Structure-tribological property relations have been studied for five high entropy alloys (HEAs). Microhardness, room and elevated (100°C and 300°C) temperature sliding friction coefficients and wear rates were determined for five HEAs: Co0.5 Cr Cu0.5 Fe Ni1.5 Al Ti0.4; Co Cr Fe Ni Al0.25 Ti0.75; Ti V Nb Cr Al; Al0.3CoCrFeNi; and Al0.3CuCrFeNi2. Wear surfaces were characterized with scanning electron microscopy and micro-Raman spectroscopy to determine the wear mechanisms and tribochemical phases, respectively. It was determined that the two HEAs Co0.5 Cr Cu0.5 Fe Ni1.5 Al Ti0.4 and Ti V Nb Cr Al exhibit an excellent balance of high hardness, low friction coefficients and wear rates compared to 440C stainless steel, a currently used bearing steel. This was attributed to their more ductile body centered cubic (BCC) solid solution phase along with the formation of tribochemical Cr oxide and Nb oxide phases, respectively, in the wear surfaces. This study provides guidelines for fabricating novel, low-friction, and wear-resistant HEAs for potential use at room and elevated temperatures, which will help reduce energy and material losses in friction and wear applications.

This report describe the wear of the protruding areas on the sides of the grate plates in the grate-kiln process in the hematite pellet production in LKAB, Kiruna. The steel plates are exposed to a hostile environment with heat cycles and corrosive atmosphere. An evaluation of the plates was made in co-operation with LKAB Metlab in Luleå and LKAB mechanical workshop in Kiruna. Instruments used are stereomicroscope, LOM, SEM, Spectroscope, Vickers Hardness and a surface nish meter. Results show the protruding areas of the plates are exposed to a tribochemical wear, where tops of the rough areas are torn down. A coating test is carried out at Tribolab, LTU in Luleå, using an SRV. Samples with a wear and corrosion resistant coating called Diamalloy 4276 abrade against eachother at high temperature and pressure. The coating do help to resist wear, but the environment of the test is to unrealistic to say by certain that it will help in the grate. A FEM-model in COMSOL Multiphysics 4.4 is made to calculate thermal stresses between coating and metal, the result show stresses up to 1 GPa will occur, this can be explain by the big dierence in thermal expansion coefficients of the materials. It will probably create cracks in the coating surface. Two solutions are presented, a coating is not recommended. The tribochemical wear is decreased by using a better surface nish. Therefore one can either machine the areas by drilling or milling, or one can change the casting method. Today sand casting is used, by using shell casting or precision casting, for example Shaw process, the surface nish is better over the whole plate, which also is better for corrosion resistance since less initiation points exist. / Denna rapport presenterar en undersökning av slitaget på sidorna av grateplattor som används i gratekilnprocessen i hematitpelletstillverkningen på LKAB i Kiruna, även lösningar presenteras. Plattorna benner sig i en svår miljö med termiska cykler och korrosiva substanser. Utvärderingen av slitaget gjordes i samarbete med LKAB Metlab i Luleå och LKAB mekaniska verkstad i Kiruna. Utrustning som användes var Stereomikroskop, LOM, SEM, Spektroskop, Vickers hårdhetsmätare och ytnhetsmätare. Resultatet visar att sidorna av plattorna utsetts för ett tribokemiskt slitage där toppar av den grova utan slits ner. Ett ytbeläggningstest utfördes på Tribolab, LTU i Luleå, med en SRV. Prover med en beläggning har gnidits mot varandra under tryck och hög temperatur och jämförts med prover utan beläggning som utsattes för samma test. Ytbeläggningen som används står främst emot korrosion, men även slitage, den kallas Diamalloy 4276. Resultatet visar att beläggningen skyddar bra mot slitage, men miljön under testet var för orealistiskt för att med säkerhet kunna säga att det kommer hjälpa i graten. En FEM-modell gjordes med hjälp av COMSOL Multiphysics 4.4 för att beräkna de termiska spänningarna som uppstår mellan ytbeläggningen och metallen. Resultatet visar att spänningar på upp till 1 GPa kommer uppstå, detta kan förklaras med den stora skillnaden i termisk utvidgningskoecient mellan de två materialen. De höga spänningarna kan skapa sprickor i ytan. Två lösningar presenteras, en ytbeläggning rekommenderas inte i dagsläget. Det tribokemiska slitaget kan motverkas genom att förbättra ytnheten. Detta kan antingen utföras genom att bearbeta ytan, med fräsning eller slipning, eller att man byter gjutningsmetod. Idag används manuell formtillverkning, om man istället skulle använda skalformsgjutning eller precisionsgjutning, till exempel Shawprocessen, skulle man få en bättre ytnhet över hela plattan. Detta leder även till bättre korrosionsbeständighet då färre initieringspunkter nns.

