Plate-Element

The Nastran plate-Element, also referred to as shell-element (because it is used for normal and shear as well as for bending stress calculation), can be processed by WeldFEM in it's appearance as CTRIA3, CTRIA6, CQUAD4 and CQUAD8 elements.

The CQUAD4-element is the recommended element type to use for a weld evaluation with WeldFEM. The thickness of the elements is given in the property definition section. In case CTRIA6 and CQUAD8 are used, the 1D-line-element representation of welds is provided from corner node to corner node.
The normal stress components σx and σy as well as the shear stress component τxy are result values of the preceding FE-analysis. Both, normal and shear stress components are defined in the local coordinate system of the element. The definition of the CQUAD4-element local coordinate system is shown below as an example.



For the assessment of welds, stresses are to be evaluated in components in the local weld coordinate system. Therefore, a transformation of the provided stress components in the local element coordinate system is required.

This calculation step is done by WeldFEM automatically, thus the engineer nor has to bother to transform the stresses manually neither to orient the element coordinate system of every element in the evaluation range according to the local weld coordinate system.


Stress-Gauge-Elements

Stress gauge elements are plate elements as described above with a thickness of lower than 1 mm, e.g. 0.1 mm.

These elements are utilized to pick up the stresses at faces of 3D-Solid-elements while not affecting the stiffness of the underlying structure. WeldFEM detects them automatically by their small thickness and treats them in general similarly as their counterparts of normal thickness for the stress assessment but specifically with regard to the default settings of adequate weld seam thicknesses, calculation of evaluation distances and input monitoring in the weld editor.


RBE2-Element

The RBE2-element (Rigid Body Element, Type 2) is not a typical element. It uses constraint equations to couple the motion of two or more nodes.
RBE2-elements are often used to simulate weld-like connections. Therefore WeldFEM will detect connections created with those types of elements.

Examples of welds being modelled with RBE2-elements are shown in Weld Detection Considerations.


Note:        So called "spider" rigid elements which couple an independent centre node to a set of dependent nodes are recognised by WeldFEM skipped in the weld detection process.


1D-line-Element

1D-line-elements are used in WeldFEM as dummy-elements to represent the detected welds. These elements are written into the model currently stored in the FEA software.

Informations about the weld in detail are stored in the property name as described e.g. in Weld Editor GUI for DVS 1608 And DVS 1612.

An example is shown below.

Example:        T|a|17.5|25.0-25.0|F3.E4|H-|S235J|st
A fillet weld at a corner joint with an effective cross-section value of 17,5 mm. Both of the welded plates have a thickness of 25 mm. F3 has been chosen for the perpendicular normal stress MKJ-σ, E4 for the parallel normal stress MKJ-σ and H- for shear stress MKJ-τ. The weld is made out of S235J, which is a steel based alloy.


Note:        The same notation is used in the tables of WeldFEM.


For the interaction with Femap, the Spring/Damper element type is used for the weld depiction.
These elements are generated by WeldFEM with a small torsional damping only, see picture below.
With this setting repeated static analysis with the FE-model modified by WeldFEM may be performed without issues. Although the Spring/Damper elements do not affect a static calculation it is recommended to follow the steps mentioned in General Procedure For Weld Assessment.
When re-running dynamic analyses the torsional damping value should be revised as it may have a small effect on the results of the FE-calculation.




For the interaction with Apex, the Beam element type is used for the weld depiction using a PBEAML property definition.

The shape is Rod and the radius is set according to the weld cross section value. No material is assigned.
It is not advised to perform any re-calculations with the model after the weld detection by WeldFEM has been conducted, because beam elements affect the model stiffness and the missing material assignment will cause issues.