Need advice on FEA results 2

[CobusvanJ]

Hi,

The model being analysed is that of a lifting lug welded to the bottom ring of a support ring halfway up along the vessel.

In the FEA results I am reviewing, the overall von Mises stress plot comes out as 614.99MPa. The person doing the FEA then took a Stress Classification line at this spot through the thickness of the bottom support ring plate, and the membrane+bending stress came to 490.8MPa.

Now membrand+bending stress of 490.8MPa is less than 3 times S, with S being 173MPA (2/3 of the yield strength of SA-516 70), and thus passes.

My concern is the 615MPa von Mises stress. I am not sure of how to approach this value. The value seems very high, does it mean the analysis shows that the model will fail?

 

[TGS4]

The difference between the M+B and the total stress is classified as the peak stress (F). If the M+B stress can be classified as P+Q, then the interpretation is correct. Peak stress is only relevant in fatigue.

I would caution that classifying the M+B stress as P+Q may not necessarily be conservative for your specific situation.

Make sure that the SCL is "valid" per Appendix 5-A. Also, the current limit on P+Q is Sps, which is the greater of 3S or 2Sy.

 

[PaulV7427]

It is hard to say for sure without seeing the actual FEA setup and results. You could be getting false stress concentrations depending on how the analysis was setup. I agree with TGS4 in terms of the conservative aspect. When in doubt I usually go for the more conservative route to be safe. Also, where are you getting your factor of safety for the lifting lug. I recently had to design some lifting lugs for the company I work for (based in Alberta, Canada) and found that regulations dictate that the lifting lug not see more than 5 times the load it was rated for. So we had to use a factor of safety of 5.