Hello,
I have to model the contact between two surfaces. To do that, I use a constitutive contact model, in which I need the 3 roughness parameters Rq (RMS rugosity), etha (number of asperities /m²) and R (asperity radius).
The problem is : I know how to obtain these values with 3D surfaces measurements with PSD or fractal means, but for ONE surface. When I have to study a contact, I have TWO, so I need some equivalent properties to put in the model.
From what I read, it seems I have to take Rq,eq = Rq,1+Rq,2, 1/R,eq=1/R,1+1/R,2 and for etha I don't know...
I am not sure about these relationships and I don't know if they are always true.
Does anybody have some clue ?
Thanks a lot
Rémi
Bonjour,
La formule ressemble beaucoup au calcul de résistance équivalente en électronique!!
Le paramètre R ne semble pas être un paramètre normalisé de rugosité.
Etant donné qu'il s'agit de surface je me serais orienté vers des critères de rugosité 3D genre Sa ou Sq ou Sz Spk....
En réalité pour choisir le bon critère de rugosité, il faut connaitre le but de cette modélisation? le contact est modélisé pour étudier l'usure, le frottement, ou l’étanchéité?
Hi,
Considering the McCool's paper (Wear, 107 (1986) 37 - 60), for an isotropic rough surface the following holds:
Rq = sqrt(m0)
R = 0.375sqrt(pi/m4)
etha = m4 / (6pisqrt(3)m2)
Therefore, with Rq, R, and etha of one surface, you can find the equivalent m0, m2, and m4 of that surface. The equivalent m(0, 2, 4) for two surfaces are the summation of the same parameter of each of them, i.e. m0_eq=m0_s1+m0_s2, and so on.
Hi,
It is not an answer, more a question along the post before:
Isn´t the material type relevant for your simulation (soft vs. hard material)
Isn´t the contact type relevant for your simulation (force, friction, dynamics...)
What is the purpose of the simulation? You want to simulate friction coefficients? Wear behavior?
Sometimes a simple Mr1/other Bearing Curve parameters will give a good estimate for the total contact area for heat/force transfer.
KR, M
Hello everyone,
thank you all for your answers. Most of them are really helping.
I need these parameters to define a friction contact model in quasistatic loading. I am not trying to model wear or heat generation or other more complex things.
The model I used is an equivalent stochastic surface model, the separation between surfaces is a mean parameter for all the surface and the tangential displacement is assumed to be the same on all the surface. I am not trying to model some local phenomenons.
For now, I measure the 3 roughness parameters I need by using the procedure described by Soheil. I do that for each surface and then I sum the spectral moments of the PSD for the equivalent contact surface.
But I would like to have a completely analytical model, without need of surface measurement. So I am trying to link the usual parameters Ra, Sm, etc. to the 3 I need. I have found some relationships but they seem to be very noisy...for example, an empiric formula linking the mean radius of asperity to the Ra, etc.
Thanks again.
Rémi
Ht-index might be of use for characterizing roughness:
https://www.researchgate.net/publication/236627484_Ht-Index_for_Quantifying_the_Fractal_or_Scaling_Structure_of_Geographic_Features
https://zenodo.org/record/49059#.VwX9Y3ouf6D
Article Ht-Index for Quantifying the Fractal or Scaling Structure of...
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