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This paper presents the investigation of dielectric analysis of degraded stator bars by Polarization and Depolarization Current (PDC) measurement. The stator bars obtained from the 30-year in-service synchronous machine were divided into two groups. The first group was the unmodified stator bars. The second group was the simulated degradation stator bars which were composed of the thermal stress stator bars, conductive tap abrasion stator bars, multiple air cavity stator bars, multiple oil filled stator bars and multiple water filled stator bars. PDC test experiment was performed with the stator bar samples. PDC test results were analyzed in time domain and in frequency domain with the derived parameters i.e. R dc , real and imaginary part of complex capacitance, C ratio, conduction loss factor and polarization loss factor. It was found that PDC shapes obtained from the conductive tape abrasion stator bar and multiple water filled cavity stator bar were clearly different from that of the unmodified stator bar. For other case studies, the derived parameters showed the usefulness in analysis the degraded stator bar characteristics. For example, the increase in the imaginary capacitance and conduction loss factor can be observed from most cases of degraded stator bar test results.

Al matrix composites reinforced with ceramic particles show excellent wear resistance and have great potential to replace convectional materials in many fields. In this paper, a high proportion (∼ 60%) of large ZrO2 particles reinforced Al matrix composites were manufactured by a high pressure infiltration method. The tribological behavior of the Al/ZrO2 composite and non-reinforced Al were investigated and compared using a GCr15 ball-on-disc apparatus under dry sliding wear condition. The microstructure, elements distribution and wear track morphology were analyzed to understand their tribological behavior and wear mechanisms. The wear rate of Al is 2.0 × 10−3 mm3 N−1 m−1, while the wear rate of Al/ZrO2 composite is only 0.15 × 10−3 mm3 N−1 m−1. The experimental results showed that Al is a combined wear mechanism of adhesive wear and abrasive wear. It also proved that the high proportion of large ceramic particle reinforced composite is stable under low load wear condition. The ceramic particles were firmly embedded in the Al matrix, and no ejection or removal of the particles was observed. The results showed that the wear mechanism of this composite is mainly three body abrasion in the stable wear stage.

The dry sliding wear behavior of A7075 based composites strengthened with particulates of ZrB2 was examined using the pin-on-disc device. The composites were synthesized by reinforcing different weight % (5, 10, and 15) of the ZrB2 using a stir casting technique followed by hot extrusion. The dry sliding wear resistance is optimized under varying conditions of sliding velocity, sliding time, and load. The sample's worn-out surfaces were examined using scanning electron micrographs to obtain the composites' wear mechanism. Delamination, abrasion adhesive modes of deformation were observed. The wear parameters were optimized with Grey relational analysis (G.R.A.) and ANOVA techniques and obtained the optimal combination of input parameters.

The influences of different compositions of the reinforcement particles on phase compositions, microstructure characteristics, corrosion resistance, and tribological behavior of the AZ31 magnesium matrix composites (MMCs) were investigated. The defects-free AZ31 MMCs reinforced by Al, Al–Si and Al–SiC composite particles were prepared using friction stir processing (FSP). The phase composition of the MMCs is the same as that of the as-received AZ31 alloy and still consists of α-Mg solid solution and β-Al12Mg17 intermetallic. In addition to an obvious decrease in the average grain sizes, the sizes and distributions of the β-Al12Mg17 intermetallics in the MMCs are also significantly decreased and homogenized. The MMCs reinforced by Al–SiC composite particles exhibit maximum self-corrosion potential, while the MMCs reinforced by Al–Si particles present minimum self-corrosion current. The maximum self-corrosion potential and minimum self-corrosion current of the MMCs are −1.19 V and 4.37 × 10−5 A, respectively. In addition to an obvious enhancement in mean microhardness, the average friction coefficients of all the particles reinforced MMCs are higher than that of the AZ31 alloy, but the mass loss of the Al–Si composite particles reinforced MMCs is less than that of the AZ31 alloy. The wear mechanism of the AZ31 alloy is severe abrasion and adhesion, while the MMCs reinforced by Al–Si particles are mild abrasion.

Currently, there is a rising demand to develop composite materials with outstanding tribological properties along with excellent thermal-mechanical properties for harsh tribological applications. In view of this demand, the tribological behaviour of spark plasma sintered (SPS) nano-alumina (∼150 nm)-based composites reinforced with 10, 20 and 30 wt.% uncoated and nickel-coated cubic boron nitride (cBN) particles was evaluated using a ball-on-disc configuration against three different counterface materials (WC, Si3N4 and Al2O3) under dry sliding conditions. A variety of techniques were used to evaluate the phase composition and to study the dispersion, wear behaviour and wear mechanisms. The nano-alumina composites exhibited improved wear resistance and coefficient of friction (COF). These results were attributed to the unique combination and uniform dispersion of the reinforcing particles within the composites. Moreover, Ni-coated cBN particles displayed high wear resistance, primarily due to the excellent interfacial bonding provided by the nickel coating. The wear resistance of the sample reinforced with 30% cBN-Ni was improved by at least 85%. The wear mechanisms involved during sliding wear were abrasion, matrix grain pullout (dislodgement of matrix material), microcracking, chipping, and tribolayer formation. Keywords: Alumina nanocomposites, Cubic boron nitride, Microstructural analysis, Wear, Tribophysics

AISI 4340 and AISI 4140 are normally used for different structural applications in quenched and tempered state due to their high strength, high abrasion and fatigue resistance but they lack toughness. Presence of dual phase microstructure such as ferrite-bainite and ferrite-martensite in steels have been reported to improve toughness but at the cost of strength. It is believed that development of bainite-martensite dual phase microstructure may help in obtaining better combination of mechanical properties. In this research work, development of bainite-martensite dual phase microstructure has been carried out at different austempering temperatures and times to study microstructure evolution and its effect on mechanical properties. Microstructural characterization of samples was carried out by scanning electron microscope (SEM) whereas mechanical characterization was done by performing hardness and impact testing. Development of dual phase bainite-martensite microstructure has shown to impart better combination of strength and toughness. In comparison with AISI 4140 steel, AISI 4340 provided better combination of hardness and toughness in the austempered state. It has been observed that decrease in the austempering temperature helped in obtaining better combination of hardness and impact strength in both grades of steels due to formation of lower bainite martensite dual phase microstructure at lower temperature. Keywords: AISI 4340, AISI 4140, Austempering, Bainite, Martensite

