slip coefficient

[italia]

How can I calculate the slip coefficent between two different surfaces?

Where can I find the slip coeffients (min and max) to determine the bolt torque of a bolt (according NASA NSTS 08307)?

Thanks for your attention

 

[Metalguy]

Best sources for bolting in general I know of are by John Bickford, but I don't know about the NASA reference.

 

[Biggadike]

Coefficients of friction can only be measured, not calculated.
If you have both surfaces then it is a simple process, otherwise you need a table of someone elses measurements.

There seems to be a great deal of information and interest in torques for bolts. There are a number of threads already which talk around this problem.
I assume you want to know the correct torque to use on a bolt to give the required compressive force? If you put a washer below the bolt then you have achieved a very standard arrangement. This could help you get accurate data.
This information is bound to be readily available - my first stop would be the bolt suppliers themselves.

 

[CoryPad]

If you want to determine fastener friction coefficients by lab testing, you can use the following procedures:

DIN 946 Determination of coefficient of friction of bolt/nut assemblies under specified conditions

available from Beuth publishing company at:

http://www.beuth.de

SAE/USCAR-10 Test for evaluating the torque-tension relationship of both external and internal metric threaded fasteners

available from SAE International at

http://www.sae.org

If you want to determine friction coefficient for clamped components subjected to transverse loads, there are no standards, but you can perform simple tests. One example is measure the force required to drag one piece with known mass (normal force = mass * gravitational acceleration) across another. The friction coefficient is the ratio of dragging force divided by normal force. Another alternative is to stack the pieces together, then incline the pieces until the top piece slides relative to the bottom piece. The friction coefficient is equal to tan(theta), where theta is the inclination angle.