Allowable Shear Strength of Spring

[kranic24]

I am a design engineer designing extension (tension) springs. Does anyone have technical documents or suggestions on what to use for allowable shear strength for springs? I have seen people use 0.4 times the tensile strength (normally Rm), 0.45 times Rm, and also 0.75 times Rm. These seem like such a general rule, there must be a more equation based solution. Help is appreciated.

 

[TVP]

The ultimate strength in shear does not fit an exact equation. It is often approximated as 0.6*Rm, but as you noted, other values are used as well. This topic has been discussed here, so perform a keyword search and you should find some threads with additional information.

 

[Twoballcane]

Well first, how are you calculating the shear stress of the spring?

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[kranic24]

Thanks for the replies. Shear stress is calculated based on equations similar to:

http://www.efunda.com/DesignStandards/springs/spring_extension.cfm

I should have noted my spring material is stainless steel. Typical sizes are 48mm nominal diameter with 9mm 1.431 V2a wire. Total length typically is around 110 to 300mm.

 

[israelkk]

From the Associated Spring (SPEC)Barnes Group "Engineering Guide to Spring Design" table 7-1, For 18-8 austenitic stainless steels the recommended maximum shear for the spring body is 0.35 of minimum tensile strength. For shear stresses at the ends of the spring 0.3 of of minimum tensile strength and for bending stresses at the ends of the spring 0.55 of minimum tensile strength.

There are also issues of cyclic use (fatigue) and relaxation or creep to take into account.

 

[kranic24]

Exactly what I was looking for. This is perfect Israel. Thank you so much.