on cross sectional stiffness and 1-D beam

[aeropeng]

Dear Professor Yu,

My name is Peng Lv, I am a PhD student in ISAE, France. Now, I am working on the flexible rotor.

As far as I know, both VABS and BECAS can give the cross sectional stiffness for Timoshenko beam, as follows

[K11 ......          K16
...

...        K33...    K36
...

...

K16.....K36...    K66 ];

Let's say  K33 is axial stiffness, K66 is the torsional stiffness, K36 is the extension-twist coupling.

For a beam model based on finite element method, the element stiffness can be
Kelement=[EA/L, -g/L, -EA/L, g/L;
            -g/L, GJ/L,  g/L , -GJ/L;
            -EA/L, g/L, EA/L, -g/L;
            g/L, -GJ/L,  -g/L , GJ/L];

where L is the length of element.

My question is: if I can input K33, K66 and K36 to the beam model as EA, GJ and g, respectively, to consider the deformation of a rectangular laminate under extension-twist coupling?

Your early reply will be much appreciated.

Best regards,

Peng
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Dear Peng,

If all the other off diagonal stiffness terms are zeros, you might be able to do this. However, it will be odd that not consider bending unless you want to purposely neglect bending behavior. You can use my code GEBT to take care of all the couplings and geometrical nonlinearity you want. The code can be downloaded from my google group. Please also post questions through my google group so that Q&A can benefit other VABS users.

Wenbin
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Dear Professor Yu,

Thank you for your helpful reply.

Actually, I have downloaded GEBT. However, I have troubles to run. I am still working on it.

About the cross sectional stiffness for a beam model,  how about if I put the all of corresponding stiffness from VABS or BECAS into the following Timoshenko beam element, meanwhile fill the zeros by coupling stiffness ? By the way, my object is a rectangular laminate with length 150mm, width 30mm, thickness 0.6mm. Anyway I hope I can run GEBT as soon as possible to see the result. I will also transfer the questions to your google group.

Best regards,

Peng

[Peng LV]

Dear Professor Yu,

Thank you. It becomes clear to me.

Best regards,

Peng

On Thu, Mar 27, 2014 at 4:59 PM, Wenbin Yu <WenbinY...@gmail.com> wrote:

Dear Peng,

Dr. Qi Wang at NREL can help you with GEBT if you have any questions. Regarding the stiffness matrix, you just need to be careful when you derive the FEM. You start from the strain energy, express the strains in terms of beam nodal DOFs, then, get rid of those terms you are not interest in.

Wenbin

Wenbin

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