DAMASK_EICMD/src/phase_mechanical_plastic_dislotungsten.f90

!--------------------------------------------------------------------------------------------------
!> @author Franz Roters, Max-Planck-Institut für Eisenforschung GmbH
!> @author Philip Eisenlohr, Max-Planck-Institut für Eisenforschung GmbH
!> @author David Cereceda, Lawrence Livermore National Laboratory
!> @author Martin Diehl, Max-Planck-Institut für Eisenforschung GmbH
!> @brief crystal plasticity model for bcc metals, especially Tungsten
!--------------------------------------------------------------------------------------------------
submodule(phase:plastic) dislotungsten

  real(pReal), parameter :: &
    kB = 1.38e-23_pReal                                                                             !< Boltzmann constant in J/Kelvin

  type :: tParameters
    real(pReal) :: &
      D    = 1.0_pReal, &                                                                           !< grain size
      mu   = 1.0_pReal, &                                                                           !< equivalent shear modulus
      D_0  = 1.0_pReal, &                                                                           !< prefactor for self-diffusion coefficient
      Q_cl = 1.0_pReal                                                                              !< activation energy for dislocation climb
    real(pReal),               allocatable, dimension(:) :: &
      b_sl, &                                                                                       !< magnitude of Burgers vector [m]
      d_caron, &                                                                                    !< distance of spontaneous annhihilation
      i_sl, &                                                                                       !< Adj. parameter for distance between 2 forest dislocations
      f_at, &                                                                                       !< factor to calculate atomic volume
      tau_Peierls, &                                                                                !< Peierls stress
      !* mobility law parameters
      Q_s, &                                                                                        !< activation energy for glide [J]
      v_0, &                                                                                        !< dislocation velocity prefactor [m/s]
      p, &                                                                                          !< p-exponent in glide velocity
      q, &                                                                                          !< q-exponent in glide velocity
      B, &                                                                                          !< friction coefficient
      h, &                                                                                          !< height of the kink pair
      w, &                                                                                          !< width of the kink pair
      omega                                                                                         !< attempt frequency for kink pair nucleation
    real(pReal),               allocatable, dimension(:,:) :: &
      h_sl_sl, &                                                                                    !< slip resistance from slip activity
      forestProjection
    real(pReal),               allocatable, dimension(:,:,:) :: &
      P_sl, &
      P_nS_pos, &
      P_nS_neg
    integer :: &
      sum_N_sl                                                                                      !< total number of active slip system
    character(len=pStringLen), allocatable, dimension(:) :: &
      output
    logical :: &
      dipoleFormation                                                                               !< flag indicating consideration of dipole formation
  end type                                                                                          !< container type for internal constitutive parameters

  type :: tDisloTungstenState
    real(pReal), dimension(:,:), pointer :: &
      rho_mob, &
      rho_dip, &
      gamma_sl
  end type tDisloTungstenState

  type :: tDisloTungstendependentState
    real(pReal), dimension(:,:), allocatable :: &
      Lambda_sl, &
      tau_pass
  end type tDisloTungstendependentState

!--------------------------------------------------------------------------------------------------
! containers for parameters and state
  type(tParameters),              allocatable, dimension(:) :: param
  type(tDisloTungstenState),          allocatable, dimension(:) :: &
    dotState, &
    state
  type(tDisloTungstendependentState), allocatable, dimension(:) :: dependentState

contains


!--------------------------------------------------------------------------------------------------
!> @brief Perform module initialization.
!> @details reads in material parameters, allocates arrays, and does sanity checks
!--------------------------------------------------------------------------------------------------
module function plastic_dislotungsten_init() result(myPlasticity)

