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[pavan_m240846ce]

I am trying to validate the results in a journal paper for my M.Tech thesis work, in which they have used a hybrid consititutive model added into the ls dyna subroutine. To recreate the same thing I need to add the user defined material. I have sucessfully installed the latest veersion intel fortran compiler and microsoft visual studio. What steps do I need to follw to implement the UMAT in ls dyna and compile the constitutive model code.

[Armin]

Hi Pavan,

Below is the general workflow. You can find more information in the LS-DYNA documentation (see *MAT_USER_DEFINED_MATERIAL_MODELS section here:https://ftp.lstc.com/anonymous/outgoing/jday/manuals/LS-DYNA_manual_Vol_II_R6.1.0.pdf). There are also courses available on the Ansys Learning Hub that you can check if you have access to it.

To implement a user-defined material (UMAT) in LS-DYNA you need to follow a sequence of steps involving code preparation, integration, compilation, and simulation setup. The process requires careful attention to LS-DYNA's UMAT framework and compatibility with your compiler environment.

1. Prepare Your UMAT Source Code

Develop your hybrid constitutive model in Fortran, following LS-DYNA's UMAT interface specifications. LS-DYNA supports both scalar and vectorized subroutines (typically named UMAT41 to UMAT50 for non-vectorized routines). Ensure your code handles all required inputs and outputs, such as stress, strain, state variables, and material parameters. The first two parameters in the material definition are reserved for density treatment and integration points for failure criteria.

• Place your Fortran source files (.f, .F) in the usermat directory provided by LS-DYNA.

• Initialize critical variables (e.g., number of state variables 'nsv') explicitly in your code to avoid numerical instabilities.

2. Set Up the Usermat Package

• Unpack the LS-DYNA usermat package, which includes example source files, object libraries, and makefiles.

• Navigate to the usermat directory and review the provided makefile. Adjust compiler paths and options if necessary to match your Intel Fortran and Visual Studio installation. 

3. Compile the UMAT Code

• Use the provided makefile to compile your UMAT code. Run make clean to remove previous builds, then make to compile the new code. 

• Ensure you are compiling for the correct LS-DYNA version. If using dynamic linking, the shared object (.so) must match the LS-DYNA binary version. 

4. Integrate UMAT with LS-DYNA

• In your LS-DYNA input deck, define the material using the *MAT_USER_DEFINED_MATERIAL keyword. Assign the appropriate parameters, including the subroutine number (e.g., 41 for UMAT41) and module ID if using multiple user materials. 

• Specify material constants in the cm and/or cma arrays, ensuring bulk and shear modulus are included for time step and contact calculations. 

• If your model is hybrid or requires multiple subroutines, use the *MODULE_USE keyword to manage execution across different modules. 

5. Run and Validate the Simulation

• Execute LS-DYNA with your compiled UMAT. Monitor the log files for errors related to linking, initialization, or numerical instability. 

• Compare your results with those from the journal paper to validate the hybrid constitutive model implementation. 

Additional Considerations

• Refer to LS-DYNA documentation and training resources for advanced UMAT features such as anisotropy or complex failure criteria. 

[pavan_m240846ce]

Hi Armin, 

Thank you very much for the detailed explanation and for outlining the complete workflow for implementing a user-defined material in LS-DYNA.
I will go through the manuals and try to implement this. 

[Armin]

No problem Pavan. Throughout the process, if you have any questions, you can post them in this forum, and someone should be able to assist you.