Composite laminate

PF1PF1
I am trying out Mecway for some composites (FRP, carbon, etc). Normally I just need to analyze plates. So I created this simple laminate composed of a top mat layer and 4 biaxial layers. I have applied a load of 2 PSI (I think) in the Y direction. The edges should be fixed (could be pinned, but just want to compare to my spread sheets).

The laminate seems to be too stiff. It should have a deflection of about .01 inch, but the analysis shows .001, off by about 10X.

I am new to FEA :) , although I am quite familiar with structural modeling programs like RISA. So please excuse my lack of understanding as I learn this stuff. I think this program can be of use. Victor has been answering some questions and I thought I would put it on the forum.

TNX

Peter

Comments

  • VictorVictor
    Not sure if you uploaded the right file. This one has a zero solution.
  • PF1PF1
    You mean in the displacement min-max? It should be .001 -2 inches.

    Also not sure how to load in the Tsai-wu failure data.
  • PF1PF1
    Here is an updated model. Not sure why the displacement min-max did not show correctly. Hopefully this one does (now min=.001,Max=1). I cannot get the failure results to work (first ply failure, safety factors). This laminate should fail at a displacement of about 7/8". The laminate is 24" square. Anyway...I'm sure I am doing something wrong!
  • VictorVictor
    edited July 2020
    The file I see has only a single element with all nodes constrained so the displacement is 0 everywhere. I changed it to make it like your description but get 1.3 inch maximum displacement magnitude, not either of the solutions you described.



    Since this is a simple geometry, you could use a solid model as a reference solution, making each layer a layer of elements. There are effectively only two isotropic layers. I can make that model for you if you like, but would like to confirm I'm working with the correct material properties and everything.
  • PF1PF1
    TNX Victor! The material Gxy was off by 1000X which I fixed (should have been 410 KSI and not .41 for example). I did not bother to load the corrected one as I had bigger issues. This looks great and I can play with this. I was not setting the BCs correctly and you helped there. Let me play with this. In the big picture I would normally look at various layer types and angles. But normally the plys would be no more than 3 types, a mat and 2 structural layer types.

    There is another geometry that I will need to look at too which would be a hollow cylinder.

    TNX
    Peter
  • PF1PF1
    Hi Victor....here is the laminate that you fixed with some adjusted layer property data. The stiffness of this FEA laminate is a little over twice that of a manufacturer's spread sheet using the same figures. In other words the deflection is about 1/2 that of the spread sheet. We could refine it further which makes a small difference. I went with the same laminate type for all 5 layers for simplicity. I'm going to discuss these results with the people who wrote the spread sheet too. Not certain who is more accurate right now..

    Here is the data from the spread sheet. Load is 2 PSI.
    Stiffness
    Deflection at Design pressure 0.550 in
    Deflection at First Ply Skin Failure 1.203 in



    TNX for the help.
    Peter
  • VictorVictor
    Hello Peter. Some thoughts:

    Each layer has the same stiffness in two orthogonal directions but the layers are all orthogonal or parallel to each other so there's no effect of having multiple layers. Maybe that's because this is just artificial data and the same in the spreadsheet so it doesn't matter?

    The thickness specified in the Geometric tab is 0.228 inch but Mecway (confusingly) ignores that value and takes the actual thickness from the sum of the layer thicknesses, which is 0.24 inch. Is that what you expected?

    It should really be a nonlinear analysis because of membrane action which increases the stiffness by about 50% at this load (CCX solver, Nonlinear Static 3D). Though, I guess the spreadsheet is only a linear calculation so you wouldn't really want that.

    I wonder if you could try a single layer of isotropic material ( G=E/2*(1+ν)] ) in the spreadsheet, if it allows that? That could isolate whether the difference is due to the laminate material or the load/geometry/BCs/etc. It's also a standard problem with known a known formula for deflection.
  • VictorVictor
    I changed it to an isotropic material and the deflection is almost the same (0.3 inch) with refinement. That agrees with the formula here https://www.engineersedge.com/calculators/parallelogram_plate_edges_fixed_15142.htm which says 0.35 inch. So it sounds like either the spreadsheet is wrong or the problem is different.
  • PF1PF1
    OK TNX Victor. I'll play with a few configurations. The engineersedge is a nice site. I can run the program with 1 layer. I suspect the difference is about how the plates are fixed. I was aware of wrong thickness and that it wasnt used. The particular reinforcement I used here is a very popular one with FRP laminates.
  • PF1PF1
    well going with just 1 layer of the same reinforcement gives a deflection of .35" for the spreadsheet and .07" for Mecway (changed load to .01 PSI). So the difference is much worse at 5X. There is some non linearity somewhere!
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