Modelling and analyzing parts with composites ?

About the development of the FEM module/workbench.

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bernd
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Re: Modelling and analyzing parts with composites ?

Post by bernd »

The first thing we need is a simple composite example in ccx. Anyone around who has one?
nic
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Re: Modelling and analyzing parts with composites ?

Post by nic »

wingman
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Re: Modelling and analyzing parts with composites ?

Post by wingman »

vocx wrote: Mon Feb 10, 2020 1:29 am FreeCAD itself doesn't do the solving, it just writes a text file that is used as input for external FEM solvers, like Calculix, Z88, Elmer, OpenFOAM, etc. So, the support from FreeCAD may be quite basic. It's the solver the one that needs to support composite materials in some way.
I think the problem is that FreeCAD doesn't have a way to implement layered composite materials or materials with non uniform properties in each direction. Presently parts are built up of materials with homogeneous properties.

We'd have to add axis variant properties to the materials in FreeCAD and we'd have to give the user a method of setting the direction of those materials in their parts.

We'd also probably have to allow the user to work with layered materials to build up a composite material to use on it's own. We wouldn't want the user to have to add 6 layers of materials to ever part they build. The user probably wants to create a composite material that consists of layers of composites and apply that material to the part.

Once the part can be designed with composite and layered materials, then we can pass that part on the the FEM tool.
wingman
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Re: Modelling and analyzing parts with composites ?

Post by wingman »

bernd wrote: Mon Feb 10, 2020 1:25 pm The first thing we need is a simple composite example in ccx. Anyone around who has one?
There is one in here.
https://ntrs.nasa.gov/archive/nasa/casi ... 029045.pdf
wingman
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Re: Modelling and analyzing parts with composites ?

Post by wingman »

bernd wrote: Mon Feb 10, 2020 8:23 am I forgot to ask? Would you like to use volume mesh or shell mesh to analyse the composite structure?
Not sure yet. I'm guessing we would need both, to cover all use cases. Either one would be a start.
To implement this https://www.researchgate.net/post/CFRP_with_CalculiX for shell meshes does not seam difficault IMHO. But first I wuld play with editing the calculix input file after FreeCAD has created the input file. It needs only rare changes. If it turns out to be working we could implement it in FreeCAD FEM.
I'll test this in a bit. I want to test the outcome of Calculix alone versus use with the NASA library.

FWIW, I'm busy for the next couple weeks.
wingman
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Re: Modelling and analyzing parts with composites ?

Post by wingman »

nic wrote: Mon Feb 10, 2020 8:49 am wow! that would be a great addition!

I'm dealing on daily basis (using NX NASTRAN) with honeycombs sandwich panels. We use planar meshes with laminate (multi-plies) idealization. In the NASTRAN terminology, it is a PCOMP card.

In case of needs, I'm volunteer to write and document some test-cases and correlations. Unfortunately, I never played with calculiX, but that would be a good opportunity to begin.
There are a lot of people dealing with composites these days and there aren't a lot of (good) tools out there for working with them. Composite materials are relatively easy to work with and their cost is falling as volume increases. I think adding composite capabilities to FreeCAD would be a big drawing card for people working with composites.
wingman
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Re: Modelling and analyzing parts with composites ?

Post by wingman »

On a related note, does FreeCAD have an "unfolder" whereby the user can click on a surface and FreeCAD will create a 2D pattern for pliable material that would cover the surface ? This would be another great tool for composites...
fandaL
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Re: Modelling and analyzing parts with composites ?

Post by fandaL »

wingman wrote: Mon Feb 10, 2020 9:05 pm On a related note, does FreeCAD have an "unfolder" whereby the user can click on a surface and FreeCAD will create a 2D pattern for pliable material that would cover the surface ? This would be another great tool for composites...
I think not on simple click. But there were some trials about unfolding shapes other than classical sheet metals discussed on the forum. Perhaps @microelly2 or @looo would know more.

bernd wrote: Mon Feb 10, 2020 1:25 pm The first thing we need is a simple composite example in ccx. Anyone around who has one?
In Calculix manual ( http://dhondt.de/ccx_2.16.pdf ) there is an example in chapter 5.14 Reinforced concrete cantilever beam, which is modeled as composite.

Test examples are on the http://dhondt.de/ . The one from manual is "concretebeam.inp". Others are "shell3.inp" and "shell4.inp".

Calculix enables to define composite layers on 2D elements S8R and S6. You need to define it by (copying parts from examples)

Code: Select all

*SHELL SECTION,ELSET=Eall,COMPOSITE
2.5,,MATERIAL1,OR1
2.5,,MATERIAL1,OR2
2.5,,MATERIAL1,OR2
2.5,,MATERIAL1,OR1
means that layers have thickness 2.5 and are of MATERIAL1 with orientations OR1 and OR2 defined by

Code: Select all

*ORIENTATION,NAME=OR1,SYSTEM=RECTANGULAR
1,0,0,0,1,0
*ORIENTATION,NAME=OR2,SYSTEM=RECTANGULAR
0,1,0,-1,0,0
Material can be orthotropic, here defined by ENGINEERING CONSTANTS

Code: Select all

*MATERIAL,NAME=MATERIAL1
*ELASTIC,TYPE=ENGINEERING CONSTANTS
181000,10300,1000000,0.28,0,0,7150,5958.3333
5958.3333,295.
**E11, E22, E33, nu12, nu13, nu23, G12, G13,
**G23, (temperature)
where you need to (in contrast to 2D definition typical to other sw) set also E33, nu23, nu13 and G23, G13.

Finally, you can request stresses in local coordinate system with

Code: Select all

*EL PRINT,ELSET=Epart,GLOBAL=NO
S
which prints stresses to *.dat file at integration points - in case of composite 2 points through the thickness of each layer.


On more complicated task I had difficulties with fact that calculix does not use true 2D element but internally expands it to 3D element.

Z88 solver also enables composite definition, but I did not try it.
jcoppola
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Re: Modelling and analyzing parts with composites ?

Post by jcoppola »

wingman wrote: Mon Feb 10, 2020 9:05 pm On a related note, does FreeCAD have an "unfolder" whereby the user can click on a surface and FreeCAD will create a 2D pattern for pliable material that would cover the surface ? This would be another great tool for composites...
I started writing one yesterday and new to FreeCAD API. My immediate needs are to create the cut patterns for solid composite parts like blades. For my tidal energy project i had layered card board into a mold and sanded them to the outer profile to get layer patterns. Worked but it was not exact.

FreeCAD API learning curve is steep especially not coming from a geometry related development background but not too bad. My ultimate goal is to integrate FEA into the tool as well.

It really got to me that NASA developed an awesome tool called hypersizer using tax payer money for 7 years then spins off the group to the private sector with no open source freely available version. So I will build something similar without layer and thickness optimization. Here is a youtube video of hypersizer: https://youtu.be/14Q2NiYAVco

And this is how i learned hypersizer existed: https://youtu.be/73Kygq822RY
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