# Asperity density and asperity radius of curvature

1. Jan 6, 2012

### TLDCC

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

2. Jan 23, 2012

### Walker59

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

3. Jan 23, 2012

### TLDCC

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

4. Jan 23, 2012

### Walker59

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

5. Jan 23, 2012

### TLDCC

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

6. Jan 23, 2012

### Walker59

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

Last edited: Jan 23, 2012