VFRIC_COEF

User subroutine to define the frictional coefficient for contact surfaces.

User subroutine VFRIC_COEF:

can be used to define the isotropic frictional coefficient between contacting surfaces;
corresponds to the classical Coulomb friction model; and
can be used only with the general contact algorithm.

This page discusses:

User Subroutine Interface
Variables to Be Defined
Variables That Can Be Updated
Variables Passed in for Information

User Subroutine Interface

      subroutine vfric_coef (
C Write only - 
     *   fCoef, 
C Not applicable -
     *   fCoefDeriv, 
C Read only, except state variables within rData array - 
     *   nBlock, nProps, nTemp, nFields, 
     *   iData, rData, 
     *   surfInt, surfSec, surfMain, 
     *   props, slipData, pressure, 
     *   tempAvg, fieldAvg )
C
      include 'vaba_param.inc'
C
      dimension fCoef(nBlock,2), 
     *   fCoefDeriv(nBlock,20,2),
     *   props(nProps),
     *   slipData(nBlock,6),
     *   pressure(nBlock),
     *   tempAvg(nBlock), 
     *   fieldAvg(nBlock,nFields)
c
c    Offset parameters to various integer quantities in iData(nDataI)
c
      parameter( i_ifc_KStep   = 1,
     *           i_ifc_KInc    = 2,
     *           i_ifc_Kit     = 3,
     *           i_ifc_Node    = 4,
     *           i_ifc_nStateV = 5,
     *           i_ifc_nFDir   = 6,
     *           nDataI        = 6 )
c
c    Offset parameters to various real quantities in rData(*)
c
      parameter( i_rfc_TimStep = 1,
     *           i_rfc_TimGlb  = 2,
     *           i_rfc_DTimCur = 3,
     *           i_rfc_Drot    = 4,
     *           i_rfc_StateV  = 8 )
c
c    Offset parameters to slip variables in slipData
c
      parameter( i_SD_SlipRateMag  = 1,
     *           i_SD_SlipRate1    = 2,
     *           i_SD_SlipRate2    = 3,
     *           i_SD_SlipEq       = 4,
     *           i_SD_Slip1        = 5,
     *           i_SD_Slip2        = 6,
     *           n_SD_Length       = 6 )
C
      dimension iData(nDataI), rData(*)
C
      character*80 surfInt, surfSec, surfMain
c
C
      user coding to define fCoef
c
c	    Pointers to access blocks of data from rData
c	    For example, Solution-dependent state variables indexed from 
c           1 to number of state variables nStateV where
c           nStateV = iData(i_ifc_nStateV)
c
      pointer (ptrStateVariables,StateVariables)
      real*8 StateVariables(*) !indexed 1 to iData(i_ifc_nStateV)
      ......
c
c	    Access state variables
c
      ptrStateVariables = loc(rData(i_rfc_StateV))
      ......

c
c	    Compute fCoef
c
      ......
C
      return
      end

Variables to Be Defined

fCoef(nBlock,2): fCoef(1,1) and other entries of the first column of the fCoef array should be updated to current values of the friction coefficient for all contacting points. fCoef(1,2) and other entries of the second column of the fCoef array should not be updated for Abaqus/Explicit analyses. You can model anisotropic friction with directional preference specified as a surface property (see Anisotropic Friction with Directional Preference as a Surface Property and a nominal friction coefficient specified in fCoef(1,1) and other entries of the first column of the fCoef array.
fCoefDeriv(nBlock,20,2): This array is not applicable to Abaqus/Explicit analyses.

Variables That Can Be Updated

rData(i_rfc_StateV): The array of real values starting from this offset corresponds to the solution-dependent state variables. You specify the number of available state variables (Allocating Space for Solution-Dependent State Variables). These state variables are passed in with values at the start of the increment. Update them to their corresponding values at the end of the increment. See the user subroutine interface provided earlier for an example of how to access the array of state variables from the buffer rData.

Variables Passed in for Information

nBlock: Number of contacting points to be processed in this call to VFRIC_COEF.
nProps: User-specified number of property values associated with this friction model.
nTemp: 1 if the temperature is defined, and 0 if the temperature is not defined.
nFields: Number of user-specified field variables.
iData(i_ifc_KStep): Step number.
iData(i_ifc_KInc): Increment number.
iData(i_ifc_Kit): Not applicable to Abaqus/Explicit analyses.
iData(i_ifc_Node): Equal to 0 in Abaqus/Explicit analyses. The secondary node number varies among the contact constraints processed in a single call to this user subroutine.
iData(i_ifc_nStateV): The number of state variables you have specified. The default value is 0.
iData(i_ifc_nFDir): Equal to 1 in Abaqus/Explicit analyses. You are expected to provide a single friction coefficient for each contact constraint in the user subroutine.
rData(i_rfc_TimStep): Value of step time.
rData(i_rfc_TimGlb): Value of total time.
rData(i_rfc_DTimCur): Current time increment size.
rData(i_rfc_Drot): The list of four value entries starting from this offset corresponds to the column major storage of the 2 × 2 rotation increment matrix. For Abaqus/Explicit, this rotation increment matrix is always provided as the identity matrix.
surfInt: User-specified surface interaction name, left justified.
surfSec: Not applicable to Abaqus/Explicit analyses.
surfMain: Not applicable to Abaqus/Explicit analyses.
props(nProps): User-specified vector of property values to define the frictional coefficient at contacting points.
slipData(nBlock,6): The entries slipData(kBlock,i_SD_SlipRateMag) and slipData(kBlock,i_SD_SlipEq) contain the slip rate magnitude and total accumulated slip distance for a contacting point indexed by kBlock for the current time increment. Other entries of slipData are not applicable to Abaqus/Explicit analyses.
pressure(nBlock): Array containing the pressure at the contact point projected at the end of the current time increment.
tempAvg(nBlock): Average current temperature between the main and secondary surfaces at the contacting points.
fieldAvg(nBlock,nFields): Average current value of all the user-specified field variables between the main and secondary surfaces at the contacting points.