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# Does it matter too much whether to use the centroidal results in FEM model in fatigue analysis?

## Does it matter too much whether to use the centroidal results in FEM model in fatigue analysis?

(OP)
Hi All

a software I am using , doesn't give the centroidal results easily, does it really matter to use centroidal or elemental or nodal to be used in Fatigue analysis ?

Yes.

### RE: Does it matter too much whether to use the centroidal results in FEM model in fatigue analysis?

(OP)
Shall you please elaborate it ?

### RE: Does it matter too much whether to use the centroidal results in FEM model in fatigue analysis?

Is it solid or engineering element (beam/plate/shell), and element order?
If your fatigue analysis algorithm is based on the stress/strain values, which is originally calculated on the Gauss points in conventional FEM. Centroidal/nodal results are essentially interpolated from Gauss point solutions. Thus, in my opinion, the Gauss point stress/strain can give you the most accurate fatigue results. For your case, if the node-based fatigue algorithm is supported for your element type, use the nodal results.

### RE: Does it matter too much whether to use the centroidal results in FEM model in fatigue analysis?

Quoting:

> Thus, in my opinion, the Gauss point stress/strain can give you the most accurate fatigue results.

Not necessarily. Suppose one is doing a fatigue analysis for a cut-out corner, you cannot use gauss point results as they would not be at the edge of the cut-out. You'll have to use extrapolated nodal stresses at the edge of the cut-out to obtain the "correct" Kt stresses for a fatigue evaluation.

### RE: Does it matter too much whether to use the centroidal results in FEM model in fatigue analysis?

SFT - you need to post a lot more details for us to give you useful advice.

### RE: Does it matter too much whether to use the centroidal results in FEM model in fatigue analysis?

it depends. If you're dealing with large scale structures, without discontinuities, you can use centroidal stress to characterise the stress of a large structure.

but if you're analyzing a detail, you probably need nodal stresses ...
unless your fatigue algorithm uses centroidal stress.

clear as mud, eh?

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