Out of phase load for Fatigue

inasiopo
inasiopo New Altair Community Member
edited October 2020 in Community Q&A
Dear all,
 
As I am quite new in fatigue analysis with optistruct I would like to confirm one thing please.
 
We have two loads L1 and L2. Each of them has a FatLoad, so FATLoad1 FATLoad2. And we put them in a Fatseq - fatevn (so fatseq=fatenv=fatload1 + fatload2).
 
Each load has a table (TABFAT) with two points which is: Tabfat1 ---> y1=0, y2=1 and Tafat2 ---> y1=1 and y2=0
So as you can see the two loads are out of phase. When load1=1 then load2=0 and when load1=0 then load load2=1.
When we run the analysis, is this phase difference respected??
 
Basically I do not want to add stresses at the same time, but run fatigue as the two loads are happening on a cycle one after the other. So when we get the life out, we check how many times the part can survive the sequence: Load1-Load2 , load1-load2, load1- load2.......and not (Load1+load2), (Load1+load2), (Load1+load2)....
 
Could someone please confirm if we understand that correctly, and if optistruct will work this way (maintain phase difference)?
I hope I explained the problem clearly enough and I would be really grateful for any response.
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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited June 2017

    Hi @inasiopo

     

    Yes, out of phase loads are considered as it is in OptiStruct. Please read this section in OptiStruct help:

     

    <?xml version="1.0" encoding="UTF-8"?>out-of-phase.PNG

  • inasiopo
    inasiopo New Altair Community Member
    edited June 2017

    So is it only available in Multi-axial analysis? If we use uniaxial analysis the two different fatLoads will not be kept out of phase?

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited June 2017

    Hi,

     

    I don't see any out of phase ocefficient coming in picture when using uniaxial fatigue analysis. But when using non-proportional loads which are out of phase there comes an extra hardening coefficient with phase angle.

     

    Anyways I will cross check the same and I will get back to you. 

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