Most stressed coils in helical compression springs

[mp87]

Dear spring experts,

Every mechanical handbook provides equations to calculate the torsional stress at the coils of a helical compression spring, corrected for the curvature effect via the Wahl factor. But it is known that not all coils participate to the same extent to the load bearing action, as the edge ones are practically inactive. My question is, is there an equation that allows us to predict which are the most stressed coils of the spring?

Thank you in advance.

 

[MikeHalloran]

Uh,

... the edge ones are practically inactive.

is not quite completely true.

The intermediate coils are stressed in nearly pure torsion.
The end coils are stressed in bending, because they act as levers in order to induce the torsion.

Only completely closed penultimate coils, for which there is not usually enough space, are not greatly stressed.


Mike Halloran
Pembroke Pines, FL, USA

 

[mp87]

Hi Mike,

Thanks for the reply.

The intermediate coils are stressed in nearly pure torsion.

Isn't the Wahl factor aimed at correcting the torsional stress with the bending effect?

The end coils are stressed in bending

Is there any expression that allows to quantify this effect? Should we then brutally split the spring in two regions, one working in bending and the other in torsion + bending? (See above)

 

[MikeHalloran]

What exactly are you trying to do?

Mike Halloran
Pembroke Pines, FL, USA

 

[mp87]

I'd like to put the failure modes in relation with the local conditions the different areas of the spring are experiencing during service. Therefore I would like to estimate the local stresses, if possible with simple spreadsheet calculations.

 

[MikeHalloran]

I've seen FEA done on a spreadsheet, but that was for beams of varying cross section subject to bending with no torsion. A spring has to be a bit more complicated.



Mike Halloran
Pembroke Pines, FL, USA