Nonlocal model and simulation examples

[123fgh123]

Dear colleagues,

I am interested in the nonlocal model of DAMASK, and I want to know is there simulation examples (inputs) on this topic, which could be run directly?

Thanks in advance.

[123fgh123]

I have run a simulation as attached files show, and I did not know whether the nonlocal model has worked.
grid-nolocal.zip

[sharanroongta]

Hi, which alpha version of DAMASK are you using?

[123fgh123]

v3.0.0-alpha7

[123fgh123]

The simulation log file has been attached as follow.
grid-nolocal.zip

[sharanroongta]

So, there are a few things to keep in mind. I myself am not an expert on the non-local model and have never used it. It is a difficult model to use in terms of convergence and finding the right parameter set.

• The parameters you have used follows the thesis of Christoph Kords [http://publications.rwth-aachen.de/record/229993/files/4862.pdf]. This is fine, and I would suggest you to go through his work to understand the model better
• There is one change i have made in your material.yaml, i.e., location of plastic model output. With this correction you can visualize the different dislocation densities.

phase:
  Aluminum:
    lattice: cF
    mechanical:
      output: [F, P, F_e, F_p, L_p, O]
      elastic: {type: Hooke, C_11: 106.75e+9, C_12: 60.41e+9, C_44: 28.34e+9}
      plastic:
        type: nonlocal    
        N_sl: [12]
        output: [rho_u_ed_pos, rho_b_ed_pos, rho_u_ed_neg, rho_b_ed_neg, rho_u_sc_pos, rho_b_sc_pos, rho_u_sc_neg, rho_b_sc_neg, rho_d_ed, rho_d_sc]
        b_sl: [2.86e-10]
        V_at: 0.017e-27 # Omega
        d_ed: [1.6e-9]
        d_sc: [10.e-9]
        i_sl: [60]      # k_2 (lambda_0 in Tab. 7.1)
        f_ed_mult: 0.1  # k_1

        rho_u_ed_neg_0: [1.25e9] # 6e10 / (12*4)
        rho_u_ed_pos_0: [1.25e9] # 6e10 / (12*4)
        rho_u_sc_neg_0: [1.25e9] # 6e10 / (12*4)
        rho_u_sc_pos_0: [1.25e9] # 6e10 / (12*4)
        rho_d_ed_0: [0]
        rho_d_sc_0: [0]

        D_0: 7.e-29
        Q_cl: 0.0 # no temperature dependency
        Q_sol: 2.00272e-19 # 1.25 eV
        c_sol: 1.5e-6       # correct unit?
        f_sol: 2.0          # d_obst in multiples of b
        tau_Peierls_ed: [.1e6]
        tau_Peierls_sc: [.1e6]
        w: 10              # w_k in multiple of b

        p_sl: 1
        q_sl: 1

        nu_a: 50.e+9
        B: 1.e-2
        f_ed: 1.0  # k_3

        h_sl-sl: [0, 0, 0.625, 0.07, 0.137, 0.137, 0.122] # Table 3.4

        chi_GB: 0.5      # full blocking at GB
        chi_surface: 1.0 # no blocking at surface

        f_F: 0.0         # no line tension correction
        sigma_rho_u: 0   # no random distribution


        short_range_stress_correction: false
        rho_significant: 1.e6        

You can play around with the chi_GB to see how the dislocation distribution looks like.

• Remember that the model is size dependent, unlike other local plastic models. Therefore RVE size is important. One can vary the size to the see the effect, like the Hall Petch effect
• To understand if the model is working or not, you can make the model behave in a local way, by adding this key in your plastic dictionary of the material.yaml,

plastic:
  flux: false

This should render 0 blocked dislocation density, and could be a check if the model is atleast working correctly or not.

I hope this answers some of your questions. I would also suggest to start with a bicrystal (as used by Christoph in one of the examples in the thesis), and try to recreate that.

[123fgh123]

Ok，thank you very much.

[123fgh123]

Dear Sharan:

Is it possible to control the output frequency of increment information?

The nonlocal model need very small increment to get a convergence, and the information of every increment will be printed in the present simulation (see "28658005.out" and "Polycystal_25_64x64x1x5kmiu-step50w_shearXY-step50w.sta" in the attached file, where 50w increments are needed).

It makes output file very large, and I don't know if it will also influence the efficiency of computation.

damask-simfile-nonlocal.zip

Thank you.

Best,
Guofeng

[sharanroongta]

Dear Guofeng,

In your shearXY-step50w.yaml file, the f_out key controls which increments are going to be stored in the output file. In your case it is 1000, therefore every 1000th increment data is stored in the output hdf5 file. So this seems to be fine and your hdf5 file wouldn't be large.

Hope this helps.

[123fgh123]

Dear Sharan:

I refered to the setup of output frequency of increment convergence information, see the file of "28658005.out" and "Polycystal_25_64x64x1x5kmiu-step50w_shearXY-step50w.sta" in the attached file.

damask-simfile-nonlocal.zip

Best,
Guofeng