This paper focuses on the numerical simulation of ice abrasion induced by unbreakable ice floe. Under the assumption that unbreakable floes behave as rigid body, the Discrete Element Method (DEM) was applied to simulate the interaction between a fixed structure and ice floes. DEM is a numerical technique which is eligible for computing the motion and effect of a large number of particles. In DEM simulation, individual ice floe was treated as single rigid element which interacts with each other following the given interaction rules. Interactions between the ice floes and structure were defined by soft contact and viscous Coulomb friction laws. To derive the details of the interactions in terms of interaction parameters, the Finite Element Method (FEM) was employed. An abrasion process between a structure and an ice floe was simulated by FEM, and the parameters in DEM such as contact stiffness, contact damping coefficient, etc. were calibrated based on the FEM result. Resultantly, contact length and contact path length, which are the most important factors in ice abrasion prediction, were calculated from both DEM and FEM and compared with each other. The results showed good correspondence between the two results, providing superior numerical efficiency of DEM. Keywords: Ice abrasion, Unbreakable ice floe, Discrete element method, Finite element method, Soft contact, Viscous Coulomb friction

Gan HaShlosha national park contain two ponds of running brackish water. Dams were built on the ponds in the 80 s. Some masonary from the dams, as well as other underwater structure, have deteriorated. Mortar and concrete of the same dams is un-deteriorated. Concrete in tunnel, built during the 50’s on the same location, is also deteriorated. The depth of deterioration was quantified. Rebound of involved materials was measured by Schmidt hammer. Deterioration due to abrasion was negated. Observation shows high density of the snail Melanopsis praemorsa on deteriorated surface. The evidence lead to the conclusion that the snails are the cause for deterioration. This deterioration may be severe and fast, relatively to expected useful life of masonry structure, but is restricted to specific environments.

Wear control, which relies on understanding the mechanisms of wear, is crucial in preserving the life of mechanical components and reducing costs. Additive manufacturing (AM) techniques can produce parts with tailored microstructure, however, little has been done to understand how this impacts the mechanisms of wear. Here we study the impact of initial grain arrangement and crystal orientation on the wear mechanisms of austenitic stainless steel (SS) in dry sliding contact. Specifically, the anisotropic sliding wear behavior of as-built, AM-ed 316L SS is compared against annealed, wire-drawn counterparts. We describe, in-detail, how the sliding wear mechanisms of delamination, abrasion, oxidation, and plastic deformation are attributed to the initial surface microstructure under different loading conditions using a number of techniques. This new understanding sheds light on how different AM-induced microstructures affect wear, thereby allowing for better utilization of this technology to develop components with enhanced wear properties.

Ti-6Al-4V components are widely used in the aircrafts engine or airframe parts, as landing gears or wing boxes, where the wear by unidirectional sliding or oscillating relative motion is one of the most recurrent damage processes. Recently, the deposition by Cold-Spray (CS) has been revealed as a promising alternative to repair these damaged components, increasing their useful time and decreasing the maintenance costs. Consequently, the wear resistance of the coatings could be improved by optimizing the CS processing parameters. In this work, oscillating and unidirectional sliding wear tests were planned to determine the wear resistance of Ti-6Al-4V coatings deposited onto substrates of the same Ti alloy by CS. The coatings were sprayed using two different values for two of the main spraying parameters. First, values of 800 °C and 40 bars were used for the process gas temperature and pressure, respectively, which are widely used spray conditions by researchers; and secondly, values of 1100 °C and 50 bar were used for both parameters, respectively. Unidirectional sliding and oscillating wear tests were performed and the effect of the testing temperature was studied. The main wear mechanisms in room temperature (RT) were abrasion and adhesion, while oxidation was also distinguished during the high temperature tests. In addition, the wear processes were more severe during the unidirectional sliding tests as compared to the oscillating tests. The results showed that the coatings deposited using the first spraying conditions presented a poor wear resistance as compared to the substrate and thus they are not adequate for repairing purposes. However, the coatings deposited using higher values of gas temperature and pressure showed a comparable, or even better, wear resistance to that of the substrate under oscillating movement.

The development of wear resistant materials for drill-bit inserts are of primary importance for efficient percussive drilling in hard abrasive rock. To speed up the development of enhanced wear resistance materials, the laboratory tests are fundamental to evaluate the material performance before proceeding to the in-field drilling test which is labor-intensive and costly in time and resources. The current work aims to perform a comparative study of the wear resistances of drill-bit inserts intended for rotary-percussive drilling. Three laboratory testing methods were adapted to evaluate the abrasive sliding wear and abrasive impact wear which are the main wear components in rotary-percussive drilling. The standard abrasion value (AV) test and the standard LCPC (Laboratoire Central des Ponts et Chaussees) test which were originally developed to study the rock abrasivity, are adapted to study, respectively, the abrasive sliding wear and abrasive impact wear of drill-bit inserts. The disintegrator abrasive impact wear test was adapted to study the effect of impact velocity on impact abrasive wear. The testing setups were modified to enable testing drill-bit inserts as specimens. The drill-bit insert materials were selected to represent various cemented carbide microstructures including five WC-Co grades which differ by the volume fraction of Co and the grain size of WC, and one diamond enhanced insert. All drill-bit inserts were tested in dry condition against Kuru grey granite which is a homogenous rock and well suited as a reference in connection with hard rock testing. The wear measurements were evaluated with respect to the effects of drill-bit insert material and microstructure. The abrasive sliding wear test and abrasive impact wear tests exhibit similar behavior related to the effects of average grain size of WC and volume fraction of Co on the wear measurements for the investigated WC-Co inserts. In all performed tests, the weight losses of WC-Co inserts increased with the volume fraction of Co and average grain size of WC. The abrasive impact wear tests performed on diamond enhanced insert showed a significant improvement of the impact wear resistance by adding diamond particles. Though the removal of the composite matrix between diamond particles was observed, the diamonds particles were providing an additional protection for the composite matrix which explain the lower mass losses of diamond enhanced insert compared to WC-Co inserts. However, an initial stage of decohesion at the diamond/WC-metallic binder interface were observed indicating possibilities of diamond removal at more higher impact energy.

A high friction coefficient and a low wear rate of contacted surfaces are essential elements to friction pairs between the stator and the rotor in ultrasonic motors. It has been shown that surface textures have a significant effect on improving the tribological performance of friction pairs. In this paper, microgroove arrays are introduced to the stator surface for improving the tribological performance of friction pairs between the stator and the rotor in ultrasonic motors. Microgrooves were fabricated on a phosphor bronze surface by through-mask electrochemical micromachining (TMEMM). Parameters, namely, the electrolyte inlet pressure, applied voltage, pulse duty cycle, and frequency, were varied to investigate their influences on the dimensions and morphology of the microgrooves. Results showed that the width and depth of the microgrooves were strongly affected by the applied voltage and frequency, while the morphology of the microgrooves was dependent on the electrolyte inlet pressure and the pulse duty cycle. Compared with a smooth surface, the friction coefficient increased from 0.245 to 0.334 and less abrasion was obtained when a surface was textured with microgrooves of which the width and depth were 185.6 and 57.6 μm, respectively. Microgroove arrays might play an important role in enhancing the performance of ultrasonic motors. Keywords: Friction coefficient, Microgrooves, Through-mask electrochemical micromachining, Ultrasonic motors, Wear

