190,555 research outputs found
Running-in wear modeling of honed surface for combustion engine cylinder liners
No full textThe texture change during running-in alters the performance and efficiency of a tribo-mechanical system. During mass production of cylinder liners, a final finishing stage known as ‘‘plateau honing’’ is commonly added to reduce the running-in wear process of the liner surface. The majority of researchers think that this operation improves the engine efficiency and decreases oil consumption. It was believed that there are close links between the surface topography of honed cylinders change and their wear resistance during running-in. However, these interactions have not yet been established. Some running-in wear models were developed in the open literature to predict topographical surface changes without considering the running-in conditions. The present paper thus investigates the various aspects of the wear modeling that caused running- in problems in honed surfaces and its implications on ring-pack friction performance. To illustrate this, plateau honing experiments under different conditions were first carried out on an instrumented vertical honing machine. The plateau honing experiments characterize the surface modifications during running-in wear of cast-iron engine bores using advanced characterization method. Based on the experimental evidence, a running-in wear model was developed. Finally, a numerical extension of the developed model was applied to solve the Reynolds equation by taking into account the real surface topographies of the engine bore. This enables us to predict realistic friction performance within the cylinder ring-pack tribosystem
A new approach to numerical characterisation of wear particle surfaces in three-dimensions for wear study
No full textIn the wear and tear process of synovial joints, wear particles generated and released from articular cartilage within the joints have surface topography and mechanical property which can be used to reveal wear conditions. Three-dimensional (3D) particle images acquired using laser scanning confocal microscopy (LSCM) contain appropriate surface information for quantitatively characterizing the surface morphology and changes to seek a further understanding of the wear process and wear features. This paper presents a new attempt on the 3D numerical characterisation of wear particle surfaces using the field and feature parameter sets which are defined in ISO/FDIS 25178-2. Based on the innovative pattern recognition capability, the feature parameters are, for the first time, employed for quantitative analysis of wear debris surface textures. Through performing parameter classification, ANOVA analysis and correlation analysis, typical changing trends of the surface transformation of the wear particles along with the severity of wear conditions and osteoarthritis (OA) have been observed. Moreover, the feature parameters have shown a significant sensitivity with the wear particle surfaces texture evolution under OA development. A correlation analysis of the numerical analysis results of cartilage surface texture variations and that of their wear particles has been conducted in this study. Key surface descriptors have been determined. Further research is needed to verify the above outcomes using clinic samples
A study of the wear process related to twin-screw extruders
No full textExtruders are used in a wide range of process industries and high reliability is essential if cost
effective manufacturing is to be maintained. A critical part of twin-screw extruders is the barrel
that must withstand many different wear and corrosion environments depending on the end user.
For many applications the extruder barrel is a critical component and it is essential that it performs
in a predictable manner, providing the necessary design life-time.
This project has addressed these aims by considering the wear/corrosion behaviour of current and
potential extruder barrel materials from which a life prediction model has been developed.
A wide range of engineering materials has been evaluated in the laboratory for abrasive wear
resistance using a dry sand abrasive wear test according to ASTM G 65-93. An appraisal of the
tests and the applicability of the results to the in-service conditions of an extruder has lead to
further testing for abrasion and abrasion-corrosion resistance of four materials, namely Mild Steel,
440C, N18 and N18+5%TiC+5%TiN.
Plastic deformation was the main feature of the damaged surfaces in the form of ploughing which
has been modelled in terms of a low-cycle fatigue process. The relative hardness between material
and abrasive was found to be an important parameter in controlling the rate of material removal.
It has also been shown that the synergistic effect of abrasion-corrosion results in an accelerated
material removal rate.
The information from these tests has been used to develop a model of the wear of extruder barrels
by abrasive particles. It is shown that there is a correlation between the particle size, wear debris
size and wear groove size distributions. From a knowledge of the particle flux, the particle size
distribution and the loading conditions, metal recession is predicted based on a low-cycle fatigue
process. The wear rates for a wide range of Fe- and Ni-based materials are predicted to better
than a factor of two.
