How to include fillet welds in FE model.

[brightinstinct]

I am seeking guidelines to model welds in my FE assembly.
My need is to solve a linear static analysis on a lifting eye of a earth mover.
I have meshed the parent parts saperately (not equivalenced).Further i need to include welds in the FE assembly.Following questions are bothering me at this moment.
1) do i need to create geometry of weld fusion region and mesh it with 3d elements?
2) Or traiangular fillets would serve the purpose?
3) how would i connect weld mesh with parent meshes(parts)?
4) Can i use contact with MPC184 algorithm to connect welds with parent mesh?
5) from where i can get material properties for welds?
6) what is the current practice for modelling 3D welds in FEA?

May i have your idea on this?
Thanks in advance

 

[Drej]

All you need to know is the answer to your question number (6): which is, no-one* models welds explicitly in FEA. There are many reasons for this, but principally because there are too many unknown variables, including:

1) You do not know the exact geometry of the weld
2) You do not know the internals (the structure) of the weld (level of porosity, say). The internals (and externals) could contain holes caused by poor welding conditions, which could lead to localised stress concentrations. In extreme cases this could lead to non-intuitive load paths.
3) You do not know the behaviour at the interface of the weld
4) You do not know the properties of the weld/adjacent structure i.e. the HAZ, principally owing to the high-temperature nature of the welding process affecting the properties, how the weld was allow to cool, the rod(s) used, the level of competency of the welder...
5) And so on...

Too many unknowns here, so the standard convention is to ignore modelling the weld geometry itself, but to model the structure as-is and then carry out some standard hand calcs on the weld using the forces from the FE. Alternatively, if it's a lifting eye, you could do the whole thing as a hand calc quite easily. For a fillet weld, normally you'll need to use the "throat area" in your calculations. Search the archives here (and in the Structural Engineering forum) for more info.

* Possibly in universities or in some very high tech R&D companies, but I would say very, very rarely in "normal" industry.


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