Learning Forum

[Gaddsch]

Hello,

I made a small transient Structural Analysis of a Turbine Blade. But I am unable to calculate the "Life" in the Fatigue Tool because i do not choose "history Data"? It just shows the same lifespan over the whole shovel even thoghEquivalent Stress clearly shows weak spots where it should fail earlier.

 

I read in other Post about how to load history Data but not quite understand why i cannot use my Solution?
Same goes for the Rainflow, the reason i made the transient analysis is to calculate the loading cycles for that varying load, so why i cannot use my solution??

Thank you for any help

[Naveed]

Dear Gaddsch, 

Can u attach high resolution screenshot of your details view? What is the Display Time in fatigue tool? For example, if it is 1s, software will see stress at 1s and calculate the life based on that value of the stress. 

[Gaddsch]

Hello Naveed, thank you for your reply. Your question helped me as well, we might probably be hanging at the same thing.

"Equivalent Stress not beeing a Load but  a result" opened my eyes. I always missunderstood that completely.
Could you link me the fatigue tool handbook you were referring in your other post?

I attached you the 2 screenshots and hipe they are detailed enough. One in Exported Pressure and one of "Equivalent Stress" in Solution

So you mean, i need to deactivate "Display Time somehow?" I just put it on "P" and try what will change. If i find out anything else, i ll let you know

[jj77]

Just in case someone would look here also:

 

I think you want to use the transient analysis and do a fatigue analysis on that - now I have never done that, but I would recommend to write it up nicely what you want to do, and send it to ansys support and ask them if this is possible (they should be able to say a yes or no, and briefly tell this can be done), because there does not seem anyone even from ansys that has managed to respond to your questions (I would say it is perhaps possible if one uses advanced fatigue tools like ncode, but ask ansys support).

 

What the history data does here (this is done in static analysis normally) is to multiply a unit load case (and hence just scales/multiplies the stress results from the unit load case, that is why one can input a scale factor) case according to the history data (this says how the unit load varies with time) in a static structural and then does rainflow counting and sums the damage, and this is not what you are asking for (now I do not have any experience on this matter except of writing some simple fatigue code for Strand7 which is the software I work with).

[Gaddsch]

I answer here, because i do not want to spoil naveeds original question with some topic regarding my own problems, thus related.

I guess i switch to statical and try the following (please correct me if i missunderstood somewhere)

1) I import load in static structural to my blade, as can be seen in the image below:

2) I calculate the Equivalent Stress Via Ansys.

3) get History Data out of Meassured Signal? to do step 4: Measured signal is pressure fluctuation over time and looks like this:

4) Imply Ansys Fatigue which will use the calculated equivalent Stress and modulate with History Data, uses rainflow to calculate cycles and sums inflicted damage out of it

So step 3 is where i am hanging, (if i understood step 4 correctly out of what you and peter told me so far)

 

If i kept that going, the result would be ok for me: All other option is see, to calculate Equivalent Stress in Transient and do fatigue live calculation via S-N by myself. Problem here is, that the solution is way too low (underneath infinite life threshold)

 

 

Thank you again jj77. You wont know how much i appreciate your guys help! if I you guys help me find a solution a meal invetation is getting mandatory


And edit:
I reached out to ANSYS as you mentioned. Thank you for beeing precise on that, now at least i know there is nothing i have missed but simply no possible way without n-code.

[Gaddsch]

Edit: Would that work:

i try to get a ratio of my pressure signal to the equivalent stress.

So i plan doing few analysis what equivalent Stress is calculated at certain pressure. Out of that i want to have a factor, that transforms me the pressure signal into equivalent stress

Pressure(t)*Factor=MaxEquivalent Stress(t).

By doing that, i create the history data, that i implement in mz static structural and calculate a valid life... Does that make sense?

[Gaddsch]

Allright, no i am really kinda lost here. Any idea why i am unable to put this file into "History Data"
Did everything as usually and till now it worked fine...

 

[Naveed]

Sorry for late reply. First of all, I cant recall which fatigue handbook are u asking about. But I can send some ppts and PDFs, just leave your email here. 

Second, as Legend Peter and JJ concluded about history data and display time, it is now clear that entering the display time will show us the fatigue life at that specific stress on STRESS/TIME graph.