ALLOWABLE STRESS OF STEEL SHAFT

[gorkus]

I m trying to calculate the allowable stress of a steel shaft that is subjected to a reverse torsional load. I know calculate the applied stress, but I need this value in order to compare with the applied stress value.
Is there anywhere any formula of the maximum allowable stress value?
Do I need calculate the design endurance limit to know the value of allowable stress?

Than you very much¡

 

[aggman]

Get a copy of Machinery's Handbook. It has a whole section devoted to shaft design. You could also use Schaum's Outlines (Machine Design). Your local bookstore probably carries both.

 

[PSlem]

I just went through this and did design on Design of Welded Structures by Blodgett as other formulas seemed too conservative and it agreed well with field experience. I didn't so much find a limiting stress as limiting amount of twist.

The optimist sees the glass as half full. The pessimist sees the glass as half empty. The engineer see the glass as too big.

 

[PSlem]

I had to get back into this for a meeting next week. Turns out Machinery Hanbook uses 50% of tensile, while Dsn of Welded Struc. uses 75%. The second resource agrees better with experience.

The optimist sees the glass as half full. The pessimist sees the glass as half empty. The engineer see the glass as too big.

 

[mrMikee]

In the past I have used "Shaft Selection" Section of the Rexnord catalog (power transmission and material handling) as a quick check of a design, and I think other vendors have similar info in their component catalogs as well.

In short:

shear stress = 6000 psi for shaft with keys
shear stress = 8000 psi for shaft without keys

Where the safe shear stress is estimated at 1/10 of the average ultimate tensile stress.

There is a formula for shaft diameter that is kind of a cookbook type of approach, but it works and I have used it as a check of my other calculations. Note the significant load factors applied for combined shock and fatigue.

You need to decide however, the applicability of this info to your design requirements.

Regards,
-Mike