Peaks and valleys of surface irregularities are called

Explanation:

The machined surface is having two types of irregularities:

1. Waviness: Large wavelength deviations are called waviness secondary texture is being produced by machine vibrations chatter errors in guideways etc. 
2. Roughness: Small wavelength fluctuations are called roughness, it appears due to improper selection of cutting fluid development of temperature on the rake face.

Asperities

• Asperities on the hard surfaces act as indenter that results in developing scratches on the soft surfaces due to the relative movement between the mating surfaces under abrasive wear conditions.

Surface roughness

• Whatever may be the manufacturing process, an absolutely smooth and flat surface cannot be obtained.
• The peak and valley 
• The machine element or parts retain the surface irregularities left after manufacturing.
• The surface irregularities are usually understood in terms of surface finish, surface roughness, surface texture or surface quality.

Evaluation of surface roughness:

1. Root mean square value: r.m.s. value
2. Centreline average (CLA) or arithmetic mean deviation (Ra)
3. Maximum peak to valley height (R_t or R_max)
4. The average of five highest peaks and five deepest valleys in the sample (R_z)
5. The average or levelling depth of the profile (R_p)

Root Mean Square Value

RMS value was a popular choice for quantifying surface roughness; however, this has been superseded by the centre line average value. The RMS value is defined as the square root of the mean of squares of the ordinates of the surface measured from a mean line.

\({h_{rms}} = \frac{{\sqrt {h_1^2 + h_2^2 + \ldots + h_n^2} }}{n}\)

Centre Line Average Value

It is defined as the average height from a mean line of all ordinates of the surface, regardless of sign.

\(Ra = \frac{{{A_1} + {A_2} + \ldots + {A_n}}}{L}\)