Table 3.

The logarithmic value of the interfacial stiffness in the direction of the applied displacement $\left(log\left(\frac{\partial {\text{T}}^{\prime }}{\partial \mathrm{\Delta }}\right)\right)$ was linearly related to the Contact Index (CI), Intersection Index (II), Gap Thickness (GT) and the cosine of the loading angle (cos(α)) (r̄² =0.91, p<0.0001) (Regression model 1):

$$log\left(\frac{\partial {\text{T}}^{\prime }}{\partial \mathrm{\Delta }}\right)={\text{a}}_1\text{CI}+{\text{a}}_2\text{II}+{\text{a}}_3\text{GT}+{\text{a}}_{4}cos(\alpha )+{\text{a}}_5.$$

With GT as the only morphology parameter (Regression model 2), there is still a strong correlation between $log\left(\frac{\partial {\text{T}}^{\prime }}{\partial \mathrm{\Delta }}\right)$ and the predicted estimates (r̄² =0.81, p<0.0001).

	Regression model 1			Regression model 2
Regression Model Term	Estimate	SE	p-Value	Estimate	SE	p-Value
CI [−] (a1)	−1.346	0.242	<0.0001	-	-	-
II [−] (a2)	−0.140	0.390	0.72	-	-	-
GT [mm] (a3)	−9.646	0.735	<0.0001	−6.369	0.649	<0.0001
cos(α) [−] (a4)	−0.289	0.046	<0.0001	−0.289	0.068	<0.0001
Constant [−](a5)	3.233	0.154	<0.0001	2.439	0.086	<0.0001