UCOHESIVEOFFSET

User subroutine to define the cohesive offset for pore pressure cohesive elements.

can be used to define a cohesive offset for pore pressure, coupled temperature-pore pressure, and coupled slurry-temperature-pore pressure cohesive elements; and
is called at all material calculation points of elements for which the material definition contains user-defined cohesive offsets.

This page discusses:

User Subroutine Interface
Variables to Be Defined
Variables That Can Be Updated
Variables Passed in for Information
Example: Keeping Fracture Prop Open

User Subroutine Interface

      SUBROUTINE UCOHESIVEOFFSET( OFFSETOLD, OFFSETNEW, DELTA, OPENMAX,
     1 NOEL, NPT, COORDS, KSTEP, KINC, STIME, DTIME, TEMP, DTEMP, PREDEF, DPRED, NFIELD,
     2 JMAC, JMATYP, MATLAYO, LACCFLA, SDEGOLD, GAPINI, THICKINI, STRESSOLD, STRESSNEW,
     3 DDSDDE, NTENS, NDI, NSHR, DP, CV, JFLGOPT, STATEV, NSTATEV, NIARRAY, I_ARRAY,
     4 NRARRAY, R_ARRAY, NCARRAY, C_ARRAY)
C
      INCLUDE 'ABA_PARAM.INC'
C
      CHARACTER*80 CMNAME
      DIMENSION DELTA(*), COORDS(*), PREDEF(*), DPRED(*), JMAC(*), JMATYP(*),
     1 STRESSOLD(NTENS), STRESSNEW(NTENS), DDSDDE(NTENS,NTENS), STATEV( NSTATEV),
     2 I_ARRAY(NIARRAY), R_ARRAY(NRARRAY), C_ARRAY(NCARRAY)   

      user coding to define JFLGOPT, OFFSETNEW, DDSDDE,  
      STRESSNEW, and, if necessary, STATEV
      
      RETURN
      END

Variables to Be Defined

OFFSETNEW

Cohesive offset at the end of the increment, $δ_{o f f}$ . If this value is not defined, it is assumed to be zero.

JFLGOPT

An integer flag that must be set to either 1 or 2.

Set JFLGOPT=1 to update OFFSETNEW and the Jacobian matrix, DDSDDE.

Set JFLGOPT=2 to update OFFSETNEW; the Jacobian matrix, DDSDDE; and the stress at the end of the increment, STRESSNEW.

Variables That Can Be Updated

DDSDDE

Jacobian matrix for the traction-separation response, $C = \partial Δ t / \partial ϵ$ , where $Δ t$ are the nominal traction stress vector increments, and $Δ ϵ$ are the nominal strain increments. DDSDDE(I,J) defines the change in the Ith stress component at the end of the time increment caused by an infinitesimal perturbation in the Jth component of the strain increment array.

DDSDDE is initialized to the Jacobian matrix (stiffness matrix) of the underlying traction-separation response before UCOHESIVEOFFSET is called, and Abaqus uses these values for all subsequent calculations if DDSDDE is not updated in UCOHESIVEOFFSET.

STRESSNEW

This variable is initialized to the nominal traction stress vector at the end of the previous increment and can be updated to the corresponding values at the end of the increment.

If you set JFLGOPT=1, Abaqus will compute STRESSNEW based on the offset and the Jacobian matrix (stiffness matrix), DDSDDE. Any updates you make to STRESSNEW in this case will be ignored.

If you set JFLGOPT=2, you must update STRESSNEW.

STATEV

An array containing the solution-dependent state variables. The size of the array is defined as described in Allocating Space for Element Solution-Dependent Variables.

Variables Passed in for Information

OPENMAX: $δ_{o f f}^{\max}$ , the maximum value of $δ_{o f f}$ at a material point over the deformation history.
NSTATEV: Number of solution-dependent state variables that are associated with this material type (defined as described in Allocating Space for Element Solution-Dependent Variables).
OFFSETOLD: $δ_{o f f}$ , the cohesive separation offset at the beginning of the increment.
STRESSOLD: Nominal traction stress vector at the beginning of the increment.
DELTA(NTENS): Cohesive separations including one normal and one (2D) or two (3D) shear components.
NOEL: Element number.
NPT: Integration point number.
COORDS: Current coordinates of this point.
KSTEP: Step number.
KINC: Increment number.
STIME: Step time.
DTIME: Time increment.
TEMP: Temperature at the start of the increment.
DTEMP: Temperature increment.
PREDEF: Array of predefined field variables.
DPRED: Array of increments of predefined field variables.
NFIELD: Number of predefined field variables.
JMAC: Variable that must be passed into the GETVRM utility routine to access an output variable.
JMATYP: Variable that must be passed into the GETVRM utility routine to access an output variable.
MATLAYO: Variable that must be passed into the GETVRM utility routine to access an output variable.
LACCFLA: Variable that must be passed into the GETVRM utility routine to access an output variable.
SDEGOLD: Damage variable at the beginning of the increment.
GAPINI: Initial gap.
THICKINI: Initial thickness of the cohesive element.
NDI: Number of direct stress components at this point.
NSHR: Number of shear stress components at this point.
NTENS: Size of the stress or strain component array (NDI + NSHR).
DP: Diameter of the proppant particle.
CV: Slurry concentration.
NIARRAY: Size of array I_ARRAY.
I_ARRAY: Not used.
NRARRAY: Size of array R_ARRAY.
R_ARRAY: Not used.
NCARRAY: Size of array C_ARRAY.
C_ARRAY: Not used.

Example: Keeping Fracture Prop Open

      SUBROUTINE UCOHESIVEOFFSET( OFFSETCUR, OFFSETNEW, DELTA, OPENMAX,
     1     NOEL, NPT, COORDS, KSTEP, KINC, TIME, DTIME, TEMP, DTEMP, PREDEF,
     2     DPRED, NFIELD, JMAC, JMATYP, MATLAYO, LACCFLA, SDEG, GAPINI,
     3     THICKINI, STRESSOLD, STRESSNEW, STIFFNESS, NTENS, NDI, NSHR,
     4     DIAMETERP, CV, JFLGOPT, STATEV, NSTATEV, NIARRAY, I_ARRAY, NRARRAY,
     5     R_ARRAY, NCARRAY, C_ARRAY)
C     
      INCLUDE 'ABA_PARAM.INC'
C
      DIMENSION COORDS(*), TIME(*), TEMP(*), DTEMP(*), PREDEF(NFIELD),
     $     DPRED(*), JMAC(*), JMATYP(*), STRESSOLD(*), STRESSNEW(*),
     $     STIFFNESS( NTENS, NTENS), DELTA(*), STATEV(*)
      DIMENSION I_ARRAY(*), R_ARRAY(*)
      CHARACTER*80 C_ARRAY(*)
C
CC   THIS EXAMPLE DEMONSTRATES HOW TO SPECIFY AN OFFSET IN STEP 2 TO KEEP THE
CC   FRACTURE “PROPPED OPEN” WHEN EXTERNAL LOADING CONDITIONS WOULD
CC   OTHERWISE HAVE LED TO CLOSURE OF THE FRACTURE

      JFLGOPT = 1
      IF(SDEG.LT.0.99999 .OR. KSTEP.EQ.1) THEN
         OFFSETNEW = 0.0
      ELSE
         OFFSETNEW = 0.005
      END IF
 
      RETURN
      END