15 & 16) S. Text parameters Flashcards
What are the 3 ways a surface length can be defined?
Traverse length (overall length) - cant use the whole traverse length as acceleration and deceleration of machine can make data unreliable
Assessment/evaluation length (the overall segment of surface that is evaluated)
Sampling length (assessment length divided into smaller sample lengths)
What is the reference line?
Centreline average of peaks and valleys (calculated by least squares fit)
What is the roughness average parameter? What does it cover, and what does it not cover?
An average value of the surface roughness.
No information on the shape of the imperfections.
No distinction between peaks and valleys.
Meaningless without a cutoff length applied
What is the difference between sampling length and cut off length?
Sampling length is the physical length of the surface.
Cut off length - profile made to simulate effect of restricting the assessment to the sample length.
How is a peak defined?
The profile must cross the mean line twice.
What is max profile peak height, Rp?
The largest profile peak height (Zp) within a sampling length
What is max valley depth, Rv?
Largest profile valley depth, Zv, within the sample length.
What is maximum height, Rz?
The sum of max peak and max valley.
Rz = Rp + Rv
What is the mean height of a profile?
This is the mean value of all the profile heights within a sample length.
What is the difference between total height and max height of the profile?
The total height considers the whole evaluation length, max height focusses on one sample.
What is the Material Ratio parameter?
Simulates the effects of wear on a surface.
Rmr = a+b+c+c+d / E *100%
What are the short comings of the Material ratio parameter?
It is a function of length rather than area.
It ignores waviness and roughness
In reality, both contacting surfaces will wear.
What is amplitude distribution?
Amplitude distribution can be plotted to show the density or distribution of the peaks of a sample length.
What is the kurtosis parameter?
The sharpness of a surface. Spiky is high value, bumpy is a low value.
What is skewness?
The amount of material above or below the mean line.
Negative skew - majority of material above mean line.
Positive skew - majority of material below mean line