This paper describes an experimental study on the fretting behaviors and tribological mechanism of interface between carbon fiber reinforced polymer (CFRP) composites and titanium alloy in composite interference-fit joints under service condition. A ball-on-flat configuration was employed in the fretting tests where the effect of fiber orientation, ambient temperature, surface treatment and interface condition were evaluated. The coefficients of friction (COFs), 3D surface morphologies and microstructures of worn scars were presented to characterize corresponding fretting mechanisms. An obvious tribological anisotropy was observed in the CFRP specimens where the longitudinal surface possessed much smaller COFs and less wear damage than the normal surface. The wear damage and anisotropic properties can be reduced to a certain extent by surface treatment through improving wear resistance or serving as solid lubricant respectively. The fretting behaviors also show strong temperature dependence. The increasing temperature exaggerates deformation in longitudinal surface and aggravates abrasion in normal surface by softening matrix resin. Wet service condition contributes to reducing COF and wear owing to the formation of a tribofilm on the interface. Keywords: Fretting, CFRP composites, Coefficient of friction, Surface morphology, Service condition

Revolving heat pipe grinding wheel (RHPGW) has been proposed to realize dry grinding of difficult-to-machine materials. The RHPGW has a variable wall thickness with a thinnest part of 1.5 mm along the width direction. This investigation aims at developing an induction brazing method for RHPGW in order to prevent deformation, improve the inter-chip space, and achieve uniform grit distribution. Simulations were performed on FLUX to design a suitable induction coil and the related working parameters. Ag-Cu-Ti alloy and CBN grains were applied in the brazing experiments. The brazing temperature, geometric accuracy, microstructure and the compounds at the matrix/Ag-Cu-Ti/CBN interface were analyzed along the width direction, good consistency was achieved for different positions. Further validation experiments were carried out by dry grinding of Inconel 718 and compared with the results ground by electroplated RHPGW. Lower grinding forces and higher service life was obtained with the induction brazed RHPGW. Abrasion wear was found to be the main failure mode for the brazed grinding wheel, while both significant adhesion and wear were the failure forms for the electroplate one. Keywords: Induction brazing, Revolving heat pipe grinding wheel, Geometric accuracy, Brazing temperature distribution, Brazing quality

peer-reviewed This study investigates the effect of high speed cutting on the crater wear behaviour of PCBN tools in continuous cutting. Turning tests were performed using two PCBN grades, one high CBN content (PCBNH) and one low CBN content (PCBN-L) at two cutting speeds (150 and 300 m/min). The tool life of each grade at both speeds was determined and the associated crater wear progression charts were generated. Examination of the wear surfaces in the SEM was used to study the wear mechanisms. In order to measure crater depth and evaluate the effect of wear on the tool geometry, the cross-section profile of each cutting edge was replicated. As expected, PCBN-L was found to be the most suitable grade for continuous cutting of hardened steel. While it was the most wear resistant grade, it is also the most sensitive to cutting speed. Flank and crater wear increase with increasing cutting speed. The wear behaviour of PCBN-H is very different; flank wear is significant but is not so sensitive to cutting speed. Crater wear decreases with increasing cutting speed. The results of the machining tests in conjunction with analysis of the wear scars suggest that the wear behaviour of PCBN-L is dominated by chemical wear and diffusion with adhesion and abrasion making a secondary contribution. This ranking is reversed for PCBN-H where abrasion and adhesion are the primary wear mechanisms but during high speed cutting, plastic deformation also contributes to the wear process.

A comprehensive study of progressively ground/polished 3Y-TZP was performed with the aim of better understanding the mechanisms driving the microstructural modifications observed after such procedures, and identifying the processing parameters leading to optimal microstructures (i.e. ageing-protective and damage-free). Gradually ground/polished surfaces were produced, yielding four different topographies of increasing roughness (grades 1–4) and two different textures (unidirectionally, U, and multidirectionally, M). Phase transformation, microstructure and residual stresses were investigated by means of advanced characterization techniques. It was found that low-roughness mildly ground/polished specimens (i.e. 2-M/U) presented a nanometric layer with the ageing-related protective features generally associated with coarsely ground specimens. A lower limit for grain refinement in terms of surface abrasion was also found, in which partial recrystallization took place (i.e. 1-M/U). A mathematical relation was established between average surface roughness (Sa), monoclinic volume fraction (Vm) and surface compressive residual stresses, demonstrating that if the processing parameters are controlled, both Vm and residual stresses can be predicted by the measurement of Sa.

Wear in train and rail components in the Barcelona subway system includes brake pads, catenary wires, wheels, railways, and motor brushes. These components were characterised to evaluate their contribution to ambient particulate matter (PM) levels in two platforms (conventional F-L3 and new S-L9). The observed chemical compositions of these components were used to interpret the mineralogical, chemical, and leachability patterns of subway platform particulate matter (PM). The use of sulphides such as molybdenite (MoS 2 ), pyrite (FeS 2 ), stibnite Sb 2 S 3 ) rich in toxic elements such as in Cu, Ni, As, Hg, Cd, and Pb and abrasives such barite (BaSO 4 ) and zinzite (ZnO) in the brake pad composition, the composition of the catenary rich in Cu (98% metallic-Cu) with traces of Hg and that of the wheel/rail (98% metallic-Fe) with traces of As results in the production of fine PM particles of As, Hg, Cu, and Sb in ambient air PM in platform as a consequence of the abrasion/friction and sparking processes. The temperature reached in the aforementioned processes give rise to fine condensed and water-soluble As species (most likely As 2 O 3 and As 2 O 5 ). Moreover, the stibnite (Sb 2 S 3 ) Hg-rich lateral brake pads used in L9 also contribute to fine and relatively soluble Sb and Hg oxides. Sulphide-rich brake pads significantly increase and change the occurrence mode of the Zn, Cu, Mn, Cr, Pb, and Ni present in PM by oxidation of brake-bearing metal sulphide to relatively water-soluble sulphate and oxide species. These changes in the mode of occurrence and speciation of elements in the PM of subway platforms points to the need for in-depth PM speciation studies, as well as the need for substituting conventional friction materials with low-metal materials—such as graphite pantographs/catenaries and rubber wheels and low toxic sulphides in brake pads—to reduce exposure to metals during subway commuting. © 2019, This work was supported by the Spanish Ministry of Economy and Competitiveness, and FEDER funds within the I + D Project CGL2012-33066 (SUBWAY) and the IMPROVE LIFE project (LIFE13 ENV/ES/ 000263). Support is also acknowledged to Generalitat de Catalunya 2014 SGR33.

