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User material Development in LS Dyna

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User material Development in LS Dyna

  1. 1. Rajesh Kumar Impact Lab, DME IIT Delhi
  2. 2. User material development in LS-Dyna environment:  Learnt dynamic simulation using LS Dyna software  Learnt FORTRAN language, its compilation and implementation in FEA code development  Understood the process of implementing user material subroutine development in LS Dyna environment  Implementation of user defined material model for DP model with solid element and its verification with existing DP model (in progress)
  3. 3. User interface in LS-DYNA User Interface provides freedom to choose solution methods for the problem at hand. LS-DYNA already offers options for all imaginable tasks such as element types, materials, contacts, connections, loads, boundary conditions, etc. But sometimes, the user still wishes to implement her or his own algorithm at a particular point of the solution procedure. Therefore, LS-DYNA also provides user- defined interfaces, i.e. the source code is partly open for modifications.
  4. 4. User interface in LS-DYNA  Environment for large-scale real-world problems, no need for the comprehensive task of developing and maintaining complete FE software  Implementation concerns only to a specific field of interest  The most popular user interface is for material modeling.  There also exist user interfaces for structural elements, airbag sensors, solution control, friction, interface control, weld failure, loads, output control, adaptivity, thermal contact, and others.  Allow users to verify research results in the context of general and complicated finite element applications  Up to a total of ten different material models in a single LS-DYNA executable  An overview of the procedure of implementing UMAT in the interface will be presented.
  5. 5. User-defined materials (material modeling) Strain/ Deformation Constitutive Relation Stress/Forces Existing material models Isotropic elastic to anisotropic elasto-plastic with damage etc with constitutive laws that can predict the behavior of metals, plastics, rubber, foam, concrete, soil, composites, wood etc. Best solution for their material at hand Gives rise to the possibility to implement own material models. *MAT_USER_DEFINED_MATERIAL_MODELS defines the input for the user material interface. Main program calls subroutine usrmat in dyn21.f, and from there, different subroutines are called depending on the element type in use umatXX (or umatn) , has the provision to compute stresses from strains
  6. 6. User material interface scheme
  7. 7. usermat package available via LS-DYNA distributors contains several files such as: library files (*.a) object files (*.o) include files (*.inc) Fortran source files (*.f) and a Makefile Most important file is Fortran Source file dyn21.f Makefile specifies how to derive the LS-DYNA executable and also gives information about the specific Fortran compiler that should be used. Compilation needs - Fortran user routine - Fortran 77 or Fortran 90 compiler - Makefile - The Fortran source file dyn21.f - Object code files
  8. 8. Standard structure and arguments of a user routine Bulk modulus, K and the Shear modulus, G are used to calculate Time step
  9. 9. Writing a UMAT (User MATerial Subroutine) for LS-Dyna: Material Model Theoretical Development Material model represented as concise mathematical equations Flow stress function Change in the flow stress of the material (temperature, strain rate, etc) Stress integration scheme von Mises isotropic material model for plane stress condition: Flow stress elastic strain at yield point plastic strain material matrix plastic multiplier yield function
  10. 10. Writing a UMAT (User MATerial Subroutine) for LS-Dyna: FORTRAN Implementation of the UMAT Creation of a Fortran code using the theoretical model Insert the code in the dyn21.f file Compilation of a working copy of LS-Dyna (.exe)
  11. 11. Writing a UMAT (User MATerial Subroutine) for LS-Dyna: Implementation In LS-Dyna & Compilation √ Code development Incorporate into LS-Dyna LS-Dyna provides object files and source routine (dyn21.f) Addition of own subroutine to the supplied source routine Compilation of the modified source file using the same compiler that LS-Dyna uses Intel(R) Visual Fortran Compiler (readme.txt) Create LS Dyna solver (ls971_dpmv4.exe) Ready to run FE simulation
  12. 12. Steps required to build a UMAT:  Download the required Object files. ftp.lstc.com  Open the "dyn21.F" file in a text editor . Notepad++  Search for "subroutine umat43". This will take you to the location where you can start adding your UMAT's. (next slide)  Start Intel(R) Visual Fortran Compiler Professional Edition 11.1 for Windows* OS  Provide directory path and use "make" command to compile the code.  If compilation is successful, an executable will be created that can be used as solver to run LS-DYNA. Copy it to the directory C:LSDYNAprogram  To call the code in the LS-Dyna input file we use this in keyword file: *MAT_USER_DEFINED_MATERIAL_MODELS
  13. 13. Writing a UMAT (User MATerial Subroutine) for LS-Dyna: UMAT Verification Running a simple problem and compare the results against analytical results Successful UMAT verification guarantees a high level of confidence and quality in the developed material model Mattias Unosson, Eric Buzaud: Acceleration history of bar’s top center node Pressure history (bottom center’s solid element) L=0.6 cm D=0.32 cm Vo=227 m/s

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