Rectangular Wire Coil Spring Stress Calculation 4

[Shockdesigner331]

Hello All!
I've been trying to write a matlab program that will calculate stress and deflection of a rectangular cross section coil spring. It has been my hope that I can write an optimization sub-routine just like I have for circular cross section coil springs. I just can't get the theoretical formula to make sense to SMI software predictions!! (SMI - spring manufacturers institute, it's good software and correalates very well to FEA results)

Am i not using the right formula?! I've tried two; NASA design manual formaula, and Roarks. None of these appear to compare to the SMI prediction.

Any help would be appreciated. If you have a formula that seems to work for you please share. Then they can all be located here for all to find!

Thanks.

-Mike

 

[israelkk]

DESIGN HANDBOOK, Engineering Guide to Spring Design 1987 edition, Associated Spring, Barnes Group Inc. Pages 39-40

 

[sbozy25]

SMI formulas work fine for me.

Encyclopedia of Spring Design from SMI in the section dedicated to Compression, Extension, Garter and Torsion Springs. Pages S-18 to S-21.

 

[TVP]

Pages 24.22 to 24.35 of Shigley & Mischke's book Standard Handbook of Machine Design published by McGraw-Hill has the same information as the Associated Spring Handbook mentioned previously. I would post the equation but it references several figures for constants, so you may as well go to a library, etc. to look at the original.