In this study, asbestos-free automotive brake pads produced from palm kernel fibers with epoxy-resin binder was evaluated. Resins varied in formulations and properties such as friction coefficient, wear rate, hardness test, porosity, noise level, temperature, specific gravity, stopping time, moisture effects, surface roughness, oil and water absorptions rates, and microstructure examination were investigated. Other basic engineering properties of mechanical overload, thermal deformation fading behaviour shear strength, cracking resistance, over-heat recovery, and effect on rotor disc, caliper pressure, pad grip effect and pad dusting effect were also investigated. The results obtained indicated that the wear rate, coefficient of friction, noise level, temperature, and stopping time of the produced brake pads increased as the speed increases. The results also show that porosity, hardness, moisture content, specific gravity, surface roughness, and oil and water absorption rates remained constant with increase in speed. The result of microstructure examination revealed that worm surfaces were characterized by abrasion wear where the asperities were ploughed thereby exposing the white region of palm kernel fibers, thus increasing the smoothness of the friction materials. Sample S6 with composition of 40% epoxy-resin, 10% palm wastes, 6% Al2O3, 29% graphite, and 15% calcium carbonate gave better properties. The result indicated that palm kernel fibers can be effectively used as a replacement for asbestos in brake pad production.

Hard turning has been applied in a wide range of mechanical components based on ferrous materials. The application of these components is a function of mechanical properties and microstructure – that also has manufacturing process influences, i.e., cutting mechanism. This research aims to discuss the tool wear level and the correlation with the wear mechanisms in turning with PCBN tools, which deals with three steel alloys (AISI 4340, AISI 52100 and AISI D2) and considers six levels of hardness (on the interval from 35 to 60 HRC), applying the novel three-dimensional wear parameters based on Focus Variation Microscope (FVM) to wear evaluation. Considering the wear parameters that represent the amount of material removed from the tool (WRM) and tool affected area (WAA), tool wear intensity and abrasion wear mechanisms have a decreasing trend with the increase of hardness in the range of 35–50 HRC. Above 50 HRC, however, there is a tendency of increased tool wear intensity when steel hardness is increased. The fraction volume of carbides in the steel microstructures intensifies the abrasion wear mechanism. The adhesion wear mechanism showed a reduction with an increase of the steel's hardness – identified by wear parameters WAM (adhered material volume on the tool). Based on crater wear formation, the diffusion wear mechanism had an inverse behavior when compared to adhesion. Better results concerning tool wear can be achieved when turning steels with 50 HRC. It was evidenced that the three-dimensional wear parameters applied open new possibilities to understanding complex and specific phenomena occurring in machining processes, particularly in the machining of hardened steels.

Pantograph and overhead contact line contact point have three electric contact forms: static, sliding, and open–close. For static electric contact of a pantograph and contact line, the major problem is temperature rise at the contact point; for sliding electric contact, it is friction abrasion and lubrication of the contact material; for open–close electric contact, it is electric spark and arc. Arc can maintain continuity of current collection for an electric train, but will cause hot erosion to the pantograph and overhead contact line system equipment and electromagnetic interference to the environment. The strip and contact wire have mechanical, chemical, and electrical abrasions, resulting in abrasion of contact material.

This multi-disciplinary research paper should help solar power plant developers to perform an advanced site assessment in arid locations where the annual irradiance levels are high, but significant quantities of airborne sand and dust increase the risk of optical energy losses due to extinction, soiling, erosion damage (also known as abrasion), etc. Due to these effects sandstorms have a direct consequence on the operation and maintenance (O&M) costs. The work presented in the following characterizes airborne sand and dust material and later focuses on the resulting erosion effects. Some important meteorological and geological parameters for sandstorm occurrence and the resulting erosive damage on glass materials by impacting windblown material are extracted from literature. The respective parameters have been measured at two locations in Morocco (Zagora and Missour). After evaluation of wind and humidity data and a comprehensive soil analysis, the erosion risk was estimated to be higher in Zagora. The specular reflectance loss of exposed silvered-glass reflectors of 5.9% in Zagora and 0.8% in Missour after 25 months of exposure verified this estimation. Additionally, a specular reflectance analysis on a mirror sample that has been exposed for nine months in Kuwait is shown. On that sample specular reflectance losses of more than 40% were measured. A checklist with seven items is given in the conclusion to help solar plant developers to evaluate the risk of component aging due to sand storm erosion.

Particulate reinforcing phases in metal–matrix composites (MMCs) can provide resistance to both sliding wear and abrasion by protecting the softer metallic matrix. In this review, the wear behavior of particulate MMCs in dry and lubricated sliding, and also under conditions of abrasive wear, is discussed. Stable tribological performance can be achieved under conditions of mild sliding wear. While wear rates normally reach an equilibrium (or steady state) in the mild wear regime, accelerated wear rates (with sliding distance and load) are observed in the severe wear regime due to large scale plastic deformation, and in some instances, local melting of the surface layers. MMCs can show significantly lower wear rates compared to unreinforced alloys over a substantially wider range of pressure and sliding speed. Wear mechanism maps are effective ways of delineating the regimes of dominant sliding wear mechanism (oxidation, delamination, seizure etc.) and show the effect of frictional temperature on wear transitions. The very small wear rates observed in lubricated sliding define a new wear regime different from mild and severe wear not only in terms of the infinitesimal rate of material removal but the mechanisms of material removal involved are also different. Tribolayers that form during the running in period are responsible for the very low wear rates observed in this ultra-mild wear regime. Reinforcement can also provide excellent improvements in resistance to low-stress abrasive wear. However, major enhancement of wear resistance in the severe sliding wear regime, or to high-stress abrasion, cannot be expected from these composites.

Summary Submerged breakwaters (SBWs) were used for the first time on the Polish coast in 2006, in the western coast of Gdansk Bay, in the area of Orlowo Cliff. They were built to prevent the abrasion and inundation of areas situated in the hinterland, especially in the conditions of storm surges. The main objective of the study was to determine their effect on the morphology and grain size composition in the seashore and nearshore zone. Based on the conducted research and analysis, it has been found that the construction has a minor impact on the modification of the shore and nearshore zone morpholithodynamics, which is evidenced by a sinuate shape of the shoreline and a relatively stable cape in the central part of the area, present both before (1966–2005) and after SBWs were built. Furthermore, the progressive abrasion, the lack of significant changes in the morphology and particle size distribution of the beach and the nearshore zone, as well as the fact that those changes are limited only to the immediate surroundings of the submerged breakwaters prove their neutral impact.

