Composite failure vs failure index

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

Hello,

 

I have some doubts about composite failure and composite index, relatively to the composite analysis postprocessing. As far as i think, composite failure is a number which should be compared to one according to the composite resistance theories (Tsai-Wu, Hoffman ecc).

 

But then what does 'failure index' mean? And what 'Plies with Maximum FI'? Which is the relationship between th failure index and the composite failure?

 

Thank you

 

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2015

    Hi Fede54,

     

    When you are looking at composite failure you can see the Bond failure indices. So composite failure gives an insight of micro level results for the structure.

     

    Where as Failure index is what deals with macro level results (individual ply failure index).

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2015

    Ok thank you... so which index should be less than one in order to grant the composite resistance according to the classical failure criterions (Tsai-Wu ecc)?

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2015

    Fede54, 

     

    Failure index should be less than 1.

     

    Failure index less than 1 indicates that failure of composite is not taken place.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2015

    Anyone of you please tel me the use of Max. stress failure theory and where we have to use this? And why we are not using the other failure theories instead of Max. stress theory?

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2015

    Hi Jodha,

     

    According to this theory, Failure occurs when the response stress reaches Ultimate stress in longitudinal/ultimate stress in transverse or ultimate shear stress.