- reworked contribution of immobile dislocation density for rate equations
- flux is now calculated on the basis of interpolated velocities and densities at the interface; both incoming and outgoing fluxes are considered, so every material point only changes his own dotState
- dislocation velocity is now globally defined and calculated by subroutine constitutive_nonlocal_kinetics; the subroutine is called inside _LpAndItsTangent as well as _microstructure; therefore, microstructure now needs Tstar_v as additional input; in the future one should perhaps create a subroutine constitutive_kinetics that calls constitutive_nonlocal_kinetics separately, to clearly distinguish between microstructural and kinetic variables
- better use flux density vector as output variable instead of scalar flux values for each interface
- added output variables internal and external resolved stress
crystallite:
- added flag to force local stiffness calculation in case of nonlocal model
- misorientation angle is explicitly set to zero when no neighbor can be found
debug:
- added flag "selectiveDebugger" that is used when debugging statements should only affect a specific element, ip and grain; these are specified with the new variables debug_e, debug_i and debug_g
- debugger can now be used in its original sense
- remobilization of immobile singles immediately increases the mobile single dislocation density and therefore directly affects all other mechanisms in dotState
- changed nomenclature (rho -> rhoSgl) to distinguish precisely between single dislocation density and total dislocation density
- changed material.config accordingly
The calculation of the misorientation is now done once in crystallite init and at the end of every FE increment. This saves a lot of time compared to doing it in dotState for every crystallite subinc.
- corrected flux term
- multiplication is now aware of dislocation type
- corrected change rate for "dipole size" dupper
- corrected term for dipole dissociation by stress change
- added transmissivity term in fluxes which accounts for misorientation between two neighboring grains (yet hardcoded transmissivity according to misorientation angle)
- added more output variables
constitutive:
- 2 additional variables "previousDotState" and "previousDotState2", which are used to store the previous and second previous dotState (used in crystallite for acceleration/stabilization of state integration)
- timer for dotState now measures the time for calls to constitutive_ collectState (used to reside in crystallite_updateState, which is not critical in terms of calculation time anymore)
crystallite:
- convergence check for nonlocal elments is now done at end of crystallite loop, not at the beginning; we simple set all elements to not converged if there is at least one nonlocal element that did not converge
- need call to microstructure before first call to collect dotState for dependent states
- stiffness calculation (jacobian): if there are nonlocal elements, we also have to consider changes in our neighborhood's states; so for every perturbed component in a single ip, we have to loop over all elements; since this is extremely time-consuming, we just perturb one component per cycle, starting with the one that changes the most during regular time step.
- updateState gets a damping prefactor for our dotState that helps to improve convergence; prefactor is calculated according to change of dotState
IO:
- additional warning message for unknown crystal symmetry
- new subroutine "math_misorientation" which calculates misorientations (based on old subroutine "misorientation", which was not used previously)
- rendered some functions pure
previously was:
if (the_sum /= 1.0_pReal) then (error 170)
this condition is too strict. it may give problem with some numerical truncation error.
now becomes:
if (abs(the_sum - 1.0_pReal) >= 1.0e-10_pReal) then (error 170)
(1) subStepSizeHomog and subStepSizeCryst := size of substep when cut-back is applied (initially was hard-coded).
(2) stepIncreaseHomog and stepIncreaseCryst := step increase when calculation for substep converge (was also hardcoded).
introduced a possibility to choose different finite difference scheme, i.e., forward-, backward- and central-difference, for computing grain numerical tangent. note that central-difference scheme will slow down the computation significantly. please use it only if necessary.
parameters to set these new features have been included in numerics.f90 and numerics.config, whereas corresponding error messages have been introduced in the IO.f90
in constitutive_nonlocal.f90:
Derivatives of shear rates w.r.t. resolved shear stress HAVE to be positive.
Computation of dgdot_dtauslip is now correct.
cleaning up of twin system nomenclature
introduced lookup mechanism to calculate the twinning shears depending on the c/a ratio of the present structure (was [wrongly!!] hardcoded to Titanium)
- read in activation energy for dislocation glide from material.config
- changed naming of dDipMin/Max to dLower/dUpper
- added new outputs: rho_dot, rho_dot_dip, rho_dot_gen, rho_dot_sgl2dip, rho_dot_dip2sgl, rho_dot_ann_ath, rho_dot_ann_the, rho_dot_flux, d_upper_edge, d_upper_screw, d_upper_dot_edge, d_upper_dot_screw
- poisson's ratio is now calculated from elastic constants
- microstrucutre has state as first argument, since this is our output variable
- periodic boundary conditions are taken into account for fluxes and internal stresses. for the moment, flag has to be set in constitutive_nonlocal.
- corrected calculation for dipole formation by glide
- added terms for dipole formation/annihilation by stress decrease/increase
constitutive:
- passing of arguments is adapted for constitutive_nonlocal model
crystallite:
- in stiffness calculation: call to collect_dotState used wrong arguments
- crystallite_postResults uses own Tstar_v and temperature, no need for passing them from materialpoint_postResults
homogenization:
- crystallite_postResults uses own Tstar_v and temperature, no need for passing them from materialpoint_postResults
IO:
- changed error message 229
material.config:
- changed example for nonlocal constitution according to constitutive_nonlocal
all:
- added some flush statements
crystallite does not accelerate anymore, since, typically, longer step immediately fails and uses resources in vain. (future: remember number of successful steps to increase step size after x of those...)
Christoph Kords