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ABAQUS-global stiffness matrix-DDSDDE

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  • ABAQUS-global stiffness matrix-DDSDDE

    I realized that there are two approaches to generate global stiffness matrix.

    1- to add the *MATRIX GENERATE, STIFFNESS in the input file and,
    2- defining a UMAT subroutine and printing DDSDDE

    I have not tried the second approach, but in the first approach, ABAQUS outputs the same stiffness matrix (mtx file) for different cases of loading and deformation. while I am expecting to get different tangent stiffness matrix for a hyperelastic material with geometric nonlinearity. I have some questions:

    1- does the second approach provides a stiffness matrix as a function of the deformation gradient?
    2- Is there any other approaches that we can output the global stiffness matrix as a function of the deformation? (e.g. through input file)
    3- Basically what is the meaning of the global stiffness matrix that abaqus outputs in the first approach? How is it different from DDSDDE?

    Thank you

  • #2
    1. If you use a UMAT then you can define the DDSDDE matrix in any way you like. It can be a constant, or depend on the strain, or the deformation gradient.
    2. I don't know any other way.
    3. I don't use *MATRIX GENERATE, so I'm not sure.

    What are you trying to do?

    Jorgen Bergstrom, Ph.D. PolymerFEM Administrator