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Cross Sectional Properties script

Cross Sectional Properties script

Cross Sectional Properties script

(OP)
We are trying to extract the CROSS SECTIONAL properties about a center axis of an arbitrary hollow shape with shell element laminate. We want the stiffness properties as if looking down the center axis (like looking down a wing), not the properties on the outside face (on top of the wing). An example of this would be a hollow rectangle with stiff top and bottom of thickness A, and flexible sides of thickness B...We would want the properties EIxx, EIyy, shear centers, etc about the plane perpendicular to the center axis. (See attachment)

The current femap "tools->section properties" function only looks at the surface/surface of the elements you are asking about. In other words, it would take the stiffness of the sides of the box, not the cross section (through-thickness direction).
The current femap sectional properties tool only considers single material or standard sized "cross sections", I-beams, etc. We do not want this for 3 reasons: 1) we are modeling multiple materials and 2) our shape is arbitrary and varies along the length of the part and 3) we want to be able to select our already-modeled part and have the sectional properties be calculated about a given axis.

Our FEMAP rep says that the functionality of what we are trying to do is not in FEMAP. At his suggestion, I am downloading a trial version of VABS that calculate the cross sectional stiffnesses, but it would be extremely useful and well-used feature in FEMAP.

In ANSYS, one can define an arbitrary cross section, with a through-thickness mesh of laminate, but one still has to create the section independent of your model (using secwrite/secread commands for arbitrary shapes of laminate...see chapter 16 of their apdl help). I only list that to see if it might draw a parallel to FEMAP.

Grabbing cross sectional mass and stiffnesses is a quite common need, so I am wondering...Has anyone had to grab the cross-sectional mass and stiffness before and what did you do? Has anyone written a script that will compute the cross sectional properties of a shell laminate, ideally directly off a selected set of elements?

Thanks!

RE: Cross Sectional Properties script

looking at your pic, it looks as though you want the stiffness of the wing (the EI of the total cross-section), as opposed to the stiffness of a laminate stackup (the A, B, D matrices) ?

RE: Cross Sectional Properties script

(OP)
Correct, rb1957. Looking for the stiffness of the local/arbitrary cross section, not the stiffness matrices.

RE: Cross Sectional Properties script

when we had to create a stick model of the wing, you can apply a load at the tip of the wing model, then modelling the wing as a stick (a line of beam elements) play with the element inertia to get the same displacement ... i think thee are smarter ways to do this, but ...

RE: Cross Sectional Properties script

(OP)
Good suggestion...I guess that's one way you could do it. However, that's pretty inaccurate, and really only works for simple structures of uniform material properties. We would eventually need to get shear centers, torsional stiffness, etc, and we are dealing with numerous cross sections, so your approach won't work.

It sounds like you could have used the same thing i am requesting.

RE: Cross Sectional Properties script

no,

say you have a wing and you want the EI stiffness. start with a string of beam elements, 1 per rib bay, I = 1. apply a load to both models ... tip load, UDL, whatever. tune the stick elements to get the same displaced shape as the wing (ie matching each rib station).

RE: Cross Sectional Properties script

(OP)
I really appreciate the effort to help.

That method will not work for us. It would be better for us to compute the stiffness in a hand calc knowing the location of the materials in the cross section relative to the axis. Keep in mind that we are interested in stiffness in 3 directions (1,2, and torsion), as well as computing shear centers, mass center, linear density, etc.

Does anyone else have a script that they wrote to extract the cross-sectional properties from their shell model?

Thanks!

RE: Cross Sectional Properties script

You can try a commercial or free program for cross sectional analysis. There are many free ones out there.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-des...

RE: Cross Sectional Properties script

Hi,

I think we can help you! We have written a code for cross section analysis which has the same capabilities as VABS. It is written in Matlab (will produce the executables if needed) and we give access to the source code repository. You can read more about it here www.becas.dtu.dk .

Hope this helps!

All the best,
José

RE: Cross Sectional Properties script

Get geometrical Ixx and Iyy for each material separately using any CAE software.

Then add corresponding modulus to it.

EIxx = Material1EIxx + Material2EIxx

EIyy = MAterial1EIyy + Material2EIyy

Is this what you re looking for?

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