In recent times, there has been an increased interest in replacing conventional metals and synthetic fiber composites in various automobile parts with natural fiber polymer composites. These natural fiber composites offer benefits over conventional materials in terms of reduction in weight, lower cost, comparable high specific properties such as specific stiffness and strength, low abrasion property, and availability of these materials. Environmetal concerns and the need to make eco-friendly materials also encouraged the use of natural fiber polymer composites (NFPC) for various automotive applications, as their usage reduces the emission of harmful pollutants, thereby providing a safer and cleaner environment. The reduction in weight of these materials also helps to reduce fuel consumption in cars. Therefore, this study focused on the investigation and characterization (mechanical, thermal, and tribological) of hemp fibers reinforced polypropylene made with virgin (Biolite) and recycled (Revo) composites, consisting of different fiber loadings from 10% to 30% for possible automotive applications. The result showed an improvement in the compressive properties of the composite as hemp fiber loading increases, with the recycled composite exhibiting a better compression performance in comparison to virgin composites. Revo 41 had the best compressive strength  and a 35% higher value than Biolite 2 of the same hemp fiber loading. However, there was a decrease in the fracture toughness of the composites as hemp fiber loading increases. This was more significant at about 27% from Biolite 1 to Biloite 2, Revo 41 experienced a slight improvement of 15% in fracture toughness with 20% hemp fiber loading. Revo 35 composite which had more degradation steps showed the best thermal performance at low temperature region with a degradation temperature of 276°C, while Biolite 1 at 444°C exhibited the best thermal stability at high temperature degradation. In comparing the tribological behavior of pure polypropylene with the composites, the composites exhibited a better tribological performance as there was a slight decrease in the coefficient of friction and wear rates of composites as the hemp fiber loading increases. Revo 41 of 20% hemp fiber fiber loading had the best wear performance. Considering its strength and slightly better tribological performance, Revo 41 is considered the best performing composite for automotive applications in comparison to the other composites.

Cross-country skiing has turned into the most highly competitive winter sport, with skiers having the ability to win by merely milliseconds. Every year researchers, ski - technicians, and athletes come together to prepare the ski base surface that gives the best possible results. However, much current information is based on the ski technician’s experience. Therefore, this project has been carried out to help to bridge the gap between ski technician’s knowledge and experimental research. The ski bases are passed through several surface preparation steps before competitions. Stone grinding and hand texturing are two of them. Since grinding cannot be specifically applied as per the environmental conditions, it is followed by texturing. This application of grinding and texturing changes the surface topography of the ski base, which will affect the contact area between the ski base surface and snow/ice and the wettability of the ski base. For this project, work is focused on how the application of different grinds and hand textures affects the wettability of the ski base. This project illustrates the change in wettability of ultra-high molecular weight polyethylene (UHMWPE) and its composites under the application of ten different commercial grinds followed by three other hands texturing. Surface topography was observed under an Optical profilometer, and wettability was measured by measuring the contact angles of droplets on these ski base materials. It was found that the hydrophobicity of ski base materials can be increased to a certain level by increasing the Arithmetic mean roughness (Ra) of specimens. Different ski base materials showed different hydrophobic behaviour when roughness was increased. Applying hand textured to different ground specimens again improved the hydrophobic behaviour of the ski base.