During braking, both the rotor and the pads in disc brakes are worn. Since disc brakes are not sealed, some of the wear particles generated can become airborne. Several studies have found an association between adverse health effects and the concentration of particles in the atmosphere, so it is of interest to improve our knowledge of the airborne wear particles generated by disc brakes. However, in field tests it is difficult to distinguish these particles from others in the surrounding environment, so it may be preferable to use laboratory test stands and/or simulation models to study the amount of airborne wear particles generated. This thesis deals with a simulation methodology for prediction of airborne wear particles from disc brakes and three experimental methods for testing disc brake materials with focus on airborne wear particles. The four appended papers discuss the possibility to both measure and predict the number and size distribution of airborne wear particles that originate from the pad to rotor contact. The objective is to develop a simulation methodology that predicts the number and size distribution of airborne wear particles from disc brakes. Paper A describes how a modified pin-on-disc machine was used to study airborne wear particles originating from different disc brake materials. The results indicate that the test setup can be used to measure and rank the number concentration and size distribution of the airborne wear particles generated. Paper B describes a disc brake assembly test stand for measurements of airborne wear particles from disc brakes. The results indicate that the test setup can be used to measure the number concentration and size distribution of airborne wear particles generated from disc brake materials. The results also indicate a promising ability to rank different pad/rotor material combinations with respect to the number concentration of airborne wear particles. Paper C compares measurements made in passenger car field tests with measurements made in a disc brake assembly test stand and in a pin-on-disc machine. A promising correlation between the three different test methods is found. Paper D presents a simulation methodology for predicting the number and size distribution of airborne wear particles using finite element analysis (FEA). The simulated number distribution is compared with experimental measurements at component level. The result indicates that the proposed methodology may be used to predict the number concentration and size distribution of airborne particles generated in the pad-to-rotor contact.

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.

The desire to replace missing teeth with the aim to improve health and quality of life dates back to a thousand years ago. Although research on dental crown designs, materials and techniques has increased in recent years and is expected to grow in the future. In the past few decades, dental crown studies have gained high importance in dentistry due to their functionality, biocompatibility and good mechanical properties. This paper provides a comprehensive review of history and evolution of dental crowns. The goal of this study is to understand the dental crown materials and the differences in their properties with goals to facilitate the optimal selection and to support further development. It also describes the different methods by which wear is tested on these crowns. Finally, it describes the current technologies used for the analysis, and a comparative study is performed on various dental crown materials and it is demonstrated that the wear resistance is different for different materials.

Indiana University-Purdue University Indianapolis (IUPUI) / Erosive tooth wear (ETW) is a growing dental condition often associated with aging. This in-vitro project comprised three studies aiming to investigate the impact of tooth age on ETW susceptibility and prevention. In the first study, un-identified extracted premolars were collected and had their ages estimated using validated dental forensic methods. The premolars were examined to investigate the relationship between age and presence and severity of ETW, as well as other main dental-hard tissues conditions. ETW, dental caries, fluorosis, extrinsic staining and tooth color were evaluated using established clinical indices. In the second study, the tooth age impact on ETW susceptibility and response to preventive treatments (Sn+F, NaF, and de-ionized water control) were evaluated using representative samples from the initial study. Enamel and dentin specimens were prepared and subjected to daily erosion-treatmentremineralization cycling procedure. Surface loss (SL) was determined during and after the cycling, by optical profilometry. Similar protocol was adopted in the third study with the addition of toothbrushing abrasion to the model, in order to explore the interplay between age and toothpaste abrasivity on erosion-abrasion development. SL was measured during and after the erosion-toothbrushing-remineralization cycling. The relationships between age and the investigated variables were assessed using linear regression models. In conclusion: 1. The presence and severity of ETW, dental caries, and extrinsic staining increased with age, while of enamel fluorosis decreased. Tooth also showed to be darker with age. 2. Susceptibility of enamel and dentin to demineralization increased with age. Sn+F showed the highest anti-erosive efficacy, and was not affected by age. NaF showed lower efficacy on dentin, which increased with age. 3. Enamel and dentin SL increased with toothpaste abrasivity level. Dentin SL also increased with age. Age effect on enamel SL was observed only with low abrasive toothpaste. Age-related changes on enamel and dentin affected ETW development. / 2020-05-17

No description available.

