Two-body abrasive wear

In abrasive wear by hard particles we often find either two-body abrasive wear or three-body abrasive wear, as shown in Figure 5.3. Two-body wear is caused by hard protuberances on the counterface, while in three-body wear hard particles are free to roll and slide between two sliding surfaces. Wear rates due to three-body abrasion are generally lower than those due to two-body abrasion. Various mechanisms of material removal in these two cases differ only in relative importance. Slurry erosion belongs to the abrasive wear category. Erosion is caused by hard particles sticking to the surface entrained in a flowing liquid. 

Figure 5.3 Abrasive wear by hard particles often means either two-body abrasive wear or three-body abrasive wear (a) three body and (b) two body.

The governing principle of pad conditioning is to introduce friction between the polishing pad and the diamond disc, which characterizes a two-body abrasive wear mechanism. As illustrated in Figure 13.3, the diamond abrasives embedded on the disc create microscopic cuts or furrows on the pad surface to continually regenerate new pad surface and asperities. At the same time, they remove the glazed or accumulated particles on the polishing pad surface. 

As conditioning is primarily considered as a mechanical process characterized by a two-body abrasive wear mechanism [8], the classical Preston equation [62], originally used to model polishing of glass, has been widely used to describe material removal (polishing) rate in [61]. Considering the similarity between wafer—pad interaction and pad—conditioner interaction, the Preston s equation has been adopted by many to model pad wear caused by conditioning. The Preston equation states that MRR is proportional to the applied pressure P and the relative velocity V between the wafer and the pad and Kp is a constant, called Preston s coefficient. 

The work of Soemantri et al. [76] is presented in Fig. 6.15. Figure 6.15a shows the results of the two-body abrasion test, whereas Fig. 6.15b pertains to three-body abrasion. This work was carried out with commercially pure Al and Cu. As can be seen from Fig. 6.15, the wear rate of Cu is independent of temperature for two-body abrasion. Similarly, the two-body abrasive wear rate of Al is also nearly constant even though an increase in wear rate is noted at 323 K. In contrast, the wear rate of Cu increases with increase of temperature during three-body abrasion. However, for Al, the three-body... 

Attrition is the mechanical removal of hard tissue by direct contacts between teeth (either natural or restored) with no foreign substance intervening [5]. This mechanism causes wear by tooth-tooth contacts as well as by tooth-restoration, and indeed restoration-restoration contacts. The action of mastication and bruxism are known causes of attrition. In the field of tribology, the term abrasion refers to the loss of material from a surface by sliding, rubbing or scratching. Two-body abrasion refers to abrasion caused by two contacting surfaces in relative motion, i.e. the mechanism in dentistry that is described as attrition. Three-body abrasion refers to abrasion caused by surfaces in... 

In abrasion or erosion, particles with lower hardness cause less wear than harder particles. When particles are much harder than a surface, the exact value of their hardness matters much less. The relative wear rates by two-body abrasion are associated with a wide range of metals and ceramics, abraded by various types of grit particle. The wear rate becomes much more sensitive to the ratio of abrasive hardness //., to the surface hardness Hs when H.J1 Is is less than 1. Table 5.2 lists the bulk material hardness values for common abrasive particles.12... 

The wear situation is likely to be aggravated should hard additives of a coarser grain fraction be embedded in a softer matrix, such as clay, as the result of an upstream kneading process. This may lead to grain sliding wear (besides a two-body and even a proper three-body abrasive wear), which could, in the absence of an intermediate lubricating medium, have drastic consequences. Similarly, lack of an intermediate medium will favour any likely adhesive wear. 

Abrasion is a form of cohesive wear that can occur in two modes, viz. two-body and three-body abrasive wear. Two-body abrasion refers to a hard rough surface, of which the asperities plough through the relatively stiffer counterface. The surface penetrations cause localised plastic displacement and indentations. Three-body abrasion refers to hard particles between two sliding surfaces, ploughing through at least one of the surfaces. The two are not mutually exclusive, as two-body abrasion can often lead to three-body when hard wear particles are detached from a surface. Abrasive wear is dependent on the bulk properties of the materials and the geometry of... 

Anti-body cleavage A hard anti-body or an anti-body from soft base material with hard inclusions wears out the base body (two-body abrasion). 

Abrasive wear is defined as the material loss when a hard particle is made to slide against a soft material. Abrasive wear is classified as two-body abrasion or three-body abrasion. In two-body abrasion, abrasive particles move freely over a material face as in sand sliding down a chute. In three-body abrasion, abrasive particles act as interfacial elements between the solid body and the counter body. It can be classified as high stress abrasion or low stress abrasion depending on the applied stresses. 

