abaqus-subroutine-development

name	abaqus-subroutine-development
description	Abaqus user subroutine development in Fortran — UMAT/VUMAT custom materials, DLOAD/VDLOAD loads, DISP/VDISP boundaries, USDFLD fields, SIGINI/SDVINI initial conditions, FRIC/VRIC friction, HETVAL/FILM thermal, UEL/VUEL custom elements.
version	1.0
capabilities	["custom_material_model","distributed_load_definition","custom_boundary_conditions","user_field_variables","initial_conditions","custom_friction","thermal_subroutines","custom_elements"]
triggers	["UMAT","VUMAT","DLOAD","user subroutine","custom material","Fortran subroutine","子程序","用户材料"]
constraints	["Requires Fortran compiler (Intel Fortran 19.0+ or GNU Fortran 9.0+)","Fixed-format Fortran (cols 1-5 labels, col 6 continuation, cols 7-72 code)","Always include INCLUDE 'ABA_PARAM.INC'","Use REAL*8 for all floating-point variables","Reference documentation covers 8 of 15 subroutine types — check availability"]

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 DLOAD/VDLOAD subroutines for distributed moving loads
• Generate DISP/VDISP subroutines for custom displacement boundary conditions
• Generate USDFLD subroutines for spatially varying field variables
• Generate SIGINI subroutines for initial stress conditions
• Generate FRIC/VRIC subroutines for custom friction models
• Generate HETVAL subroutines for heat generation
• Generate UEL/VUEL subroutines for custom elements

Supported Subroutine Types

Subroutine	Analysis Type	Purpose
UMAT	Standard (Implicit)	Custom material constitutive
VUMAT	Explicit	Custom material constitutive
DLOAD	Standard	Distributed load definition
VDLOAD	Explicit	Distributed load definition
DISP	Standard	Custom displacement boundary
VDISP	Explicit	Custom displacement boundary
USDFLD	General	User-defined field variables
SIGINI	General	Initial stress definition
SDVINI	General	Initial state variables
FRIC	Standard	Custom friction model
VRIC	Explicit	Custom friction model
HETVAL	Thermal	Heat generation
FILM	Thermal	Custom convection
UEL	Standard	Custom element
VUEL	Explicit	Custom element
VRIC	Explicit	Custom friction model
HETVAL	Thermal	Heat generation
FILM	Thermal	Custom convection
UEL	Standard	Custom element
VUEL	Explicit	Custom element

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:

Requirement	Recommended Reference
Custom material model	reference/material/umat_*.md or reference/material/vumat_*.md
Moving/variable load	reference/load/dload_moving.md
Vibration/displacement control	reference/boundary/disp_control.md
Spatially inhomogeneous material	reference/field/usdfld_spatial.md
Geostress/residual stress	reference/initial/sigini_stress.md
Tribology problems	reference/friction/fric_contact.md
Thermal-mechanical coupling	reference/thermal/hetval_heat.md + UMAT
Special connection elements	reference/element/uel_spring.md

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

2. Variable Declaration:

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

3. Constant Definition:

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

4. 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

2. Minimize State Variables:

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

3. Optimize Matrix Operations:

   • Utilize matrix symmetry
   • Avoid redundant calculations

Subroutine Selection Guide

Problem Type	Recommended Solution	Alternative
New constitutive model	UMAT/VUMAT	Built-in material + field variables
Moving load	DLOAD/VDLOAD	Multi-node concentrated forces
Complex boundary	DISP/VDISP	MPC constraints
Non-uniform material	USDFLD+UMAT	Multi-layer material
Initial stress	SIGINI	*Initial Conditions
Special element	UEL/VUEL	Multi-node connectors

Troubleshooting

Compilation Errors

Error Message	Cause	Solution
"Unexpected end of file"	Continuation format error	Check column 6 continuation character
"Undefined variable"	Variable not declared	Add type declaration
"Type mismatch"	Type inconsistency	Use REAL*8 instead of REAL
"Dimension mismatch"	Array dimension error	Check array declaration and access

Runtime Errors

Error Message	Cause	Solution
"Too many attempts"	Non-convergence	Check Jacobian matrix
"Negative eigenvalues"	Stiffness matrix not positive definite	Check material stability
"Zero pivot"	Insufficient constraints	Check boundary conditions
"NaN in stress"	Numerical overflow	Check division by zero and exponential operations

Result Anomalies

Symptom	Possible Cause	Check Point
Zero stress	STRESS not updated	Check stress update statements
Excessive displacement	Stiffness too small	Check material parameter units
Non-convergence	Inconsistent Jacobian	Verify DDSDDE derivation
Hourglass modes	Reduced integration	Add hourglass control

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: 1.0
• Compatible Abaqus Version: 2020 and above
• Fortran Compiler: Intel Fortran 19.0+ or GNU Fortran 9.0+
• Last Updated: 2026-03-20