changed first elastic guess for small Tstar

changed residuum to only consider deviatoric part of Tstar
changed scaling when dTstar becomes too large to proportionally scaling all components of dTstar

trunk/CPFEM.f90

@@ -301,7 +301,6 @@
      Fg_pert = Fg_new+matmul(E_pert,Fg_old) ! perturbated Fg
      Tstar_v_pert = Tstar_v                 ! initial guess from end of time step
      state_pert = state_new                 ! initial guess from end of time step
-
      call CPFEM_timeIntegration(msg,Fp_pert,Fe_pert,Tstar_v_pert,state_pert, &
                                 dt,cp_en,CPFEM_in,grain,Fg_pert,Fp_old,state_old)
      if (msg /= 'ok') then
@@ -336,7 +335,7 @@
      Fp_old,&           ! former plastic def gradient
      state_old)         ! former microstructure
 
- use prec, only: pReal,pInt, nState,tol_State,nStress,tol_Stress, crite, nReg
+ use prec
  use constitutive, only: constitutive_Nstatevars,&
                          constitutive_homogenizedC,constitutive_dotState,constitutive_LpAndItsTangent
  use math
@@ -345,8 +344,8 @@
  character(len=*) msg
  integer(pInt) cp_en, CPFEM_in, grain
  integer(pInt) iState,iStress,dummy, i,j,k,l,m
- real(pReal) dt,det
- real(pReal), dimension(6) :: Tstar_v,dTstar_v,Rstress
+ real(pReal) dt,det, max_E, p_hydro
+ real(pReal), dimension(6) :: Tstar_v,dTstar_v,Rstress, E, T_elastic
  real(pReal), dimension(6,6) :: C_66,Jacobi,invJacobi
  real(pReal), dimension(3,3) :: Fg_new,Fp_old,Fp_new,Fe_new,invFp_old,invFp_new,Lp,A,B,AB
  real(pReal), dimension(3,3,3,3) :: dLp, LTL
@@ -369,8 +368,13 @@
  if (all(state_new == 0.0_pReal)) state_new = state_old
  RstateS = state_new
  iState = 0_pInt
-! fully elastic guess (Lp = 0), if none specified, however somewhat reduced ie. 0.3 instead of 0.5
- if (all(Tstar_v == 0.0_pReal)) Tstar_v = 0.3_pReal*matmul(C_66,math_Mandel33to6(A-math_I3))
+! elastic guess for small Tstar, however reduced to prec_max_e
+ if (all(Tstar_v < 0.1_pReal)) then
+    E =  math_Mandel33to6(A-math_I3)
+    max_E = maxval(E)
+    if (max_E > prec_max_e) E = prec_max_e * E / max_E
+    Tstar_v = 0.5_pReal*matmul(C_66, E)
+ endif
 ! QUESTION follow former plastic slope to guess better?
  Rstress = Tstar_v
 
@@ -387,10 +391,16 @@ stress:  do              ! inner iteration: stress
              msg = 'limit stress iteration'
              return
            endif
+           p_hydro=(Tstar_v(1)+Tstar_v(2)+Tstar_v(3))/3.0_pReal
+           forall(i=1:3) Tstar_v(i)=Tstar_v(i)-p_hydro
            call constitutive_LpAndItsTangent(Lp,dLp, Tstar_v,state_new,grain,CPFEM_in,cp_en)
            B = math_I3-dt*Lp
+ !          B = B / math_det3x3(B)**(1.0_pReal/3.0_pReal)
            AB = matmul(A,B)
-           Rstress = Tstar_v - 0.5_pReal*matmul(C_66,math_Mandel33to6(matmul(transpose(B),AB)-math_I3))
+           T_elastic= 0.5_pReal*matmul(C_66,math_Mandel33to6(matmul(transpose(B),AB)-math_I3))
+           p_hydro=(T_elastic(1)+T_elastic(2)+T_elastic(3))/3.0_pReal
+           forall(i=1:3) T_elastic(i)=T_elastic(i)-p_hydro
+           Rstress = Tstar_v - T_elastic
            if (maxval(abs(Tstar_v)) == 0.0_pReal .or. maxval(abs(Rstress/maxval(abs(Tstar_v)))) < tol_Stress) exit stress
 
 !   update stress guess using inverse of dRes/dTstar (Newton--Raphson)
@@ -419,10 +429,10 @@ stress:  do              ! inner iteration: stress
              msg = 'regularization Jacobi'
              return
            endif
-
            dTstar_v = matmul(invJacobi,Rstress)  ! correction to Tstar
-           forall(i=1:6, abs(dTstar_v(i)) > crite*maxval(abs(Tstar_v))) &
-             dTstar_v(i) = sign(crite*maxval(abs(Tstar_v)),dTstar_v(i))   ! cap to maximum correction
+! limit correction of Tstar
+           if(maxval(abs(dTstar_v)) > crite*maxval(abs(Tstar_v))) &
+              dTstar_v=dTstar_v*crite*maxval(abs(Tstar_v))/maxval(abs(dTstar_v))
            Tstar_v = Tstar_v-dTstar_v
 
     enddo stress

trunk/prec.f90

@@ -21,10 +21,12 @@
 !    *** Convergence criteria for outer (state variables) loop ***
  real(pReal),   parameter :: tol_State = 1.0e-6_pReal
 !    *** Maximum number of iterations in inner (stress) loop ***
- integer(pInt), parameter :: nStress    = 2000_pInt
+ integer(pInt), parameter :: nStress    = 100_pInt
 !    *** Convergence criteria for inner (stress) loop ***
  real(pReal),   parameter :: tol_Stress = 1.0e-6_pReal   
 !    *** Factor for maximum stress correction in inner (stress) loop ***
- real(pReal),   parameter :: crite     = 1.0e-1_pReal 
+ real(pReal),   parameter :: crite     = 0.1_pReal 
+!    *** Maximum strain used in elastic guess in inner (stress) loop ***
+ real(pReal),   parameter :: prec_max_e     = 1.0e-3_pReal 
 
  END MODULE prec