  logical, dimension(:), allocatable :: myPlasticity
  integer :: &
    ph, i, &
    Nmembers, &
    sizeState, sizeDotState, &
    startIndex, endIndex
  integer,    dimension(:), allocatable :: &
    N_sl
  real(pReal),dimension(:), allocatable :: &
    rho_mob_0, &                                                                                    !< initial dislocation density
    rho_dip_0, &                                                                                    !< initial dipole density
    a                                                                                               !< non-Schmid coefficients
  character(len=pStringLen) :: &
    extmsg = ''
  class(tNode), pointer :: &
    phases, &
    phase, &
    mech, &
    pl


  myPlasticity = plastic_active('dislotungsten')
  if(count(myPlasticity) == 0) return

  print'(/,a)', ' <<<+-  phase:mechanical:plastic:dislotungsten init  -+>>>'
  print'(a,i0)', ' # phases: ',count(myPlasticity); flush(IO_STDOUT)

  print*, 'D. Cereceda et al., International Journal of Plasticity 78:242–256, 2016'
  print*, 'https://doi.org/10.1016/j.ijplas.2015.09.002'


  phases => config_material%get('phase')
  allocate(param(phases%length))
  allocate(state(phases%length))
  allocate(dotState(phases%length))
  allocate(dependentState(phases%length))


  do ph = 1, phases%length
    if(.not. myPlasticity(ph)) cycle

    associate(prm => param(ph), dot => dotState(ph), stt => state(ph), dst => dependentState(ph))

    phase => phases%get(ph)
    mech  => phase%get('mechanical')
    pl  => mech%get('plastic')

#if defined (__GFORTRAN__)
    prm%output = output_as1dString(pl)
#else
    prm%output = pl%get_as1dString('output',defaultVal=emptyStringArray)
#endif

    prm%mu = elastic_mu(ph)

!--------------------------------------------------------------------------------------------------
! slip related parameters
    N_sl         = pl%get_as1dInt('N_sl',defaultVal=emptyIntArray)
    prm%sum_N_sl = sum(abs(N_sl))
    slipActive: if (prm%sum_N_sl > 0) then
      prm%P_sl = lattice_SchmidMatrix_slip(N_sl,phase_lattice(ph),phase_cOverA(ph))

      if (phase_lattice(ph) == 'cI') then
        a = pl%get_as1dFloat('a_nonSchmid',defaultVal = emptyRealArray)
        prm%P_nS_pos = lattice_nonSchmidMatrix(N_sl,a,+1)
        prm%P_nS_neg = lattice_nonSchmidMatrix(N_sl,a,-1)
      else
        prm%P_nS_pos = prm%P_sl
        prm%P_nS_neg = prm%P_sl
      endif

      prm%h_sl_sl = lattice_interaction_SlipBySlip(N_sl,pl%get_as1dFloat('h_sl-sl'), &
                                                   phase_lattice(ph))
      prm%forestProjection = lattice_forestProjection_edge(N_sl,phase_lattice(ph),&
                                                           phase_cOverA(ph))
      prm%forestProjection = transpose(prm%forestProjection)

      rho_mob_0       = pl%get_as1dFloat('rho_mob_0',     requiredSize=size(N_sl))
      rho_dip_0       = pl%get_as1dFloat('rho_dip_0',     requiredSize=size(N_sl))
      prm%v_0         = pl%get_as1dFloat('v_0',           requiredSize=size(N_sl))
      prm%b_sl        = pl%get_as1dFloat('b_sl',          requiredSize=size(N_sl))
      prm%Q_s         = pl%get_as1dFloat('Q_s',           requiredSize=size(N_sl))

      prm%i_sl        = pl%get_as1dFloat('i_sl',          requiredSize=size(N_sl))
      prm%tau_Peierls = pl%get_as1dFloat('tau_Peierls',   requiredSize=size(N_sl))
      prm%p           = pl%get_as1dFloat('p_sl',          requiredSize=size(N_sl))
      prm%q           = pl%get_as1dFloat('q_sl',          requiredSize=size(N_sl))
      prm%h           = pl%get_as1dFloat('h',             requiredSize=size(N_sl))
      prm%w           = pl%get_as1dFloat('w',             requiredSize=size(N_sl))
      prm%omega       = pl%get_as1dFloat('omega',         requiredSize=size(N_sl))
      prm%B           = pl%get_as1dFloat('B',             requiredSize=size(N_sl))

      prm%D    = pl%get_asFloat('D')
      prm%D_0  = pl%get_asFloat('D_0')
      prm%Q_cl = pl%get_asFloat('Q_cl')
      prm%f_at = pl%get_asFloat('f_at') * prm%b_sl**3.0_pReal

      prm%dipoleformation = .not. pl%get_asBool('no_dipole_formation', defaultVal = .false.)