Many automotive components are made of Al-Si coated ultra-high strength boron steel (UHSS) and are produced by hot stamping process. In this process, the workpiece is heated to an austenitizing temperature and is then formed and quenched simultaneously between the tools to achieve the desired shape and high strength. During hot stamping process, friction and wear occur which affect formability and maintenance intervals for tool replacement and repair. To repair worn tools, metal is deposited by fusion welding technique. The tribological behaviour of repair welded tool steel sliding against Al-Si coated UHSS has not been studied in detail and there is a need to investigate if the modified tool surface will affect friction and wear. Hot stamping, similar to many manufacturing processes, is affected by the global mega trend of digitalization and Industry 4.0. To monitor the process and optimize the control and operation are the main aims. In view of this, tribological condition monitoring is a promising approach that can allow measurement of physical properties such as vibrations, temperatures, and acoustic emission to be coupled to the tribological response of the system. The aim is to monitor the hot stamping process and enable early detection of changes in friction and wear which can be used for e.g. optimized maintenance and minimized scrap. The aim of this M.Sc. thesis was to improve the robustness of hot forming processes by studying the tribological behaviour of repair welded tool steel sliding against Al-Si coated UHSS under conditions relevant for hot stamping. Another aim was to obtain more predictable tool maintenance by the implementation of acoustic emission measurement system on a hot-strip tribometer and correlating condition monitoring signals to friction and wear phenomena. The tribological tests were carried out using a hot-strip tribometer in conditions representative of a hot stamping process of automotive components. Acoustic emission during sliding between hot work tool steel and different automotive component material surfaces was measured at room temperature in the same strip drawing tribometer and correlated to friction and wear of the surfaces to get more predictable maintenance intervals. Tool steel specimens were welded with the same material as the base material QRO90. Before conducting the tribological test, the repair welded tool steel pin cross-section was polished, etched, and observed under optical microscope and SEM to analyze the effect of Tungsten Inert Gas (TIG) welding process on the microstructure. The analysis was completed with EDS to study the elements in the microstructure. Microhardness was measured to obtain the microhardness profile from the repair welded tool steel pin surface to the bulk in order to study the effect of different microstructures on the mechanical properties. The weight and surface roughness of the pins were measured before the tribological test. After the test was finished, the weight of the pins was measured to calculate the weight difference. The sliding surface of the pins and the strips were photographed. The sliding surface of the pins was also observed and analyzed using SEM and EDS after the test to study wear characteristic of the repair welded tool steel at high temperatures. Acoustic emission signal from the sliding was studied using Toolox44 pins with surface roughness 300-400 nm and with lay direction parallel and perpendicular to sliding direction. Toolox44 pins were sliding against uncoated UHSS, as-delivered Al-Si coated UHSS, and heat-treated Al-Si coated UHSS strips. Acoustic emission was measured during the sliding at the same time as COF measurement. Weight of the pins was measured before and after the test and the wear damage on both surfaces was photographed. COF, AE signals in the time and frequency domain, and wear damage were compared and analyzed. It is found that repair welded tool steel has similar COF compared to the original hot work tool steel with the largest weight gain from the test at 700 ⁰C due to compaction galling mechanism with slower lump formation and the presence of wear particles, transfer layer, and formation of lumps. The weight gain is smaller from the test at 750 ⁰C due to faster lump formation. The weight loss from the test at 600 ⁰C is due to abrasive wear mechanism. SEM micrographs revealed that the repair welded tool steel surface and transfer layers can be found beneath a transfer layer. Wear particles adhered on the repair welded tool steel surface come from broken transfer layer or directly from Al-Si coated UHSS. A change in wear mechanism is indicated by acoustic emission burst signals or gradual amplitude change in the time domain. Frequency analysis of AE signals revealed a change in wear mechanism due to the formation of transferred material in the form of a lump causes AE signals with peaks at higher frequencies above 0.3 MHz to shorten.

Grease-lubricated journal bearings are widely used in heavy duty applications, such as construction equipment, agriculture- and forest machines. The main purpose of the grease-lubricated journal bearing is solely to create sustainable rotation of a given application. However, purpose seldom decides complexity of journal bearing design. Depending on application, parameters such as Load , Material  and Lubrication immensely increase complexity of the design. Tribology is a highly interdisciplinary subject, which requires knowledge concerning physics, chemistry, metallurgy and solid mechanics. Tribological aspects of a design are frequently regarded as irrelevant. Tribological issues are commonly enlightened in combination with structural design weaknesses. The main aim of the thesis was to analyze two cylinder joints found in a Komatsu Forest 951 crane and establish root cause to the structural and tribological issues. Outline of the approach was divided into three main targets: 1. Investigate mechanical and tribological aspects of the crane design. 2. Understand how these aspects influence the life time of the bearings. 3. Summarize the analysis and suggest improvements based on the discovery. Fundamental structural and tribological design guidelines regarding grease-lubricated journal bearings have been presented in this thesis. Damaged components such as cylinders, pins and journal bearings have been examined at Komatsu Forest’s factory in Umeå. Further, a scanning electron microscopy study has been done at Luleå University of Technology, to determine predominant wear mechanisms in the harvester crane joints. A non-linear finite element model of the crane has been designed to represent pressure distribution in the contact between bearing and pin. The finite element analysis gives a good approximation of the contact but leaves room for further refinements. Temperatures, in the contacts, have not been identified and will be measured outside the time frame of the master’s thesis. Design changes, with respect to discovered structural and tribological issues have been suggested. The suggested improvements can potentially increase the life time of lift cylinders, pins and journal bearings.

