Coefficient of friction of medium carbon steel

[Desner]

i've been searching for the friction coefficient between medium carbon steels but can't find it,
and also i see everywhere the yield stress of materials but i can't find the compressive stress of materials

 

[SteamKing]

i've been searching for the friction coefficient between medium carbon steels but can't find it,

http://www.engineeringtoolbox.com/friction-coefficients-d_778.html

Look toward the bottom of the table for 'Steel-steel'. The friction coefficients for the various grades of steel will not vary much. As a rule of thumb, the coefficient of friction of metal on metal tends to be relatively high, which is why railroads use steel wheels on steel rails.

and also i see everywhere the yield stress of materials but i can't find the compressive stress of materials

It's not clear what you mean here by "compressive stress".

For metals, the Young's modulus also applies when the material is under compression, but there are other effects, like buckling, which must be considered. If you can be more specific about what you are looking for ...

 

[Desner]

thank you for the quick answer :).
I'm using a very long power screw - loaded with compressive force, I used euler equation for buckling and i know that it is the most risky case,Therefore i already chose a matching screw, But - because it is a project in college, I must show that the screw is not failing at other effects like crush,shear..and i did show that, But i used (Yield stress / Safety facor) as the allowable stress even though i know that the yield stress is only for tension and i need the yield stress for !compressive! force. Maybe you know where can i find the allowable compressive stress.
I'm sorry for my english, I hope everything is clear now.

 

[SteamKing]

Well, it depends on the type of compressive stress you are analyzing and the type of structure/machine being analyzed.

In most structural codes, compressive stress due to bearing or shear is limited to a certain factor of the yield stress, like tensile stresses are. To account for the interaction of the various types of stress, things like Unity Check values were developed by the AISC to determine an overall measure of suitablity for a particular combination of loads. A lot of stress analysis involves a combination of tensile/compressive/pure shear loadings, bending/torsion, thermal, etc.

Since you are designing a power screw, about the only advice I can give you is to check the codes of an organization like AGMA or ASME and see what is recommended for your particular design.

 

[Desner]

Thank you for your helpful and detailed explanation, you helped me alot.

 

[OldEngr63]

http://www.engineeringtoolbox.com/friction-coefficients-d_778.html

Look toward the bottom of the table for 'Steel-steel'. The friction coefficients for the various grades of steel will not vary much. As a rule of thumb, the coefficient of friction of metal on metal tends to be relatively high, which is why railroads use steel wheels on steel rails.

The surface finish of the two part is a significant factor as well as any lubrication present