Effect of test temperature on abrasive wear rate (a) two-body abrasion (b) three-body abrasion [76]. 

Results of two-body abrasion testing on experimental and commercial composites and resins are shown in Table 1 (1,3). These data indicate the effect of silanation, amount of filler, type of filler, and characteristics of the resin on the rate of abrasion. Wear characteristics of various experimental dimethacrylate resins have been studied also as shown in Table 2 (4). Two-body abrasion is a useful method for comparison of differences in formulation of composites. 

Wear. Ceramics generally exhibit excellent wear properties. Wear is deterrnined by a ceramic s friction and adhesion behavior, and occurs by two mechanisms adhesive wear and abrasive wear (43). Adhesive wear occurs when interfacial adhesion produces a localized Kj when the body on one side of the interface is moved relative to the other. If the strength of either of the materials is lower than the interfacial shear strength, fracture occurs. Lubricants (see Lubricants and lubrication) minimize adhesion between adj acent surfaces by providing an interlayer that shears easily. Abrasive wear occurs when one material is softer than the other. Particles originating in the harder material are introduced into the interface between the two materials and plow into and remove material from the softer material (52). Hard particles from extrinsic sources can also cause abrasive wear, and wear may occur in both of the materials depending on the hardness of the particle. 

Friction is the resistance against change in the relative positions of two bodies touching one another. If the area of contact is a plane, the relative motion will be a sliding one and the resistance will be called sliding or kinetic friction. If the material in the area of contact is loaded beyond its strength, abrasion or wear will take place. Both phenomena are affected by numerous factors such as the load, relative velocity, temperature, and type material. 

Abrasive wear is a two-bodied wear that is found in a large number of applications where polyurethane is moving over a second object without lubrication. Wheels used on forklifts, trolleys, or any other situation under load are typical examples of abrasive wear. 

Abrasion tests indicate the relative resistance of the polyurethane to two-bodied wear. When choosing a test, the test most suited to the application should be used. The ranking of the results varies with the type of... 

For testing dental restorative materials, many regimes exist that use similar principles to those described for assessing toothpaste abrasivity. These tests may be conducted under conditions of two-body or three-body wear [25], i.e. focussing either on attrition or abrasion. Two-body tests for restorative materials either use human enamel [26] or a hard material, such as alumina [27] or steatite [28], as the abrader. For three-body tests, an abrasive medium, such as toothpaste slurry [29, 30], or an abrasive food, such as rice or millet seeds [31,32], is typically used. These test methods are usually not truly representative of the oral environment rather, they are designed to assess the wear resistance of restorative materials under extreme conditions. 

Abrasive Wear Categories. Abrasion is typically categorized according to types of contact, as well as contact environment. Types of contact include two-body and three-body wear. The former occurs when an abrasive slides along a surface, and the latter, when an abrasive is caught between one surface and another. Two-body systems typically experience from 10 to 1000 times as much loss as three-body systems for a given load and path length of wear. Contact environments (Fig. 5) are classified as either open (free) or closed (constrained). 

Fig. 5 Types of contact during abrasive wear, (a) Open two-body, (b) Closed two-body. (c) Open three-body, (d) Closed three-body...

Keywords Abrasive wear, grooving wear, rolling wear, two-body wear, three-body wear. Microscale abrasion, Polyoxymethylene, Polyamide 6.6, Polybuthylene terephthalate, Polytetrafluoroethylene. 

Probably, the change in wear coefficient with slurry concentration can be explained by the ease of particle entrainment into the contact area and as a result of that, by the transition in wear mechanism from three- to two-body wear. Trezona et al showed that a minimum concentration of abrasive particles is needed to ensure three-body rolling wear [6]. The abrasive particle concentration in the contact area will decrease with increasing load and with decreasing slurry concentration. This means that on the left-hand side in figure 5, with a normal load of 0.5 N, wear will be predominantly two-body grooving. 

When comparing a series of materials, it is important that the measurements are performed under similar abrasive wear conditions. The results obtained in our measurements showed that a wear transition from two- to three body wear can occur depending on the applied normal load and slurry concentration. This is illustrated in figure 10. 

Figure 9. Scanning Electron Microscopy image of the abrasive wear of POM at a SiC concentration of 350 g/1 and a load of 0.5 N. The sliding direction in the photograph is from top to bottom. The surface is worn by predominantly two-body wear.

Reply bv the Authors Fresh slurry is used during the experiments and, therefore, it is unlikely that the switch from two- to three-body wear occurs due to blunting of the abrasive particles. It is unlikely that particles break or blunt as the polymer and the 100Cr6 hardened steel ball are softer than the SiC particles. We expect that at higher load or lower slurry concentration fewer particles are able to enter the contact area, resulting in primarily two-body wear. 

---