Durability / Fatigue FE Simulation
Durability / Fatigue FE Simulation
(OP)
Dear All,
Is there any approximate simple way to calculate the Fatigue life or durability of metal parts under cyclic loading.
Can I do few cycles of Loading and Unloading and based on the stress / strain results by using some formulae I can approximately predict the critical area under cyclic loading.
How to calculate the permissible stress for durability ?
Thanks
Nidhee
Is there any approximate simple way to calculate the Fatigue life or durability of metal parts under cyclic loading.
Can I do few cycles of Loading and Unloading and based on the stress / strain results by using some formulae I can approximately predict the critical area under cyclic loading.
How to calculate the permissible stress for durability ?
Thanks
Nidhee





RE: Durability / Fatigue FE Simulation
RE: Durability / Fatigue FE Simulation
Another non-free software that integrates with several FE packages is Fatigue Wizard (www.fatiguewizard.com).
Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
RE: Durability / Fatigue FE Simulation
ht
You can't just use this program blindly--by that I mean, fracture mechanics is still more art than science. Do you what Stress Intensity Factor is? Do you know what a crack growth rate curve is and how it is obtained? These are the kinds of questions you need to answer to understand what comes out of these crack growth analysis programs.
The question I would have is what are you trying to do? What is your design criterion? Stress based, or crack (damage tolerance) based? Is your design criterion from some code or manual? What does it specify?
RE: Durability / Fatigue FE Simulation
Well what I have to do there is an assembly of 5 components welded together. During the Loding unloading cycles the weld came out and at another location near the welding there is a crack. So I have to check whether the modification will satisfy the cyclic loading or not.
RE: Durability / Fatigue FE Simulation
RE: Durability / Fatigue FE Simulation
corus
RE: Durability / Fatigue FE Simulation
Doug
RE: Durability / Fatigue FE Simulation
From my experience, you can't weld two parts the same twice, It's also depend on the welder for the quality. If you have access to CatiaV5-Elfini and LMS Virtual Lab durabilty, your job would be easy. If not, your task would be to obtained grid point stresses on the part to convert global load history to grid point stress spectrum for durability analysis.
-h
RE: Durability / Fatigue FE Simulation
Not to take away from all of the previous suggestions but rather to try and stay on topic, your problem is one of fatigue not crack growth. Welds particularly do not lend themselves to this method. First off, you would need to know the actual material crack growth rate and fracture toughness which is kind of hard to do for material that has been welded unless you have tons of test data. What heat treat would one even use? All fracture mechanic evaluations of welds I have seen in my career (far and few) have been related to actual testing. Anyways, my suggestion would be to stay away from fracture mechanics on this one.
My best suggested approach would be for you to perform a very simple but thorough fatigue analysis to ensure that your new design meets requirements. This would mean developing stress concentrations and calculating fatigue lives from Sn curves and using an appropriate scatter factor reduction. In addition, if your loading is well known, you should compare your analytical Kt to that derived from your in-service failure as a correlation point. The best source I know of that is readily available with plenty of fatigue data on welds is ESDU. Here is a listing of their documents on fatigue of welds:
75016 : Fatigue strength of transverse fillet and cruciform butt welds in steels.
76007 : Fatigue of longitudinal fillet welded attachments and joints in steels under axial loading.
76032 : Fatigue strength of longitudinal flange-to-web welds in steel I-beams and T-sections.
77011 : Fatigue strength of transverse butt welds in steel plate under axial loading.
78016 : The effect of post-weld treatments on fatigue at fillet welded attachments.
78023 : Fatigue strength of transverse welded joints and attachments in steels under bending loading.
81007 : Fatigue strength in bending of steel I-beams with welded attachments.
86013 : Guide to the use of Data Items on the fatigue strength of welded joints in steels.
91039 : Static and fatigue strength of butt welded joints in aluminium alloys.
92017: Fatigue strength of cruciform and other fillet welded joints in aluminium alloys.
Good Luck
RE: Durability / Fatigue FE Simulation
Thanks for your valuable comments.