Surface metrology

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Surface metrology is the measuring of small-scale features on surfaces, and is a branch of Metrology. Surface primary form, surface waviness and surface roughness are the parameters most commonly associated with the field. It is important to many disciplines and is mostly known for the machining of precision parts and assemblies which contain mating surfaces or which must operate with high internal pressures.

Surface Metrology is the study of surface geometry, also called surface texture or surface roughness. The approach is to measure and analyze the surface texture in order to be able to understand how the texture is influenced by its history, (e.g., manufacture, wear, fracture) and how it influences its behavior (e.g., adhesion, gloss, friction).

1 Equipment
2 Roughness Parameters
3 Filtering
4 See also
5 References

[edit] Equipment

[edit] Contact

Profilometer - traditionally called a stylus and works like a phonograph
Atomic force microscope

[edit] Non-Contact (optical microscopes)

Vertical scanning:

Horizonal scanning:

SLM - Scanning Laser Microscope

[edit] Resolution

The scale of the desired measurement will help decide which type of microscope will be used.

[edit] Roughness Parameters

The real surface geometry is so complicated that a finite number of parameters cannot provide a full description. If the number of parameters used is increased, a more accurate description can be obtained. This is one of the reasons for introducing new parameters for surface evaluation. Surface roughness parameters are normally categorised into three groups according to its functionality. These groups are defined as amplitude parameters, spacing parameters, and hybrid parameters.^[1]

Parameters used to describe surfaces are largely statistical indicators obtained from many samples of the surface height. Some examples include:

Table of useful surface metrics
Parameter	Name	Description	Type	Formula
R_a, R_aa, R_yni	arithmetic average of absolute values	Mean of the absolute values of the profile heights measured from a mean line averaged over the profile	Amplitude	$R_a = \frac{1}{n} \sum_{i=1}^{n} \left \| y_i \right \|$
R_q, R_RMS	root mean squared		Amplitude	$R_q = \sqrt{ \frac{1}{n} \sum_{i=1}^{n} y_i^2 }$
R_v	maximum valley depth	Maximum depth of the profile below the mean line with the sampling length	Amplitude	$R v = min i y i$
R_p	maximum peak height	Maximum height of the profile above the mean line within the sampling length	Amplitude	$R p = max i y i$
R_t	Maximum Height of the Profile	Maximum peak to valley height of the profile in the assessment length	Amplitude	$R t = R p - R v$
R_sk	Skewness	Symmetry of the profile about the mean line	Amplitude	$R_{sk} = \frac{1}{n R_q^3} \sum_{i=1}^{n} y_i^3$
R_ku	Kurtosis	Measure of the sharpness of the surface profile	Hybrid	$R_{ku} = \frac{1}{n R_q^4} \sum_{i=1}^{n} y_i^4$
RS_m	Mean Peak Spacing	Mean Spacing between peaks at the mean line	Spatial	$RS_{m} = \frac{1}{n} \sum_{i=1}^{n} S_i$

This is a small subset of available parameters described in standards like ASME B46.1 [1] and ISO 4287 [2]. Most of these parameters originated from the capabilities of profilometers and other mechanical probe systems. In addition, new measures of surface dimensions have been developed which are more directly related to the measurements made possible by high-definition optical gauging technologies.

Most of these parameters can be estimated using the SurfCharJ plugin [3] for the ImageJ.

Surfaces have fractal properties, multi-scale mesurements can also be made such as Length-scale Fractal Analysis or Area-scale Fractal Analysis [[4]]

[edit] Filtering

To obtain the surface characteristic almost all measurments are subject to filtering.

[edit] See also

Roughness

[edit] References

^ Gadelmawla E.S.; Koura M.M.; Maksoud T.M.A.1; Elewa I.M.; Soliman H.H., Roughness parameters, Journal of Materials Processing Technology, Volume 123, Number 1, 10 April 2002 , pp. 133-145(13)