tumbling mill, the grinder and the “Standard Test Method for Wear Testing with a Pin-On- Disk Apparatus” correspond to the requirements best. Ovako AB is recommended to continue the work with these testing methods. / Nötning är en vanlig mekanism som orsakar nedbrytning på material i gruvindustrin. Nötningen kan förekomma som abrasiv eller adhesiv nötning. Korrosion och närvaro av vatten eller andra smörjande vätskor med eller utan lösa partiklar kan påverka beteendet. Den eller de mekanismer som styr nötningen såväl som nötningstalet beror på de aktuella förhållanden vilka materialet eller materialen verkar i. I denna studie har en generell testmetod för att utvärdera nötning på höglegerat kolstål har undersökts. Arbetet har genomförts genom litteratursökning samt studiebesök vid tribologiska laboratoriet på KTH samt på Ångströmska i Uppsala. Utifrån arbetet har det visat sig att det inte förekommer några generella nötningstest för alla applikationer, då det krävs ett test som är anpassat efter verkligheten för att få ut korrekt nötningstal. Utifrån Ovako ABs önskemål om ett generellt test som är ekonomiskt hållbart samt kan användas för att utveckla nötningsbeständigheten i de stål där nötning förekommer har följande testmetoder jämförts: pinne/skiva-maskin, blött/torrt sand/gummihjul, blött/torrt sand/stålhjul, roterande trumma, ”Erofugen”, partikelsprutare och en slipmaskin. De test som motsvarar kravprofilen bäst är den roterande trumman, slipmaskinen samt den standardiserade pinne/skiva-maskinen. Utifrån dessa testmetoder rekommenderas Ovako AB att fortsätta arbetet.