subroutine fric_coef(fCoef, fCoefDeriv, nBlock, nProps, 
     *   nTemp, nFields, iData, rData, surfInt, surfSec, surfMain, 
     *   props, slipData, pressure, tempAvg, fieldAvg )

      include 'aba_param.inc'
c
      parameter( i_ifc_KStep   = 1,
     *           i_ifc_kinc    = 2,
     $           i_ifc_kitgen  = 3,
     $           i_ifc_node    = 4,
     $           i_ifc_nStateV = 5,
     $           i_ifc_nFDir   = 6)
c
      parameter( i_rfc_TimStep = 1,
     *           i_rfc_TimGlb  = 2,
     *           i_rfc_DTimCur = 3,
     $           i_rfc_Drot    = 4,
     $           i_rfc_StateV  = 8)
      
      parameter( idfdSlipRate = 1,
     *           idfdPressure = 2,
     *           idfdtemperature = 3)

      dimension fCoef(nBlock), fCoefDeriv(nBLock,20),
     *   props(nProps),slipData(nBlock,*),pressure(nBlock),
     *   tempAvg(nBlock), fieldAvg(nBlock,nFields),
     *   iData(*), rData(*)
c
      parameter (nDataSize=10)
      dimension array(nDataSize),jarray(nDataSize)
      character*3 flgray(nDataSize)
c
      character*80 surfInt, surfSec, surfMain 
      pointer (ptrDrot,Drot)
      dimension Drot(2,*)
      pointer (ptrSdv,Sdv)
      dimension Sdv(*)
c
      real*8 mu_initial,mu_final,SlipScaleFac,cslipeq,mu_Cur

      ptrSdv = loc(rData(i_rfc_StateV))
      ptrDrot= loc(rData(i_rfc_Drot))
      nStateV = iData(i_ifc_nStateV)
c
c     Access equivalent contact slip at the beginning of the increment
c      
      call GETVRC('CSLIPEQ',array,jarray,flgray,nDataSize,jrcd)
c
      kstep = iData(i_ifc_KStep)
      kinc  = iData(i_ifc_kinc)
      kitgen= iData(i_ifc_kitgen)
      iNode = iData(i_ifc_node)
c

 100  format('Step/Inc/Iter/Node=', 4(1x,i3),'MU= ',(1x,e19.11),' SDV',4(1x,e19.11))
      
      mu_initial = props(1)
      mu_final   = props(2)
      alpha      = props(3)
      beta       = props(4)
c
      cSlipEQ = array(1)
c
c**        SDV(1) = Current friction coefficient for visualization purposes only
c**        SDV(2) = Solution dependent variable that depends on equivalent contact slip
      
      Sdv(2)   = alpha*cSlipEQ + beta
      fCoef(1) = mu_initial + (mu_final - mu_initial)*(1.d0 - exp(Sdv(2)))
      Sdv(1) = fCoef(1)
c
c      if (iNode .eq. 121.or. iNode .eq. 123) then
c         write(7,100) kstep,kinc,kitgen,iNode,fCoef(1),(Sdv(k),k=1,nStateV)
c      end if
c
      do k1=1,nBlock
        fCoefDeriv(k1,idfdSlipRate) = 0.d0
        fCoefDeriv(k1,idfdPressure) = 0.d0
        fCoefDeriv(k1,idfdTemperature) = 0.d0
      end do

      return
      end