Wear mechanisms for asbestos-reinforced automotive friction materials

An asbestos-reinforced automotive friction material was evaluated by dynamometer testing for its wear characteristics at elevated temperatures. Wear rate constants were obtained for different temperatures, and an activation energy was obtained for the high-temperature wear process. It is concluded that the wear is controlled by a pyrolysis mechanism at elevated temperatures (above 450°F drum temperature) and by adhesive and abrasive mechanisms at low temperatures.     

Wear of dimethacrylate resins used in dental composites

Wear of dimethacrylate resins used as the matrix phase in dental restorative composites was characterized by two-body abrasion and singlepass sliding. Ranking of the resins was obtained by both tests. Two resins that had low values of tangential force and track width also showed relatively ductile modes of surface failure for the normal loads tested. A monomethacrylate fluorine-containing resin did not show improved wear properties by these methods of testing.     

Wear of filled and unfilled dental restorative resins

The influence of double-pass sliding on the surface failure of filled and unfilled dental restorative resins was evaluated. Damage was more severe for double-pass than for single-pass sliding. Wear of restorative resins and composites was influenced by the resistance to penetration and by the mode of deformation during sliding.     

Wear mechanisms of boundary-lubricated surfaces

Examination of steel specimens tested under boundary lubrication conditions indicates the existence of three distinct processes which lead to wear particle formation: deformation and fracture of original machining marks; deformation and fracture of edges of plowing tracks; delamination. Deformation and fracture of original machining marks and the raised edges of the plowing furrows generate wear particles which are 1–15 μm in the largest dimension. The process of delamination, however, generates particles that are 100 μm wide. The formation of these large wear particles coincides with a high rate of wear and scuffing failure.     

Wear mechanisms with coated abrasives

A metallographic study is described of the grit failure mechanisms operating with coated abrasives when grinding a wide variety of engineering materials. Scanning electron microscopy has been used to both characterise and monitor the incidence of the various grit failure mechanisms for a standard aluminium oxide resin-bonded belt and a similar belt containing a grinding aid additive. The two predominant mechanisms are capping, where swarf becomes firmly attached to the grit surface preventing any further grinding action and dulling, which is a combination of attrition by chemical degradation or plastic flow and small-scale grit fragmentation, which leads to the formation of flats on the grit surfaces. These mechanisms are discussed and the reasons for changes in both the incidence and rate of development of these failure modes are examined for belts containing coating additives which are responsible for improved grinding performance.     

Wear mechanisms in unlubricated chains

This paper describes the results of wear tests on unlubricated articulating chains. Experiments with a martensitic stainless steel chain showed that under certain conditions of load, motion and environment, unexpected wear patterns could develop, with high and low wear alternately on adjacent pins and bushes. Examination of specimens tested in different atmospheres showed that the same fundamental wear mode, severe adhesive wear, was involved throughout. The variation in wear rate, both environmental and geometric, was caused by wear debris acting as a solid lubricant of variable efficacy. A second, surface hardened chain material was also tested. Whilst this wore relatively evenly at a very low rate indeed, it also suffered from progressive surface spalling and this feature would probably be life-limiting     

Wear mechanisms in oscillating bearings

Surface examination of dry oscillating bearings reveals three different contact zones and indicates that various frictional behaviours take place during the process. The relation between wear and applied conditions such as load and amplitude of oscillation is obscured by the complex behaviour of most frictional materials. Studies of initial destruction, transfer and elimination are easier with materials that show simple behaviour. Friction and wear are governed by load-carrying third bodies transported in the contact. Transport was confirmed during observation through a hollow glass ring rubbing on a chalk sector. Wear debris motion explains the manner in which geometry modification occurs with time. Circumferential debris transport due to ring motion is modified at the centre of the sector where transverse flow takes place. The initial O-shaped sector can change into an ω configuration. Thus the calculation of wear or of eliminated material must allow for the new ω shape. The new shape also controls bearing clearance. The effects of load and oscillating motion on wear parameters are presented. More than one wear mechanism can exist in a single contact.     

Analysis of rapid method for the quality index of phenolic resins and benefit

The traditional analytical methods used to determine phenolic resin are slow and produce environmentally unfriendly waste. In this work, Near-infrared (NIR) spectroscopy has been applied for resin content of phenolic resins. The partial least square regression was used to develop the calibration model of the resin content. 8 samples were withdrawn at different time stages for analysis with the proposed quantitative models; the data thus obtained were compared with those provided by reference methods. The maximal predicted error and the standard deviation of the differences were 0.96 and 0.51% for resin content. The results of the paired t-test revealed that there was no significant difference between the NIR method and the reference method. NIR spectroscopy is an effective choice for the accurate, expeditious analyzing quality of phenolic resin.     

