User Material Subroutine

Development in

LS-Dyna Environment

Rajesh KumarImpact Lab, DMEIIT Delhi

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)

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.

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.

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

User material interface scheme

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

Standard structure and arguments of a user routine

Bulk

modulus, K and the Shear modulus, G are used to calculate Time step

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

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)

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

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:\LSDYNA\program

To call the code in the LS-Dyna input file we use this in keyword file:

*MAT_USER_DEFINED_MATERIAL_MODELS

Add the material properties as specified for material model.

Writing a UMAT (User MATerial Subroutine) for LS-Dyna:UMAT Verification

Running a simple problem and compare the results against analytical resultsSuccessful 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 cmD=0.32 cmVo=227 m/s

THANK YOU