Mean stress correction for seam welds

If you calculate the fatigue life of seam welds using SN-curves from like the International Institute of Welding (IIW) or Eurocode catalogs, special mean stress corrections are recommended.

The mean stress correction parameters in Specialist Durability are:

• SW/NS/EC3 High RS

• SW/NS/EC3 Low RS

• SW/NS/FKM Recommend

• SW/NS/IIW High RS (cat III)

• SW/NS/IIW Med RS (cat II)

• SW/NS/IIW Low RS (cat I)

Seam weld SN-curves from the mentioned recommendations are determined for R=0.5. Hence the mean stress correction lowers the equivalent amplitude for tension-compression loads. If there are high residual stresses, you should therefore use no mean stress correction—this is done by the parameters SW/NS/EC3 High RS and SW/NS/IIW High RS (cat III).

Eurocode 3 Recommendation

FKM Recommendation—Choose Appropriate M

IIW Recommendations

Example

In the following the method is shown at an example for the mean stress influence factors (without the seam weld parameters).

We consider a cycle with real amplitude 100 MPa. We calculate the equivalent stress amplitude for different values of the R-ratio value. We set the slopes to their default values: M = 0.3, M1 = 0.3, and M3 = 0.1.

Example: R=0.5; parameter NS/3 Segments

In this case the loop cycles between 100 MPa and 200 MPa, and the mean stress is 150 MPa.

In the following table, we show the resulting equivalent stresses for different parameters and mean stresses:

Parameter	R = –¥	R = –1	R = 0	R = 0.5
NS / None	100	100	100	100
NS / Goodman	85	100	115	145
NS / 3 Segments	85	100	115	136
Torsion / 1 Segment	115	100	115	145
Torsion / 2 Segments	115	100	115	136

Learn more

Mean stress correction for normal loads

Mean stress correction for shear loads

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Mean stress correction for seam welds, Simcenter 3D 2021.1 Series

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