UXFEMCRACK

User subroutine to define the interactions between the cracked element surfaces for enriched elements using a small sliding formulation.

User subroutine UXFEMCRACK:

can be used to specify the crack opening offset for contact of cracked element surfaces;
can also be used to define the mechanical (normal and shear) interactions between the cracked element surfaces;
is called at all the points of intersection between the crack surface and the element edges;
can include the effects of slurry concentration and the proppant particle size; and
is only available for contact of cracked enriched element surfaces using a small-sliding formulation.

This page discusses:

User Subroutine Interface
Variables to Be Defined
Variables That Can Be Updated
Variables Passed in for Information
Example: Example: User-Defined Offset for Enriched Cracked Element Surfaces

User Subroutine Interface

      SUBROUTINE UXFEMCRACK_API(OFFSETCUR,OFFSETNEW,DELTA,
     1     OPENMAX,NOEL,NPT,COORDS,KSTEP,KINC,TIME1,DTIME1,TEMP,DTEMP,
     2     PREDEF,DPRED,NFIELD,STATEV,NSTATEV,PROPS,NPROPS,JMAC,JMATYP,
     3     MATLAYO,LACCFLA,SDEG,GAPINI,DV,STRESSOLD,STRESSNEW,
     4     STIFFNESS,DIAMETERP,CV,JFLGOPT,NIARRAY,I_ARRAY,NRARRAY,
     5     R_ARRAY,NCARRAY,C_ARRAY)

Variables to Be Defined

OFFSETNEW: New offset value defined by the user.
STRESSNEW: Stresses at the end the current increment
JFLGOPT: An option flag: If JFLGOPT=1, only STIFFNESSneeds to be updated; otherwise, if JFLGOPT=2, both STIFFNESSand STRESSNEWneed to be updated.

Variables That Can Be Updated

OPENMAX: Maximum crack opening
STATEV: An array containing the user-defined solution-dependent state variables at this point. This array will be passed in containing the values of these variables at the start of the increment unless the values are updated in user subroutine USDFLD. They can be updated in this subroutine to their values at the end of the increment.
STIFFNESS: Penalty stiffness of the cracked surfaces

Variables Passed in for Information

OFFSETCUR: Offset of the cracked surfaces at the end of previous increment.
DELTA: Current crack opening
NOEL: Element number.
NPT: Integration point number.
COORDS: An array containing the current coordinates of this point.
KSTEP: Step number.
KINC: An array containing the current coordinates of this point.
TIME1(1): Value of step time at the beginning of the current increment.
TIME1(2): Value of total time at the beginning of the current increment.
DTIME1: Time increment.
TEMP: Temperature at the start of the increment.
DTEMP: Increment of temperature during the time increment.
PREDEF: An array containing the values of all of the user-specified predefined variables at this point at the start of the increment .
DPRED: An array containing the increments of all of the predefined variables during the time increment.
NFIELD: Number of user-specified predefined variables.
NSTATV: Number of solution-dependent state variables associated with this material.
PROPS(NPROPS): User-specified array of material constants associated with this material.
NPROPS: User-defined number of material constants associated with this material.
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.
SDEG: Damage variable at the end of the last increment.
STRESSOLD: Stresses at the end of previous increment.
DV: Integration point volume.
DIAMETERP: Diameter of slurry particles
CV: Slurry concentration at the end of previous increment.
GAPINI: Initial crack opening.
NIARRAY: Size of array I_ARRAY.
I_ARRAY: Integer array for future expansion.
NRARRAY: Size of array R_ARRAY.
R_ARRAY: Real array for future expansion.
NCARRAY: Size of array C_ARRAY.
C_ARRAY: Character array for future expansion.

Example: Example: User-Defined Offset for Enriched Cracked Element Surfaces

A simple example to specify offset for cracked element surfaces by using UMIXMODEFATIGUE:

SUBROUTINE UXFEMCRACK(OFFSETCUR,OFFSETNEW,DELTA,
     1     OPENMAX,NOEL,NPT,COORDS,KSTEP,KINC,TIME1,DTIME1,TEMP,DTEMP,
     2     PREDEF,DPRED,NFIELD,STATEV,NSTATEV,PROPS,NPROPS,JMAC,JMATYP,
     3     MATLAYO,LACCFLA,SDEG,GAPINI,DV,STRESSOLD,STRESSNEW,
     4     STIFFNESS,DIAMETERP,CV,JFLGOPT,NIARRAY,I_ARRAY,NRARRAY,
     5     R_ARRAY,NCARRAY,C_ARRAY)

      INCLUDE 'ABA_PARAM.INC'

C
      DIMENSION COORDS(*), TIME1(*), TEMP(*), JMAC(*), JMATYP(*), STRESSOLD(*),
     1 STRESSNEW(*), STIFFNESS(3,3), DELTA(*), PROPS(NPROPS),STATEV(NSTATV),
     2 PREDEF(NFIELD),DPRED(NFIELD), I_ARRAY(NIARRAY), R_ARRAY(NRARRAY), 
     3 C_ARRAY(NCARRAY)

	    JFLGOPT=1
     IF(KSTEP.LE.2) THEN
         OFFSETNEW = 0.0
     ELSE
         OFFSETNEW=0.15
     ENDIF
C
     IF(KSTEP.EQ.2) OPENMAX = max(DELTA(1),openmax) 
C
     RETURN
     END