Eigenstrain

solid-solid phase transformations, influence of stresses and strains
Bernd
Posts: 1505
Joined: Mon Jun 23, 2008 9:29 pm

Re: Eigenstrain

Post by Bernd » Sun Apr 30, 2023 4:33 pm

Dear Jane,

While for the "normal" molar volume all elements are counted, the "mechanically relevant" molar volume only refers to the lattice-building (=substitutional) atoms. If coupling to database is used, the distinction is made automatically.

Bernd

Jane
Posts: 50
Joined: Tue Mar 29, 2022 1:06 pm
anti_bot: 333

Re: Eigenstrain

Post by Jane » Tue May 02, 2023 6:34 am

Dear Bernd,

I am very happy to receive your reply. Here I have another question to ask you.
I used "fix_normal_pressure" for the boundary condition of elastic stress, and I took several different sets of "External pressure" for comparison, and found that "von Mises" did change. But ".phase", that is, the phase change process, has not changed. I don't understand why?
# Stress related properties for all phases
# ----------------------------------------
# Phase number of the matrix phase (int)
1
# Notation for Eigenstrain?
# Options: volume matrix
volume

# Boundary condition for elastic stress calculation
# Options: constant_volume normal_expansion free_expansion
# fix_isostatic_pressure fix_normal_pressure
# fix_isostatic_strain fix_normal_strain
fix_normal_pressure

# Boundary condition for elastic stress calculation
# -------------------------------------------------
# Input type for normal pressure?
# Options: constant time_dependent
constant
# External pressure in the 2 normal directions xx [MPa], zz [MPa]? (real) (real)
500 0
Jane

Bernd
Posts: 1505
Joined: Mon Jun 23, 2008 9:29 pm

Re: Eigenstrain

Post by Bernd » Tue May 02, 2023 11:06 am

Dear Jane,

If you use stress coupling (stress_mc* or stress _ce*), then elastic stresses may have an effect on the phase transformation. You can see this effect primarily as a mechanical driving force (.dGsp output). The effect can be strong or weak, depending on the size of this driving force (absolute and relative to the chemical driving force .driv), and naturally also depends on the interface mobility. Thus, your first focus should be on the .dGsp output.
Furthermore, if you apply anisotropic external stresses, the effects on phase transformation further depend on the orientation of the interface to the stress direction.

Bernd

Jane
Posts: 50
Joined: Tue Mar 29, 2022 1:06 pm
anti_bot: 333

Re: Eigenstrain

Post by Jane » Tue May 09, 2023 8:51 am

Dear Bernd,

As shown below, what do the "{U|CE|MC}{1|2|3}" after stress mean? How should I write when coupling stress? Is it the form I'm considering (concentration stress_XXX)?

# Type of coupling?
# Options: phase concentration [volume_change] temperature temp_cyl_coord
# [stress{U|CE|MC}{1|2|3}] [flow] [flow_coarse] [dislocation]
concentration stress_XXX

Jane

Bernd
Posts: 1505
Joined: Mon Jun 23, 2008 9:29 pm

Re: Eigenstrain

Post by Bernd » Tue May 09, 2023 12:03 pm

Dear Jane,

please take care that there should be no underscore "_" in the keyword. In MICRESS Version 7.0 the syntax for stress coupling was

stressUx: uncoupled (i.e. no effect on driving force)
stressCEx: chemo-elastic coupling (i.e. elastic effects on driving force for phase transformation)
stressMCx: mechano-chemical coupling (i.e. further including interaction between stress and diffusion)

x=1,2,3: Voigt-Taylor, Khachaturyan, Reuss-Sachs homogenisation at interface

In the newer versions the input is more intuitive as there are explicit keywords for those options...

Bernd

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