hello everyone!
based on the strength reduction method in clay hypoplasticity, firstly, I used two steps belong to the static_general, the first step is impose a gravity load, and not given the initial stress, the second step is the strength reduction, the two steps were completed, the friction angle was reduced to 17.2 from 30. but a clear failure surface was not seen in E or U field, as shown is fig 3,4. seeing from the f field ( all is less than zero, fig.5), i think the correct_dev_stress is work.
Then, i used the geostatic step as the first step by import the ODB file (just with the Elastic model) as the initial stress state, then the second step is the strength reduction, as a result , the geostatic step was completed, but the step-2 was failed with one increntment , as shown is fig 6,7,8.
may be the set of step is wrong ?
Anyone’s help is appreciated.

8-4.png 7-3.png 5-2.png 4-1.png 3-0.png

  1. Shen Wang
    Shen Wang 1 month ago

    This reply may not be helpful to your question, but from the distortion shape of element in Fig.1, it looks like hourglass mode. Did you use linear brick elements with reduced integration?

    • Yang Xue Author
      Yang Xue 1 month ago

      Thank you for your reply. The Fig.1 shows the E field after the geostatic step. I considered your suggestion, but it does not work.

      • Shen Wang
        Shen Wang 1 month ago

        Hi Yang,

        To be clear, I mean using linear quadrilateral/brick elements with reduced integration may lead to hourglass mode. I then discretized all my simulation models to elements with full integration which is more simulation expensive. In your picture, the deformation looks like hourglass mode occurs but I am not 100% sure.


    • Yang Xue Author
      Yang Xue 1 month ago

      Hi shen,

      Thanks for your explanation. The element type I use is the CPE4. Then, I replace the step 2 which is the strength reduction with a static_general step. A very small body force was applied to the model in the static_general step, but the model is not converged.

      After the geostatic step, once the force or stress changes, the model is not converged. So I wonder if the geostatic step is necessary, and non-convergence often occurs after the geostatic step. Maybe the Initial stress is not accurate enough?


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