Variable fillet to minimize stress concentration

[rstupplebeen]

I am trying to find the description of the variable radius fillet that minimizes stress concentrations. I do not currently have access to Roark's or similar reference. Thank you.

Rob Stupplebeen

 

[rb1957]

petersen has a nice write up, briefly, something elliptical is better than a radius.

 

[cbrn]

Hi,
I presume what Rstupplebeen is looking for is a "polycentric" fillet, i.e. a fillet beginning with a "big radius" and then ending with a "small radius" tangent to the first one.
This kind of fillet is very frequently used in steppings for power transmission shafts, and is the easiest "approximation" of an elliptical fillet (the polycentric one is much easier to machine with CNC machines).
Unfortunately, I don't have any theory reference about how to choose the two radii in order to minimize one (or more) of the SCFs. Where I work, the ratio btw the two radii has been standardized and what I make is usually only a verification of the resulting SCFs.
Regards

 

[MikeHalloran]

Here's a place where you can buy the information:

http://www.esdu.com/graphics/dataitem/75033.htm

Mike Halloran
Pembroke Pines, FL, USA

 

[rstupplebeen]

Thank you all. I was hoping to go more of the elliptical route. So I am going to purchase Roark's and Peterson and hopefully find the appropriate equation or description. Thanks again.

Robert Stupplebeen