[Question] Is Elastic Perfectly Plastic Material Model working?

[wme7]

Hi Mr. Shi,

I come again with another question regarding ElasticPerfectlyPlastic material model as I'm trying to simulate an elastic-plastic material in another simulation.

I found no example on how to use this model, but I can see some development on infinitesimal_strain folder .

To test, I choose the MPM example ULBar.py.
In it, the only modification I'm producing on the script is to define the beam material as:

mpm.add_material(
    model="ElasticPerfectlyPlastic",
    material={
       "MaterialID": 1,
       "Density":  2650.,
       "YoungModulus": 2e7,
       "PossionRatio": 0.3,
       "YieldStress": 5e4
})

I run the example as

$ python ULBar.py 

and obtained the following log

[Taichi] version 1.7.3, llvm 15.0.4, commit 5ec301be, linux, python 3.11.11
Using device x86_64 (Core: 128, Logic: 128)
[Taichi] Starting on arch=x64
# =================================================================== #
#                                                                     #
#        Welcome to GeoTaichi -- Material Point Method Engine !       #
#                                                                     #
#       A High Performance Multiscale and Multiphysics Simulator      #
#                                                                     #
# =================================================================== # 

----------------------- MPM Basic Configuration -----------------------
Simulation Type: Arch.x64                                          
Simulation Domain: [5. 3. 5.]                                      
Boundary Condition: [-1, -1, -1]                                   
Gravity: [ 0.   0.  -9.8]                                          


------------------------ MPM Solver Information -----------------------
Initial Simulation Time: 0.0                                       
Finial Simulation Time: 6.0                                        
Time Step: 1e-05                                                   
Save Interval: 0.05                                                
Save Path: OutputData                                              


------------------------ MPM Engine Information -----------------------
Background Damping: 0.02                                           
alpha Value: 0.0                                                   
Stabilization Technique: None                                      
Boundary Direction Detection: False                                
Free Surface Detection: False                                      
Mapping Scheme: USF                                                
Shape Function: Linear                                             
Velocity Projection: PIC/FLIP                                      


-------------------- Constitutive Model Information -------------------
Constitutive model: Elastic Perfectly Plastic Model
Model ID:  1
Density:  2650.0
Young Modulus:  20000000.0
Poisson Ratio:  0.3
Yield Stress:  50000.0


--------------------------- Grid Information --------------------------
Grid Type: Rectangle
The number of grids =  1
Grid Size =  [0.1 0.1 0.1]
The number of nodes =  [51 31 51]


-------------------------- Region Information -------------------------
Region Name: region1
Region Type: Rectangle
Bounding Box: [0.5 1.  3.5] [4.2 0.5 0.5]
Rotate angle: [0. 0. 0.] 

# Start adding material points ......
Traceback (most recent call last):
  File "/gpfs/projects/cenaero/p_virtuallab_anim/geoTaichi_SFI_runs/cantilever/ULBar.py", line 58, in <module>
    mpm.add_body(body={
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/mpm/mainMPM.py", line 170, in add_body
    self.generator.add_body(body, self.sims, self.scene)
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/mpm/GenerateManager.py", line 54, in add_body
    generator.begin(scene)
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/mpm/generator/BodyGenerator.py", line 65, in begin
    self.add_body(scene)
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/mpm/generator/BodyGenerator.py", line 133, in add_body
    self.generate_material_points(scene, self.myTemplate)
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/mpm/generator/BodyGenerator.py", line 223, in generate_material_points
    scene.material.state_vars_initialize(materialID, particleNum, particleNum+particle_count, scene.particle)
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/physics_model/consititutive_model/ConstitutiveModelBase.py", line 52, in state_vars_initialize
    kernel_initial_state_variables(start_particle, end_particle, particle, self.matProps[materialID], self.stateVars)
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/ti17/lib64/python3.11/site-packages/taichi/lang/kernel_impl.py", line 1117, in wrapped
    raise type(e)("\n" + str(e)) from None
taichi.lang.exception.TaichiCompilationError: 
File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/physics_model/consititutive_model/MaterialKernel.py", line 38, in kernel_initial_state_variables:
        matProps._initialize_vars(np, particle, stateVars)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/src/physics_model/consititutive_model/infinitesimal_strain/ElasticPerfectlyPlastic.py", line 99, in _initialize_vars_update_lagrangian:
            stateVars[np].epdstrain = 0.
            ^^^^^^^^^^^^^^^^^^^^^^^
Traceback (most recent call last):
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/ti17/lib64/python3.11/site-packages/taichi/lang/ast/ast_transformer_utils.py", line 27, in __call__
    return method(ctx, node)
           ^^^^^^^^^^^^^^^^^
  File "/gpfs/home/cenaero/mdiaz/Depots/GeoTaichi_v04/ti17/lib64/python3.11/site-packages/taichi/lang/ast/ast_transformer.py", line 1040, in build_Attribute
    node.ptr = getattr(node.value.ptr, node.attr)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: '_IntermediateStruct3' object has no attribute 'epdstrain'

Thus, my question(s):

• Is this model working or complete? or
• is there a way to fix this missing attribute?

kind regards.