Coulombic friction

Savage [29] derived flow rate equations for a frictional Coulomb material by assuming radial body forces and neglecting wall friction ... 

G. Metcalfe, S.G.K. Tennakoon, L. Kondic, D.G. Schaeffer, and R.P Behringer. Granular friction, coulomb failure, and the fluid-solid transition for horizontally shaken granular materials. Physical Review E, 65 031302, February 2002. 

The friction force g is unknown in general. The Coulomb law assumes g = a and provides the more general relations as compared with (1.48) (Hlavacek et al., 1988 Duvaut, Lions, 1972 Demkowicz, Oden, 1982 Haslinger, Panagiotopoulos, 1984 Namm, 1995)... 

Namm R.V. (1995) On uniqueness of smooth solution to the static problem with the Coulomb friction condition and contact. Appls. Maths. Mechs. 59 (2), 330-335 (in Russian). 

Powder Mechanics Measurements As opposed to fluids, powders may withstand applied shear stress similar to a bulk solid due to interparticle friction. As the applied shear stress is increased, the powder will reach a maximum sustainable shear stress T, at which point it yields or flows. This limit of shear stress T increases with increasing applied normal load O, with the functional relationship being referred to as a yield locus. A well-known example is the Mohr-Coulomb yield locus, or... 

Figure 5-22b shows this phenomenon. When contact is made between the surface and the rotating shaft, the coulomb friction will induce a tangential force on the rotor. This friction force is approximately proportional to the... 

When two bodies are in contact and there is a tendency for them to slide with respect to each other, a tangential friction force is developed that opposes the motion. For dry surfaces this is called dry friction or coulomb friction. For lubricated surfaces the friction force is called fluid friction, and it is treated in the study of fluid mechanics. Consider a block of weight W resting on a flat surface as shown in Figure 2-5. The weight of the block is balanced by a normal force N that is equal and opposite to the body force. Now, if some sufficiently small sidewise force P is applied (Figure 2-5b) it will be opposed by a friction force F that is equal and opposite to P and the block will remain fixed. If P is increased, F will simultaneously increase at the same rate until... 

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... 

For the tangential component of the contact force, a Coulomb-type friction law is used ... 

This P -I type of response curve can also be easily shown to apply to a simple rigid-plastic mechanical system, in the manner shown in Figure 16 (see Refs. 15 and 22). Here, the spring in the system is replaced with a pure Coulomb friction element, with resisting force f, which is independent of displacement once the mass starts to move. All other symbols are defined above. 

We want to analyze here the effect of these long-range Coulomb forces in the large friction limit (396) we shall thus consider the Brownian-dynamic approximation, which, as we shall see presently, gives exactly the same result as the classical semi-phenomenological theory developed in Section V-A. 

Apart from the elastic stress transfer at the perfectly bonded interface, another important phenomenon that must be taken into account is the stress transfer by friction, which is governed by the Coulomb friction law after the interface bond fails. Furthermore, matrix yielding often takes place at the interface region in preference to interfacial debonding if the matrix shear yield strength, Xm is significantly smaller than the apparent interface bond strength, tb. It follows thus... 

In the debonded regions L z - (L - ) and (L - )<,z L), frictional slip occurs between the fiber and matrix and the stress transfer is governed by the Coulomb friction law for a constant coefficient of friction, p... 

Based on the Coulomb friction law, which governs the frictional stress transfer in the debonded interface, and combining Eqs. (4.12) and (4.18) yield the MAS at the interface (r = a)... 

However, some theoretical treatment considers only the special case of friction sliding of a single fiber along a mechanically bonded interface, particularly for some ceramic matrix composites, where the Coulomb friction law applies. See for example Zhou and Mai (1995) and Shetty (1988). Assuming a constant friction at the fiber-matrix interface and neglecting the Poisson effects, Shetty (1988) reported a simple force balance equation for the frictional shear strength, Tfr... 

When an ion with charge q (coulombs) is placed in an electric field E (V/m), the force on the ion is qE (newtons). In solution, the retarding frictional force is /uep, where ncp is the velocity of the ion and/is the friction coefficient. The subscript ep stands for electrophoresis. The ion quickly reaches a steady speed when the accelerating force equals the frictional force ... 

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 ... 

In this section we discuss dry friction, also called solid or Coulomb friction. Solid friction occurs when two solid surfaces are in direct contact without any other components like lubricants or adsorbed surface layers involved. The reader might object that in practice no such... 

The validity of Coulomb s law has been verified also on the nanoscale Zworner et al. [484] showed that, for different carbon compound surfaces, friction does not depend on sliding velocity in the range between 0.1 /xm/s and up to 24 /xm/s. At low speeds, a weak (logarithmic) dependence of friction on speed was observed by Gnecco et al. [485] on a NaCl(lOO) surface and by Bennewitz et al. [486] on a Cu (111) surface. This can be modeled when taking into account thermal activation of the irreversible jumps in atomic stick-slip [487],... 

The second empirical law for dry, macroscopic friction is that of Coulomb Friction does not depend on the sliding velocity. 

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