Summary There are several techniques such as surface profilometry, advanced technique of electron microscopy and optical methods which have been used by researchers to determine the measurement of wear and it is found useful to understand the surface geometry of the material. In mining industries, wear is acute in rock crusher. This work explores the characterization of wear observed on the surface of liner material of roll crusher crushing coal. Wear characterization like ploughing, scratching, cavities has been observed on the surface of liners. To correlate wear characterization due to abrasion on roll crusher liner wear, experiments have been performed. To perform abrasive wear test, pin-shaped sample of liner material has been developed for the purpose of testing. The abrasive wear experiment was conducted using pin-on-disc tribometer. During the investigation, experiments based on full factorial design adopted from statistical modelling software. In this methodology, the input parameters like load, sliding distance, hardness of coal, hardness of liner material are taken into consideration, and weight loss was considered as the output response. The influence of each input parameters were examined to understand its effect for weight loss. The regression equation obtained from analysis of variance table was used for the prediction of weight loss. The regression equation developed was validated with the experimental results. The percentage error was observed less than ±10%.

Contamination by microplastic particles and fibres has been observed in sediment and animals sampled from the Firth of Clyde, West Scotland. In addition to microplastics released during clothes washing, a probable source is polymer ropes in abandoned, lost and discarded fishing and recreational sailing gear. The fragmentation of polypropylene, polyethylene, and nylon exposed to benthic conditions at 10 m depth over 12 months was monitored using changes in weight and tensile properties. Water temperature and light levels were continuously monitored. The degree of biofouling was measured using chlorophyll a, the weight of attached macroalgae, and colonising fauna. Results indicate microplastic fibres and particles may be formed in benthic environments despite reduced photodegradation. Polypropylene, Nylon, and polyethylene lost an average of 0.39%, 1.02%, and 0.45% of their mass per month respectively. Microscope images of the rope surface revealed notable surface roughening believed to be caused by abrasion by substrate and the action of fouling organisms.

The wear behaviour of a fine grained and dense CaZrO3-MgO composite is presented. Un-lubricated Pin-on-disc tests at room temperature have been performed using 10 N as normal force and 0.10–0.15 ms-1 as sliding rate and ZrO2 and steel counterparts. The coefficient of friction versus the sliding distance and the specific wear, together with a complete microstructural analysis of the worn surfaces by field emission scanning electron microscopy is reported. The composite presents a wear resistance similar to other ceramics under ceramic/ceramic sliding contact and improved wear resistance in contact with steel. Initial wear is dominated by abrasion independently of the chemical nature of the counterpart. The second stage wear depends on the characteristics of the third body formed. Zirconia leads to a brittle particulate third body with little protective capability. Steel forms a strongly bonded and plastic cermet third body that protects the material limiting the level of further wear. Fil: Silva, Abílio. Instituto de Ceramica y Vidrio de Madrid; España. Universidade Beira Interior; Portugal Fil: Booth, Raul Fernando Nicolas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina. Instituto de Ceramica y Vidrio de Madrid; España Fil: Garrido, Liliana Beatriz. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Aglietti, Esteban Fausto. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Pena, Pilar. Instituto de Ceramica y Vidrio de Madrid; España Fil: Baudín, Carmen. Instituto de Ceramica y Vidrio de Madrid; España

A new method of friction surfacing assisted hybrid friction stir welding (FS-HFSW) technique was developed to improve the joint efficiency and avoid the pin abrasion for joining of dissimilar Ti/Al joints. The FSW tool with enlarged head and concave end-face was designed to broaden the lap width and promote material flow. The maximum tensile load reached 12.2 kN, representing 85.3% of the parent Al alloy, with a ductile fracture locating at the heat affected zone of base Al. The excellent bonding of Ti and Al was based on the combined effects of nanoscale TiAl3 IMCs layer and complex mechanical inter-locking.

Surface cleaning is becoming increasingly important in modern manufacturing. Traditional cleaning processes are predominantly thermal processes and may not be applicable for the next generation of devices that include parts manufactured at the micro/nanoscale that are sensitive to heat and abrasion. This problem with such parts can be overcome by a new surface-cleaning technique called droplet-assisted laser cleaning (DALC). The DALC uses a Q-switched Nd:YAG laser to vaporize a stream of water droplets to produce a succession of impacting shock waves at the surface of the component of interest. The generated shock waves can be used for various material processing applications, including removal of contaminants. The process exploits the combined potential of laser shock cleaning (LSC) and optohydrodynamic processing through explosive vaporization of water droplets. In this chapter, we discuss traditional laser cleaning processes from direct beam/contaminant interaction to LSC. The DALC process discussed in this chapter was specifically designed to induce explosive vaporization of a 300-μm water droplet above the contaminated substrate surface. The shock pressure magnitude was analyzed using high-precision force and acceleration sensors. The effect of laser energy, number of pulses per position, gap distance and scanning speed on the cleaning performance was investigated in detail. A contaminated substrate with micropolystyrene particles was used to evaluate the performance of the DALC system, and the results, in comparison to those obtained from the traditional LSC process, show that DALC can be an excellent alternative to the existing laser-based cleaning process (ablation and shock).

Wear processes involving hard particles can involve abrasion (in which the particles slide or roll over the surface) or erosion (which involves particle impact). The chapter considers the role of particle properties in these processes: hardness, shape and size. It then discusses abrasive wear in detail, starting with simple models for wear by plastic deformation and by brittle fracture. These are followed by consideration of the abrasive wear of a wide range of engineering materials, the effects of environment and lubrication, and combined abrasion and corrosion. Laboratory test methods are reviewed. The treatment of erosive wear is similar: presentation of models for erosion by plastic and fracture-based mechanisms, discussion of the erosion of engineering materials and testing methods.

Data presented here demonstrates the utility of quantitative analysis of sediment-induced microabrasion on bone's surface. Fresh sheep (Ovis aries) bone, acting as a human analogue, was bombarded by mobile sediments from silt, sand and gravel classes (ranging 20 μm–3.35 mm) in a series of flume-based experiments. Controlled bombardment produced unique abrasion patterns on bone which were recordable using scanning electron microscopy. Imaging abrasion at both × 100 and × 1000 magnifications allowed quantitative and qualitative distinction to be made concerning the sediment class that the bone was abraded by; bombardment by gravel classes caused abrasion to advance through cyclical cracking, whereas smoothing of bone's surface occurred more frequently in sand and silt classes. A stepwise multi-linear regression model identified changes in sediment grain size (p < 0.001), duration of exposure to abrasion (p < 0.001), sphericity of the abrasive (p = 0.002), and T value (abrasive force) (p = 0.013) respectively, as the strongest rate limiting factors controlling microabrasion propagation. The methodology presented herein demonstrates analytical value by allowing diagnostic modifications to bone's surface to be correlated with specific taphonomic processes. Data developed from flume-based experimentation was applied in four separate case studies; abrasion data recorded on bones recovered from different aquatic contexts, was linked to hydrological and marine seabed sediment data to demonstrate how documented microabrasion can reflect the different sedimentary contexts bone has passed through. In light of these results we suggest that a quantitative approach to analysing abrasion on bone retrieved from water has potential to allow remains' submersion times and transport pathways to be established with a higher degree of resolution than is currently possible. The development of improved methodologies for the interpretation of submerged human bone is vital due to the increasing risks posed by flooding and coastal erosion to archaeological sites.

