Learning Forum

[Gaddsch]

I have an issue that lets me loose hope on fatigue calculation.

I have an SN Curve (Figure1) and implied it to ANSYS (figure2).

 

 

Now the calculated equivalent stress of 105MPa is way higher than infinite life (that starts at 80Mpa).It results in a stress maximum spot as can be seen in figure below.

In fatigue tool, i applied 4sec of history Data, consisting of approx5000 loadsteps, as can be seen in figure below.

 

Since the variation is in between ~0.8-1.2*Equivalent stress, which is above infinite life, it should calculate valid failure but. Result always looks as below: Whole body is red, showing same number for everything.



Now i noticed that i can change infinite live (red circle in 2 Pictures above) blocks and read in ANSYS help:

"For Stress Life, another available option when conducting a variable amplitude fatigue analysis is the ability to set the value used for infinite life. In constant amplitude loading, if the alternatingstress is lower than the lowest alternating stress on the fatigue curve, the fatigue tool will use thelife at the last point. This provides for an added level of safety because many materials do not exhibit an endurance limit. However, in non-constant amplitude loading, cycles with very small alternating stresses may be present and may incorrectly predict too much damage if the number of the small stress cycles is high enough. To help control this, the user can set the infinite life value that will be used if the alternating stress is beyond the limit of the SN curve. Setting a higher value will make small stress cycles less damaging if they occur many times. The Rainflow and damage matrix results can be helpful in determining the effects of small stress cycles in your loading history."

i figured, that i can play along with that value, however, if i change it what exactly does happen? I get lower result but the min life is calculated and shown on the whole blade instead of highest stress region?

I have no further idea on that, since my load is above infinite load, every help is welcome!!

[YasirLambawala]

Yes, I have also same issue. Can someone help to solve this?