form factor

[scarecrow55]

What's the difference between Form Factor & Stress Concentration Factor when relating to stresses in a stepped shaft - Not the Form Factor as used for gears?

 

[scarecrow55]

I now know (I think) it has something to do with the shape when stressing into the plastic range. Does anyone know where I can get figures from?
Thanks

 

[rb1957]

a form factor is relevant to plastic bending, it is the factor that a linear elastic bending stress can exceed the ultimate strength of the material. In your example, of a stepped shaft, the smaller shaft would be loaded into it's plastic zone, where the larger shaft could still be elastic. You could use a form factor on a gear tooth, but there could well be design "issues" with putting this much load on a gear tooth (most likly fatigue issues).

stress concentration is relevant to fatigue, how much higher the local stress is (say at the step in a staft) than the nominal (average) nett section stress.

 

[rb1957]

most stress analysis books have plastic form factors. bruhn, niu (i think), try a gooogle search ...

 

[valleyboy]

Form factors (or shape factors) are given for a range of differing sections in Roark's Formulas for Stress and Strain.

VB

 

[unclesyd]

Here is an excellent site form University of Illinois, Urbana, posted originally by metengr that should answer your questions.

http://www.fatiguecalculator.com/index.htm

 

[scarecrow55]

Great site Unclesyd, thanks to all