Rainflow Fatigue Damage Calculation

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  • Rainflow Fatigue Damage Calculation
Stuart Smyth

Posted on 01.07.2020 17:58

Hi


Was there any further update to the forum post below?



I am experiencing similar issues. As a test setup I have strain gauged a tuning fork and analysed two loading scenarios, one that is repeatably loading the fork at its natural frequency so the cycles are high and the load range changes over time due to the damping and the other is manually bending the forks. Which produces much less cycles but higher stress ranges.


Like the previous post the Damage value that is calculated vs the dewesoft value are very different. I have attached a number of files below outlining the issue. Is it possible to extract the actual values etc and the equation that is used for the damage calculation within the module.


Attached files:
Stuart Smyth

Posted on 01.07.2020 18:26

In the training documentation the SN curve is defined as the stress range from EN 1993-1-9. I'm using a very similar curve from DNV CP203 (base material not weld detail). However, whenever the stress is defined as the stress amplitude (Stress range / 2) and not the stress range, the results appear much closer to the hand calculation.



Another example



Is this just a coincidence or should the stress be defined as the amplitude?

Jernej Sirk
NVH Application Engineer
Posted on 02.07.2020 14:28

Dear Mr. Smyth,


in the previous version the SN curve needs to be defined in Amplitude. In the newer version (SP12) you can select in SN curve editor, if you want to define your SN curve in Amplitude or Range.



Best regards,


Stuart Smyth

Posted on 02.07.2020 15:51

Hi Jernej


Thanks for your response - I updated to SP12 and can confirm that everything is working great. Obviously the values are highly dependant on the bin width etc.



Thanks.

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