Asperity density and asperity radius of curvature

AI Thread Summary
Asperity density refers to the number of roughness peaks per unit area on a surface, while asperity radius of curvature is the radius at the top of these peaks. In contact analysis of rough surfaces, the average radius of curvature is typically used due to the complexity of analyzing individual asperities. The Greenwood-Tripp model is mentioned as a framework for understanding these concepts, with references to relevant literature for further exploration. Measuring the asperity radius of curvature can be approached through specific models and graphs found in academic sources. Understanding these terms is crucial for analyzing surface interactions in engineering applications.
TLDCC
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Hi guys,

The terms above (asperity density and asperity radius of curvature) have confused me for quite a while. I've no clue what they are. Could anyone give me a hand? And is there any relation between them and the summit radius & area per summit? Thanks!

CC
 
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TLDCC said:
Hi guys,

The terms above (asperity density and asperity radius of curvature) have confused me for quite a while. I've no clue what they are. Could anyone give me a hand? And is there any relation between them and the summit radius & area per summit? Thanks!

CC
Hi TLDCC,

I guess you refer to the contact analysis of rough surfaces? In that case, the asperity density is the number of asperities (roughness peaks) per unit area. The radius of curvature is the radius of the top of these asperities (that makes contact with the other body).

Jaap
 
Walker59 said:
Hi TLDCC,

I guess you refer to the contact analysis of rough surfaces? In that case, the asperity density is the number of asperities (roughness peaks) per unit area. The radius of curvature is the radius of the top of these asperities (that makes contact with the other body).

Jaap

Hi Jaap, Thanks for your reply! That does help me. Do you mean the radius of curvature is the average of the radius of all the tops?

Thanks,
TLDCC
 
Hi TLDCC,

In a general contact of rough surfaces, there will be multiple asperities in contact and its undo-able (virtually impossible) to analyze each asperity individual. So yes, the average value will be a good measure.

What is the background of your question?

Jaap
 
Walker59 said:
Hi TLDCC,

In a general contact of rough surfaces, there will be multiple asperities in contact and its undo-able (virtually impossible) to analyze each asperity individual. So yes, the average value will be a good measure.

What is the background of your question?

Jaap

I'm using the Greenwood-Tripp's model but some of the variables confused me. Is there any way to measure the asperity radius of curvature?

TLDCC
 
Hi TLDCC,

That is a coincidence. I'm looking into this model too. I'm busy updating my freeware program HertzWin (see under Toolkit at en.vinksda.nl) with surface roughness influence.

The best I've found so far is to use the graph of the model with the coefficient alpha against P_rough/P_Hertz. You can find in the book of K.L Johnson. Or online in articles like "Deformation due to contact between a rough surface and a smooth ball" from Jamari and Schipper (they did a curve-fit). Or "a compact model for spherical rough contacts" from M. Bahrami et all.

The factor that has the asperities in it is of second order importance.Jaap
 
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