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udar (Structural) (OP)
29 May 06 13:59
Hi,

Which program performs fatigue analyses by FEM, both elastic and elasto-plastic domain? I am interested in thermo-mechanical fatigue.
Thank you!
Udar
Stringmaker (Mechanical)
29 May 06 14:31
To my knowledge (I may be putting my foot in my mouth here) there are no FEA programs which do fatigue calculations via the FEM.  Fatigue calculations are typically performed by taking user-specified criteria (mean and alternating stress life curves, etc) and using this data a calculation is performed on the areas of interest from an analysis.  I think if you search this forum a little bit you'll find some more postings similar to your question.  The FEM is useful for predicting failures such as fracture, delamination, and catastrophic events (such as a bladeoff or bird strike within a turbine engine).
Helpful Member!  johnhors (Aerospace)
29 May 06 15:25
There are several fatigue softwares that can directly take FEM stress results for use in a spectrum of cases and perform fatigue damage or life calculations on every node, and then pass the results back to your post processor for viewing. I can suggest that you take a serious look at www.fatiguewizard.com which can do either stress-life or strain-life based fatigue analysis and out performs most if not all of its more expensive competitors.
Stringmaker (Mechanical)
29 May 06 16:54
Sorry I should have been more clear in my posting.  Almost every major FE software company has some sort of fatigue capability available.  Fatigue is not calculated via the FEM however.
johnhors (Aerospace)
29 May 06 18:42
FEM is based or directly derived from theory of structures (or whatever phenomena you are modelling) using well established formulae. Fatigue is empirically based, that is there is no theory to follow, just a bunch of rather strange (IMHO) methodologies that appear to fit remarkably well with test data, e.g. rainflow analysis, Miner's rule, Goodman equivalent stress and so on, which really has nothing to do with FEM, since the source of stress history is quite commonly taken from hand calculations or strain gauge readings. For this reason you will only find fatigue software in the form of add on modules when using FEM.
Helpful Member!  cbrn (Mechanical)
30 May 06 3:00
Hi,
adding to JohnHors:
- Fatigue add-ons of commercial FEA programs performs automatically post-processings you can perform yourself "by hand" (well, at least with Excel...)
- without having a Fatigue add-on, you can proceed like this:

1- a) run a solution for every loadcase which composes your load history, or b) run a transient analysis in which you save the result data for every time step
2- for every loadcase, have your program list the nodal or element stress values you are interested in
3- import the data in Excel (if you have more than 65000 nodes, split the results files)
4- set up in Excel the Voeller or Design Fatigue curve, the Haigh correction, etc, as needed
5- calculate the cumulative damage node by node, and then find the MAX value.
You're done winky smile  !!

Regards
udar (Structural) (OP)
30 May 06 3:09
Thanks to all for advises!
What dou you think about fe-safe software? (which works with major FEA programs) see:www.safetechnology.com
Does anybody work with it?
tanks in advance
udar
Helpful Member!  corus (Mechanical)
30 May 06 4:17
Fe-safe is worth considering but it's best to go on one of their training courses, run by John Draper who started the business, before clicking on buttons to produce pretty pictures. CosmosWorks Advanced Professional also produces a life prediction based upon SN data (from user input or library data) and a load history, though I doubt if it's advanced as FE-Safe for looking at biaxial stress, for instance.

corus

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