Surface roughness can be regarded as the quality of a surface of not being smooth and it is hence linked to human (haptic) perception of the surface texture. From a mathematical perspective it is related to the spatial variability structure of surfaces, and inherently it is a multiscale property. It has different interpretations and definitions depending on the disciplines considered.

In surface metrology

Surface roughness, often shortened to roughness, is a component of surface finish (surface texture). It is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. In surface metrology, roughness is typically considered to be the high-frequency, short-wavelength component of a measured surface. However, in practice it is often necessary to know both the amplitude and frequency to ensure that a surface is fit for a purpose.

Roughness plays an important role in determining how a real object will interact with its environment. In tribology, rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good predictor of the performance of a mechanical component, since irregularities on the surface may form nucleation sites for cracks or corrosion. On the other hand, roughness may promote adhesion. Generally speaking, rather than scale specific descriptors, cross-scale descriptors such as surface fractality provide more meaningful predictions of mechanical interactions at surfaces including contact stiffness^[1] and static friction.^[2]

Although a high roughness value is often undesirable, it can be difficult and expensive to control in manufacturing. For example, it is difficult and expensive to control surface roughness of fused deposition modelling (FDM) manufactured parts.^[3] Decreasing the roughness of a surface usually increases its manufacturing cost. This often results in a trade-off between the manufacturing cost of a component and its performance in application.

Roughness can be measured by manual comparison against a "surface roughness comparator" (a sample of known surface roughness), but more generally a surface profile measurement is made with a profilometer. These can be of the contact variety (typically a diamond stylus) or optical (e.g.: a white light interferometer or laser scanning confocal microscope).

However, controlled roughness can often be desirable. For example, a gloss surface can be too shiny to the eye and too slippery to the finger (a touchpad is a good example) so a controlled roughness is required. This is a case where both amplitude and frequency are very important.

Parameters

A roughness value can either be calculated on a profile (line) or on a surface (area). The profile roughness parameter (${\displaystyle Ra}$, ${\displaystyle Rq}$, ...) are more common. The area roughness parameters (${\displaystyle Sa}$, ${\displaystyle Sq}$, ...) give more significant values.

Profile roughness parameters^[4]4">edit

The profile roughness parameters are included in BS EN ISO 4287:2000 British standard, identical with the ISO 4287:1997 standard.^[5] The standard is based on the ″M″ (mean line) system. There are many different roughness parameters in use, but ${\displaystyle Ra}$ is by far the most common, though this is often for historical reasons and not for particular merit, as the early roughness meters could only measure ${\displaystyle Ra}$. Other common parameters include ${\displaystyle Rz}$, ${\displaystyle Rq}$, and ${\displaystyle Rsk}$. Some parameters are used only in certain industries or within certain countries. For example, the ${\displaystyle Rk}$ family of parameters is used mainly for cylinder bore linings, and the Motif parameters are used primarily in the French automotive industry.^[6] The MOTIF method provides a graphical evaluation of a surface profile without filtering waviness from roughness. A motif consists of the portion of a profile between two peaks and the final combinations of these motifs eliminate ″insignificant″ peaks and retains ″significant″ ones. Please note that ${\displaystyle Ra}$ is a dimensional unit that can be micrometer or microinch.

Since these parameters reduce all of the information in a profile to a single number, great care must be taken in applying and interpreting them. Small changes in how the raw profile data is filtered, how the mean line is calculated, and the physics of the measurement can greatly affect the calculated parameter. With modern digital equipment, the scan can be evaluated to make sure there are no obvious glitches that skew the values.

Because it may not be obvious to many users what each of the measurements really mean, a simulation tool allows a user to adjust key parameters, visualizing how surfaces which are obviously different to the human eye are differentiated by the measurements. For example, ${\displaystyle Ra}$ fails to distinguish between two surfaces where one is composed of peaks on an otherwise smooth surface and the other is composed of troughs of the same amplitude. Such tools can be found in app format.^[7]

By convention every 2D roughness parameter is a capital ${\displaystyle R}$ followed by additional characters in the subscript. The subscript identifies the formula that was used, and the ${\displaystyle R}$ means that the formula was applied to a 2D roughness profile. Different capital letters imply that the formula was applied to a different profile. For example, ${\displaystyle Ra}$ is the arithmetic average of the roughness profile, ${\displaystyle Pa}$ is the arithmetic average of the unfiltered raw profile, and ${\displaystyle Sa}$ is the arithmetic average of the 3D roughness.

Each of the formulas listed in the tables assumes that the roughness profile has been filtered from the raw profile data and the mean line has been calculated. The roughness profile contains ${\displaystyle n}$ ordered, equally spaced points along the trace, and ${\displaystyle y_{i}}$ is the vertical distance from the mean line to the ${\displaystyle i^{\text{th}}}$ data point. Height is assumed to be positive in the up direction, away from the bulk material.