This diploma work is performed at Sandvik Mining and Rock Technology, Rock Tools division, a world-leading mining equipment manufacturer. The aim is to study the wear of cemented carbide rock drill inserts worn against granite and sandstone countersurfaces, with focus on the impact of binder phase composition and flushing agent chemistry. A brief introduction to rock drilling, cemented carbides and the wear and degradation mechanisms of cemented carbides in rock drilling is given. Wear is induced in a lab test by sliding cemented carbide inserts against granite and sandstone countersurfaces while flushing with deionized water or synthetic mine water. The wear is quantified by measuring material weight loss, and worn inserts are studied by SEM. All wear marks feature crushed, fragmented and heavily deformed WC grains and cavities left after individually removed WC grains. Rock adhere strongly on inserts worn against both granite and sandstone, and adhered material from both rock types sometimes endure the mechanical contact between insert and rock without significant spalling. Inserts tested with deionized water against sandstone wear 2.2 - 5.1 times more relative to against granite, and the only distinct difference observed is the distribution of adhered rock. The use of synthetic mine water relative to deionized water impacts the wear of all inserts, though corrosion products are only found on some of them. Further, the tribological contact greatly impacts the corrosive attack. The relative wear difference using different water chemistries is larger for inserts with a smaller relative amount of binder. In most cases, increased wear is measured for inserts tested with synthetic mine water. For reasons yet unknown, this trend is reversed for inserts with a high relative amount of binder tested against sandstone, where a decrease in wear is measured instead. / Detta examensarbete har utförts åt Sandvik Mining and Rock Technology, Rock Tools avdelningen, som är en världsledande utrustningstillverkare inom gruvindustrin. I arbetet undersöks nötningen av så kallade bergborrstift av hårdmetall. Berg är generellt ett mycket hårt och sprött material, och borrning i berg går därför i huvudsak ut på att krossa och spola bort krossad sten. Längst fram på bergborrar sitter borrkronor som till största del är gjorda i stål. Då stål är för mjukt för att effektivt kunna avverka berg monterar man in stift av hårdmetall längst fram på borrkronan. Hårdmetall är ett kompositmaterial av mycket hårda men spröda wolframkarbidkorn (WC) som hålls ihop av en, jämfört med WC, mjuk och formbar metall som kallas bindefas. Resultatet är ett mycket hårt men fortfarande relativt segt material som dessutom klarar de mycket höga temperaturer som uppstår vid bergborrning. Traditionellt används kobolt som bindefas, men nu tros det finnas hälsorisker med kobolt och dessutom sker en stor del av världens koboltutvinning under oetiska förhållanden i konfliktländer i Afrika. Detta i kombination med att koboltpriserna ökat dramatiskt de senaste åren leder till att man nu söker efter alternativa bindefaser. Bland annat undersöker man olika legeringar av nickel och järn. I detta arbete jämförs nötningen av stift med nickel-, järn- och olika koboltbindefaser. I ett labtest fås nötning genom att stiften trycks mot en roterande stencylinder av antingen granit eller sandsten. I verkliga förhållanden används ofta så kallat gruvvatten som sipprar in i gruvan som spolvatten för att ta bort stenkrosset och kyla borrkronan. För att se hur kemin i spolvattnet påverkar nötningen spolas kontaktytan mellan stift och stencylinder med antingen avjoniserat vatten eller syntetiskt gruvvatten under testerna. Stiftens materialförlust under provningen beräknas genom att mäta deras vikt innan och efter. För att se om skillnader i nötningshastighet mellan olika stifttyper eller testvillkor avspeglas i olika utseenden på slitytorna undersöks stiften med hjälp av ett svepelektronmikroskop (SEM). Från SEM-bilderna ser man att alla stift från alla testvillkor har krossade och fragmenterade WC-korn på ytan och att stora delar av slitytorna täckts av påkletat berg. Bergpåsmetningarna är ibland mycket tunna (< 1 μm) och delvis inblandade i bindefasen, och ibland betydligt tjockare (flertal μm). De tjockare påsmetningarna är bundna så pass hårt till ytan att de kan upprätthålla delar av kontakten mellan stiftet och berget under testningen utan att lossna. Huruvida detta skyddar hårdmetallen från att nötas eller om det påkletade berget reagerar med, och därmed ökar den kemiska nedbrytningen av stiftet är inte utrett. Berget skyddar dock den underliggande hårdmetallen mot den korrosion som uppstår i kontakt med spolvattnet. Resultaten visar att stiften nöts betydligt mer mot sandsten än mot granit. Förutom att bergpåsmetningarna har en annan fördelning över ytan så syns inga tydliga skillnader mellan stiften testade mot de båda bergarterna. De flesta stiften nöts mer när de testas med gruvvatten än med avjoniserat vatten. Detta gäller alla stift utom de som har hög relativ mängd bindefas och som testats mot sandsten. Dessa stift nöts tvärt om mindre när de testas med gruvvatten än med avjoniserat vatten. Hittills har ingen anledning till denna konsekventa avvikelse hittats.