Wear causes both significant economic and environmental losses by shortening the service life of machinery. Earthmoving machinery is an example of machinery subjected to heavy wear in extreme conditions, where materials suffer from both impacts and scratching by the abrasives. In this work, we have determined the wear surface deformation of four impact-abraded steels to reveal the possible differences between materials and impact conditions. The tested materials include a structural steel and three wear resistant steels with different microstructures. The tests were conducted with impeller-tumbler wear testing equipment. The duration of the tests and the sample angle varied. The longer test duration decreased the relative amount of wear in the harder samples. The sample angle did not have a distinct effect on the wear surfaces in the center areas of the samples. In the edges, however, the larger sample angle caused more wear. Despite some microstructural differences, the correlation between higher hardness and decreased wear was linear in the steady-state wear. The ferrite grains and retained austenite in the martensitic matrix of the 650HB steel had only a small effect on the overall impact-abrasion wear resistance of the material when compared to steels with a fully martensitic microstructure.

The rail wear rates per traffic unit (mm/MTon) in the curves of a 4.5 km-long commercial line over a period of 9 years were measured and related to specific operation conditions. The rail corrugation was analyzed using a Corrugation Analysis Trolley (CAT) and visual inspection was carried out in order to identify the defects in the railroad. Since Rolling Contact Fatigue (RCF), artificial abrasion and corrugation were found to be the most important issues the grinding procedures used during maintenance of the railroad were evaluated to assess their effectiveness on removing the defects from the rail surface. The results showed that the wear rates in the studied railroad were several times higher than those typically found in the literature, mainly as a consequence of inappropriate grinding regimes. White layer formation and only partial removal of cracks emerged as the most relevant drawbacks of rail grinding procedures.

The use of cemented femoral stems is common practice worldwide with strong clinical data supporting their use. Over the years, different surface processing techniques have been employed to enhance the performance of the stem–cement interface. As a result different clinical outcomes and visual presentation at revision has been observed. Whilst research has focussed on increasing adhesion and better load bearing capacity, the effects of surface processing on the degradation of cemented femoral stems has not been investigated. The aims of this study was to investigate the effects of surface processing on the subsurface microstructure, surface chemistry and tribocorrosion degradation mechanisms of cemented tapered femoral stems subjected to polishing and blasting (Vaquasheen) processes. Cemented femoral stems were orientated and loaded according to ISO 7206-4 for 500,000 cycles in 0.9% NaCl at 37 °C. A three-electrode electrochemical cell was integrated into the mechanical test to facilitate in-situ corrosion measurements. The severity and mechanism of damaged were assessed scanning and transmission electron microscopy, X-ray photoelectron spectrometry, solution mass spectrometry and white light interferometry. Surface processing influenced the level of tribocorrosion at the interface with polished surfaces demonstrating higher levels of tribocorrosion and ion release when compared to the blasted surfaces. Surface analysis consistently demonstrated the presence of a SiO 2 layer on the vaquasheened stems thought to originate from the glass bead blast matrix. This resulted in lower levels of corrosion both under static and tribocorrosion assessment. In conclusion, blasted surfaces resulted in lower wear induced corrosion when compared to the polished surfaces. However the total metallic ion levels did not follow the same trend. This is thought to be due to the formation of metallic debris and dissolution of debris due to abrasion of the femoral stems.

Dental composite resins have increased in prevalence over the past 10 years. As the materials replace missing tooth structure, it is critical that they have comparable wear properties as natural enamel. Dental composites wear during mastication which produces abrasive, erosive, fatigue, and erosive wear mechanisms. The wear of a dental composite is dependent upon the size, concentration, bonding, and dispersion of its filler particles. Additionally, the strength of the resin matrix may affect wear. There are several devices used to approximate wear in vitro and different methods for measuring in vitro and in vivo wear. Several clinical studies have measured annual wear rates for composites. New materials are being developed in dentistry that should be optimized for wear performance.

Coating materials are widely used in refractory lining to prevent different deleterious effects such are reactions on the mold-metal contact surface, abrasion from liquid metal or alloy, gasses, slags, and other materials in contact with the coating. In this paper, behavior of cordierite based coating exposed to the cavitation erosion was investigated. Cordierite samples sintered at 1200 and 1400 degrees C were used for the tests. Mass loss, level of surface degradation obtained using image analysis and thermal imaging analysis were applied for the cavitation erosion evaluation. Results showed that the cordierite samples can be successfully used in conditions where the cavitation resistance is required. This is the peer-reviewed version of the article: Pavlović, M., Dojčinović, M., Martinović, S., Vlahović, M., Stević, Z.,& Volkov-Husović, T. (2016). Non destructive monitoring of cavitation erosion of cordierite based coatings. Composites Part B-Engineering, Elsevier., 97, 84-91. [https://doi.org/10.1016/j.compositesb.2016.04.073] The published version: [https://cer.ihtm.bg.ac.rs/handle/123456789/1858]

Tool flank wear severely affects process performance during hard turning. This work discusses tool wear and various parameters affecting tool wear. Our study shows that the machining parameters used, tool and workpiece material microstructures, cutting tool geometry, and tool coatings greatly affect the wear behavior of the tool. Process performance issues that arise during hard steel turning and machining with worn-out tools are discussed.

More and more slurry transport systems are used in mining operations to efficiently and cost-effectively transport ores and tailings. The materials used for slurry transport are often subjected to severe wear attack. In this study, the wear modes and wear resistance of materials commonly used for slurry transport are discussed. Slurry jet erosion, Coriolis slurry scouring erosion and slurry sliding abrasion tests are used to simulate these wear modes and to characterize the wear resistance of the materials. The wear resistance of selected materials from each material category commonly used for slurry transport, including steels, high chromium white cast irons, chrome carbide-based and tungsten carbide-based overlays, elastomers, plastics, ceramics and cermets, are reported. The relationships of the wear resistance of these materials with their mechanical properties are also briefly discussed.

Wear is a critical issue related to the performance of hip joint implants, namely for ultra-high molecular weight (UHMWPE) fabricated components. A greater knowledge and understanding of the attributes and capabilities of UHMWPE related to wear, at macro to nano scale levels, is crucial in the context of engineering design aiming the improvement of the implants’ behaviour. Various multi-scale characterization techniques (gravimetry, geometrical analysis using coordinate measuring machine, profilometry, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy and Raman spectroscopy) were combined for the wear assessment of UHMWPE/metal (stainless steel and cobalt–chromium) implants tested in a hip joint simulator. The wear rate of the UHMWPE was about 48 mg/10 6 cycles, equivalent to a linear wear rate of 0.16 mm/year, independently of the femoral head material. Two main mechanisms determined polymer wear: a) abrasion, by second-body action of counterface metal asperities and by third-body debris; b) adhesion/fatigue, disclosed by micro-scale ripples, resulting from cyclic plastic strain accumulation. Going deeply into the analysis by AFM and Raman spectroscopy it was also observed that the structure of the material changes after wear but in distinct modes: the scratched areas became more crystalline while the smooth areas remained without structural modifications.