Amplitude parametersedit

Amplitude parameters characterize the surface based on the vertical deviations of the roughness profile from the mean line. Many of them are closely related to the parameters found in statistics for characterizing population samples. For example, ${\displaystyle Ra}$ is the arithmetic average value of filtered roughness profile determined from deviations about the center line within the evaluation length and ${\displaystyle Rt}$ is the range of the collected roughness data points.

The arithmetic average roughness, ${\displaystyle Ra}$, is the most widely used one-dimensional roughness parameter.

Parameter	Description	Formula
Ra,[8] Raa, Ryni	Average, or arithmetic average of profile height deviations from the mean line.[9]	${\displaystyle Ra={\frac {1}{l_{r}}}\int _{0}^{l_{r}}\left|z(x)\right|dx}$[4][5]
Rq, Rms[8]	Quadratic mean, or root mean square average of profile height deviations from the mean line.[9]	${\displaystyle Rq={\sqrt {{\frac {1}{l_{r}}}\int _{0}^{l_{r}}z(x)^{2}dx}}}$[4][5]
Rvi; Rv	Maximum valley depth below the mean line, within a single sampling length; Average Rv value over assessment length [4]	${\displaystyle Rv_{i}=|\min z(x)|}$; ${\displaystyle Rv={\frac {\sum _{i=1}^{n}Rv_{i}}{n}}}$[4]
Rpi; Rp	Maximum peak height above the mean line, within a single sampling length; Average Rp value over assessment length[4]	${\displaystyle Rp_{i}=\max z(x)}$; ${\displaystyle Rp={\frac {\sum _{i=1}^{n}Rp_{i}}{n}}}$[4]
Rzi; Rz	Maximum peak to valley height of the profile, within a single sampling length; Average Rz value over assessment length[4]	${\displaystyle Rz_{i}=Rp_{i}+Rv_{i}}$;[4] ${\displaystyle Rz={\frac {\sum _{i=1}^{n}Rz_{i}}{n}}}$
Rsk	Skewness, or measure of asymmetry of the profile about the mean line.[9]	${\displaystyle Rsk={\frac {1}{Rq^{3}}}\left{\frac {1}{l_{r}}}\int _{0}^{l_{r}}Z^{3}(x)dx\right}$[5]
Rku	Kurtosis, or measure of peakedness (or tailedness) of the profile about the mean line.[9]	${\displaystyle Rku=\frac{1}{{R_q}^4}\frac{1}{l_r}{\int <!--\; \int \; -->}_0^{l_r}{Z}^4(x)dx}$Zdroj:https://en.wikipedia.org?pojem=Surface_roughness Text je dostupný za podmienok Creative Commons Attribution/Share-Alike License 3.0 Unported; prípadne za ďalších podmienok. Podrobnejšie informácie nájdete na stránke Podmienky použitia.  Navigácia: Veda > Analytika Antropológia Aplikované vedy Bibliometria Dejiny vedy Encyklopédie Filozofia vedy Forenzné vedy Humanitné vedy Knižničná veda Kryogenika Kryptológia Kulturológia Literárna veda Medzidisciplinárne oblasti Metódy kvantitatívnej analýzy Metavedy Metodika Metodológia vedy Náboženstvo a veda Náučná literatúra Podvody vo vede Popularizácia vedy Potravinárstvo Prírodné vedy Pseudoveda Scientometria Spoločenské vedy Teórie Teatrológia Technické vedy Technika Terminológia Umenie Výskum Veda Veda a technika podľa štátu Veda a technika podľa kontinentu Veda a technika podľa roka Veda v kozme Vedci Vedecká literatúra Vedecké databázy Vedecké experimenty Vedecké konferencie Vedecké metódy Vedecké ocenenia Vedecké organizácie Vedecké parky Vedeckí spisovatelia Vzdelávanie Záhady Príbuzné výrazy: Text je dostupný za podmienok Creative Commons Attribution/Share-Alike License 3.0 Unported; prípadne za ďalších podmienok. Podrobnejšie informácie nájdete na stránke Podmienky použitia. www.astronomia.sk | www.biologia.sk | www.botanika.sk | www.dejiny.sk | www.economy.sk | www.elektrotechnika.sk | www.estetika.sk | www.farmakologia.sk | www.filozofia.sk | Fyzika | www.futurologia.sk | www.genetika.sk | www.chemia.sk | www.lingvistika.sk | www.politologia.sk | www.psychologia.sk | www.sexuologia.sk | www.sociologia.sk | www.veda.sk I www.zoologia.sk