jasonanewcoder/abaqus_skills/abaqus-subroutine-skills

Abaqus Subroutine Development Skill

Skill Description

This skill provides AI-assisted programming guidance for developing Abaqus user subroutines. It includes standardized Fortran code templates, detailed theoretical explanations, and complete engineering examples to help users quickly and accurately develop custom subroutines for finite element analysis.

Capabilities

• Generate UMAT (User Material) subroutines for custom constitutive models
• Generate VUMAT subroutines for explicit dynamic analysis
• Generate CREEP subroutines for creep and viscoplasticity
• Generate UMATHT subroutines for thermal constitutive behavior
• Generate DLOAD/VDLOAD subroutines for distributed moving loads
• Generate DFLUX subroutines for moving heat sources (welding)
• Generate UAMP subroutines for custom load amplitudes (control laws)
• Generate DISP/VDISP subroutines for custom displacement boundary conditions
• Generate USDFLD subroutines for spatially varying field variables
• Generate ORIENT subroutines for material orientation
• Generate SIGINI subroutines for initial stress conditions
• Generate FRIC subroutines for custom friction models
• Generate HETVAL subroutines for heat generation
• Generate UEL/VUEL subroutines for custom elements
• Generate UEXTERNALDB subroutines for data file management
• Generate URDFIL subroutines for results file monitoring

Supported Subroutine Types

Usage

Step 1: Determine Requirements

Before using this skill, clarify:

1. Analysis Type: Implicit (Standard) or Explicit?
2. Physical Phenomenon: What material behavior or boundary condition needs simulation?
3. Coupling Requirements: Do multiple subroutines need to work together?
4. Complexity: Linear or highly nonlinear problem?

Step 2: Select Appropriate Skill

Based on requirements, select the corresponding reference file:

Step 3: Understand the Skill File

Each skill file contains:

1. Skill Description: Applicable scenarios and main functions
2. Theoretical Formulas: Mathematical basis and physical models
3. Interface Definition: Detailed subroutine parameter descriptions
4. Code Template: Complete, ready-to-use Fortran code
5. Input File Example: Abaqus keyword reference
6. Verification Methods: How to verify implementation correctness
7. Extension Suggestions: Directions for further development

Step 4: Modify and Adapt

Modify the code for your specific problem:

C  Modify material parameter section
C-----------------------------------------------------------------------
C  Read material parameters
C-----------------------------------------------------------------------
      E  = PROPS(1)    ! Modify to your parameter name
      NU = PROPS(2)
      YOUR_PARAM = PROPS(3)  ! Add new parameter

Step 5: Compile and Test

Compilation Commands

# Windows environment
abaqus make library=your_subroutine.f
 
# Or run job directly
abaqus job=your_job user=your_subroutine.f interactive

Testing Recommendations

1. Single Element Test: Verify constitutive relationship correctness
2. Simple Boundary Condition Test: Verify subroutine is correctly called
3. Benchmark Comparison: Verify numerical accuracy
4. Convergence Test: Verify Jacobian matrix correctness

Step 6: Debug and Optimize

Common Debugging Methods

C  Add debug output (note: affects performance)
      WRITE(*,*) 'DEBUG: NOEL=', NOEL, ' STRESS=', STRESS(1)

Best Practices

Code Standards

1. Use Fixed-Format Fortran:

• Columns 1-5: Statement labels
• Column 6: Continuation character (non-zero)
• Columns 7-72: Code body
• After column 73: Ignored

1. Variable Declaration:

      REAL*8 E, NU, STRESS(6)    ! Use REAL*8 instead of REAL
      INTEGER I, J, NDI          ! Explicitly declare all variables

1. Constant Definition:

      REAL*8 PI
      PARAMETER(PI=3.141592653589793D0)  ! Use D0 for double precision

1. Error Checking:

C  Parameter range check
      IF (E .LE. 0.0D0) THEN
        WRITE(*,*) 'ERROR: Young modulus must be positive'
        CALL XIT    ! Terminate analysis
      END IF

Performance Optimization

1. Vectorization for Explicit Subroutines:

• VUMAT/VUEL use block loops
• Avoid scalar operations

1. Minimize State Variables:

• Only store necessary history variables
• Clean up unused variables promptly

1. Optimize Matrix Operations:

• Utilize matrix symmetry
• Avoid redundant calculations

Subroutine Selection Guide

Troubleshooting

Compilation Errors

Runtime Errors

Result Anomalies

Subroutine Interface Quick Reference

UMAT (Standard)

SUBROUTINE UMAT(STRESS,STATEV,DDSDDE,SSE,SPD,SCD,
     1 RPL,DDSDDT,DRPLDE,DRPLDT,
     2 STRAN,DSTRAN,TIME,DTIME,TEMP,DTEMP,
     3 PREDEF,DPRED,CMNAME,NDI,NSHR,NTENS,NSTATV,
     4 PROPS,NPROPS,COORDS,DROT,PNEWDT,
     5 CELENT,DFGRD0,DFGRD1,NOEL,NPT,LAYER,KSPT,
     6 KSTEP,KINC)

VUMAT (Explicit)

subroutine vumat(
     1 nblock, ndir, nshr, nstatev, nfieldv, nprops, lanneal,
     2 stepTime, totalTime, dt, cmname, coordMp, charLength,
     3 props, density, strainInc, relSpinInc,
     4 tempOld, stretchOld, defgradOld, fieldOld,
     5 stressOld, stateOld, enerInternOld, enerInelasOld,
     6 tempNew, stretchNew, defgradNew, fieldNew,
     7 stressNew, stateNew, enerInternNew, enerInelasNew)

DLOAD

SUBROUTINE DLOAD(F,KSTEP,KINC,TIME,NOEL,NPT,LAYER,KSPT,
     1 COORDS,JLTYP,SNAME)

DISP

SUBROUTINE DISP(U,KSTEP,KINC,TIME,NOEL,NPT,COORDS,JLTYP,
     1 SNAME)

USDFLD

SUBROUTINE USDFLD(FIELD,STATEV,PNEWDT,DIRECT,T,CELENT,
     1 TIME,DTIME,CMNAME,ORNAME,NFIELD,NSTATV,NOEL,NPT,LAYER,
     2 KSPT,KSTEP,KINC,NDI,NSHR,COORD,JMAC,JMATYP,MATLAYO,
     3 LACCFLA)

Version Information

• Skill Version: 1.1
• Compatible Abaqus Version: 2023 and above (Python 3.9+)
• Fortran Compiler: Intel Fortran 19.0+ or GNU Fortran 9.0+
• Last Updated: 2026-08
• Errata: see docs/ERRATA.md for fixed bugs and unverified API items