Failure in the weld nugget

Forces and Moments on the Weld Connect for Failure at the Weld

Stresses in the middle of the weld connection are calculated based on elastic beam bending, tension, and torsion formulas:

with:

In these equations, the spot weld diameter is given by d. The forces and moments are calculated at the middle of the weld connection. Weld nugget failures are typically rare if the spot weld connections are produced according to the given rule-of-thumb. A keyword can be set in the Specialist Durability initialization file so that only the sheet failure mode is considered.

For non-proportional loading, the direction of the maximum radial stress can change with time and a critical plane approach is necessary. In this event, the appropriate stresses are mapped into different planes in the same manner that a usual critical plane approach is conducted. The material properties used in this approach are fatigue test results of spot welded structures calibrated with weld or sheet stress. As such, they will depend on the finite element modeling technique. Rupp and co-workers [3] have material property information available for certain materials, notably St1403 as shown in the following figure.

Maximum Radial Stress Amplitude vs. Fatigue Life for Spot Weld Connections in Various Structures (Rupp et al.)

Typically, only the SN-curve for the sheet failure mode is specified. The failure mode of the weld nugget can either use the same SN-curve or a sheet SN-curve with a modification factor applied to it. This is described in the section dealing with the stress-life approach. The default shift factor applied to the sheet SN-curve to obtain the weld nugget SN-curve is 0.7.

Parameter	Unit	Preset	Set in
Diameter	Depends on FE model	5.0	Solution parameters
Calculate Weld Nugget	Boolean	True	Solution parameters
Nugget SN-curves	1	0.7	Solution parameters

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Failure in the weld nugget, Simcenter 3D 2021.1 Series

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