030070104 Cebrail Yıldırım 9th week

Dry Friction(new&better)[Type of Friction]

When a body slides or is made to slide over the surface of another body, some resistance is encountered which is known as friction. Dry friction is said to occur between two dry and unlubricated surfaces in contact. Dry friction is further divided into sliding friction and rolling friction.

            Sliding friction: When the two surfaces have a sliding motion relative each other, it is called as sliding friction. (e.g. nuts and bolts.)

            Rolling friction: When two surfaces have a rolling motion relative to ech other, it is called as rolling friction. (e.g. ball and rooler bearings)

Moreover, dry friction depends upon the following:

1.      The friction force is directly proportional to the normal reaction between the surfaces for a given pair of matertials.

2.      The friction force depends upon the material of which the contact surfaces are made.

3.      The friction force is independent of the area of contact.

4.      The force of friction is independent of the velocity of sliding.

(H.G. Phakatkar,Theory of Machines and Mechanisms – II, pg. 2)

 

 

Dry Friction (previous)
Dry friction which is also called "Coulomb" friction, describes the tangential component of the contact force that exists when two dry surfaces move or tend to move relative to one another. If the solid bodies are loaded together and a tangential force (F) is applied then the value of the tangential force that is required to initiate motion is the static friction force . It may take a few miliseconds before relative motion is initiated at the interface.
(Bharat Bhushan, Introduction to Tribology, p.207)

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Fluid friction (new&better)[Type of Friction]

When two solid bodies in contact are separated by a thin layer of fluid (gas or oil) the friction is called fluid friction. It is also known as fluid film lubrication. When intervening fluid film is very thin it is called boundary lubrication and when a abundance of lubricating fluid available it is termed as hydrodynamic lubrication. The magnitude of frictional resistance in this case depends upon the magnitude of the relative velocity. This frictional force alse depends on the viscosity of the intervening lubricating fluid present between two bodies.Furthermore, the laws of lubricated surfaces are as follows:

1.      The frictional force is nearly independent of the normal force between the surfaces in contact.

2.      The force of friction is nearly independent of the nature of the frictional surfaces.

3.      The force of friction depends primarily upon the viscosity of the lubricant present between the two bodies.

4.      The force of friction decreases as the temperature increases.

5.      The force of the friction decreases as the relative velocity between the bodies increases.

 

(I.S. Gujral, Engineering Mechanics, pg. 266)

 

 

Fluid friction (previous)

Fluid friction is internal friction in the lubricating film between the friction body surfaces, the surfaces being completely separated by the lubricating film. A difference is frequently made between fluid friction in conformal contact surfaces (hydrodynamics) and in nonconformal contact surfaces (elastohydrodynamics). While rigid surfaces and lubricant viscosity only dependent on temperature are generally assumed in the first case, this cannot be assumed in the second case, in which not only the deformations of the surfaces but also the lubricant viscosity’s dependence on pressure, temperature, and shear rate must be taken into account.
(Springer Handbook of Mechanical Engineering, Grote, Antonsson (Eds.),part B, p302)

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Liga Process (first&best) [Fabrication Process]

The liga process is used worldwide for the fabrication of high aspect ratio microstructures. The main steps of Liga process are the generation of three dimensional structure by means of deep X-ray lithography (DXRL) and electroforming of a complementary metal structure, which can be used as final product or as a mould insert for replication processes.

There is no previous definition.

( Wolfgang Menz, Stefan Dimov, Bertrand Fillon ,4M 2006 - Second International Conference on Multi-Material Micro Manufacture ,Pg. 91)

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İon implantation (first&best) [İmplantation Technique]

Ion implantation is now well-established technique for highly controlled introduction of dopants into semiconductors. Its incrasing use in very large scale integrated (VLSI) device fabrication attests to its fundamental advantages over conventional thermal diffusion techniques: a high degee of reproducibility and precise control of dopant purity, dose and spatial distribution can be achieved by ion implantation doping techniques.

There is no previous definition.

 

(Gérard Ghibaudo,  Effect of Disorder and Defects in Ion-Implanted Semiconductors, Pg. 129) 

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Magnetic Particle Testing (new&better) [Non-Destructive Testing]

Magnetic-particle inspection is based on the fact that when a ferromagnetic material is magnetized, discontinuities that lie in a direction generally transverse

to the direction of the magnetic field cause a leakage field to form at and above the surface. The presence of the leakage field, and therefore the presence of the discontinuity,

is detected by finely divided ferromagnetic particles applied over the surface. Some of the particles are gathered and held by the leakage field.

The magnetically held particles form an outline of the discontinuity and generally indicate its location, size, shape, and extent.

Magnetic particles are applied over a surface either as dry particles, or as wet particles in a liquid carrier such as water or oil.

The magnetic-particle method is a sensitive means to locate small, shallow surface cracks. Those large enough to be seen by the naked eye can produce an indication, but very wide cracks do not produce a particle pattern if the surface opening is too wide for the particles to bridge. Discontinuities that do not actually break through the surface also are indicated in many instances within certain limitations. Fine, sharp discontinuities close to the surface (a long stringer of nonmetallic inclusions, for example) can produce an indication. However, indications of deeper discontinuities are less distinct.

(Guide to nondestructive Testing Advanced Materials & Processes/june 2008, ASM International)

More comprehensive definition.

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Magnetic Particle Testing (previous)

Magnetic particle testing (MPT) is used for the testing of materials (ferromagnetic materials) which can be easily magnetized. This method is capable of defecting flaws open-to-surface and just below the surface.

(Raj, B., Jayakumar, T., Thavasimuthu, M., Practical Non-Destructive Testing, p. 17)