Patran composite sandwich structure modelling 1

[IdeaEngineer]

Hello everybody I could really use some help in modelling sandwich coupons (a honeycomb core between two composite faacesheets) in Patran/Nastran. I am new at the software so excuse me if my questions seem too elementary.

I have identified three methods in which I can model my sandwich.

1) I can model each composite ply and the honeycomb core as a 3-d. My question is when I create each ply as a group how do I specify the bond strength and contact type with the other lamina? I will be looking at interlaminar failure so this is important to me.

2) The second method is modeling the facesheets as a 2-d with the core being 3-d. I will draw a 2-d surface then using PCOMP I will assign the ply properties, however, when I want to "bond" my facesheet to the core do I have to offset by the thickness of my laminate or can I just place on the face of my 3-d core

3) My third method is to just model the whole thing using PCOMP.

Also if someone can tell me the advantages and disadvantages of modeling using one method over the other I would be very appreciative.

Thank you so much,

 

[SWComposites]

It all depends ...

What exactly are you modelling and why? what is the shape/configuration of the structure? how is it loaded? what are the boundary conditions? what do you want to get from the model? displacements, stresses, or something else? what are you going to do with those results? do you have test data to compare the analysis results to?

 

[IdeaEngineer]

ok so just to give you a little background about what I am trying to do. I have tested a few sandwich coupons in a lab till failure, I have done uniaxial tension, compression, 3 point, and 4 point bending tests. Now what I am trying to do is model the test conditions in patran in order to get the same results, once I model the test conditions, I will then try and optimise my structure.

I hope this helps, if you have any more questions just ask.

 

[SWComposites]

method 3 is by far the easiest and probably sufficient for what you are trying to do. presumably the 4 point bend test failed in the facesheet in compression, and the 3 point bend test failed in shear between the core and facesheet - correct? if so, the only test where you need to consider interlaminar stresses is the 3 point bend test. if I recall correctly, you can output interlaminar shear stresses from the CQUAD/PCOMP combination; you can check this with a hand calculation of the core-facesheet interface stress