New concepts for FEMFAT spot

There are four significant new aspects for the FEMFAT spot module in the release of FEMFAT 5.3: 

  1. Additional modeling options for the SPOT nuggets 
  2. Revision and enhancement of the database
  3. Improved calculation options
  4. Database reading within the FEMFAT session

The following article provides an overview of these new aspects and shows how to successfully transition into the new database.

For a stress-based analysis, it was previously only possible to use one nugget row for the analysis. Now the SPOT analysis can also be done with an additional nugget row, whereby the nugget can be modeled using up to 64 elements; refer to Figure 1.

Figure 1: Model of an extended spot weld nugget with max. 64 nodes

To accomplish this, the nodes must be assigned different colors or displacement coordinate systems and the element types of the inner and outer nugget element rows must be given different material labels or corresponding groups must be created. Details on this are described in the SPOT user manual.

The revision of the SPOT database has resulted in several improvements:

  • Conversion of the database to XML format
  • Definition of the SPOT joints using node colors and MAT labels that can be specified freely or using group names that can be specified freely (previously, areas for node colors, MAT labels, and group names were fixed and could not be modified by the user)
  • Definition of various different fatigue properties for different SPOT connections within a single calculation run
  • The settings for the graphical user interface (GUI) can now also be defined in the database in a connection-specific manner. The database settings overrule the GUI settings.
  • When the SPOT database is read once again, the structure is searched again for the SPOT joints defined in the database (previously, the search for SPOT connections was conducted only when the FEM entities were read)

A converter has been included in FEMFAT 5.3 release package in order to convert old SPOT databases to the new XML format. Version 5.3 no longer supports the old database format. The following FEMFAT start command can be used to convert from the old format to the new format: femfat.bat –spotconv path\old.dbs path\new.xml

With the new SPOT calculation concept, it is now possible to analyze a wide variety of joint types (spot welds, punch rivets, etc.) in a single calculation run.

As can be seen in Figure 2, the different analysis types can be enabled and disabled individually on the FEMFAT GUI:

  • SPOT STRESS (stress-based spot weld analysis)
  • SPOT FORCE (force-based spot weld analysis)
  • RIVET STRESS (stress-based punch rivet analysis)

Figure 2: GUI for defining the SPOT connection types