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Amonton friction

The model proposed by Bowden and Tabor has been regarded as the most successful one for presenting a simple and logical theory capable of explaining the Amontons friction law. However, suspicions concerning the two fundamental assumptions in the model were gradually aroused over past years. Friction has been attributed, in Bowden and Tabor s model, to the adhesion between asperities in contact and torn-off of the adhesive junctions when the shear stress exceeds a critical value. This implies that plastic flow and surface destruction may occur at the moment of slip, and that friction is dominated by the shear strength of the adhesive conjunctions, which is material dependent. [Pg.171]

The coefficient of friction /x between two solids is defined as F/W, where F denotes the frictional force and W is the load or force normal to the surfaces, as illustrated in Fig. XII-1. There is a very simple law concerning the coefficient of friction /x, which is amazingly well obeyed. This law, known as Amontons law, states that /x is independent of the apparent area of contact it means that, as shown in the figure, with the same load W the frictional forces will be the same for a small sliding block as for a laige one. A corollary is that /x is independent of load. Thus if IVi = W2, then Fi = F2. [Pg.431]

Although friction between objects is a matter of everyday experience, it is curious that Amontons law, although of fairly good general validity, seems... [Pg.431]

The basic law of friction has been known for some time. Amontons was, in fact, preceded by Leonardo da Vinci, whose notebook illustrates with sketches that the coefficient of friction is independent of the apparent area of contact (see Refs. 2 and 3). It is only relatively recently, however, that the probably correct explanation has become generally accepted. [Pg.432]

Thus if Amontons law is obeyed, the initial velocity is determined entirely by the coefficient of friction and the length of the skid marks. The mass of the vehicle is not involved, neither is the size or width of the tire treads, nor how hard the brakes were applied, so long as the application is sufficient to maintain skidding. [Pg.438]

Substances in this category include Krypton, sodium chloride, and diamond, as examples, and it is not surprising that differences in detail as to frictional behavior do occur. The softer solids tend to obey Amontons law with /i values in the normal range of 0.5-1.0, provided they are not too near their melting points. Ionic crystals, such as sodium chloride, tend to show irreversible surface damage, in the form of cracks, owing to their brittleness, but still tend to obey Amontons law. This suggests that the area of contact is mainly determined by plastic flow rather than by elastic deformation. [Pg.440]

TWo limiting conditions exist where lubrication is used. In the first case, the oil film is thick enough so that the surface regions are essentially independent of each other, and the coefficient of friction depends on the hydrodynamic properties, especially the viscosity, of the oil. Amontons law is not involved in this situation, nor is the specific nature of the solid surfaces. [Pg.443]

Carpick et al [M] used AFM, with a Pt-coated tip on a mica substrate in ultraliigh vacuum, to show that if the defonnation of the substrate and the tip-substrate adhesion are taken into account (the so-called JKR model [175] of elastic adliesive contact), then the frictional force is indeed proportional to the contact area between tip and sample. Flowever, under these smgle-asperity conditions, Amontons law does not hold, since the statistical effect of more asperities coming into play no longer occurs, and the contact area is not simply proportional to the applied load. [Pg.1710]

The often-cited Amontons law [101. 102] describes friction in tenns of a friction coefiBcient, which is, a priori, a material constant, independent of contact area or dynamic parameters, such as sliding velocity, temperature or load. We know today that all of these parameters can have a significant influence on the magnitude of the measured friction force, especially in thin-film and boundary-lubricated systems. [Pg.1743]

Combining the two previous relations for contact area and friction force gives Amonton s law ... [Pg.233]

Scientific studies of friction can be traced back to several hundreds years ago when the pioneers, Leonardo da Vinci (1452-1519), Amontons (1699), and Coulomb (1785), established the law of friction that "friction is proportional to the normal load and independent of the nominal area of contact, which are still being taught today in schools. Since then, scientists and engineers have been trying to answer two fundamental questions where friction comes from and why it exhibits such a behavior as described above. Impressive progress has been made but the mystery of friction has not been resolved yet. In an attempt to interpret the origin of... [Pg.171]

Microscopic Theory of Amontons s Laws for Static Friction. [Pg.121]

It would appear that no account of friction is complete without first stating Leonardo da Vinci s (or Amonton s) laws and Coulomb s law of friction and pointing out that, in general, polymers do not obey them. The laws are ... [Pg.220]

The first recorded systematic studies on static friction have been carried out by Leonardo da Vinci.1 He had already stated that friction does not depend on the contact area and that doubling the weight doubles the friction. The most important empirical law found for describing friction was published in 1699 by Guillaume Amontons.2 Like da Vinci he measured the force Ff required to slide a body over a solid surface at a given load Fp (Fig. 11.1). The load is usually the weight of the body but it can also contain an additional external force pushing the body down. Amonton found that the frictional force is proportional to the load and does not depend on the contact area. For example, in Fig. 11.1 the loads F[ = Fp are equal, then the frictional forces are also equal Fp = Fp. In other words the coefficient of friction p defined by... [Pg.224]

Figure 11.1 Amontons Law of Friction the frictional Force does not depend on the contact area and is proportional to the load. Figure 11.1 Amontons Law of Friction the frictional Force does not depend on the contact area and is proportional to the load.
For both cases, the assumption that friction is proportional to the true contact area Areai directly leads to Amontons law of friction. [Pg.226]

In his original studies Amontons found a coefficient of friction of 0.3. Meanwhile it has become clear that friction coefficients can assume a whole range of values. With metals, a clear difference exists between clean metal surfaces, oxidized metal surfaces, and metal surfaces with adsorbed gas. Clean metals have coefficients of friction of 3-7. With oxidation, the value decreases to 0.6-1.0. A consequence is that the coefficient of friction can depend on the load. For small loads, friction is determined by the oxide coating. At high loads the microcontacts penetrate the oxide coating, the bare metals come into contact, and the coefficient of friction increases. [Pg.232]

Amontons law of macroscopic, dry friction states that the friction force is proportional to the load and does not depend on the apparent contact area ... [Pg.244]

Assume that Amontons s law of sliding friction can be applied at each elementary area of the interface, such that... [Pg.64]


See other pages where Amonton friction is mentioned: [Pg.185]    [Pg.391]    [Pg.185]    [Pg.391]    [Pg.432]    [Pg.435]    [Pg.1710]    [Pg.1710]    [Pg.1711]    [Pg.273]    [Pg.1]    [Pg.89]    [Pg.74]    [Pg.74]    [Pg.191]    [Pg.273]    [Pg.224]    [Pg.224]    [Pg.226]    [Pg.228]    [Pg.229]    [Pg.235]    [Pg.316]    [Pg.67]    [Pg.64]    [Pg.76]    [Pg.146]   
See also in sourсe #XX -- [ Pg.2 , Pg.391 ]

See also in sourсe #XX -- [ Pg.2 , Pg.391 ]




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