Why do i get Different Fatigue results by different mesh size?

Altair Forum User

I'm working on automotive wheel fatigue. I meshed the geometry with Tetra-Volume Tetra (R-trias,Iso layers,elemet size=5)& the fatigue life results is>>>> (min life=0.2, Min simple Average life= 5.9 e 4)
& with mesh element size=6 >>>>>>>>(min life=1.53 e 4 , Min simple Average life= 7.5 e 6)

Would you tell me please Why are the results So different?




I have another question I used the *Solid element* for Fatigue analysis...isn't it better that I use A skin on Solid mesh & i use *Shell elements* in fatigue analysis for better results like it was suggested in Hypermesh tutorial (RD-2070: Fatigue (Stress - Life) Method)?

Altair Forum User

Hi,

Longitudinal element size effect on load sharing, internal loads, and fatigue life.

It is better to use skin if your component acts under bending too as the shell elements compute bending as compared to solid one. Degree of freedom for solid elements are 3 instead of 6 as in shell elements which gives better results in bending, longitudinal and other internal bearing loadings.

But it solely depends on your model and application what to select.

Hope it will help you.

Altair Forum User

Thank you a lot pritam126 for your help...I'll consider your guides about the shell elements.. but my problem with Fatigue life results with different mesh sizes is still unsolved. /emoticons/default_sad.png' alt=':(' srcset='/emoticons/sad@2x.png 2x' width='20' height='20'> ..They're so different ...I'm working on it..I'm trying to keep mesh size the same...where the loads & Constraint are applied...& changing the mesh size for other elements to see if it work for me or not....

Altair Forum User

Hi,

 

could you please let us know, how much does stress vary at the failure zone  with the element size from 5 to 6 mm.

Altair Forum User

hi Prakash Pagadala ...Thank you for attention

 

I have 4 load subcases....and i report max von mises stress from each load for you..

 

with mesh size 5>>>>>stress1=33.1   , Stress2=1.41  , Stress 3=29.86  , Stress4= 9.26

with mesh size 6>>>>>Stress1=30.16 , strees2=1.28 , Stress3=28.38, Stress4=9.29

 

I should mention that because At first the load magnitudes that i used in my Static subcases result in fatigue analyis life=1e20 for all elements..& it's not beneficial for me because I wanna optimize the fatigue life by hypermesh later..and.....I used *Scale= 10* in FATLOAD cards for each load to result in different lifes from Scale 1 result. ..This scale that I changed in fatigue analysis settings doesn't have effect on Results of Static Subcases that I report to you above ...But it consider the (Magnitude of Loads*10) in fatigue analysis..

Altair Forum User

Sepehr.b

 

could you please share the model with us?

 

Please use the dropbox link https://ftin.india.a...iledrop/~BDR1DN to share your model.