When corrosion is also present, the mechanism of metal recession depends on whether passive
surface films are formed. For the Fe-based materials which exhibit direct dissolution of material,
the wear/corrosion rate can be estimated by combining the metal loss rate under pure wear and
pure corrosion conditions only. For the Ni-base alloys, thin passive films form in all the aqueous
environments studied and corrosion rates are extremely low. However, during abrasive wear the
passive films are removed and the overall metal recession rate is a combination of metal loss due
to abrasive wear of the substrate and the continual formation and removal of surface passive films
Predicting wear of UHMWPE: decreasing wear rate following a change in direction
No full textComputational tools are emerging as design tools for the development of total joint replacement with improved wear performance. The current wear models of polyethylene assume that wear is linearly proportional to sliding distance; however, it is hypothesized that the wear rate varies and is higher near a change in direction, but diminishes with continued unidirectional sliding, which eventually exhibits negligible wear. Our goals were to (1) reveal the presence of a variable wear rate in polyethylene; (2) identify the sliding distance required to reestablish unidirectional sliding subsequent to a change in sliding direction. The wear of polyethylene was evaluated in pin-on-disk testing for several different sliding distances (0 mm, 1 mm, 2 mm, 5 mm, 10 mm, and 100 mm) after a 90° change in direction. The results indicate the wear rate immediately following the change in direction is high, but with continued linear sliding the wear rate appears to drop to near zero--returning to the low wearing condition of unidirectional sliding. Furthermore, this transition appears to occur nonlinearly below 5 mm from the change in direction. While more studies are required to explore other paths and uncover the underlying mechanisms, these results should aid the development of computational tools for the design of advanced joint replacement
Degradation modes and tool wear mechanisms in finish and rough machining of Ti17 Titanium alloy under high-pressure water jet assistance
No full textThis article presents the results of an experimental study on the Ti17 titanium alloy, which was carried out to analyze tool wear and the degradation mechanisms of an uncoated tungsten carbide tool insert. Two machining conditions, roughing and finishing, have been studied under different lubrication conditions. The experimental procedure included measurement of the cutting forces and the surface roughness. Different techniques have been used to explain the tool wear mechanisms. Distribution maps of the elemental composition of the titanium alloy and the tool inserts have been created using Energy Dispersive X-ray Spectroscopy (EDS). An area of material deposition on the tool rake face, characterized by a high titanium concentration has been observed. The width of this area and the concentration of titanium, decrease when increasing water jet pressure. The study shows that wear mechanisms, with and without high-pressure water jet assistance (HPWJA) are not the same. For example, for the roughing condition using conventional lubrication, the temperature in the cutting area becomes very high, this causes plastic deformation of the cutting edge which results in its rapid collapse. By contrast, this problem disappears when machining with HPWJA. In addition, the evolution of flank wear (VB) is stabilized with high-pressure lubrication. In this case, the most critical degradation mode is due to notch wear (VBn) leading to the sudden rupture of the cutting edge.Région Pays de la Loir
The tribological and wear properties of carbon-graphite composites
No full textA range of carbon-graphites with differing properties has been evaluated for wear resistance. These include carbons with a high degree of graphitic order (natural and synthetic graphite), those with little or no such order (pitch bonded cokes, glassy carbons) and impregnated grades. Testing has been carried out using abrasive wear, dry sliding wear, particle erosion, slurry erosion, cavitation erosion and the corresponding wear rates have been related to the bulk properties of the different materials. In all tests; hardness, elastic modulus, porosity and the presence of fillers were found to influence the wear rates of the various grades. Maximum wear rates were consistently observed with the softer, more porous unfilled carbons
Sliding wear of a-C:H coatings against alumina in corrosive media
No full textThis paper reports the results obtained from the study of friction and sliding wear in two corrosive solutions of an a-C:H coating deposited on 316L stainless against an alumina ball, employed as static counter part. Calculations of the values of the von Mises stresses developed at the coating–substrate interface, as soon as the ball touches the coated sample, and how this state of stress influences the response of the coated system under the corrosion environment, are presented and discussed. The results obtained from these calculations, as well as from the experiments conducted in the present research, are compared with other experiments published in the literature, where a-C:H coatings deposited on different substrates and with different coating architectures were tested in similar corrosive media. It has been determined that in those systems, where the von Mises stress in the coating, found in the vicinity of the interface, exceeds the threshold value of approximately 370MPa, coating failure with spallation will take place, regardless of the substrate nature on which this coating has been deposited. From this analysis it has been concluded that the coating yield strength is of utmost importance in conferring the a-C:H coated system there quired stability in a corrosive solution