Wear mechanisms in coated carbide tools

Micrographic evidence is presented which shows the retention of thin, 5μm carbide coating even when the ‘crater’ depth far exceeds the original coating thickness. Whereas earlier authors have attributed this retention to chip smearing, the present authors have shown that cratering can occur by plastic deformation with the coating remaining almost intact. X-ray images from the electron microprobe analyser and from the energy dispersive X-ray analyser support the micrographic findings. Plastic deformation results in flank bulging which causes the coating to wear rapidly by abrasion: the substrate, however, is able to withstand further deterioration. Chip notching on the rake face and grooving wear on the clearance faces also cause removal locally. Severe grooving wear on the end cutting edge as a possible result of oxidation and catalytic action is highlighted     

Wear mechanisms of polytetrafluoroethylene and its composites

It is shown analytically that the empirical wear law takes account of two fundamentally different wear mechanisms. Whether adhesive or fatigue wear predominates will depend on the selection of the frictional power. Comparison of the coefficients in the empirical law demonstrates the role of the filler in reducing the wear rate of composites.     

Wear mechanisms of diamond coated dental burs

Abstract

Wear mechanisms of diamond burs consist of diamond wear-out, diamond pull-out, clogging by debris and degradation of the diamond binder material. These have been reported in the scientific literature and several discrepancies were found by the authors, which in itself, justifies an independent study. Diamond coated dental burs before and after use on human teeth were, therefore, compared in order to identify the predominant cause of wear. Fifteen new diamond coated burs were characterised using scanning electron microscopy before and after use on human teeth. The study focused on the condition of the same diamond particles before and after use. Clear evidence of diamond particle wear was detected rather than evidence of diamond pullout, clogging by debris or degradation of the diamond binder material.     

Wear mechanism of multiphase friction materials with different phenolic resin matrices

Wear of the brake friction materials with straight phenolic resin, silicon modified phenolic resin, or boron–phosphorous (B–P) modified phenolic resin was investigated. A simple formulation was used to produce friction material specimens and wear tests were carried out using a Krauss type friction tester. Friction stability and wear rate of the three friction materials were compared as a function of temperature up to 400 °C and the mechanisms associated with the wear processes at different temperature ranges were analyzed using Arrhenius type plots and worn surface morphology after tests. The results showed that the wear process below the critical temperature was mainly attributed to the gradual stripping of the heat affected surface layers of the friction material, while the wear rate at elevated temperatures was determined by the detachment of subsurfaces that was caused by the thermal decomposition of the resin. Among the three friction materials investigated in this study, the friction material containing B–P modified resin showed the best wear resistance and friction stability.     

Wear and frictional mechanisms of copper-based bearing alloys

The present study investigated the role of alloy microstructure and surface roughness on wear and friction behavior of leaded and unleaded tin bronzes. Ball-on-disk experiments were carried out under dry conditions with steel balls sliding against bronze disks. Scanning electron microscopy (SEM), energy dispersive electron microscopy (EDX), x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy were performed to analyze the sliding tracks and the ball scars. The wear reducing effect of lead was associated to the formation of an oxidized lead rich layer. When no such film formed on the leaded bronze wear was more severe than in case of unleaded bronze. Nevertheless, the presence of lead in the alloy was a necessary but not sufficient condition to obtain a smeared layer and thus a lubricating effect of the leaded alloy. Two mechanistic hypotheses were formulated to explain the formation of the smeared layer.     

Wear mechanisms and scale effects in two-body abrasion

The ‘particle size effect’ and its manifestation in abrasion still attracts considerable debate as to its origins and the ranking of its likely causes. Experiments have been conducted to study the important contribution that the formation of wear debris can have on the progression of wear. The experiments consist of unlubricated (dry) pin-on-disk tests with silicon carbide coated paper of varying particle size, with different pin material, diameter and loads. It has been observed that the influence of debris formation on wear rate is more pronounced for fine abrasives and soft-wearing materials. Consequently, it is proposed that the particle size effect can be explained in terms of geometrical scaling and the evolution of third-body effects with diminishing particle diameter.     

Wear mechanisms of the C/SiC brake materials

The C/SiC brake materials were fabricated by chemical vapor infiltration combined with liquid melt infiltration. The wear mechanisms of C/SiC brake materials were investigated. The main wear mechanisms were grain-abrasion, oxidation-abrasion, fatigue wear, and adhesive wear. These wear mechanisms always occurred simultaneously , and showed mutual enhancing effects between them. Grain-abrasion mainly was the result of hard SiC grain action. Adhesive wear could cause high wear rates and a large unstable friction coefficient. Si was the significant factor on the adhesive wear, so Si in the C/SiC brake materials must be removed.     

Wear mechanisms of cutting tools in high-speed cutting processes

Contemporary cutting tools used for High Speed Cutting (HSC), made on the basis of micro-grained cemented carbides with multi-layer protective coating, allow for effective machining of hardened and tempered steels of hardness over 50 HRc. The characteristic wear of such tools is affected by the fact that the cutting speed is no longer the main influential factor on wear; the wear can also be the consequence of the high-speed tool movements in the feed direction. The paper presents some original research into the wear types, as well as the phenomena in the cutting zone and their relationships to the causes and main wear mechanisms (adhesion, abrasion and diffusion) for the tools used in HSC.     