      ! expand: family => system
      rho_mob_0          = math_expand(rho_mob_0,       N_sl)
      rho_dip_0          = math_expand(rho_dip_0,       N_sl)
      prm%q              = math_expand(prm%q,           N_sl)
      prm%p              = math_expand(prm%p,           N_sl)
      prm%Q_s            = math_expand(prm%Q_s,         N_sl)
      prm%b_sl           = math_expand(prm%b_sl,        N_sl)
      prm%h              = math_expand(prm%h,           N_sl)
      prm%w              = math_expand(prm%w,           N_sl)
      prm%omega          = math_expand(prm%omega,       N_sl)
      prm%tau_Peierls    = math_expand(prm%tau_Peierls, N_sl)
      prm%v_0            = math_expand(prm%v_0,         N_sl)
      prm%B              = math_expand(prm%B,           N_sl)
      prm%i_sl           = math_expand(prm%i_sl,        N_sl)
      prm%f_at           = math_expand(prm%f_at,        N_sl)
      prm%d_caron        = pl%get_asFloat('D_a') * prm%b_sl

      ! sanity checks
      if (    prm%D_0          <= 0.0_pReal)  extmsg = trim(extmsg)//' D_0'
      if (    prm%Q_cl         <= 0.0_pReal)  extmsg = trim(extmsg)//' Q_cl'
      if (any(rho_mob_0        <  0.0_pReal)) extmsg = trim(extmsg)//' rho_mob_0'
      if (any(rho_dip_0        <  0.0_pReal)) extmsg = trim(extmsg)//' rho_dip_0'
      if (any(prm%v_0          <  0.0_pReal)) extmsg = trim(extmsg)//' v_0'
      if (any(prm%b_sl         <= 0.0_pReal)) extmsg = trim(extmsg)//' b_sl'
      if (any(prm%Q_s          <= 0.0_pReal)) extmsg = trim(extmsg)//' Q_s'
      if (any(prm%tau_Peierls  <  0.0_pReal)) extmsg = trim(extmsg)//' tau_Peierls'
      if (any(prm%B            <  0.0_pReal)) extmsg = trim(extmsg)//' B'
      if (any(prm%d_caron      <  0.0_pReal)) extmsg = trim(extmsg)//' d_caron(D_a,b_sl)'
      if (any(prm%f_at         <= 0.0_pReal)) extmsg = trim(extmsg)//' f_at or b_sl'

    else slipActive
      rho_mob_0= emptyRealArray; rho_dip_0 = emptyRealArray
      allocate(prm%b_sl,prm%d_caron,prm%i_sl,prm%f_at,prm%tau_Peierls, &
               prm%Q_s,prm%v_0,prm%p,prm%q,prm%B,prm%h,prm%w,prm%omega, &
               source = emptyRealArray)
      allocate(prm%forestProjection(0,0))
      allocate(prm%h_sl_sl         (0,0))
    endif slipActive

!--------------------------------------------------------------------------------------------------
! allocate state arrays
    Nmembers = count(material_phaseID == ph)
    sizeDotState = size(['rho_mob ','rho_dip ','gamma_sl']) * prm%sum_N_sl
    sizeState = sizeDotState

    call phase_allocateState(plasticState(ph),Nmembers,sizeState,sizeDotState,0)

