Wear

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Zakonodaja predpisuje proizvajalcem avtomobilov vse strožje omejitve glede izpustov škodljivih emisij, zato je razvoj motorjev z notranjim zgorevanjem usmerjen predvsem v zmanjšanje porabe goriva pa tudi njegovega popolnega zgorevanja v vsakem trenutku delovanja motorja. Ena izmed danes splošno sprejetih tehnologij, ki omogoča do 10 % zmanjšanje porabe goriva, zlasti pri vožnji v urbanem okolju, je tehnologija start-stop. Sistem start-stop zmanjša porabo goriva s samodejnim izklopom motorja z notranjim zgorevanjem med čakanjem pred semaforjem ali v zastojih in s tem skrajša čas, ko motor deluje v prostem teku. Po drugi strani pa uporaba te tehnologije dodatno obremenjuje ostale elemente avtomobilskega zagonskega sistema, kot so akumulator, zaganjalnik in vžigalne ali grelne svečke itd., ker bistveno poveča število zagonov motorja. V raziskavi sem se usmerila v razvoj grelnih svečk dizelskih motorjev. Žarilne svečke služijo kot pomoč pri zagonu hladnega dizelskega motorja. Njihova na...

The influence on the wear properties of ductile iron with Cr-containing steel inserts has been investigated before and after austempering. The microstructure of locally reinforced ductile iron, with and without an austempering treatment, has been characterized using optical microscopy, scanning and transmission electron microscopy and secondary ion mass spectrometry. The introduction of such inserts during casting leads to the precipitation of carbides M3C, M7C3 and M23C6 (M stands for Fe and/or Cr) inside the inserts and to M3C and M7C3 in the region surrounding the inserts. After austempering, a partial dissolution of these latter carbides and transformation of the matrix to ausferrite occur. The wear properties of these materials have been evaluated under reciprocating sliding motion using cylinder-on-disc line contact configuration. The results of the present investigation show a better wear behavior of the reinforced material related to the microstructural changes observed.

15 Ti-Mo alloys were fabricated via powder metallurgy (PM), and microstructure, corrosion 16 and tribocorrosion behaviorsbehaviours of the manufactured alloys were investigated. 17 The microstructure of Ti-(8-16) Mo alloy consisted of α and β phases while Ti-20Mo 18 alloy only contained the β phase. With Mo content increased, the corrosion resistance of 19 Ti-Mo alloys improved, and all Ti-Mo alloys showed better corrosion resistance than as20 cast pure Ti and Ti-6Al-4V. The tribocorrosion resistance of Ti-Mo alloys enhanced 21 firstly and then decreased slightly with Mo increased. Ti-16Mo alloy presented highest 22 tribocorrosion resistance. All these results suggest that PM-fabricated Ti-16Mo alloy is a 23 * Corresponding author: Xin Lu, Tel.: +86 10 6233 3981; E-mail address: luxin@ustb.edu.cn; † These authors contributed equally. promising material for bone-tissue applications. 24

In recent years, there has been growing concern regarding the use of petroleum-based lubricants. This concern has generated interest in readily biodegradable fluids such as vegetable oils. The present work evaluated the rheological and tribological characteristics of sunflower oil modified with silicon dioxide (SiO2) and titanium dioxide (TiO2) nanoparticles as lubricant additives at different concentrations. A parallel plate rheometer was used to evaluate the effects of concentration and shear rate on the shear viscosity, and the experimental data was compared with conventional models. The wear protection and friction characteristics of the oil-formulations were evaluated by conducting block-on-ring sliding tests. Surface analysis-based instruments, including scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and profilometry, were used to characterize the morphology and structure of the worn surfaces. The experimental results showed that the coefficient of f...

