c
c User subroutine VFRICTION to define friction forces
c
      subroutine vfriction (
c Write only - 
     *   fTangential, 
c Read/Write - 
     *   state,
c Read only - 
     *   nBlock, nBlockAnal, nBlockEdge, 
     *   nNodState, nNodSec, nNodMain, 
     *   nFricDir, nDir, 
     *   nStates, nProps, nTemp, nFields, 
     *   jFlags, rData, 
     *   surfInt, surfSec, surfMain, 
     *   jConSecUid, jConMainUid, props, 
     *   dSlipFric, fStickForce, fTangPrev, fNormal, 
     *   areaCont, dircosN, dircosSec, 
     *   shapeSec, shapeMain, 
     *   coordSec, coordMain, 
     *   velSec, velMain, 
     *   tempSec, tempMain, 
     *   fieldSec, fieldMain )
c
c Array dimensioning variables:
c
c      nBlockAnal = nBlock    (non-analytical-rigid main surface)
c      nBlockAnal = 1         (analytical rigid main surface)
c      nBlockEdge = 1         (non-edge-type secondary surface)
c      nBlockEdge = nBlock    (edge-type secondary surface)
c      nNodState  = 1         (node-type secondary surface)
c      nNodState  = 4         (edge-type secondary surface)
c      nNodSec    = 1         (node-type secondary surface)
c      nNodSec    = 2         (edge-type secondary surface)
c      nNodMain    = 4         (facet-type main surface)
c      nNodMain    = 2         (edge-type main surface)
c      nNodMain    = 1         (analytical rigid main surface)
c
c Surface names surfSec and surfMain are not available for
c general contact (set to blank).
c
      include 'vaba_param.inc'
      dimension fTangential(nFricDir,nBlock),
     *   state(nStates,nNodState,nBlock),
     *   jConSecUid(nNodSec,nBlock), 
     *   jConMainUid(nNodMain,nBlockAnal), 
     *   props(nProps),
     *   dSlipFric(nDir,nBlock),
     *   fStickForce(nBlock), 
     *   fTangPrev(nDir,nBlock),
     *   fNormal(nBlock), 
     *   areaCont(nBlock),
     *   dircosN(nDir,nBlock),
     *   dircosSec(nDir,nBlock), 
     *   shapeSec(nNodSec,nBlockEdge), 
     *   shapeMain(nNodMain,nBlockAnal), 
     *   coordSec(nDir,nNodSec,nBlock), 
     *   coordMain(nDir,nNodMain,nBlockAnal), 
     *   velSec(nDir,nNodSec,nBlock), 
     *   velMain(nDir,nNodMain,nBlockAnal), 
     *   tempSec(nBlock), 
     *   tempMain(nBlockAnal),
     *   fieldSec(nFields,nBlock),
     *   fieldMain(nFields,nBlockAnal)
c
      parameter( iKStep    = 1,
     *           iKInc     = 2,
     *           iLConType = 3,
     *           nFlags    = 3 )
      parameter( iTimStep      = 1,
     *           iTimGlb       = 2,
     *           iDTimCur      = 3,
     *           iFrictionWork = 4, 
     *           nData         = 4 )
c
      dimension jFlags(nFlags), rData(nData)
      character*80 surfInt, surfSec, surfMain
      parameter( zero=0.d0 )
c
      u = props(1)
c
      do k = 1, nBlock
         fn = fNormal(k) 
         fs = fStickForce(k)
         ft = min ( u*fn, fs )
         fTangential(1,k) = -ft
         fTangential(2,k) = zero
      end do
c
      return
      end