Effect of crystal plasticity parameters on stress-strain response in BCC fitting for prisms-fatigue

Itsuki Fujita

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Apr 21, 2025, 7:12:33 PMApr 21

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Hi PRISMS team,

I am currently working on computing FIPs using prisms-fatigue for BCC steel sheets.
As a first step, I am performing curve fitting using prisms-plasticity.

I have constructed a stiffness matrix with E = 206 GPa and ν = 0.3, and I am conducting a parameter study on:

RSS of the slip systems
Hardening moduli of the slip systems
Power law coefficient
Saturation stress

I observed that CRSS has a significant influence on the yield point (Yp), but other parameters seem to have little to no effect on the plastic portion of the stress-strain curve.

For prisms-fatigue, I believe that macroscopic kinematic hardening is typically used to accurately capture tension-compression behavior.

So I would like to ask:

Does modifying the macroscopic kinematic hardening influence the slope of the plastic curve?
Or is there a reason why parameters other than CRSS seem to have limited effect under the current settings?

I’ve attached below the parameter settings I used.

####################################
# Elasticity parameters
####################################
# Flag to indicate if User Material Model is enabled
set Enable User Material Model = true

# Number of User Material State Variables in a Material model Phase 1
set Number of User Material State Variables 1 = 62

# Elastic Stiffness Matrix -Voigt Notation (MPa)
set Elastic Stiffness row 1 = 170.0e3, 124.0e3, 124.0e3, 0, 0, 0

# Elastic Stiffness Matrix -Voigt Notation (MPa)
set Elastic Stiffness row 2 = 124.0e3, 170.0e3, 124.0e3, 0, 0, 0

# Elastic Stiffness Matrix -Voigt Notation (MPa)
set Elastic Stiffness row 3 = 124.0e3, 124.0e3, 170.0e3, 0, 0, 0

# Elastic Stiffness Matrix -Voigt Notation (MPa)
set Elastic Stiffness row 4 = 0, 0, 0, 75.0e3, 0, 0

# Elastic Stiffness Matrix -Voigt Notation (MPa)
set Elastic Stiffness row 5 = 0, 0, 0, 0, 75.0e3, 0

# Elastic Stiffness Matrix -Voigt Notation (MPa)
set Elastic Stiffness row 6 = 0, 0, 0, 0, 0, 75.0e3

####################################
# Slip parameters
####################################
# Number of Slip Systems
set Number of Slip Systems = 12

# Latent Hardening Ratio
set Latent Hardening Ratio filename = LatentHardeningRatio.txt

# RSS of the slip sytems
set Initial Slip Resistance = 16.0, 16.0, 16.0, 16.0, 16.0, 16.0, 16.0, 16.0, 16.0, 16.0, 16.0, 16.0

# Heardening moduli of slip systems
set Initial Hardening Modulus = 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0

# Power law coefficient
set Power Law Exponent = 2.25, 2.25, 2.25, 2.25, 2.25, 2.25, 2.25, 2.25, 2.25, 2.25, 2.25, 2.25

# Saturation stress
set Saturation Stress = 148.0, 148.0, 148.0, 148.0, 148.0, 148.0, 148.0, 148.0, 148.0, 148.0, 148.0, 148.0

# Slip Directions File
set Slip Directions File = slipDirections.txt

# Slip Normals File
set Slip Normals File = slipNormals.txt

#Flag to indicate if kinematic hardening is enabled
set Enable Kinematic Hardening = true

# C_1 Slip Kinematic Hardening parameters
set C_1 Slip Kinematic Hardening = 200.0, 200.0, 200.0, 200.0, 200.0, 200.0, 200.0, 200.0, 200.0, 200.0, 200.0, 200.0

# C_2 Slip Kinematic Hardening parameters
set C_2 Slip Kinematic Hardening = 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0

Any guidance would be greatly appreciated.

Best regards,
Itsuki

Chaitali Patil

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Apr 22, 2025, 5:39:50 PMApr 22

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Hi Itsuki,

If I understand correctly, you are using crystalplasticity.cc file from prisms fatigue. It uses rate dependent model, and hence, firstly the input prm file should be accordingly modified. You can also find example prm files at https://doi.org/10.13011/m3-rcyy-gx13 , where you can see the kinematic hardening is given using "set User Material Constants 1" as opposed to "set C_1 Slip Kinematic Hardening " in your case . Please modify the prm files and check the influence of the parameters.

You will also find useful recent answer in this regard:

https://groups.google.com/g/prisms-cpfe-users/c/Blo3zMmLi40/m/NVHzRBQTDQAJ

Regards,

Chaitali

Itsuki Fujita

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Apr 22, 2025, 6:49:03 PMApr 22

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Hi Chaitali,

Thank you very much for the detailed explanation and the helpful links.
I’ll study the rate-dependent input format and give it a try.

Really appreciate your support!

Best regards,
Itsuki

2025年4月23日水曜日 6:39:50 UTC+9 Chaitali Patil:

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