Wear mechanisms of laser-hardened martensitic high-nitrogen-steels under sliding wear

High-nitrogen tool steels (Fe, 15% Cr, 1% Mo, 0.3% C, 0.3% N) are applied, e.g. in bearings and gears in aeronautics and space technology. Their advantage compared to conventional, nitrogen-free tool steels is a superior corrosion resistance, which can be attributed to Cr, Mo, and N dissolved within the solid solution. In order to gain a sufficient toughness for application, these steels are tempered above 600°C bringing about precipitated carbides and nitrides, which bind Cr and N and, therefore, deteriorate the chemical properties. Within a DFG (German Research Council)-funded research project the authors show, that by means of laser hardening it is possible to dissolve a part of these precipitates — mainly nitrides resulting in improved properties under fatigue, wear and corrosion. This is brought about by a newly generated martensite with compressive residual stresses (fatigue, sliding wear), dissolution of Cr and N (corrosion) and a higher mechanical stability of the surfaces (sliding wear). This contribution focuses on the acting wear mechanisms under dry sliding wear. The investigations are carried out with pin-on-disk tests, with the disk as the actual specimen and a pin made of conventionally hardened 52100 bearing steel (100Cr6). It can be shown, that the wear properties of the high-nitrogen-steel are better than those of comparable conventional tool steels and that a laser treatment leads to a further improvement. Due to the fact that there is a tempered zone between overlapping laser-hardened areas, there is a change of acting mechanisms and, thus a distinct difference in wear rates. For the conventional corrosion resistant martensitic tool steel the difference between the tempered and the hardened zone is not as marked. Neither the wear mechanisms nor the wear rates differ distinctly. These effects and their influence on the wear behaviour is correlated with the microstructure of both steels before and after laser-hardening.     

Wear mechanisms in ball-cratering tests with large abrasive particles

Three-body abrasive wear resistance of mild steel and 27%Cr white cast iron was investigated using a ball-cratering test. Glass beads, silica sand, quartz and alumina abrasive particles with sizes larger than 200 μm were used to make slurries. It was found that the wear rates of mild steel increased with sliding time for all abrasive particles tested, while the wear rates of 27%Cr white cast iron were almost constant with sliding time. This increase in the wear rates of mild steel was mainly due to the gradual increase in ball surface roughness with testing time. Abrasive particles with higher angularity caused higher ball surface roughness. Soft mild steel was more affected by this ball surface roughness changes than the hard white cast iron. Generally, three-body rolling wear dominated. The contribution of two-body grooving wear increased when the ball roughness was significant. The morphological features of the wear scars depended on the shape of the abrasive particles and also on the hardness and microstructure of the wear material. Angular particles generated rough surfaces similar to those usually observed in high angle erosion tests. Rounded particles generated smoother surfaces with the middle area of the wear craters having similar morphology to those observed in low angle erosion.     

Wear mechanisms and residual stresses in alumina-based laminated cutting tools

The outstanding performances of the Al₂O₃ cutting tools in terms of potential cutting speed can lead to substantial economies in the machining of metallic materials.Nevertheless, their widespread use is limited by some drawbacks such as the tendency to edge chipping and to the propagation of microcracks, which can lead to premature failures.These shortcomings are due to the intrinsic low toughness of the ceramic material, which is in turn related to its characteristics non-metallic bonds.A well-recognised method of increasing the toughness of brittle materials is the introduction of surface compressive stresses, which can be obtained through a suitable lamination geometry of the tools as consequence of the different coefficients of thermal expansion (CTE) of the constituent layers.The performances of an alumina/zirconia laminated cutting tool used for machining steel have been investigated and compared to those of a non-laminated commercial alumina/zirconia cutting tool. The different wear mechanisms are explained on the basis of the different microstructures and chemical compositions. We have shown that residual compressive stresses, measured by Piezo-Spectroscopy, are effective in avoiding the microchipping on the flank zone but cannot avoid larger fractures caused by the residual porosity.     

Wear mechanisms in polymer matrix composites abraded by bulk solids

An experimental study of the wear of polymer matrix composite materials subjected to abrasion from bulk materials has been conducted. Three examples of vinyl ester resin systems were considered: (a) unreinforced, (b) reinforced with glass fibres, and (c) reinforced with particles of ultra high molecular weight polyethylene (UHWMPE). Soft and hard bulk materials used for abrasion were granular forms of coal and the mineral ignimbrite. The bulk material was presented to the wear surface on a conveyor belt in a novel wear tester. While UHWMPE reinforcement enhanced the wear resistance to both hard and soft abrasives, the situation for fibre reinforcement was more complicated. With coal as the abrasive, it was found that glass fibre reinforcement reduced the wear rate, whereas in the case of the harder ignimbrite, fibre reinforcement increased the wear rate. Microscopy indicated significant differences in the mechanism of wear in each surface/abrasive combination. Wear textures, consistent with both two and three-body wear, were observed with, respectively, soft and hard abrasive particles.