Tribological Theory Of Tribology

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1.6 TRIBOLOGY
The greek word tribo means rubbing (William 1994). It is the science of intermingling of the surfaces which are in sliding and/or rolling motion. In 1996, Tribology was first reported by Jost, England. It has 3 portions. These are A) friction B) Lubrication and C) wear. To understand the tribological behavior, it entails the knowledge of various subjects such as Physics, chemistry, Mathematics, Thermodynamics, Heat Transfer, Material science etc., Tribological problem leads to the reason of metal failures than the mechanical problem such as fracture, fatigue and plastic deformation.
1.6.1 Friction
Friction is the opposes that the motion (either sliding or rolling) of the object. This oppose force acts against to its motion is called friction force as shown in fig.1.7. The friction is not a property of material, but it is a system response. The ratio of
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If the contact surfaces are free from lubricant, then it is called dry friction. Otherwise it is called fluid friction. The friction is commonly controlled by kinematics of the surfaces in contact, external load, environmental conditions, texture of surface and properties of the materials.

Figure 1.7 Friction force required to cause relative motion by (a) sliding (b) rolling
1.6.2 Mechanism of Sliding Friction
Always the engineering surfaces are not perfectly smooth and flat. It has asperities (ie.,short range perturbations from the mean) and waviness (i.e., long range perturbations from the mean).
At the time of contact of the two surfaces, they touch only at asperities. The applied load is supported by the deformation of contacting asperities. To understand the sliding friction, Coulomb(1992) has developed a model which it is called coulomb model and its schematic diagram is shown in figure. 1.8 Figure 1.8 A schematic diagram for illustration of Coulomb model for sliding

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