The paper presents an analytical multi-scale approach for the modelling of rough surfaces in regard to rubber friction properties. In addition to a fractal description of the micrometer range within the length-scale interval [5-100 m], the macrotexture is considered via the introduction of a second scaling regime for the contact interval [300-1000 m]. As a result, the hysteresis friction coefficient is decomposed in two distinct contributions. The macrotexture mostly contributes to hysteresis friction, while the microtexture is found to be determining for the amount of contact patches, e.g. the real area of contact. Experimental friction tests carried out for carbon black and silica filled S-SBR 5025 on rough surfaces and road pavement under wet conditions point out the relevance of a two-scaling-ranges approach for the modelling of hysteresis friction. Finally, predictions of the load dependent hysteresis friction coefficient are formulated for rough surfaces and give a deeper insight into the physical mechanisms involved in rubber friction properties.

Nickel–MoS2composite coatings were obtained by electrodeposition from a nickel electrolyte containing suspended MoS2particles. The coating composition, morphology, crystalline structure, microhardness, and frictional behavior were studied as a function of MoS2concentration. The results obtained in this study revealed that the codeposited lubricant particles strongly influenced the composite nickel coating properties. It was found that increasing codeposited MoS2decreases the average grain size of nickel crystallites and leads to the formation of clusters which, in turn, lead to rough coatings with a high and variable thickness. The results of tribological response indicated that the reduction of friction coefficient and the improvement of wear resistance were performed until an optimal value of MoS2concentration, which provided the best condition that promoted the tribo-layer stability and maintained the matrix integrity. A comparison of tribological and micromechanical properties b...

TiCN and TiAlN gradient coatings were deposited on the AISI 316L stainless steel substrates by lateral rotating cathode arc (LARC) physical vapour deposition (PVD) technology. Corrosion and tribocorrosion behaviour was studied in 3.5 wt. % NaCl solution. The thickness of coatings was about 3 μm. For both coatings the corrosion potential shifted to more positive values as compared to the uncoated substrate. The corrosion current density decreased for TiCN and TiAlN coatings indicating up to 40 folds higher polarization resistance. The coefficient of friction value of TiCN coating is three times lower and durability is six times higher than that of TiAlN coating under the same tribocorrosion conditions.

Nickel–MoS2composite coatings were obtained by electrodeposition from a nickel electrolyte containing suspended MoS2particles. The coating composition, morphology, crystalline structure, microhardness, and frictional behavior were studied as a function of MoS2concentration. The results obtained in this study revealed that the codeposited lubricant particles strongly influenced the composite nickel coating properties. It was found that increasing codeposited MoS2decreases the average grain size of nickel crystallites and leads to the formation of clusters which, in turn, lead to rough coatings with a high and variable thickness. The results of tribological response indicated that the reduction of friction coefficient and the improvement of wear resistance were performed until an optimal value of MoS2concentration, which provided the best condition that promoted the tribo-layer stability and maintained the matrix integrity. A comparison of tribological and micromechanical properties b...

In this study, the fluid flow together with solid particles has been studied using Computational Fluid Dynamics (CFD). The gas-solid flow (air and sand particles with the size of 150 µm) inside a 76.2 mm diameter pipe with various bend angles including 45, 60, 90, 120, 135, and 180° was modelled at the fluid flow velocity of 11 m/s. The k-ω turbulence model was employed to model the flow turbulence and the E/CRC erosion model have been used to predict erosion rates. The hydrodynamics of the flow, the particles motion as well as the probable erosion regions were predicted. The CFD simulation results showed that increasing the curvature angle increases the erosion rate. While, increasing the pipe diameter, decreases the erosion rate. The maximum erosion rate was predicted at the end part of the curvature for 45 and 60 ° angles, while it was observed in the middle region for 120 and 135 ° curvatures. Finally, the maximum erosion rate for the 180 ° curvature was observed in two regions at the end of the first and second half. Using these results, precautionary considerations for the erosion, and the suitable plans for the repair and maintenance of the equipment can be offered.