!--------------------------------------------------------------------------------------------------
! state aliases and initialization
    startIndex = 1
    endIndex   = prm%sum_N_sl
    stt%rho_mob => plasticState(ph)%state(startIndex:endIndex,:)
    stt%rho_mob =  spread(rho_mob_0,2,Nmembers)
    dot%rho_mob => plasticState(ph)%dotState(startIndex:endIndex,:)
    plasticState(ph)%atol(startIndex:endIndex) = pl%get_asFloat('atol_rho',defaultVal=1.0_pReal)
    if (any(plasticState(ph)%atol(startIndex:endIndex) < 0.0_pReal)) extmsg = trim(extmsg)//' atol_rho'

    startIndex = endIndex + 1
    endIndex   = endIndex + prm%sum_N_sl
    stt%rho_dip => plasticState(ph)%state(startIndex:endIndex,:)
    stt%rho_dip =  spread(rho_dip_0,2,Nmembers)
    dot%rho_dip => plasticState(ph)%dotState(startIndex:endIndex,:)
    plasticState(ph)%atol(startIndex:endIndex) = pl%get_asFloat('atol_rho',defaultVal=1.0_pReal)

    startIndex = endIndex + 1
    endIndex   = endIndex + prm%sum_N_sl
    stt%gamma_sl => plasticState(ph)%state(startIndex:endIndex,:)
    dot%gamma_sl => plasticState(ph)%dotState(startIndex:endIndex,:)
    plasticState(ph)%atol(startIndex:endIndex) = pl%get_asFloat('atol_gamma',defaultVal=1.0e-6_pReal)
    if(any(plasticState(ph)%atol(startIndex:endIndex) < 0.0_pReal)) extmsg = trim(extmsg)//' atol_gamma'

    allocate(dst%Lambda_sl(prm%sum_N_sl,Nmembers), source=0.0_pReal)
    allocate(dst%tau_pass(prm%sum_N_sl,Nmembers),  source=0.0_pReal)

    end associate

!--------------------------------------------------------------------------------------------------
!  exit if any parameter is out of range
    if (extmsg /= '') call IO_error(211,ext_msg=trim(extmsg)//'(dislotungsten)')

  enddo

end function plastic_dislotungsten_init


!--------------------------------------------------------------------------------------------------
!> @brief Calculate plastic velocity gradient and its tangent.
!--------------------------------------------------------------------------------------------------
pure module subroutine dislotungsten_LpAndItsTangent(Lp,dLp_dMp, &
                                                         Mp,T,ph,en)
  real(pReal), dimension(3,3),     intent(out) :: &
    Lp                                                                                              !< plastic velocity gradient
  real(pReal), dimension(3,3,3,3), intent(out) :: &
    dLp_dMp                                                                                         !< derivative of Lp with respect to the Mandel stress

  real(pReal), dimension(3,3), intent(in) :: &
    Mp                                                                                              !< Mandel stress
  real(pReal),                 intent(in) :: &
    T                                                                                               !< temperature
  integer,                     intent(in) :: &
    ph, &
    en

  integer :: &
    i,k,l,m,n
  real(pReal), dimension(param(ph)%sum_N_sl) :: &
    dot_gamma_pos,dot_gamma_neg, &
    ddot_gamma_dtau_pos,ddot_gamma_dtau_neg

  Lp = 0.0_pReal
  dLp_dMp = 0.0_pReal

  associate(prm => param(ph))

  call kinetics(Mp,T,ph,en,dot_gamma_pos,dot_gamma_neg,ddot_gamma_dtau_pos,ddot_gamma_dtau_neg)
  do i = 1, prm%sum_N_sl
    Lp = Lp + (dot_gamma_pos(i)+dot_gamma_neg(i))*prm%P_sl(1:3,1:3,i)
    forall (k=1:3,l=1:3,m=1:3,n=1:3) &
      dLp_dMp(k,l,m,n) = dLp_dMp(k,l,m,n) &
                       + ddot_gamma_dtau_pos(i) * prm%P_sl(k,l,i) * prm%P_nS_pos(m,n,i) &
                       + ddot_gamma_dtau_neg(i) * prm%P_sl(k,l,i) * prm%P_nS_neg(m,n,i)
  enddo

