Example on using stiffness matrices in Abaqus 1

[AminKB]

Hi all,

I'm trying to use stiffness matrices to define material behaviour. I've never used this method before and I find the documentation from Abaqus quite confusing.
I've tried to use *USER ELEMENT and *MATRIX, TYPE=STIFFNESS
But I'm sure I've been using them wrong as I have no idea what I'm doing and I didn't get the expected result!
The last variation I tried before importing the part from the .inp file did not return an error and an orphan mesh part was imported, but it was empty!
Can someone please provide an example of how stiffness matrices can be used to define element-by-element behaviour in Abaqus?

Many thanks for any help.

 

[FEA way]

Check the documentation chapter Elements --> Special-Purpose Elements --> User-Defined Elements, paragraph Defining a Linear User Element in Abaqus/Standard. And if you are looking for an example, you can find one in the Verification --> User Subroutines --> User subroutine verification --> UEL chapter (the uellinea.inp file uses this procedure with matrix definition).

Perhaps you are just missing the necessary *UEL PROPERTY keyword.

 

[AminKB]

Thanks for your answer, FEA way!
I tried creting a single element following a code similar to the example you pointed to in your response.
Following the stiffness matrix structure from the documentation as below
A11
A12,A22
A13,A23,A33
A14,A24,A34,A44
A15,A25,A35,A45
A55
A16,A26,A36,A46
A56,A66
returned an error saying I have too few elements in my stiffness matrix.
I also tried other structures that returned the same error as well.
I attached the input file for reference.
Any idea how to fix this?

Many thanks

 

[FEA way]

The size of the stiffness matrix depends on the number of nodes and their degrees of freedom. That example from the documentation involves an element with 2 nodes and 3 DOFs each so the stiffness matrix is 6x6. Your element has 4 nodes with 6 DOFs each so the stiffness matrix must be 24x24.