Friction interaction between brake materials see a rise in temperatures of over 1000 oC contributing to thermal fade of brakes and deterioration/cracking of rotors. Various microstructural features like graphite, ferrite and pearlite could influence the mechanical and thermal properties and related friction performance of the brake materials. Even more relevant impact on properties and friction performance of rotors can be expected after coatings or surface treatments. The primary purpose of this research is to identify the impact of microstructure and surface treatment on properties and friction performance of four types of pearlitic gray cast irons. The C30, C20 and FC150 rotors were surface treated by bombarding with heavy ions which diffused into cast iron and created a coating with different chemistry and properties when compared to the “non-treated” rotors. Complete chemical and material characterization of the brake rotors using optical emission spectrometer (OES), carbon-sulfur combustion analyzer, polarized light microscopy, density (analytical balance and Archimedes principle), Brinell hardness tester, laser flash apparatus, scanning electron microscopy, and energy dispersive X-ray microanalysis. The pearlitic gray cast iron rotors are typified by the presence of graphite, carbides, and inclusions in an almost fully pearlitic matrix with a minimum amount (2-4 vol.%) of “free” ferrite. Graphite can be further classified based on its morphology. The investigated cast irons contained two different graphite types: type VII-E5 for the F150 OEM rotor, and type VII-C5 characteristic for the ASTM A48 classes C30 and C20, as well as the “Japanese” JIS G5501 FC150 rotors. It was identified from the initial curve fitting models that the observed microstructural differences in individual cast iron types are responsible for the observed mechanical (density – decreases with increasing ferrite and decreasing pearlite contents; hardness – decreases with increasing ferrite contents) and thermal properties (increase with increasing ferrite and pearlite contents), and friction performance (increases with increasing ferrite and decreasing graphite contents) of the studied rotors. The applied surface treatment also contributed to the modification of the mechanical and thermal properties, as well as friction performance of the studied rotors. However, there were not enough statistically relevant models developed from the generated data, which could identify the combined influence of various microstructural features observed and applied surface treatment over the properties and friction performance of the studied rotors.

CMOS feature size scaling has been a source of dramatic performance gains, but it has come at a cost of on-chip wear-out. Negative Bias Temperature Instability (NBTI) is one of the main on-chip wear-out problems which questions the reliability of a chip. To check the accuracy of Reaction-Diffusion (RD) model, this work first proposes to compare the NBTI wear-out data from the RD wear-out model and the reliability simulator - Ultrasim RelXpert, by monitoring the activity of the register file on a Leon3 processor. The simulator wear-out data obtained is considered to be the baseline data and is used to tune the RD model using a novel technique time slicing. It turns out that the tuned RD model NBTI degradation is on an average 80% accurate with respect to RelXpert simulator and its calculation is approximately 8 times faster than the simulator. We come up with a waveform compression technique, for the activity waveforms from the Leon3 register file, which consumes 131KB compared to 256MB required without compression, and also provides 91% accuracy in NBTI degradation, compared to the same obtained without compression. We also propose a NBTI ΔVth estimation/prediction technique to reduce the time consumption of the tuned RD model threshold voltage calculation by an order of with one day degradation being 93% within the same of the tuned RD model. This work further proposes to a novel NBTI Degradation Predictor (NDP), to predict the future NBTI degradation, in a DE2 FPGA for WCET benchmarks. Also we measure the ΔVth variation across the 4 corners of the DE2 FPGA running a single Leon3, which varies from 0.08% to 0.11% of the base Vth.

The production of faulty parts poses significant challenges for production facilities, as it leads to increased inventory levels, operating costs, and impedes overall productivity. Despite its fundamental nature, this issue remains prevalent in manufacturing operations. To effectively reduce the rate of faulty parts, it is crucial to have a thorough understanding of the manufacturing process and exercise control by monitoring various parameters.  The aim of this study is to investigate the right prerequisites which enable quality assurance through in-line failure detection by vibration analysis. The research questions formulated for this thesis are as follows:  RQ1: What are the essential prerequisites for quality assurance through in-line failure detection by vibration analysis in the machining of splines? RQ2: How suitable is the use of vibration measurements in identifying and sorting out poor quality in the specific machining process of splines? The study was conducted through a literature review and a single case study of a gear hobbing process in an industrial manufacturing company.  The collection of data was acquired via interviews, observations, and vibration measurements during the spline manufacturing process. To analyse the collected data several tools got used. Python was used as the tool for performing several operations on the dataset, such as FFT of the vibration signals. To later visualize the results which facilitated the analysis of the entire dataset.  The results of the study indicate several similarities between the documented fault progression in gear systems and the manufacturing of splines. However, further research is needed to identify the core differences between these two fault progressions.  Furthermore, the study identified the essential prerequisites for implementing vibration analysis as an in-line failure detection method in spline manufacturing operations. Additionally, it concluded on the suitability of vibration analysis for identifying faults in this context.