  end associate

end subroutine dislotungsten_LpAndItsTangent


!--------------------------------------------------------------------------------------------------
!> @brief Calculate the rate of change of microstructure.
!--------------------------------------------------------------------------------------------------
module subroutine dislotungsten_dotState(Mp,T,ph,en)

  real(pReal), dimension(3,3),  intent(in) :: &
    Mp                                                                                              !< Mandel stress
  real(pReal),                  intent(in) :: &
    T                                                                                               !< temperature
  integer,                      intent(in) :: &
    ph, &
    en

  real(pReal), dimension(param(ph)%sum_N_sl) :: &
    dot_gamma_pos, dot_gamma_neg,&
    tau_pos,&
    tau_neg, &
    v_cl, &
    dot_rho_dip_formation, &
    dot_rho_dip_climb, &
    d_hat

  associate(prm => param(ph), stt => state(ph), dot => dotState(ph), dst => dependentState(ph))

  call kinetics(Mp,T,ph,en,&
                dot_gamma_pos,dot_gamma_neg, &
                tau_pos_out = tau_pos,tau_neg_out = tau_neg)

  dot%gamma_sl(:,en) = (dot_gamma_pos+dot_gamma_neg)                                                          ! ToDo: needs to be abs

  where(dEq0(tau_pos))                                                                              ! ToDo: use avg of pos and neg
    dot_rho_dip_formation = 0.0_pReal
    dot_rho_dip_climb     = 0.0_pReal
  else where
    d_hat = math_clip(3.0_pReal*prm%mu*prm%b_sl/(16.0_pReal*PI*abs(tau_pos)), &
                      prm%d_caron, &                                                                ! lower limit
                      dst%Lambda_sl(:,en))                                                          ! upper limit
    dot_rho_dip_formation = merge(2.0_pReal*d_hat* stt%rho_mob(:,en)*abs(dot%gamma_sl(:,en))/prm%b_sl, & ! ToDo: ignore region of spontaneous annihilation
                                  0.0_pReal, &
                                  prm%dipoleformation)
    v_cl = (3.0_pReal*prm%mu*prm%D_0*exp(-prm%Q_cl/(kB*T))*prm%f_at/(2.0_pReal*PI*kB*T)) &
         * (1.0_pReal/(d_hat+prm%d_caron))
    dot_rho_dip_climb = (4.0_pReal*v_cl*stt%rho_dip(:,en))/(d_hat-prm%d_caron)                      ! ToDo: Discuss with Franz: Stress dependency?
  end where

  dot%rho_mob(:,en) = abs(dot%gamma_sl(:,en))/(prm%b_sl*dst%Lambda_sl(:,en)) &                      ! multiplication
                    - dot_rho_dip_formation &
                    - (2.0_pReal*prm%d_caron)/prm%b_sl*stt%rho_mob(:,en)*abs(dot%gamma_sl(:,en))    ! Spontaneous annihilation of 2 edges
  dot%rho_dip(:,en) = dot_rho_dip_formation &
                    - (2.0_pReal*prm%d_caron)/prm%b_sl*stt%rho_dip(:,en)*abs(dot%gamma_sl(:,en)) &  ! Spontaneous annihilation of an edge with a dipole
                    - dot_rho_dip_climb

  end associate

end subroutine dislotungsten_dotState


!--------------------------------------------------------------------------------------------------
!> @brief Calculate derived quantities from state.
!--------------------------------------------------------------------------------------------------
module subroutine dislotungsten_dependentState(ph,en)

  integer,      intent(in) :: &
    ph, &
    en

  real(pReal), dimension(param(ph)%sum_N_sl) :: &
    dislocationSpacing


  associate(prm => param(ph), stt => state(ph),dst => dependentState(ph))