The object of this investigation was to determine the effect of lubricant film thickness on the coefficient of friction and on the wear life of solid lubricants. Bonded molybdenum disulphide and bonded graphite were the lubricants tested. Dow Corning's LFW-1 and Falex lubricant tester were the two machines used for testing these lubricants. The lubricants were sprayed on the specimen surface. ll Pretreatment, spraying and curlng were done according to standard or manufacturer's recommended procedures. During the entire research, the procedure for experimentation was followed according to ASTM No. 2625 on Falex and CRC recommendations on LFW-1 machine. It was found that the film thickness lS an important factor in deciding performance of a solid lubricant. The coefficient of friction increases with increase in film thickness for thicknesses in the range tested (0.0017 in. to 0.0007 in.). For a maximum wear life, there is a definite optimum film thickness, above and below which the wear life decreases.

We have studied a historical group of patients who underwent metal-on-metal hip arthroplasty more than 30 years ago. Those retaining their original metal-on-metal articulation (average follow-up 33 years) had an average Harris Hip Score of 75 (range 53–93) and an average Musculoskeletal Tumour Outcome Score of 75 (range 63–90). Those that have been revised (at an average of 22 years) maintain good functional outcome. The original implant is still in situ in five of the 11 survivors (follow-up 26–38 years).Retrieval analysis using a Mitutoya form tracer and an electron microscope demonstrated the self-polishing capacity of the metal-on-metal articulation. The surface roughness (Ra) of the worn articulating surface (Ra 0.05 mm) was smoother than that of the original unworn surface (Ra 0.32 mm). We believe our case series highlights the potential longevity of metal-on-metal articulation.

Mild wear in a rolling-sliding contact may gradually worsen the contact conditions. The probability for surface fatigue will then increase due to changes in the surface topography. This phenomenon has been observed for cam-follower contacts in automotive engines. A simulation model of the wear of a follower based on the principal of single point observation has been developed. The wear is simulated using a modified version of Archard's wear equation. The simulation is carried out in steps, recalculating the pressures as the surface topography gradually changes. The results show good agreement with corresponding worn surfaces. It can be concluded that the simulation method presented here, using a modified Archard's wear equation, can be used to simulate the mild wear in a rolling-sliding contact. This work highlights the importance of including follower rotation in the wear simulation and the use of the single point observation method in the derivation of a wear simulation model.

In turbomachinery, it is well known that tighter operating clearances improve the efficiency. However, this leads to unwanted potential unilateral and frictional contact occurrences between the rotating (blades) and stationary components (casings) together with attendant thermal excitations. Unilateral contact induces discontinuities in the velocity at impact times, hence the terminology nonsmooth dynamics. Current modeling strategies of rotor–stator interactions are either based on regularizing penalty methods or on explicit time-marching methods derived from Carpenter's forward Lagrange multiplier method. Regularization introduces an artificial time scale in the formulation corresponding to numerical stiffness, which is not desirable. Carpenter's scheme has been successfully applied to turbomachinery industrial models in the sole mechanical framework, but faces serious stability issues when dealing with the additional heat equation. This work overcomes the above issues by ...

Hip resurfacing arthroplasty has become a popular alternative to conventional hip surgery. Surface replacements with bearing sizes of 55 mm (n = 5) and 39 mm (n = 5) were tested in a hip simulator for 15 million cycles (Mc). Wear debris was isolated from the serum lubricant and characterized by field emmitting gun scanning electorn microscopy, and ion levels were measured via inductively coupled plasma mass spectroscopy at intervals throughout the test. The 39 mm bearings showed significantly greater bedding in volumetric wear (2.58 mm3) compared with the 55 mm bearings (1.15 mm3). There was no significant difference between the steady state wear rates (1–15 Mc) between the two sizes (0.10 and 0.09 mm3/Mc, respectively); however, this parity only became clear after 7 Mc. The wear debris isolated was oval in morphology with a mean particle size of 28 nm and a range of 9–108 nm. The Co levels measured at 0.13 Mc were significantly greater than at 3.6 Mc for both bearing sizes (10926 p...

