# enlarge the stiffness or not?

Hi All,

I use the original particle size distribution(PSD) curve in a small triaxial test, then I calibrate and validate the deviatoric stress- axial strain and the volumetric strain- axial strain curve. Finally, I got a set of microscale parameters, for instance, contact stiffness, Poisson's ratio.

after that, I want to use this set of parameters to do another test (the material is the same), due to the large dimension of the sample. I enlarged the PSD curve by 20 times.

Here is my question: do I need to increase the contact stiffness as well as other parameters by 20 times? or I don't need to change all the parameters?

thanks!

yong

## Question information

- Language:
- English Edit question

- Status:
- Solved

- For:
- Yade Edit question

- Assignee:
- No assignee Edit question

- Solved by:
- Chareyre

- Solved:
- 2020-04-02

- Last query:
- 2020-04-02

- Last reply:
- 2020-04-02

Hi,

Think you might find [1] useful.

Looking forward to comments from the more experienced members of the community myself. :)

[1] https:/

Regards,

Vasileios

Jérôme Duriez (jduriez) said : | #2 |

Assuming you're using FrictMat and related classes, there is no scaling to perform, if I understand correctly your question.

For instance, as long as FrictMat.young is constant (and the various numerical packings "similar"), the macroscopic stress-strain stifness will be constant. It does not depend on Discrete Elements' size. That's the point of using stress-like quantities for this FrictMat.young (instead of imposing directly force / length stiffnesses)

ytang (ytang116) said : | #3 |

Hi Jerome,

In my simulation, I use the following models:

#######

InteractionLoop(

[Ig2_

[Ip2_

[Law2_

)

#######

So the CohFristMat is not belong to FrictMat. Am I right?

Besides, in YADE, if you are using different material (for instance, FrictMat ), some of them need to scale while some don't need to scale, it depends on which kind of material class you choose. The precondition is that I scaled up the PSD curve after the calibration and validation process.

Am I right?

ytang (ytang116) said : | #4 |

Hi Jerome,

I derived the normal stiffness for my model. If I increase the diameter the normal stiffness will increase automatically by the same times as the diameter.

however, I have a very simple question, does the "FrictMat.young" will change when we change the size of the particle?

best,

Yong

Chareyre (bruno-chareyre-9) said : | #5 |

> does the "FrictMat.young" will change when we change the size of the

particle?

No

B

ytang (ytang116) said : | #6 |

Hi Chareyre and Jerome,

thank you very much!

This means the contact stiffness of my model will automatically increase with the same times as the diameters.

best,

Yong

ytang (ytang116) said : | #7 |

Thanks Chareyre, that solved my question.