    dislocationSpacing = sqrt(matmul(prm%forestProjection,stt%rho_mob(:,en)+stt%rho_dip(:,en)))
    dst%tau_pass(:,en) = prm%mu*prm%b_sl &
                       * sqrt(matmul(prm%h_sl_sl,stt%rho_mob(:,en)+stt%rho_dip(:,en)))

    dst%Lambda_sl(:,en) = prm%D/(1.0_pReal+prm%D*dislocationSpacing/prm%i_sl)

  end associate

end subroutine dislotungsten_dependentState


!--------------------------------------------------------------------------------------------------
!> @brief Write results to HDF5 output file.
!--------------------------------------------------------------------------------------------------
module subroutine plastic_dislotungsten_results(ph,group)

  integer,          intent(in) :: ph
  character(len=*), intent(in) :: group

  integer :: o

  associate(prm => param(ph), stt => state(ph), dst => dependentState(ph))
  outputsLoop: do o = 1,size(prm%output)
    select case(trim(prm%output(o)))
      case('rho_mob')
        if(prm%sum_N_sl>0) call results_writeDataset(stt%rho_mob,group,trim(prm%output(o)), &
                                                     'mobile dislocation density','1/m²')
      case('rho_dip')
        if(prm%sum_N_sl>0) call results_writeDataset(stt%rho_dip,group,trim(prm%output(o)), &
                                                     'dislocation dipole density','1/m²')
      case('gamma_sl')
        if(prm%sum_N_sl>0) call results_writeDataset(stt%gamma_sl,group,trim(prm%output(o)), &
                                                     'plastic shear','1')
      case('Lambda_sl')
        if(prm%sum_N_sl>0) call results_writeDataset(dst%Lambda_sl,group,trim(prm%output(o)), &
                                                     'mean free path for slip','m')
      case('tau_pass')
        if(prm%sum_N_sl>0) call results_writeDataset(dst%tau_pass,group,trim(prm%output(o)), &
                                                     'threshold stress for slip','Pa')
    end select
  enddo outputsLoop
  end associate

end subroutine plastic_dislotungsten_results


!--------------------------------------------------------------------------------------------------
!> @brief Calculate shear rates on slip systems, their derivatives with respect to resolved
!         stress, and the resolved stress.
!> @details Derivatives and resolved stress are calculated only optionally.
! NOTE: Against the common convention, the result (i.e. intent(out)) variables are the last to
! have the optional arguments at the end
!--------------------------------------------------------------------------------------------------
pure subroutine kinetics(Mp,T,ph,en, &
                 dot_gamma_pos,dot_gamma_neg,ddot_gamma_dtau_pos,ddot_gamma_dtau_neg,tau_pos_out,tau_neg_out)

  real(pReal), dimension(3,3),  intent(in) :: &
    Mp                                                                                              !< Mandel stress
  real(pReal),                  intent(in) :: &
    T                                                                                               !< temperature
  integer,                      intent(in) :: &
    ph, &
    en

  real(pReal),                  intent(out), dimension(param(ph)%sum_N_sl) :: &
    dot_gamma_pos, &
    dot_gamma_neg
  real(pReal),                  intent(out), optional, dimension(param(ph)%sum_N_sl) :: &
    ddot_gamma_dtau_pos, &
    ddot_gamma_dtau_neg, &
    tau_pos_out, &
    tau_neg_out
  real(pReal), dimension(param(ph)%sum_N_sl) :: &
    StressRatio, &
    StressRatio_p,StressRatio_pminus1, &
    dvel, vel, &
    tau_pos,tau_neg, &
    t_n, t_k, dtk,dtn
  integer :: j

  associate(prm => param(ph), stt => state(ph), dst => dependentState(ph))

  do j = 1, prm%sum_N_sl
    tau_pos(j) = math_tensordot(Mp,prm%P_nS_pos(1:3,1:3,j))
    tau_neg(j) = math_tensordot(Mp,prm%P_nS_neg(1:3,1:3,j))
  enddo