This work consists on a deep tribological study of the WX system composed by a mechanical blend in different compositions of NiCrBSi and WC-12Co powders: 20% NiCrBSi (W2), 40% NiCrBSi (W4) y 60% NiCrBSi (W6). The coatings have been obtained by high velocity oxy-fuel process (HVOF). The measurements made by Ball-On-Disk test are: the friction coefficient is lower than 0.5 and the exchanged energy between the counterparts is under 10 KJ. To quantify the friction wear rate, the volume loss and the track depth, Scanning White Light Interferometry and SEM have been used. The track depth is proportional to the amount of NiCrBSi. A higher percentage of WC-12Co increases the friction wear resistance and decreases the abrasion wear rate (Rubber Wheel test). In all the coatings studied, no diffusion processes are found between the mixed phases, the adhesion between the coatings and the substrate is excellent, the porosity level is below 2% and an increase of microhardness of the coating due to a strengthening of the matrix produced by impacts of solid particles, takes place.El trabajo consta de un completo estudio tribológico del sistema WX que consiste en la mezcla mecánica de WC-12Co y NiCrBSi en diferentes proporciones: 20% NiCrBSi (W2), 40% NiCrBSi (W4) y 60% NiCrBSi (W6). Los recubrimientos se han obtenido por proyección térmica de alta velocidad (HVOF). Para todos los sistemas, el coeficiente de fricción es menor que 0.5 y la energía intercambiada entre el par friccionante y el recubrimiento es inferior a 10 KJ. Para cuantificar el desgaste por fricción se han utilizado la profundidad de la huella y el volumen perdido durante el ensayo, obtenidos mediante Interferometría de Barrido de Luz Blanca (SLWI) y SEM. La profundidad de la huella sigue una evolución directamente proporcional al contenido en NiCrBSi. Un mayor contenido en WC-12Co aumenta la resistencia al desgaste por fricción y disminuye la velocidad de desgaste por abrasión (ensayo Rubber Wheel). En los recubrimientos obtenidos, no se observa difusión entre las fases, la adherencia con el sustrato es excelente, la porosidad menor al 2% y se produce un incremento de la dureza del recubrimiento debido al endurecimiento por trabajo de la matriz causada por impacto.

7 pages, 6 figures, 1 table, There is a paucity of quantitative knowledge on the contributions of non-exhaust (abrasion and re-suspension) sources to traffic emissions. Abrasive emissions can be broadly categorised as tyre wear, brake wear and road dust/road surface wear. Current research often considers road dust and tyre dust as externally mixed particles, the former mainly composed of mineral matter and the latter solely composed of mainly organic matter and some trace elements. The aim of this work was to characterise tyre wear from both laboratory and field studies by using Aerosol Time-Of-Flight Mass Spectrometry (ATOFMS). Real-time single particle chemical composition was obtained from a set of rubber tyres rotating on a metal surface. Bimodal particle number size distributions peaking at 35nm and 85nm were obtained from SMPS/APS measurements over the range 6-20,000nm. ATOFMS mass spectra of tyre wear in the particle size range 200-3000nm diameter show peaks due to exo-sulphur compounds, nitrate, Zn and ions of high molecular weight (m/z>100) attributed to organic polymers. Two large ATOFMS datasets collected from a number of outdoor studies were examined. The former was constituted of 48 road dust samples collected on the roads of London. The latter consisted of ATOFMS ambient air field studies from Europe, overall composed of more than 2,000,000 single particle mass spectra. The majority (95%) of tyre wear particles present in the road dust samples and atmospheric samples are internally mixed with metals (Li, Na, Ca, Fe, Ti), as well as phosphate. It is concluded that the interaction of tyres with the road surface creates particles internally mixed from two sources: tyre rubber and road surface materials. Measurements of the tyre rubber component alone may underestimate the contribution of tyre wear to concentrations of airborne particulate matter. The results presented are especially relevant for urban aerosol source apportionment and PM2.5 exposure assessment. © 2014 Elsevier Ltd.

The tribological behavior of a thermoplastic polyurethanes (TPU) sliding against a non-polished steel counterface was studied as a function of load, velocity and temperature under dry conditions. Thermomechanical and chemical analyses were carried out on the TPU using DSC, FTIR and DMTA devices prior to the sliding tests. Contact changes were followed using a speed camera and an acoustic emission device. A simple thermal numerical simulation, to calculate temperature rise generated by friction, completes these analyses. To characterize wear performances, a wear rate was determined by considering the linear dependence between the wear volume and the product of the normal load by the travel distance (Archard model). Finally, wear mechanisms of TPU involve both abrasion scratches and adhesion patterns (Schallamach ridges). To conclude, a wear process description using the third body approach was proposed to gather the whole tribological results.

Mechanisms of abrasive machining are considered through the study of material deformation. Consideration is given to the effects of friction and grain contact geometry on the forces in grinding. Material removal in grinding has many similarities with the processes of abrasion as studied in the subject of friction and wear. Parameters are described that cause enormous differences in both forces and wear rates that occur in grinding. The importance of the environment and of effective lubrication is emphasized. Consideration is also given to the effects of wear on the grinding wheel and dressing tool. Some key points are: Rubbing – effect of flat grains Ploughing – effect of grain angles Cutting – requirements for chip formation Adhesion – sticking friction Interface friction – effect of oxides and lubrication at grain surfaces Junction growth – effect of material deformation Stresses and crack propagation Tool wear – adhesion, fatigue, crack propagation, corrosion, tribo-chemical wear and loading. Additional material has been included in this edition on wear of abrasives and materials that are difficult to grind, including ceramics. Numerical examples are included and references to published work are given.

This chapter describes the principal mechanisms of wear and reviews the main categories of hardmetal wear and how the wear depends on their makeup and structure. Abrasion is the first category examined where the volume of wear has been found to be related to the hardness. The effects of using different abrasives and other parameters such as the size of abrasive, the applied load, and the chemical environment are also described. The next category is erosion where the wear of hardmetals shows features characteristic of the classical classes of erosion behavior representative of both ductile and brittle materials. The microstuctural basis of hardmetal wear is then explored in some detail. Common features of both abrasion and erosion are removal of the binder phase in the early stages of wear, accumulation of plastic strain in the tungsten carbide (WC) grains, fracture and fragmentation of the WC grains and removal of grains. A feature that is sometimes seen is reembedment of small WC fragments into binder to form wear-resistant surface layers. The chapter also discusses other modes of wear such as sliding wear, impact loading and thermal fatigue.

