Femap 6060.Laminate Max. Failure Index calculation

[Mat_Aero]

Hello everyone,

I have a question regarding the 6060. Laminate Max. failure Index computation in Femap. I’ve created basic 2D model of rectangular CFRP plate(M55J prepreg) with layup [(0/+-25/0)2/0]s. I’ve applied tensile load on one end and fixed constraint on the other and performed the analysis. As failure criteria I’ve selected the Tsai-Wu. When I plot the 6060. Laminate Max. failure Index output vector, I see max FI≈0.91 in central bottom part of CFRP plate, however when I checked the FI for each ply independently I’ve noticed that maximum FI was ≈0.11 and lowest FI was ≈-0.91. From that it seems to me that Femap puts the absolute value of FI into 6060. Laminate Max. failure Index output vector which is confusing and does not correspond to real values. I understand that strength ratio is more relevant value to look on, especially for non-linear criteria like Tsai-Wu but can anybody confirm that it is software bug or is there something that I am missing? Thank you for reply. I’ve attached the bdf file of FEM model.

Mat

Images:

https://files.engineering.com/getfi...d1-45af-80ee-edeeb5904942&file=Lam_Max_FI.png

https://files.engineering.com/getfi...5-465b-a183-df33187e5597&file=Lam_Ply2_FI.png

BDF:

https://files.engineering.com/getfi...203-b277-665baa07662e&file=Tsai_Wu_FI_FEM.bdf

 

[rb1957]

what does a -ve FI mean ?

have you asked the help desk ? (sometimes they can be very helpful.)

another day in paradise, or is paradise one day closer ?

 

[Mat_Aero]

FI means Failure Index. I've contacted the Nastran support as well and waiting for their answer. I forgot to attach the printscreen from f06 file.

f06 printscreen:

https://files.engineering.com/getfi...c9-a39c-66ce9bfade46&file=f06_printscreen.PNG

 

[rb1957]

I know what FI means, it is the combination of ratios which should be positive.

I don't understand a "-ve FI" … unless it's coming from the shear term, then taking the absolute value would be correct.

Can you investigate the components of the FI ?

another day in paradise, or is paradise one day closer ?