How to define Stiffness values to each element in Abaqus ?

[PPOLA]

Hello all.

I am very new to abaqus , I am trying to give the stiffness values to each element in abaqus, how to do define them user defined value to each element. And after applying the loads and boundary conditions , I need to generate a stiffness matrix of the component/each element.

Please help me on this , how to do it. I greatly appreciate it.

Thank you
Pola

 

[SWComposites]

So your “stiffness” value is a modulus value, such as Ex, units of msi or GPa, correct? Or something else?

If yes to first question, then you enter the value as a user defined material and assign it to elements like any other material.

Might help if you share the specific stiffness values you have from experimental data.

 

[PPOLA]

I have values like 634 MPa,554 MPa,400 MPa . These values are at different directions. I have taken three values currently.

One question , as stiffness is material property.

Does stiffness and youngs modulus both are same ?

Thank you
Prudhvi Pola

 

[rb1957]

I don't think we (well, I don't) understand what you mean by "stiffness" nor how you calculated it, especially for specific elements/locations on your bar.

Your stiffness could be the same as "elastic modulus", if stress = "stiffness"*strain

You have defined a material with E, nu, and G ... maybe you can tune these to get the values you've calculated.

My thought was that you measured strains and worked from these (to calculate stiffness) ? if so, the FEM gives you strains, proportional to E and G.

Are you using sold (3D) elements, or 1D beam elements ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[PPOLA]

If stiffness is same as Young's modulus/elastic modulus , then I can assign the different values to the different element right by changing the youngs modulus value in the materials section?

Then If I do the analysis , then I will able to generate the strains right ?

I am using 3D elements here ..

 

[rb1957]

ok, 3D elements have no geometry term in their stiffness, only material.

You can assign material id to elements (so different elements can have different materials, different stiffness).

I'd probably use one on the Anisotropic material forms. I'm not sure what you calculated but maybe E11, E22, and G12 ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[PPOLA]

Like creating a different materials and assigning a modulus value to it , then creating a set for each element and assigning an each material to it . Does this make sense ?

Does this mean stiffness and youngs modulus both are same ?

 

[FEA way]

I think that this discussion went the wrong way. From what I understand, the OP just wants to vary the linear elastic material properties spatially. This is possible in Abaqus with the distribution feature.

Using the distribution feature, does I need to input the different file or do I need to write those lines in the .inp file of the abaqus.

You can define it using:

*DISTRIBUTION TABLE, NAME=table_name
MODULUS, RATIO
*DISTRIBUTION, NAME=distribution_name, LOCATION=element, TABLE=table_name
 , E_default, v_default
element_1/elset_1, E_1, v_1
element_2/elset_2, E_2, v_2
...
*MATERIAL, NAME=material_name
*ELASTIC
distribution_name

 

[SWComposites]

Yes, “stiffness” is an often used imprecise term for elastic (Young’s) modulus.

 

[PPOLA]

Thank you for all the responses.

Firstly, stiffness is a material property which is same as youngs modulus.Which means I have to create different materials for assigning a value to different elements right ?

Another thing is distribution feature , which we can use for the assigning the values of material properties to each element ( I think so , we can do it by creating a set for each element and assigning a property/material to that element.)Does this make sense ? I think it should work same as distribution feature.

I concluded, these points from the discussion . Please clarify above both points.

Thank you
Prudhvi Pola

 

[rb1957]

is stiffness the same as E , Young's modulus ? Only you know how you've calculated "stiffness". If stress = stiffness*strain, then yes stiffness = E.
Not at all clear on how you calc this, but how to account for poission effects ?

I don't know this "distribution" thing, but I'd start by defining a different material ID for the different elements ... no need for "sets" of elements.
Maybe "distribution" smears the change in material properties ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[PPOLA]

Thank you for your answer.
I understand, how do I get the stiffness values and many more clarifications you need but still

For assigning user-defined value like stiffness , where do I need to assign those values at each element?

The Distribution code , which was present at top , where do I need to input the those lines in the abacus CAE?

 

[FEA way]

You can enter this in the Keyword Editor but it would be better to export the input file (right-click on the job name and select Write input) and edit it using any text editor (even basic Notepad).

 

[PPOLA]

Okay , I should it in the .inp file . I should define this feature in the near the material properties in the file right ?

Is this same as creating sets and assigning the material property to it.

 

[FEA way]

Place it right above the material definition like in my example. You have to reference the distribution under *ELASTIC (also shown in my example).

 

[PPOLA]

Thank you ,

The distribution feature and assigning the material, by creating a set for each element. Does these both are same ?

 

[rb1957]

how will you know if it's done what you intend ?

it sounds like this is a very powerful tool, and if misused it may be more like a loaded gun ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[FEA way]

Yes, you could also do it manually - apply a different section to each element. But it would be quite a lot of work. There are also more advanced approaches when modeling functionally graded materials but they involve Fortran subroutines.

 

[PPOLA]

Thank you for all the answers.

I have generated a global stiffness matrix, with the input given as matrix= coordinate. So I got the MTX file with rows and columns with values .
Now , how to convert this file into a matrix form? is it by using Matlab ? if yes, what code need to written.

 

[rb1957]

excel ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[PPOLA]

The matrix we get , is a sparse matrix . It is too long to do it in the excel .