Welds in FEM
Welds in FEM
(OP)
Hi. During struture simulations how do I specify the welded unions between the parts/bars composing the structure?
Thanks
Thanks
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RE: Welds in FEM
corus
RE: Welds in FEM
RE: Welds in FEM
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RE: Welds in FEM
The same principle would apply in general to fillet welds.
Generally if the throat thickness of the weld, or the total throat thickness at the joint, is equal to or larger than the parent plate then the weld stiffness won't be a factor.
corus
RE: Welds in FEM
RE: Welds in FEM
RE: Welds in FEM
- it reduces resistant area with respect to reality
- it induces stress concentrations at the corner/edges (of course you have to properly interprete these concentrations)
RE: Welds in FEM
i'd be interested to know how you get on with your weld modelling.
Other than yield and ultimate, which will need to be in the dirction of the weld and across the weld, I am unsure how you will enter the test results into the material model. I am thinking more of the fracture toughness, which will almost without doubt be significantly lower than the parent plate.
In turn will you not need to calibrate the descritisation of the mesh around your weld? I can't see how an element can be partially cracked (other than specific crack elements such as ZenCrack which i have heard of but not personally used.)Therfore the crack would step its' way along the elements. This would seem unrealistic other than for a macroscopic model i.e. where the element size equaled the metal grain size (bit unwieldy for any realistic sized structure). In turn if your tests are Charpy (strain rate 1s^-1) is this applicable to your loading/strain rate?
Any way of taking the macroscopic behaviour of the weld outwith the FE model?
Apologies if it's a case of more questions than answers but just bulking the welds in with the rest of the structure just doesn't sit right if you know what i mean.
RE: Welds in FEM
We model the structure without the welds, assuming they will be effective in transmitting the loads.
We later verify the validity of that assumption by extracting from the FEA the nodal forces at weld locations, and then we use hand calculations with code specified weld strengths.
Clearly, for full pen welds, this approach is unnecassary because if the parent metal is not overstressed, neither is the weld, but for fillet welds, esp. intermittent ones, this is a crucial step in the structural analysis/design.
I also agree with crisb's comment as it is a common error with junior/inexperienced FE analysts.
tg
RE: Welds in FEM
Weld joint stress concentrations by using a saftey factor. Also, in the saftey factor should include the lower material strength found in welds due to pores and inclusions. My advice to you is to work with a materials engineering guy who know the details of welding.
Regards
Modey
RE: Welds in FEM
In general for a continuous weld you model it as a continuum but use different material data when analysing for strength and fatigue. Here fatigue is the critical one because welds are usually as strong as the parent material after allowing for any change in properties because of the heat. The big difference comes in fatigue strength.
You also need to consider whether the weld has been dressed to smooth it out. There will be a factor of about 10 difference on fatigue life between dressed and un-dressed welds.
The basic rule of thumb is not to put a weld in a high stress area if you can avoid it. You would need to give more information on your particular components, materials weld geometries etc to get a more specific answer.