Table 5 Three-dimensional profile characteristic parameters.

Maximum surface peak height S_p

The distance from the highest point in the sampling area to the reference plane:\(S_{{\text{p}}} = \max (S_{p1} ,S_{p2} , \cdot \cdot \cdot ,S_{pn} )\)。

Maximum valley depth on the surface S_m

The distance from the lowest point in the sampling area to the reference plane:\(S_{m} = \max (S_{m1} ,S_{m2} , \cdot \cdot \cdot ,S_{mn} )\)。

Maximum profile height S_h

It is the sum of S_p and S_m: \(S_{h} = S_{p} + S_{m}\), which can better reflect the height of the largest peak and valley of the section

Arithmetic mean deviation S_a

The arithmetic mean of the distance from each point on the surface to the reference plane: \(S_{a} = \frac{1}{A}\iint\limits_{{D_{xy} }} {\left| {z(x,y)} \right|}dxdy\). It is an important parameter reflecting the surface roughness

Height root mean square S_q

The square root of the sum of the squares of the distances from each point on the surface to the reference plane: \(S_{q} = \frac{1}{A}\sqrt {\iint\limits_{{D_{xy} }} {z^{2} (x,y)dxdy}}\), which can better reflect the discrete and volatility of the surface topography

Kurtosis coefficient Sku

It is used to quantitatively describe the flatness and concentration of the surface height distribution. If Sku = 3, it means that the section surface height distribution is a normal distribution. Sku < 3 and Sku > 3 respectively indicate that the height distribution is relatively scattered and relatively concentrated

Autocorrelation length Sal

The autocorrelation length is the length that decays to 0.2 fastest. The larger the Sal, the higher the correlation between points on the surface, that is, the gentle changes in surface height have major low-order undulations

Texture aspect ratio Str

Indicates the degree of homogeneity and anisotropy on the surface. The value of Str is 0 ~ 1. If Str > 0.5 and Str < 0.3, it indicates that the surface has strong allotropic and anisotropic features, respectively