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How does a simple fatigue study actually work?

Question asked by Jacek Michalski on May 24, 2020

Hi,

 

I'd like to understand how fatigue study works for simple cases like the one described below.

Let's say that I have a model with complex shape subjected to combined loading (some kind of machine part). I perform static analysis and then proceed to fatigue study selecting "Constant amplitude events with defined cycles". I define the S-N curve data for my material and add new event specifying the number of cycles, loading type (let's assume zero-based) and associate static study. How will the software calculate the number of cycles to failure with these settings ? Will it simply compare the stress intensity (difference between max and min principal stress) at each point (known from static study) with S-N curve or perform some additional operations too ?  From what I've seen in analysis options, mean stress correction is turned off by default so this factor won't be included in such analysis (even for zero-based cycle). Rainflow counting also won't apply since the amplitude is constant. Is there anything else the software calculates in a case like that ? What about the cumulative damage ? I guess that it's not used as well for constant amplitude cycles. By the way, why do we have to specify the number of cycles in even settings ? Is it needed only for damage calculations ?

 

Thanks in advance for your help

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