COMSOL 6.2 - Evaluating Stresses in Welds

Evaluating Stresses in Welds

Weld evaluation consists on the calculation of stresses and forces transmitted by the weld. These are computed on the plane of the weld throat, and different criteria can be used to compute equivalent stresses and safety indexes. It is currently possible to perform weld verification in the interface for double-sided and single-sided fillet as well as butt joints. It is assumed that the 3D solid model can be approximated by shells.

To perform a weld evaluation, you select the check box in the feature in the Shell interface.

The weld evaluation is a postprocessing tool and it is performed during result presentation. It is not necessary to recompute the solution if the welding type, the weld size, or the allowable stresses are changed. It is enough to update the solution.

The evaluation is based on the shell section forces at the weld edge on the source side of the connection. From these forces, available from the interface, only the components that are transmitted through the weld are kept. The forces are transformed to the weld reference frame. The equivalent stress is computed as follows:

where the contribution of the normal stress parallel to the weld throat is neglected because it does not transfer any load through the weld.

For a single-sided fillet, the top and bottom options switch the sign of the eccentricity used to compute the additional stresses due to bending.

Different safety indexes are available to evaluate the weld: failure index, damage index, safety factor, and margin of safety.

Source and Destination Selection

When interested in weld evaluation the source and destination in the feature needs to be selected in a proper way to obtain meaningful results for the one-sided and double-sided fillet joints. The source has to be the edge belonging to the plate that would have both top and bottom sides welded if a double-sided fillet was to be used.

Limitations

The weld evaluation for the fillet welds assumes that the connecting shells are perpendicular to each other and the angle between the shell and the throat plane is 45 degree.

When using a double-sided fillet weld, one side is more critical than the other. The results will always show the safety factors on the most critical side, where usually the shear stresses are greater. The single-sided fillet is treated in the same manner.

Variable Names

When the weld evaluation check-box is selected, a set of new variables are defined. All of them are item scoped and the most important are listed below.

Table 2-20: Variables for weld evaluation.
variable	description
weld_di	Damage index
weld_ms	Margin of safety
weld_fi	Failure index
weld_sf	Safety factor
weld_seq	Equivalent stress along the edge
weld_tfwavgi	Traction vector average in the weld reference system, i component
weld_tfeavgi	Traction vector average in the edge reference system, i component