  if (present(tau_pos_out)) tau_pos_out = tau_pos
  if (present(tau_neg_out)) tau_neg_out = tau_neg

  associate(BoltzmannRatio  => prm%Q_s/(kB*T), &
            dot_gamma_0     => stt%rho_mob(:,en)*prm%b_sl*prm%v_0, &
            effectiveLength => dst%Lambda_sl(:,en) - prm%w)

  significantPositiveTau: where(abs(tau_pos)-dst%tau_pass(:,en) > tol_math_check)
    StressRatio = (abs(tau_pos)-dst%tau_pass(:,en))/prm%tau_Peierls
    StressRatio_p       = StressRatio** prm%p
    StressRatio_pminus1 = StressRatio**(prm%p-1.0_pReal)

    t_n = prm%b_sl/(exp(-BoltzmannRatio*(1-StressRatio_p) ** prm%q)*prm%omega*effectiveLength)
    t_k = effectiveLength * prm%B /(2.0_pReal*prm%b_sl*tau_pos)

    vel = prm%h/(t_n + t_k)

    dot_gamma_pos = dot_gamma_0 * sign(vel,tau_pos) * 0.5_pReal
  else where significantPositiveTau
    dot_gamma_pos = 0.0_pReal
  end where significantPositiveTau

  if (present(ddot_gamma_dtau_pos)) then
    significantPositiveTau2: where(abs(tau_pos)-dst%tau_pass(:,en) > tol_math_check)
      dtn = -1.0_pReal * t_n * BoltzmannRatio * prm%p * prm%q * (1.0_pReal-StressRatio_p)**(prm%q - 1.0_pReal) &
          * (StressRatio)**(prm%p - 1.0_pReal) / prm%tau_Peierls
      dtk = -1.0_pReal * t_k / tau_pos

      dvel = -1.0_pReal * prm%h * (dtk + dtn) / (t_n + t_k)**2.0_pReal

      ddot_gamma_dtau_pos = dot_gamma_0 * dvel* 0.5_pReal
    else where significantPositiveTau2
      ddot_gamma_dtau_pos = 0.0_pReal
    end where significantPositiveTau2
  endif

  significantNegativeTau: where(abs(tau_neg)-dst%tau_pass(:,en) > tol_math_check)
    StressRatio = (abs(tau_neg)-dst%tau_pass(:,en))/prm%tau_Peierls
    StressRatio_p       = StressRatio** prm%p
    StressRatio_pminus1 = StressRatio**(prm%p-1.0_pReal)

    t_n = prm%b_sl/(exp(-BoltzmannRatio*(1-StressRatio_p) ** prm%q)*prm%omega*effectiveLength)
    t_k = effectiveLength * prm%B /(2.0_pReal*prm%b_sl*tau_pos)

    vel = prm%h/(t_n + t_k)

    dot_gamma_neg = dot_gamma_0 * sign(vel,tau_neg) * 0.5_pReal
  else where significantNegativeTau
    dot_gamma_neg = 0.0_pReal
  end where significantNegativeTau

  if (present(ddot_gamma_dtau_neg)) then
    significantNegativeTau2: where(abs(tau_neg)-dst%tau_pass(:,en) > tol_math_check)
      dtn = -1.0_pReal * t_n * BoltzmannRatio * prm%p * prm%q * (1.0_pReal-StressRatio_p)**(prm%q - 1.0_pReal) &
          * (StressRatio)**(prm%p - 1.0_pReal) / prm%tau_Peierls
      dtk = -1.0_pReal * t_k / tau_neg

      dvel = -1.0_pReal * prm%h * (dtk + dtn) / (t_n + t_k)**2.0_pReal

      ddot_gamma_dtau_neg = dot_gamma_0 * dvel * 0.5_pReal
    else where significantNegativeTau2
      ddot_gamma_dtau_neg = 0.0_pReal
    end where significantNegativeTau2
  end if

  end associate
  end associate

end subroutine kinetics

end submodule dislotungsten