This thesis summarizes the work done on tribological characterization of multifunctional hardfacing coatings with self-lubricating properties, intended for use in mechanical components operating in high temperature applications for which conventional lubricants are no longer effective. Deposition techniques like laser cladding have a great potential in reworking/repair of high value industrial components in order to extend their lifetime. It is expected that the use of self-lubricating laser claddings could be useful in high temperature applications like metal forming, leading to decreased friction and wear. In this study, the tribological behavior of self-lubricating claddings has been studied against steel and aluminum counter surfaces, using ASI52100 bearing steel in addition to AA6082 and AA2007 aluminum flat pins as the counter bodies. Nickel- and iron-based powders have been chosen for the preparation of claddings. Self-lubricating properties of Ag/MoS2 have been compared to an untreated reference cladding and grade 1.2367 tool steel. For steel counter surfaces, tribological properties in the temperature range between RT and 600⁰C have been investigated and at 300°C for aluminum counter surfaces. Tribological tests were done by a high frequency linear oscillation (SRV) test machine under reciprocating conditions. The wear scar and volume of coatings were measured by using a 3D optical profilometer. SEM/EDS analysis were additionally performed for the characterization of microstructure and wear scar. The results indicated that MoS2 reduced friction and wear of the Fe-based cladding material when tested against steel at room temperature compared to the reference alloy and grade 1.2367 tool steel, and that the addition of silver further decreased wear in addition to early stage friction. It was also observed that the tribolayer, which was formed during the sliding of Ni-based - 5 Ag - 10 MoS2 and against aluminium under lubricated conditions, was protective and provided low and steady friction.

Additive manufacturing is gaining popularity at a rapid rate and has been a resourceful production process to reduce material usage, wastage (scrap) and manufacturing costs for various applications. The project conducted, emphasizes on Thermoplastic Elastomer (TPE SE6300C-65A) material, which is a highly versatile compound, and has the ability to exhibit properties of both rubber (Elastomers) in terms of flexibility and plastic (Polymers) in terms of recyclability. Cost reduction without compromising quality is one of the important factors for industries. The project involves the use of TPE pellets to extrude filaments that could be used for 3D Printing. Filament extrusion involves process variables like Nozzle Temperature, De-humidification of pellets, Diameter of the nozzle, Distance of collection, Cooling and Angle of inclination of the extruder. These process variables are optimized to accomplish the desired quality of filament. The filament produced through extrusion is further used to make products using Fused Deposition Modeling (FDM). FDM also involves numerous process variables like Layer Thickness, Build Orientation, Print Infill, Print Speed etc. In this study, different test specimens, in terms of geometrical shapes are printed from the material, TPE SE6300C-65A and tested in order to understand how the surface features as well as the dimensional accuracy change with different process variables. It is observed that the surface topography produced throughout FDM process is majorly affected by the angle of orientation of the printed part. The main goal of this thesis is to give the reader a better understanding on which process variable, such as layer thickness, temperature and print speed affect the surface roughness of the models and also a comparison between these three variables, highlighting which is more or less affecting. It is also observed the dimensional accuracy of the real specimen deviate from the value input into the CAD software. The results obtained in this study clearly suggest that there is a lot of opportunities for future improvements especially regarding the dimensional accuracy, it is imperative to achieve the highest precision possible in order to have commercial values for the FDM 3D printing.

