FEMFAT provides various different weld-analysis modeling options. This allows FE shell elements or mixed models (solid and shell elements) to be assessed very efficiently (see figure 1). An additional option is 3D fine modeling using modeling- dependent material data (see figure 2).
Figure 1: 2D Shell elements and 2D & 3D elements
These methods require either the derivation of a shell model from a CAD solid model or a very fine local mesh with or without equivalent radii in the root and toe notches. The latter procedure requires FEMFAT material data for the root and toe nodes.
Figure 2: 3D elements
Figure 3: SolidWELD
In the SolidWELD method which has been available for Channel-MAX since FEMFAT 5.2, the weld roots and toes are analyzed with the help of a modified Critical Distance Method based on a relatively coarse volume mesh (element length less than one third of the plate thickness). The modeling of fine rounding radii for the weld roots and toes is not necessary in this case. The FE mesh is angular at these locations (see Figure 3). A point worth mentioning here: with the ANSA pre-processor, it is possible to create a solid weld betweentwo solid components fully automatically.
Figure 4 und figure 5: Critical Distance Method
The actual calculation is carried out in two steps. The direction of the critical cutting plane is determined for every Solid-WELD node which is identified by means of a specific naming
convention in a set. Initially, the node is assessed as a “normal” base material node for this purpose using the Standard material.
In a second analysis, the node is assessed as a SolidWELD node in the direction of the projection of the surface normal onto the previously determined cutting plane (see figure 5). As sketched in figure 4, the stresses at the two points a1 and a2 are determined and extrapolated onto the position a0 in the direction of the surface. The assessment spacing can be defined in the weld database. The extrapolated stress tensor is determined for the ChannelMAX calculation for every channel and superimposed from all channels. The master S/N curve based on numerous tests used for the analysis is taken from the weld database for the weld toe, root, start and end. Afterwards, the damage or safety factor calculation is carried out taking certain influencing factors into account. Figure 6 shows a visualization of the weld analysis in the FEMFAT visualizer. The nodal results are saved in the .fps file and displayed in the result file (.pro file) with the note “SolidWELD.”
Since the release of FEMFAT 5.2, there is now a convenient additional method for the analysis of welds available to the user. This requires neither the derivation of a shell model nor a fine modeling of the radii at the root and toe. All that is required is the definition of the weld toe and root nodes in sets encoded specially for this purpose.
Figure 6: Results for an Overlap-Joint