×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Friction: Static vs Dynamic

Friction: Static vs Dynamic

Friction: Static vs Dynamic

(OP)
I'm doing an analysis of two mating parts, in which friction plays a prominent role.  Both parts are aluminum.

All the data sources I can find show that the static friction coefficent for aluminum-on-aluminum ranges from 1.05 to 1.35.  However, the dynamic coefficent is given as 1.40.

Here's a typical source:  http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm

How can this be ?  I always thought that the static coefficent had to be greater than the dynamic, i.e., it requires less force to move an object once it's already in motion.  If the dynamic coefficent is higher, wouldn't it effectively BE the static coefficent ?  Somebody please explain how this works !

RE: Friction: Static vs Dynamic

I think that there is something is worng.  I would think that something is worng.  Dynamic coefficent is always less static friction coefficent.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

RE: Friction: Static vs Dynamic

You're (or the link - I didn't check it) is off by one decimal point.  Static values would range closer to .10-.135.

RE: Friction: Static vs Dynamic

and, continuing my last last post, the dynamic friction coefficient is less than the static coefficient.

RE: Friction: Static vs Dynamic

Friction coefficient (FC) can vary as a function of applied load, speed and the environment. I have measured FC for aluminium against steel and also against itself. For Al-steel couple, FC varied from 0.4 to 0.6 whereas Al-Al 0.4 to 0.8, depending on the operating conditions.

The static FC may be lower if it slides on the oxide layer that exists on all aluminium surfaces under low load and speed conditions. In other words, the contact is essentially between oxides of aluminium. Once the rubbing starts, the oxide layer is broken leading to metal to metal contact and thus the dynamic FC is higher.

In any case, it seems odd for FC higher than unity. FC at 0.1 and 1.0 seem to be out of range for dry sliding of Al under ambient conditions.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources