Zero composite thickness

Altair Forum User

Hi All,

 

I'm currently attempting to run an analysis on a carbon fiber/honeycomb structure.  The composites is set up off of a meshed 2D surface by creating plys to determine the direction, thickness, material, and selecting the designated elements.  They were than organized by creating a symmetric laminate and than a PCOMPP property is assigned to the same 2D elements as the plys.  When I put the 3D element representation on and turn on the composite layers, everything looks exactly how it should, but I am receiving the warning below warning when I run a check in Optistruct.

 

*** WARNING # 1569

for property id =        19.

Thickness is zero for this composite. This will produce meaningless stress

results and may cause singularity of the global stiffness matrix.

 

Property 19 is the property where it assigns the PCOMPP property.  The analysis does run up until it hits error #153 which seems to be caused by the above warning.

 

*** ERROR #  153 ***

 Exactly zero pivoting encountered during Numerical Factorization;

 the model may have rigid body mode.

  Solver error no. =       -503

        spc set id =          2

             index =          1

 Possible reasons are:

 1) insufficiently constrained model,

 2) having rigid body mechanisms within the model,

 3) extremely ill-conditioned rigid element sets,

 4) extremely thin shells (as used for  'skinning') that have MID2/MID3,

 5) gap elements with extremely high stiffness (KA, especially KT or MU).

 Check the model and rerun the problem.

 (MECHCHECK may be used to find the rigid body modes.  To do so,

  change the input to be an eigenvalue analysis and add MECHCHECK.)

 (WARNING: results obtained with MECHCHECK cannot be used because

           the model is changed internally.)

 This error was detected in subroutine bcsmtxfct.

 

Does anyone know what might be causing the initial warning in this model?  It seems weird to me that it says that it has zero thickness but when it's in 3D element representation it shows the thickness of the carbon layers and the honeycomb core.

 

 

 

Altair Forum User

Hi ZDecker3

 

Please check if any plies in the laminate has zero thickness or missing a ply card image.

Altair Forum User

Hi Prakash,

 

Thanks for the response.  I double checked all of the plies and all of them have a thickness and have the PLY card image.  Any other ideas of what it could be?

 

If it helps, I have set up the carbon fiber/honeycomb structure using the steps in 'Composite Optimization with OptiStruct 11.0 on the example of a Formula-Student-Monocoque' tutorial off the Altair website.  The hypermesh version that I am using is v12.0.

Altair Forum User

Is it possible to share the model with us?

 

Please use the dropbox link below in my signature to share the model.

Altair Forum User

Shared in the Dropbox

Altair Forum User

Hi,

 

Edit the laminate and assign the STACK image card to the laminates.

 

also, I can see few elements have missing properties. Please assign relevant property to those elements.

<?xml version="1.0" encoding="UTF-8"?>

Altair Forum User

The elements that didn't have any properties were actually parts of the mesh I was taking out due to those spots having holes so I just deleted those and it fixed the error.

 

Thanks for the help!