tribology presentation

1. SURFACE TOPOGRAPHY
Presented by
A. Sabiha Khathun
M.TECH (Machine Design)
16481D1501
Subject: Tribology
GUDLAVALLERU ENGINEERING COLLEGE
Sheshadri Rao Knowledge Village, Gudlavalleru,PIN:521356

2. Why surface finish is important in engineering
application?
Surface texture has marked influence on
 Function
Lubrication
pressure holding capacity
resistant to wear and corrosion
noise reduction
bearing area
friction etc.

3. Surface topography
 It comprises the small local deviations of a surface from the
perfectly flat ideal (a true plane).
 Engineering surfaces never have an ideal geometrical shape,
but instead include different deviations.
 With regards to the level of approximation they can be
considered:
• smooth and even,
• smooth and wavy,
• rough and even,
• rough and wavy

4. So let’s begin by looking
closely at a surface…

5. Micro-geometrical deviations – roughness (important for
interaction of surfaces)
Macro-geometrical deviations – waviness

6. Continued…
Surface texture is one of the important factors that control friction and
transfer layer formation during sliding.
It is the nature of a surface as defined by the three characteristics of
1. Lay
2. Surface roughness and
3. waviness

7.  Lay - The direction of the predominant surface pattern.
 Surface roughness - Closely spaced irregularities.
 Waviness - More widely spaced irregularities.

8. Importance of surface topography
 For many engineering applications the surfaces are
manufactured in order to get some special functioning properties
as bearing, sealing and lubricant retaining capabilities. These
surfaces may be designed to have specific topographical features
that are beneficial for specific functioning applications.

9. Surface roughness measurement methods
and parameters
1. Profilometer
2. Optical interferometer
3. Atomic Force Microscope (AFM)
Parameters: arithmetic mean value (Ra) and root mean square
average (Rq)

10. 1. Profilometer (stylus measurement)

11. 1. Profilometer

12. 2. Optical interferometer

13. 3. Atomic Force Microscope (AFM)

14. Analysis of the measured
surface roughness parameter

15. • Traversing length (LT)-represents the distance that is
traversed across the surface by the stylus when characterizing
the surface,
i.e. measurement length.
• Assessment length(LM) is the length over which surface data
is acquired and assessed.
• Sampling length (LV reference length) -It is a length of a
section inside the assessment length and it is equivalent to
wavelength of the filter

16. Parameters of roughness:
1. Arithmetic mean value (Ra)
2. Root mean square average (Rq)
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Ra
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Rq
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17. 1. Arithmetic Mean Value (Ra)
 The most widely recognized and used parameter for surface
roughness characterization.
 Ra is arithmetical mean deviation of all the measured values in
the assessed profile (LM) from the mean line of that profile.

18. 1.Arithmetic Mean Value (Ra)
Averaging of data:
⇒ Ra
does not differentiate
between profile peaks and valleys!!
⇒ Raor any other parameter by
itself: not sufficient.
⇒ Additional parameters necessary:
more sensitive & able to distinguish
between surfaces with different
shapes and/or ratios of peaks and
Valleys.

19. 2. Root mean square (Rq) : (RMS) deviation of the assessed
roughness profile

20. Surface Roughness in Practice
 Surface roughness design requirements for typical engineering applications
can vary by as much as two orders of magnitude for different parts. The
reasons and considerations for this wide range include:
– Precision required on mating surfaces,
– Frictional considerations
– Fatigue and notch sensitivity,
– Electrical and thermal contact resistance, Corrosion resistance,.
– Subsequent processing,.
– Appearance
– Cost considerations,

21. CONCLUSION
 These factors should be carefully considered before a decision
is made as to the recommendation about surface roughness for
a certain product. As in all manufacturing processes, the cost
involved in the selection should also be a major consideration.

22. THANK YOU