Asperity density and asperity radius of curvature

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Discussion Overview

The discussion revolves around the concepts of asperity density and asperity radius of curvature, particularly in the context of contact analysis of rough surfaces. Participants seek clarification on these terms and their relationship to summit radius and area per summit, as well as their application in models like Greenwood-Tripp's.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Asperity density is described as the number of asperities (roughness peaks) per unit area.
  • The radius of curvature refers to the radius of the top of the asperities that make contact with another body, with some participants suggesting it could be considered as an average value across multiple asperities.
  • One participant inquires about the possibility of measuring the asperity radius of curvature and mentions using the Greenwood-Tripp model.
  • Another participant shares resources and references for understanding the influence of surface roughness in contact models, including specific articles and a book by K.L. Johnson.
  • There is mention of the factor involving asperities being of second order importance in the context of the discussed models.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of asperity density and radius of curvature, but there is no consensus on the specifics of measuring these parameters or their implications in different models.

Contextual Notes

Some participants express confusion regarding variables in the Greenwood-Tripp model, indicating that further clarification on these terms and their applications may be needed.

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
 
Last edited:

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