Equivalent stress range of fatigure analysis

[DavidLX]

Hi,

That's for Sec VIII Div 2 Part5 and using Solidworks Simulation. How to get equivalent stress range? Under pressure vessel design, obtain peak stresses by linearizing of both high and low load, then get the difference of them. Or, make difference when sum results by pressure vessel design, then linearize the difference to get delta Spk?

Thanks!

David

 

[TGS4]

For a fatigue analysis, you should be concerning yourself with peak stresses. Therefore, I would not linearize anything. And make sure that you perform the stress differencing calculations at the component level (and not at the invariant level)

 

[DavidLX]

Hi TGS4,

I don't quite understand "at the component level". I checked ASME code again. On P547 equation 5.29, the delta Spk should be von Mises, and need to get the difference first for every node. Am I right?

Thanks for your help?

David

 

[TGS4]

If you follow equation 5.29, you will find that the stress ranges are first calculated on at the component level, and then rolled up into an equivalent stress range, delta Spk. The k refers to the fact that this calculation needs to be done at every node. The equation shows that the stress ranges are first calculated at the stress component level.

In other words, you don't take the difference of the von Mises stresses, you take the differences of the component stresses, and use those component stress ranges to calculate an equivalent stress range.