Sigma 1

[buran2000]

What is the meaning of the sigma number that appears in the materials properties? Example:

Max Principal
-2 Sigma Life 6.0E+06
-3 Sigma Life 8.0E+05

Thank you for your help

 

[TVP]

Usually sigma means stress or strength measured in MPa (N/mm²). There are various strengths, such as Yield Strength, Ultimate Tensile Strength, Fatigue Strength, etc.

 

[NickE]

Or it could be the statistics of teh failure band of the material....

 

[MintJulep]

Need more info on the context, but I think Nick is on the right track. Sigma is commonly used to identify the standard deviation.

 

[prost]

I would agree with NickE and MintJulep--these numbers give you the statistical variation in fatigue life for a given stress level on the S/N diagram. The Fatigue lives for several coupons tested at the same stress level will vary, sometimes as much as one order of magnitude or more. I would guess that whoever derived these numbers used a normal distribution to fit fatigue data at various stress levels. "Sigma" then is the standard deviation of a normal distribution fit to the fatigue data at a given stress level.

 

[buran2000]

Thanks a lot mates.