Static Friction (Stiction) Values

How about buying some samples of these materials, some weights, and a linear scale--and performing some experiments?

I'm reduced to experimentation on a limited budget if I can't find the tables, but that gets too expensive to contemplate for the myriad combinations involved.

ME nor Material Science is my engineering field. However, I've had to work with motion control in a wide range of environments. I doubt that you will find a single, simple answer to static friction between any two materials. Many different conditions will change the initial force required to dislodge two things in contact: atmosphere or any lubricating fluid between surfaces, deformation of either surface, cold welding, Van der Waals attraction, hydrogen bonding, redox reaction, length of time between motion. I added the length of time to this list because I believe that all of the other static friction contributers have a time based differential component that will asymptotically approach a maximum value. So one cannot easily predict what the static friction value will be.

At the same time, my motion control experience says that providing a force margin of 50% above the kinetic friction will be sufficient for overcoming the added static friction. Don't forget the force needed to get the desired acceleration.

Yes, I know that static friction is usually greater than 120% of kinetic friction, but where are the kinetic tables for polymers and elastomers?

My search is not for 'how much force is needed to overcome',rather it is 'how much force can it reliably resist before movement'.

Relying on static friction to keep something in place sounds like a recipe for failure to me.

If the static friction is 1000 lbs and the max force is only 200 lbs, then there is more than sufficient over-engineering for safety.

Yes, in the given condition motion will not happen. However, you're ignoring my earlier point. Static friction is not constant. A nominal maximum is 20% of the friction coefficient.

A nominal maximum is 20% of the friction coefficient.
What do you mean by and refer to this?

What, exactly are you doing?

Tornado's suggestion makes even more sense now.

If you are dealing with O-rings it can get complicated.

I'd like to lock a 1"x1"x33" PEEK member that rides through a 4" long PEEK housing. The locking element can be elastomeric, but you see that the other side is PEEK. I could put an elastomer on that side too, but I need low kinetic friction when repositioning .

No O-rings. This is slab of PEEK on slab of ....

All that I'm looking for is a table of COEFFICIENTS OF STATIC FRICTION for PLASTICS and ELASTOMERS. I know that these coefficients have been measured.....so where are they? I see kinetic friction tables all over the place but almost none referring to plastics or elastomers.Those that do only list the outliers like teflon and nylon and "rubber" on metals,wood,stone,etc.

It's like I'm the first person in the universe to think that teflon might touch buna-n!

Just tell me where this information IS! If it's in a book, tell me! I'll buy it. If it's on the web.,give me a link...god bless you and the horse you rode in on.

Maybe you're just the first person on the planet who wants the information presented to them without any personal effort.

Bearings are not normally made of this combination of polymers. O-rings, maybe.

You may find Pv values, but you may have to do your own testing for this.

Manufacturers will be the best source, if the information exists..

This information relevant to your requirement probably will only be obtained from your own specific testing / experimentation since the specs are going to be limited to a particular material. It's doubtful you will find something directly related to the stiction between PEEK and Viton(which one?) unless you just happen to know of a manufacturer that has done the testing for some reason.

Good luck with it though.

http://www.dupontelastomers.com/Tech_Info/techInfo.aspx

You will need to know which material you are after since Viton is simply a trademark name and there are a ton of different formulations.

http://www.interstateplastics.com/specifications.php?material=PEEK&vid=201206031324-4p

PEEK