Prediction of Sliding Wear of Artificial Rough Surfaces
No full textWhen two surfaces are brought in contact, deformation takes place at asperity level. The local pressure distribution and deformation of the contacting surfaces are importance with respect to wear. This paper describes a wear model to predict the wear of rough sliding contacts. The wear model is based on the general Archard’s wear equation in combination with finite element analysis (FEA). In this paper the roughness is represented by uniformly distributed spherical asperities. The proposed model, FE in combination with Archard’s wear law, has proven to be a powerful tool in predicting wear of rough surfaces
Effect of surface finishing such as sand-blasting and CrAlN hard coatings on the cutting edge’s peeling tools’ wear resistance
No full textThe authors would like to thank IonBond (Chassieu-France) who made the sand-blasting treatments and the Regional Council of Burgundy and CTBA (Wood and Furniture Technical Centre) for their financial support.The aim of this study is first to define the effect of a surface finishing such as sand-blasting on the geometry of a wood cutting tool and its wear resistance. In addition, the effectiveness of surface coatings like CrAlN deposited by physical vapor deposition (PVD) technique on conventional and sand-blasted cutting edges was studied. A reference tool and different sand-blasted ones were tested by micro-peeling of beech in a laboratory. Microscopic observations, cutting forces measurement and cutting wear tests were carried out to quantify the behavior of these tools. The results obtained showed that the artificial wear by sandblasting leads to an increase in the wear resistance and coating effectiveness, and completely changes the type of damage done to the tools. The sand-blasting application combined or not with CrAlN coating showed an improvement in the wear resistance of the tools and a modification of the forces during the peeling process. The effectiveness of the CrAlN layers was improved thanks to the sand-blasting treatment and then the duplex ones performed better.Regional Council of Burgundy CTBA (Wood and Furniture Technical Centre
Metal ceramic wear mechanisms
No full textSliding wear of metal-on-ceramic, ceramic-on-metal, and
ceramic-on-ceramic have been investigated using a tri-pin-on-disc machine. A technique has been developed for thin foil preparation for transmission electron microscopic examination perpendicular to the wear surface. The role of transformation toughening in the wear behaviour of zirconia ceramics has been investigated. In addition, the role of
high strain deformation in a steel surface has been evaluated.
The wear factor of 316L stainless steel pins worn against a
zirconia disc was found to decrease as the load was increased, believed to be associated with metal oxide formation. TEM of the stainless steel revealed a worn surface which consisted of a mechanical mixture
of metal oxide and heavily deformed metal. Deformation of the metal had occurred by shear banding with a microstructure similar to that observed in rolled specimens, although the texture formed was a wire
texture rather than a rolling texture. The crystallite size was found to decrease towards the surface, demonstrating that the shear stress was a maximum at the surface. The shear bands at the surface had always been formed by the passage of the last asperity indicating that contact was plastic over the load range 6-60N/pin. The majority of
wear occurred by transfer resulting from plastic overload, although a contribution to the material loss was made by metal extruded off the end of the pin as a result of the high strains. The depth of deformation correlated closely with the wear volume.
The wear of the zirconia discs was found to be dominated by metal transfer. With Mg-PSZ, transformation occurred cooperatively in crystallographically determined bands. Microcrack coalescence led to preferential wear in these bands. However, with a Y-TZPdisc transformation appeared to have been responsible for widespread surface fracture.
The wear of zirconia pins against a bearing steel disc gave limited metal transfer. Very little transformation of tetragonal to monoclinic was observed. However, milder forms of the transformation related wear mechanism did occur. Zirconia had formed a solid solution with the
iron oxide, leading to the conclusion that the wear mechanism was tribochemically based.
TZP worn against a ZTA disc showed evidence of very high
temperature rises at the interface. The surface layer was amorphous and contained a mixture of alumina and zirconia suggesting that melting had occurred at the interface during sliding. At a depth of O.5pm. the surface consisted of heavily elongated tetragonal grains, with a low
dislocation density, indicating a strain of at least 1.7. At a depth of 2-4pm a layer of monoclinic was found. There was evidence that the stresses imposed by friction extended to at least 8-10pm from the surface.
TZP containing 20vol% SiC whiskers gave exceptionally low wear rates when worn against a ZTA disc. The greater wear resistance is believed to be a result of the improved load bearing capacity and of the higher thermal conductivity. It is clear that the poor thermal conductivity of zirconia dominates its tribological behaviour. Temperature generation was high enough to substantially reduce the
driving force for transformation of the tetragonal to monoclinic, with a high enough temperature for plastic' deformation where a low thermal conductivity counterface was used. Where transformation occurred, its effect was to increase the wear rate
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