Metal-on-metal (MOM) hip joint bearings are currently under discussion as alternatives to metal-on-polymer (MOP) bearings. Some criteria under scrutiny are the wear resistance, the influence of wear particles on the surrounding tissue, as well as the frictional torque. In order to understand and control the wear behavior of such a bearing a close correlation between the microstructures of the alloys used and the acting wear mechanisms has to be found. Thus, commercially available CoCrMo-balls were tested against self mating concave pins in a physiological fluid at 37°C under reciprocating sliding wear (1 Hz). The compressive load was 750 N (body weight). For 2×106 cycles tests were carried out continuously and with periodically occurring resting periods. On the basis of the observed wear appearances the acting wear mechanisms are defined and evaluated as to their contribution to the wear behavior. Due to the high local contact stresses surface fatigue prevails initially. Cr– and Mo–carbides are fractured and torn off the surfaces bringing about additional surface fatigue by indentations and initiating abrasion. The weight loss can be predominately attributed to these mechanically dominated wear mechanisms. In a parallel occurring tribochemical reaction layers are generated from denatured proteins. These adhere rigidly to the surfaces and cover parts of the contacting surfaces avoiding adhesion. Thus, the wear behavior is mainly influenced by the alternating balance between surface fatigue and abrasion on the one side and by tribochemical reactions on the other side.

The interaction of water and sediment at the glacier base controls glacier motion, and it is the resultant till that provides a dynamic record. These processes can change on a spatial (mobile and ‘sticky spots’) and temporal (annual and diurnal) scale. Deformation within the deforming layer occurs by simple shear, by rotation and longitudinal extension, as well as abrasion and fracture, of both clasts and grains. This produces a resultant till fabric, which can be used to interpret till genesis. Water flow in channelized forms either as ‘fast’ R-channels or ‘slow’ cavities, water films, and ‘microcavities’ will produce stratified sediments.

Aeolian abrasion is the process whereby rocks and landforms are eroded by saltating particles, contributing to the formation of ventifacts, yardangs, deflation basins, and inverted relief. Sand is the predominant or sole abrasive agent. Abrasion is sensitive to the highest velocity winds in a region, which controls the directionality of ventifact features. As high-velocity winds are infrequent, many decades, centuries, or even millennia may be required for ventifact formation. Ventifacts, yardangs, and inverted relief are also common on Mars, and although abrasion is infrequent, the process does not require winds or atmospheric densities different than those found today.

The term ‘wear’ could be defined as an undesirable progressive loss of material from one or both surfaces in relative motion between them. Wear is not a basic material property, but is a system response of the material; because of this, the mechanism can have a variegate nature. The mechanism of wear is very complex and there are two broad approaches to the classification of wear: the first is descriptive of the results of wear, while the second is based on the physical nature of the underlying processes. It is, however, the second form of classification that is most useful. According to this approach, five wear processes have been clearly recognized: abrasion, adhesion, fatigue, erosion and corrosion. It has been agreed that wear cannot be totally prevented, but most of these mechanisms can be attenuated and, in some cases, can be avoided. It is very important for a designer to know the amount a component can wear before it must be replaced. Since manufacturers must recommend replacement or overhaul times for the equipment they supply, they must be able to ascertain, for each component, when sufficient wear has occurred so that the component is no longer usable.

In apatite (U–Th)/He thermochronology the helium distribution in a crystal is a function of the simultaneous processes of radiogenic production, thermally activated volume diffusion and the ejection of He caused by long alpha stopping distances. These processes are further complicated by zonation of U, Th and Sm within the grain and implantation of 4He from neighboring U–Th–Sm bearing minerals. We use a refined version of the 3D Monte Carlo diffusion code of Gautheron and Tassan-Got (2010) to simulate the interplay between ejection and diffusion with or without zonation, ejection and abrasion for a suite of thermal histories. We examine the phenomenon of over-correction produced by the alpha ejection correction parameter (FT or FZAC for homogeneous or heterogeneous eU repartition) by comparing the raw (measured) and FT- or FZAC-corrected ages for a number of scenarios to the ejection-free age (AEF), which we define as the age that would be obtained if alpha ejection had not occurred, or equivalently if the stopping distance was zero. We show that the use of FT- or FZAC-corrected ages generally reproduces the ejection-free age to within typical (U–Th)/He uncertainties (±8%), even for zoned apatites. We then quantify the effect of alpha implantation on (U–Th)/He ages, showing that implantation from a single external source with modest relative U or Th enrichment can generate as much as 50% excess He. For more extreme cases where an apatite is surrounded by multiple external sources the measured age can be >300% of that determined from an isolated crystal. While abrasion of the outer 20–25 μm can significantly reduce the age dispersion for rapidly cooled samples, slowly cooled samples can still retain 10–30% excess He. The removal of the rim of the crystal reduces the thermal information from very low temperatures (

Hip fracture represents a major health problem facing elderly people. Hip prosthesis is the greatest challenge of biomaterial design to meet the needs of joint arthroplasty. The loads experienced by the lower limbs are very severe; in the femur they can be several folds higher than the body weight. Unusual combinations of mechanical, chemical, and physical properties are required by hip prostheses. High strength and toughness, long-life resistance, tailored stiffness, resistance to impact, abrasion and corrosion, adequate transparency to electromagnetic waves for diagnostic purposes, are the combination of properties relevant for tissue substitute design. Composite hip prostheses, that is, continuous fibre-reinforced polymers, have gained an increasingly important role in the development of prosthetic devices. Composite materials can be engineered more accurately than monolithic structures (single-phase materials, such as metals), thus allowing the development of more effective tissue substitutes. Basic biomechanical properties of tissues composing the hip joint and the concept of composite material and anisotropy are introduced in first section. The following section reports the state of the art of the materials used to manufacture the prosthetic components of a total hip prostheses. It is divided in three subsections where bone cements, the acetabular cup, and the hip stem are considered. A dedicated section is devoted to manufacturing, state of the art, modelling, and testing of polymer-based composite hip stem. Finally, future trends are reported in the last section.

This chapter provides a brief introduction to tribology. Tribology is the science and technology of surfaces in contact with each other and therefore covers friction, lubrication, and wear. Tribological properties are most often of concern when the materials are used in bearing applications. Especially when engineering plastics are used for bearing materials, they must have a suitable combination of mechanical and tribological properties under the conditions experienced in use. The three main performance areas that need to be examined for bearing are friction, wear, and limiting PV. Frictional properties of plastics differ markedly from those of metals. The coefficients of friction vary with applied load, velocity, and temperature. A unique characteristic of most thermoplastics is that the static coefficient of friction is typically less than the dynamic coefficient of friction. Lubrication is the common approach to reducing friction. There are perhaps a hundred designs of machines called tribometers that may be used to measure wear and coefficient of friction. There are so many designs because one tried to simulate the expected endues environment and conditions as close as possible.