Torsion Spring Creep 1

[xr4titis]

Hello Forum,

I'm using a rectangular wire torsion spring in a safety device to indicate applied torque. The assembly environment is outdoors and cycles in lifetime < 500.

min tensile strength (not min yield) = 256 ksi
max design stress = 167 ksi
preload stress = 110 ksi

I just wanted to verify some things I've heard with the bright people on this forum.

1. Creep (relaxation) for torsion springs <5%
2. Max design stress should be < 75% of min Tensile stress

Thank you

 

[desertfox]

Hi xr4titis

Provided the ratio of mean coil dia to wire dia is less than 8 then 75% of UTS as a design stress is used particularly if its a spring that operates only infrequently.
I would use a design stress of abou 40-50% personally.
Creep will depend on material used and whether its at an elevated temperature, at room temp your 5% is reasonable.

desertfox