# Triaxial test using polyhedra

Hi YADE community,

I’m wondering if modeling triaxial test using polyhedra is possible using YADE using built-in TriaxialStressC

Sharing any experiences is highly appreciated.

Cheers,

## Question information

- Language:
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- Expired

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- Yade Edit question

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- Last query:
- 2020-07-10

- Last reply:
- 2020-07-26

Jérôme Duriez (jduriez) said : | #1 |

Hi,

Yes, we can.

As a engine controlling boundaries, TriaxialStressC

Except for the measure of TriaxialStressC

If porosity is of interest to you, it will be easier to recompute it yourself, from your own solid volume (your Polyhedra) and using TriaxialStressC

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Nima Goudarzi (nimagoudarzi58) said : | #2 |

Thanks so much Jerome,

Porosity is for sure of interest but as you mentioned, I have the tools for its calculations. My issues are at larger extent:

1- aabbwalls does not work with polyhedra therefore I am forced to use walls instead

2- wall does not work properly as well especially in the confining phase. I have never been able to reach to the predefined triaxial goals. Most of the time the collision between walls and polyhedra does not occur and when I reduce the time step, the analysis becomes hatefully slow.

3- I use PSD for polyhedra in my simulations by first generating a sphere pack following a certain PSD and then converting them to polyhedra. Also I run triaxial tests in two phases with two different scripts: in the first one I generate the sample with my desired porosity using multi-layer compaction and export the particles (sphere, clumps, or polyhedra). I, then, import the particles in a separate script, and apply the confining presses and deviatoric loading.

In close, I have issues in box-polyhedra interaction . BTW do you by chance have a sample of triaxial tests with polyhedra?

Hi all,

Some thoughts I find relevant to this thread:

I can confirm that aabbWalls does not work for non-spherical particles, since it uses aabbExtrema(). If we teak aabbExtrema() to extract the extrema from the Aabbs of the particles rather than the radius, it has the capacity to work for any particle shape. In such a case, we should pay attention to whether we want to consider the enlarged Aabbs when a non-zero verletDist is used.

Also, if we calculated "particlesVolume" as mass/density inside the TriaxialStressC

Last, the normal stiffness coefficient "kn" in "PolyhedraPhys" can have a variety of different units, e.g. N/m^3 if Law2_PolyhedraG

Hope these help,

Vasileios

Jérôme Duriez (jduriez) said : | #4 |

> the normal stiffness coefficient "kn" in "PolyhedraPhys" can have a variety of different units

Indeed, I missed this point.. This would greatly affect (and not positively) the measure of packing-wall stiffness and stress servo control by the engine.. TriaxialStressC

Maybe a simple solution could be to use bodies of Polyhedra shape, but stick with a classical FrictMat material (I do not know how much built-in functions for bodies creation, like utils.polyhedron or polyhedra_

Using classical ScGeom through Ig2_Polyhedra_

As for the boundary bodies, I did not get whether you intend to use Box-shaped or Wall-shaped ones (both are possible with TriaxialStressC

(from a personal point of view, I can share I'm sometimes trying to play with Polyhedra shapes at the moment, but never ran a triaxial test myself. And I'm looking forward to feedback from other Polyhedra users..)

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[**] see the history at https:/

Nima Goudarzi (nimagoudarzi58) said : | #5 |

Thank you both Jerome and Vasileios,

Vasileios: "If we teak aabbExtrema() to extract the extrema from the Aabbs of the particles rather than the radius, it has the capacity to work for any particle shape"

How? I have no idea regarding this. Is there any example available?

The porosity calculation is my least concern. I do it outside YADE using 3d cad modeling and weight/volume relationships. my approach has been successful for clumps. The same applies for polyhedra.

Regarding Vasileios's comment and Jerome's reply, it turns out that built-in YADE triaxialStressC

Jerome: "As for the boundary bodies, I did not get whether you intend to use Box-shaped or Wall-shaped ones (both are possible with TriaxialStressC

I'm running triaxial and need something functioning as triaxial chamber boundaries for polyhedra. Whatever works in the context of triaxialStressC

Thanks,

Launchpad Janitor (janitor) said : | #6 |

This question was expired because it remained in the 'Open' state without activity for the last 15 days.