(Fixing Load) Conditions for Creep Test

[Srijan7Y]

How can I fix the load, along with the strain as a limiting condition?
I want to fix 80 MPa stress on my microstructure (created using NEPER), for 15% strain as limiting condition.

[mkasemer]

@Srijan7Y

You will have to use the triaxial constant load rate loading to apply dwell episodes. Please view https://fepx.info/doc/loading.html#legacy-multiaxial

Regarding termination of the simulation, you can set the simulation to terminate at a maximum equivalent strain using the max_eqstrain option. Please view https://fepx.info/doc/running.html#general-convergence

[Srijan7Y]

Apologies for my late reply. Actually, I want to model creep behavior (at constant stress) using crystal plasticity finite elements. Is this possible in FEPX?? Basically the material is a HEA with two phases, which has undergone creep, so I want to observe the stress concentration in and between the two phases, so is it possible to do this simulation using FEPX??
Thanks

[mkasemer]

That, actually, is what I described. Use the constant load rate module. Utilize dwell episodes, which sets the load rate to 0, effectively holding your load fixed. The state will continue to evolve.

[Srijan7Y]

Okay. Thanks a lot. I will try this out.

[Srijan7Y]

I tried running the simulation but got few errors. Can you please help me out with any possible mistakes or what could be the reason for this. I am attaching my .cfg fiel and the errors.

FEPX Configuration File

Material Parameters

number_of_phases 2

phase 1

crystal_type FCC

c11 289570.0
c12 124100.0
c44  82700.0

m 0.05
gammadot_0 0.001

hard_type isotropic
h_0 125.0
g_0  56.0
g_s 113.0
n 1

phase 2

crystal_type BCC

c11 291700.0
c12 125000.0
c44  83350.0

m 0.05
gammadot_0 0.001

hard_type isotropic
h_0 158.0
g_0 133.0
g_s 245.0
n 1

Deformation History

def_control_by triaxial_constant_load_rate
number_of_steps 1
target_clr_load 0.0 0.0 80.0 1 print_data

number_of_dwell_episodes 1
dwell_episode 1 100. 20. print_data

Boundary Condition

boundary_conditions triaxial

loading_direction Z

load_rate 20

Printing Results

print coo
print crss
print forces
print ori
print stress
print strain
print rss
print stress_eq
print strain_eq

Error:

========================== F E P X ==========================
Info : A finite element software package for polycrystal plasticity.
Info : Version 2.1.0
Info : Running on 1 cores.
Info : https://fepx.info
Info : Copyright (C) 1996-2023, DPLab, ACME Lab, CNRS.
Info : ---------------------------------------------------------------
Info : Start time: 2025-6-26 at 12:21
Info : Loading simulation...
Info : [i] Parsing file simulation.cfg'... Info : - Material parameters: Info : > Number of phases: 2 Info : > phase 1 - crystal type: fcc Info : > m: 0.500000E-01 Info : > gammadot_0: 0.100000E-02 Info : > h_0: 0.125000E+03 Info : > g_0: 0.560000E+02 Info : > g_s0: 0.113000E+03 Info : > n: 0.100000E+01 Info : > c11: 0.289570E+06 Info : > c12: 0.124100E+06 Info : > c44: 0.827000E+05 Info : > phase 2 - crystal type: bcc Info : > m: 0.500000E-01 Info : > gammadot_0: 0.100000E-02 Info : > h_0: 0.158000E+03 Info : > g_0: 0.133000E+03 Info : > g_s0: 0.245000E+03 Info : > n: 0.100000E+01 Info : > c11: 0.291700E+06 Info : > c12: 0.125000E+06 Info : > c44: 0.833500E+05 Info : [i] Parsed file simulation.cfg'.
Info : [i] Parsing file simulation.msh'... Info : - Mesh parameters: Info : > Node number: 2126 Info : > Elt number: 1275 Info : [i] Parsed file simulation.msh'.
Info : Initializing simulation...

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.

Backtrace for this error:
#0 0x7aba02a23e59 in ???
#1 0x7aba02a22e75 in ???
#2 0x7aba0264532f in ???
#3 0x7aba02789510 in ???
#4 0x5e1d3dec7558 in driver_triaxclr_mod_MOD_driver_triaxclr
#5 0x5e1d3dcef3bf in MAIN
#6 0x5e1d3dcee5ee in main
Segmentation fault (core dumped)

I am trying to run it first on a simple microstructure, will then try running on my main microstructure.