Fatigue analysis "Life" result

Dear OptiStruct users,

I would like to know, in the case of a Fatigue analysis, how to interpret 'Life' results values. If I have a time-based input signal (of y seconds), and the minimum life result vlaue is, let's say 1 000 000, does that mean that my system will resist to 1 000 000 * my input before it fails due to damage? So, in terms of time it will resist during 1 000 000 * y secondes?

Thank you for your help

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Koushik Chandrashekhar_21806

Hi Nathan,

Sytem will resist 1000000 * load input.

But, you can't say, that is true for time.

Nathan_22110

Hi Koushik,

Thanks for your answer. Well, if it resists to 1000000 times my input load, then why it would not be true for time, at least in order of size?

Nathan_22110

Hi Nathan,

Sytem will resist 1000000 * load input.

But, you can't say, that is true for time.

By the way, I asked my question for a time-based input signal. So there is a 'time dimension'. But in the case where One work with frequency-based input such as a PSD.

If the 'Life' result after Fatigue analysis is 1 000 000, and because there is not 'time dimension', what does that mean in term of 'Life time' ?

PSD is computed with FFT from a time history source, am I right? So do we need to know the time duration of this time history source to interpret the 'Life' result from fatigue analysis ?

EDIT : I found for this one, you have to check 'Real' box in Fatseq load collector to define the time duration T

Rex_22369

you need to learn the theory of the fatigue simulation first......

How do you think the damage be calculated?

The software need to find how many cycles at different stress range/amplitude, then use the material S-N curve to find the allowable cycles at different stress range/amplitude......

The damage will be calculated using the test cycles(even you input is in time, but the software will find the cycles) and the allowable cycles.....

Damage=test cycles/allowable cycles

Nathan_22110

Hi,

Thanks for you answer. It's been a while now since I wrote that post, and it is completely clear now. It can be considered as a 'closed' topic /emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />