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Important Note to students(Applies to all course material related to Tribology)

This material is only an excerpt of the class room lectures prepared as per the syllabus

contents.

It needs to be supplemented with material from text book and other sources.

P.M. Anil Asst. Professor S.G SMBS VIT Universit

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.

You need to prepare additional notes wherever required.

Evaluation questions may be expected from material not covered in the slides but discussed

during the lectures.

Few Figures/photos/Graphs etc. have been removed because of upload limit.

To be used for internal circulation only.

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Tribology

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Tribology


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FrictionWear

Lubrication

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PEOPLE Leonardo da VinciLeonardo di ser Piero da Vinci (April 15, 1452 May 2, 1519) was an Italian Renaissancepolymath: painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor,

anatomist, geologist, cartographer, botanist and writer. Leonardo has often been described asthe archetype of the Renaissance Man, a man of "unquenchable curiosity" and "feverishlyinventive imagination.

Considered to be one of the greatest painters of all time and the most diverselytalented person ever to have lived.

Amontons' Laws of Friction were first recorded in books during the late 17th century.

Guillaume Amontons(1663 1705)


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Charles-Augustin de CoulombCharles-Augustin de Coulomb (14 June 1736 23 August 1806) was a French physicist. He is bestknown for developing Coulomb's law, the definition of the electrostatic force of attraction andrepulsion. The SI unit of charge, the coulomb, was named after him.

BEAUCHAMP TOWER (1845-1904)Towers Spherical engine was a unique contender in the

rotary steam engine market

His experiments led to the revelation of

pressure development in a fluid film.

Source : http://www.wikipedia.org/

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Why Tribology ?

Losses resulting from ignorance of Tribology amountto 4 % of the GDP of every country


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One third of worlds energy resources in present use

appear as Friction in one form or other

A saving of 1% of GDP can be realized by research

and better tribological practices

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Surface

Surface Characteristics


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GeometricCharacteristics

Physico-ChemicalCharacteristics

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GEOMETRIC CHARACTERISTICS

ERROR OF FORM

+


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WAVINESS

+

ROUGHNESS

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Error of form : -

Any deviation from the intended surface profile.

Caused due to the errors in the manufacturing


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process.

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Waviness :-

Large waves generated on the surface due to machine toolvibrations


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Features on the surface other than error of form andwaviness.

Lay : - The direction of the predominant surface pattern.

Flaw :- Any defect on the surface (Inclusions, voids,

porosity, cracks, etc.)

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PHYSICO-CHEMICAL CHARACTERISTICS


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Physisorbed Layer:

Gases like Oxygen, Argon, Krypton, etc. andwater vapor gets adsorbed to a clean surface

Thickness of the layer- 0.3 nm


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Chemisorbed Layer:

Electron sharing between the chemisorbed species

and the solid surface-covalent bonds Energy required to remove these bonds are high

Depends on the purity of the surface

Layers are monomolecular

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Chemically reacted layer:

Most of the metals react with oxygenForms oxides on the surface

Interaction continues till a thick layer is formed(10-100 nm)


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Beilby Layer:

Melting and surface flow during machining ofmolecular layers

Generally amorphous or microcrystalline


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ayers ge ar ene ue o e a acen co me a Thickness 1-100 nm

Heavily deformed layer and Lightly deformed layer:

Machining makes surfaces highly strained

Smaller grains due to recrystallisation of the layers

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ROUGHNESS MEASUREMENT

1. Contact type instruments (stylus measurements):-

Stylus measurements transform the vertical movements

of the stylus to corresponding electrical signals.


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2. Non-contact type of instruments :-

a. Pneumatic devices

b. Optical devicesc. Transmission electron microscopy

d. Reflection electron microscopy

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ROUGHNESS PROFILE


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ROUGHNESS MEASUREMENT

Methods

1. Mean or M-System:- The mean line is taken as thecentroid of the profile. Areas above and below the lineare equal.


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. -The average heights/depths of five highest peaks andfive lowest valleys is determined.

3. Method of least squares

A reference line is fixed in such a way that the squareroot of sum of squares of the vertical deviations fromthis line is minimum

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SCHEMATIC OF A SURFACE PROFILE


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Extreme value height descriptors

Rp Distance between the highest asperity and mean line

Rv Distance between the lowest valley and mean line

ROUGHNESS PARAMETERS


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Rt Distance between the highest asperity and lowest

valley

Rz Difference between the averages of five highest

asperities and five lowest valleys.

Rpm Distance between the average of five highest peaks

and mean line

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1. Mean of a profile

2. Variance

Roughness height distribution


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. an ar ev a on

4. Skewness

5. Kurtossis

Surfaces with same Ra Value

Bearing Area curve

Bearing Ratio

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ROUGHNESS HEIGHT DISTRIBUTIONS


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Non-Gaussian DistributionGaussian Distribution

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ROUGHNESS

Gaussian distribution:- The Gaussian (normal) distribution washistorically called the law of errors. It was used by Gauss to model errorsin astronomical observations, which is why it is usually referred to as theGaussian distribution. Gaussian probability distribution is perhaps the mostused distribution in all of science.


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The probability density function for the Gaussian distribution with mean and standard deviation is given by the following formulas.

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ROUGHNESS HEIGHT DISTRIBUTIONS

Non-Gaussian Distribution


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Turning, shaping, EDM, Milling,

Honing, Grinding, Abrasion processes

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BEARING AREA CURVE


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True area and Geometric area

Conformal contact

Contents


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on con orma con ac

Elastic Half space

Hertzian contact

Friction

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ELASTIC HALF SPACE

In Non- conformal contacts the pressures at the contact

spots are very high.


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as c con ac eory.

A semi-infinite elastic solid bounded a plane surface.

Strains are small within the contact region.

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HERTZ CONTACT THEORY(1882)

Assumptions

1. Surfaces are smooth, continuous and

(1857 1894)German physicist


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2. Strains are small

3. Each solid is an elastic half-space in the contact region

4. Surfaces are frictionless

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P

HERTZ CONTACT THEORY(1882)

Contact area will be circular


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3

1

*4

3

=

E

PRaContact radius = a

Ball radius = R

Maximum contact pressure = Po

=

20

2

3

a

PP

a

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