The addition of lead to the copper alloys increases its machinability and reducesthe overall production cost, despite copper being expensive, which makes achallenging task to replace lead. But the alarming effects of lead on human healthand the recycling problems has led to the increase in concern forreducing/eliminating the use of lead in brass and other copper alloys. Manymaterials are considered to replace lead in brass; silicon is one such alternative.The turned brass sample are investigated using the state of the artequipments at Halmstad University. The results obtained are controlled readingsof surface parameters and is categorized using surface imaging and mappingsoftware, Mountains Map.This thesis characterizes the lead and the lead free brass's surfaceintegrity for a certain cutting data. The study deals with the evaluation ofselection of appropriate surface integrity parameters and summarizes theappropriate combination of cutting data to maintain the surface of the ecobrass/unleaded brass on par with the leaded brass surface. The 2D and 3Dsurface parameters illustrates the surface functionality and its effect on thematerial in contact.The research results suggest a detailed methodology for the analysis ofsurface topography and a comparison exemplifying differences between the twomaterials under study. The research provides a perplexed results and forms thebasis for further investigations of the samples machined at different cutting data.Second set of test includes comparing the Leaded brass with the unleaded brasssamples machined at 0.06, 0.1, 0.15 and 0.2mm/rev respectively. The studyfocuses on the correlation of cutting feed and the surface parameters. Comparingthe results of two tests, the unleaded brass machined @ feed rate 0.2mm/rev,200m/min, 1.5mm depth of cut posses similar surface functionality as leadedbrass.

The ease of manufacturing complex geometries using fused deposition modeling (FDM) 3D-Printing reduces the overall production cost compared with the traditional manufacturing techniques. Because of the benefits of 3D printing technologies, it is proposed to be used in the manufacturing of different products. But there is still no definite characterization of the surface quality of objects manufactured by 3D printing. Hence in order to define the texture of the surfaces produced, measurements from different samples are taken and quantified.In this study, a 3D test model consisting of various slopes is printed at different layer thicknesses and different print speeds using different 3D printers.Thus, the effect of the surface orientation on the surface roughness was studied in relation to the different layer thicknesses and different print speeds. The study samples are measured using the state of the art equipment at Halmstad University.This thesis studies the surface roughness at different slopes of FDM models.A related study on the dimensional variation between the CAD model and the actual3D printed model, and causes/reasons for the variations are analyzed.It is observed that FDM produced part surface topography is directly affected by the orientation of the surface. Also, the surface roughness increases with increase in layer thickness. The observed correlations between surface roughness and layer thickness and surface orientation could be used to better understand the behavior of FDM surfaces, thus to better quantify the surface roughness. To improve quality, it must first be quantified. It is well observed that dimensional inaccuracy exists between the CAD model and the printed part. These results suggest that there is a lot of work and improvements to be done in order to close the gap of dimensional inaccuracy and achieve a high precision commercial FDM 3Dprinting.

Increasing environmental awareness has driven a lot of research to look into various environmentally friendly lubricants which can replace more conventional mineral oil based lubricants. This is true in particular for marine and hydropower applications where the risk of lubricant leakage can be damaging to the local environment. Glycerol is an organic compound produced as a byproduct when producing Biodiesel. It is environmentally friendly and has been used by the pharmaceutical and food industries for a long time. Recent research has shown that glycerol has very good tribological properties and can be used as a lubricant in some applications. However, its high viscosity and high static friction are disadvantageous and needs improvement. The purpose of this study is to investigate possible surface active environmentally adapted additives in glycerol and water solutions. 14 additives have been selected for testing and were tested in a pin-on-disc start-stop friction test to see their effect on the static and dynamic friction coefficients. From these 14 additives two were selected due to their superior performance and were further studied. The effect of concentration of water and additive in glycerol was also investigated using the same test conditions. A phosphor based additive has been found to be the best performing.