Osteoarthritis-oriented synovial fluid (OASF), i.e., that typical of a patient with osteoarthritis, has different physical and biological characteristics than bovine serum (BS), a lubricant widely used in biotribological investigations. Micro-dimpled and diamond-like carbon-(DLC) coated surfaces are key emerging interfaces for orthopedic implants. In this study, tribological performances of dimpled surfaces, with and without DLC coating, have been investigated under both BS and OASF. The friction tests were performed utilizing a pin on a disk tribometer, whereas contact pressure, speed, and temperature were simulated to a 'medium walking gait' of hip joint conditions. The mechanical properties of the specimen and the physical properties of the lubricant were characterized before the friction test. Raman analysis was conducted to identify the coating condition both before and after the test. The DLC-coated dimpled surface showed maximum hardness and residual stress. A DLC-coated dimpled surface under an OASF lubricated condition yielded a lower friction coefficient and wear compared to those of plain and dimpled specimens. The higher graphitization of coated materials with increasing load was confirmed by Raman spectroscopy.

Tribological behavior of two alloyed steels subjected to shot peening was investigated, under dry and lubricated sliding. 36CrNiMo4 and 36NiCrMo16 alloy steels were investigated at block-on-disc sliding testing machine, and three different applied loads (10 N, 30 N, 50 N) and sliding speeds (0.25 m/s, 0.5 m/s, 1 m/s) were observed. Shot peened surfaces were compared to ground ones, from aspects of their micro hardness and friction and wear properties. Microhardness tests were realized for both steel materials, ground and shot peened samples. Shot peening increased hardness of the near surface layers with approximately 10% increase near the top surface, in comparison to ground surfaces. Both friction and wear properties of the investigated steels showed improvement after shot peening, especially under high loads and speeds for dry sliding and low speeds and high loads for lubricated sliding. For all test conditions, 36NiCrMo16 steel showed better wear resistance and frictional characteristics than 36CrNiMo4 steel. Shot peening produced lowering of the friction coefficient, as well as wear rate, in comparison with ground surfaces, in both dry and lubricated sliding and for both materials. Wear tracks exhibited severe abrasive wear, accompanied with adhesive wear, in all test conditions, but in case of lubricated sliding of shot peened surfaces, at the lowest speed and the highest load, wear tracks showed regions with mild wear also. Important result was significantly lower number of cracks, with smaller sizes within wear tracks of shot peened surfaces, in comparison with ground surfaces.

The wear interaction between piston ring and piston groove in a radial piston hydraulic motor was studied in regard to mass loss and changes in form and surface roughness. A specially developed test rig that simulates the tilting movements of pistons at the end of strokes was used in the test. The results show that wear on the piston ring groove can be up to 10 times greater than the wear on the piston ring. For both interacting surfaces, the dominant wear mechanism was mild wear. The results from a factorial design show that the form of the piston groove significantly influences the amount of wear.

Aluminum-based metal matrix composites (MMCs) offer potential for advanced structural applications when high specific strength and modulus as well as good elevated temperature resistance along with light weight are important. In the present work, aluminum alloy-silicon carbide composite (Al-3Mg-10SiC) is developed using the stircasting technique and is subjected to study the wear behavior. Solid particle erosion on Al-3Mg-10SiC was conducted. Implementation of design of experiments (through Taguchi and statistical techniques) in analyzing the erosion behavior of composites is made. The surface morphology is investigated by electron microscopy. The roughness of the eroded surface is measured throughout the course of erosion to study the mechanisms operating during the erosion.

Certain micro-devices require sliding contact between components; micro-engines, micro-motors, micro-gears, and near-contact or contact recording hard disk drives are some examples. In these devices tribological problems--namely friction, wear and stiction-determine device efficiency and lifetime. Newly developed carbon films show ultra low friction (lower than 0.05), low wear coefficient (lower than 10 -8 ), and high contact angle of water (higher than 85 degrees). This film has very low adherent property that results in ultra low friction and high contact angle. The hardness and elastic modulus are lower than H-DLC but the ratio of hardness to modulus is similar to values for H-DLC that results in low wear rate. Even though these carbon film has low hardness (2 to 10 GPa), it can be used as a protective layer in micro-devices because the X applied load is very light and contact area is large in micro-device applications. A new oscillating compliant beam method was used to measure friction and wear.