Fatigue analysis according to EN 13445-3

[ta_hr]

Hi!

I would appreciate some help with fatigue analysis of a pressure chamber using EN 13445-3. I did finite element analysis and got maximum stress, i.e stress range for the given load cases. Firstly, I'm not sure if I can use Clause 17, instead of Clause 18. I planned on using Clause 17 since under Conditions of applicability it says 'For fatigue assessment of parts designed in accordance with Annexes B or C, use of this clause is allowed under the condition that the stress ranges taken into account are those resulting from a detailed stress analysis, instead of those given by Equation (17.6-1).' So, I took pseudo-elastic stress range from the results of the FE analysis, instead of using the given formula.

My second question is regarding formulas for welded/unwelded region in Clause 17. I have reinforcements on the chamber which are welded so I assume I should be using both of these formulas depending on the location of the maximum stress? I used surface model for FE analysis and didn't model the welds if that's important.

Thanks in advance!

 

[TomLee777]

Clause 17 is simplified and conservative - stresses are by "code calcs". Clause 18 is detailed analysis, more accurate and less conservative. Since you have done stresses by FEA, why not use Clause 18. Code calcs does not capture notch stresses; FEA does. Which FEA software are you using? If you are using ANSYS, you can import your results to Fatigue+ software for EN 13445-3 fatigue calculations.

For your second question, the reinforcement on the chamber plays a critical role for the fatigue life, which you should include that in your model, but you don't have to model the welds though. The reinforcements will be stress risers that impact fatigue life of the chamber; the welds will inevitably create residual stresses and weld imperfections that would become potential fatigue crack initiation sites. For that reason, lower stress classes are assigned for welded details.