Allowable Contact Stress

You can get an estimation via the equivalent "von Mises" stress. For it you should compute all stresses in the directions x and z (i assume that the cylinder axis is "y") and build up the von mises maximal value which will appear at a depth roughly 50% of the contact width. If you use hardened steels you should consider the Re limit at the hardness you expect to obtain. In the different books SKF or FAG or INA put at the disposal of the users you can find a lot of indications. What you have to consider is that 2 cylinders with parallel axis in contact will present at the ends of the shorter stress peaks which are VERY important and could lead to destruction. In roller bearings the rolling elements are NOT cylindrical but have a profile for stress optimization especially at roller ends. For Bearing steels as 100Cr6 for instance (it is an European steel with 1% C and 6%Cr) you can have up to 3.000N/mm^2 for ball contacts and about 2000 N/mm^2 for cylindrical contacts.

You can do also an attempt of inverse engineering taking several roller bearings and computing back the stresses by use of the Hertz equations. Since you have the safe loads (from catalogues) you can determine the capability of your design.

If you have more questions I shall be happy to help you and since I doubt that details are interesting for all you can send a direct message with your questions.

The contact stresses between cylindrical parts (compressive) shall not exceed the allowable tensile strength of the given material at design temp. If you specify your material in ASTM, we can find its allowable tensile strength.

My analysis, using Roark Table 33-2b, and the design parameters, indicate a calculated max compression of 57000psi. I am using 316L HR Stainless Steel, with a reported tensile strength of 70ksi. My design factor would be about 1.2. Are compressive stresses allowed to be at this magnitude for rolling elements?

Does your design allow you to work in the elastic-plastic range? If that is so, you can limit your design based on the tensile strength. Otherwise design should be based on the yield strength.

Hi,

Could you please give more specific details on which stress has to be considered.

Thanks

Thanks, nick name, for all your help. Your offline instruction and assistance was much appreciated. I now clearly understand the stresses involved and how they impact my design.