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How to define Stiffness values to each element in Abaqus ?

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PPOLA

PPOLA

Student
Oct 11, 2023
32
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
 
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Spatial variation of linear elastic material properties can be defined using the distribution feature (*DISTRIBUTION keyword). Stiffness matrix generation is possible with the *MATRIX GENERATE and *MATRIX OUTPUT keywords. Check them all in the documentation.
 
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Thank you for the response, FEA way .

Can you elaborate the first part of the answer ( how to input the user defined values of stiffness for each element of the part in abaqus ) . Where can I find the distribution feature in the documentation? And how to use it ?
 
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you're saying that you need to "generate a stiffness matrix of the component/each element". The stiffness matrix depends on geometry.

I guess it's possible to have ABAQUS export this but I think you're being asked to calculate the stiffness matrix ? I assume simple elements (like RODs, axially loaded elements) ... this can be found in any FEA text book.

Then of course the nuanced question is "do you want stiffness in local or global axes ?"

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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Thank you the response (rb1957).

I will brief my question here, I am creating a some model in CAE and generated mesh for that. Now I want to allot stiffness values for the elements. After that I apply some boundary conditions and load to the part. Again I want to generate the stiffness matrix of the part. Elemental and global both .

What do you mean like local/global axes , can you explain me that ?

Thank you
Prudhvi pola
 
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Check the Keywords guide in the Abaqus documentation first. There you will find each of the aforementioned keywords (they are listed alphabetically) and links to corresponding sections in other parts of the documentation.
 
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are you building a model in ABAQUS ? Then you don't need to assign stiffness, you need to define the geometry (thickness of shells/webs, the area of rods, etc). You can see what elements ABAQUS has in their manual. ABAQUS will build the stiffness matrix for you and solve it to !

But we're dealing with a very simple model now, aren't we ? Can you describe it ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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I am building a abaqus model in abaqus CAE, see I want to assign stiffness values(experimental values) to the each element in the model.After that again I want to generate the stiffness matrix.

Currently , I am dealing with a very simple one.
 
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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.

How to use those files/lines in the abaqus CAE ?
 
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why would you want to define the stiffness of an element ? Why wouldn't you do like the rest of us ... define the geometry of the element (area, thickness, I, ...) depending on the type of element and the material ??

I haven't used ABAQUS or "ABAQUS CAE" ... but "surely" ABAQUS has a front end pre-processor that helps you build the model (from geometry of the nodes, through defining elements, to applying loads and constraints.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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I made the part in abaqus by defining the geometry of the part like length, width and extruded height. After the , I have done meshing part. Now I want to define the stiffness values to each element ( which I want give from the experimental values).

I hope so , you got some clarity now.

 
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There must be a language issue here.

Do you mean you want to define the material properties for the elements? And all elements will have the same properties?
 
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yes, I want to define the material property (stiffness) here for each element.
 
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ok, you've defined the geometry of the model. what elements ? sounds like shell/quads, maybe 3D solids ? Then you've defined the geometry of the element, the thickness of the shell. Now define the material and ABAQUS will work out the stiffness. If you want to know what ABAQUS is doing, you can use the manual (probably the developers manual) to determine exactly how ABAQUS is calculating the stiffness. You could "back-door" this by a single element test ... active individual modes, change the variables, see how the deflection (the stiffness) changes. but that seems a lot of work.

You've got some experimental results of this structure that you are trying to match in FEA ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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So then you enter the material properties and assign a property id. Then apply that property id to the elements.

Is your material isotropic? Or something else?
 
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And there should be examples in the Abaqus manuals showing how to assign material properties.
 
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Ah, the material property is not the stiffness ! I'm not sure you can create an element with defining the material property to be used (the MID number). Defining the material property in detail is a separate command. Is the material Aluminium, Steel, composite ? Isotropic or Anisotropic ?

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

1. I made a bar with some defined geometry and then I have assigned material values like steel elastic values and density and it is isotropic.
2. Then I have meshed it with elements (quads/tet or others).
3. Defined boundary conditions and loads to it .
4. Then I perform the analysis job.

This is normal procedure , which do I follow in the abaqus CAE for FEA analysis.

Now I am trying to use some stiffness values which I have calculated experimentally for the same elements at certain points ( like at certain element points). Now I want to assign those stiffness values to the part and do the analysis of the part. Now again I can generate the stiffness matrix after the job analysis right.

Only the question is how to assign the stiffness values to the certain elements in the part , does this can be done in abaqus or can it done other FEA softwares ?


Thank you all for your responses. It means a lot , I am trying to do this for last couple of months but I am not able to do it .
Please help me on this how to proceed further.

Thank you
Prudhvi Pola
prudhviraj.pola@gmail.com

 
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ok, how did you experimentally determine stiffness ? did you measure deflection ?

You can assign a stiffness to an element by changing the geometry or material properties.
If you dig into the developer manuals you should be able to see the calculation ABAQUS does for stiffness.

I'm pretty sure you can't override the calculated stiffness, but you can tweek the inputs to get the stiffness you want.

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

I have a stiffness value(I established based on some empirical relation). Now, I want to assign the stiffness value to the same geometry element without changing geometry of it. Do you know anything , how can we assign the stiffness value to the element.

Thanks
pola
 
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