Clumps made of rigid blocks

PFC
1

Hello,

In one of my projects, I need to make clumps out of rigid blocks and have those clumps come into contact with regular rigid blocks. However, whenever I run my models, I get one of the following two problems: 1) either PFC crashes after I define contacts or 2) I can run my simulation, but as soon as I save my file and try to restore the save file, PFC crashes.

To illustrate the issue, I wrote a simple code where I create one clump from a single rigid block and then create a new rigid block. I subsequently use the flat joint contact model as the constitutive law for clump-rblock interactions.

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When I save the model and restore the saved file, attempting to cycle the model will result in PFC crashing. The issue also happens when I use other contact models such as the linear contact model. Can you please tell me why?

Additionally, I noticed that PFC does not recognize clumps made of rigid blocks as being made of pebbles. I needed to define the contact type between the clump and rigid block and rblock-rblock for the model to work. Can you please tell me why this is happening?

Can results obtained from simulations where contacts between rblocks and clumps made from rblocks be trusted given the issues I am encountering?

I am attaching the code I wrote below.

Thank you!

;CODE

model new
model random 10000
model large-strain on
model domain extent [-0.5] [0.5] condition destroy

;--------------Geometry----------------
;Dimension
[d=50e-3]; brick’s length in m

rblock create box [-d/2] [d/2] 0 [d] group ‘rblock’
rblock create box [-d/2] [d/2] [-d] 0 group ‘clumps’

rblock attribute density 2750 damp 0.7

rblock clump create calculate from-rblocks range group ‘clumps’

;-------------Contacts------------------

;contact cmat default type rblock-rblock model linear …
; property fric 0.4 lin_mode 1 …
; method deformability emod 4.e+10 kratio 1.5

contact cmat default type rblock-rblock model flatjoint method deformability …
emod 4.e+10 krat 1.5 property fj_fric 0.4 …
property fj_ten 0.14e+6 fj_coh 0.55e+6 fj_fa 10

model clean all

contact method bond gap 0

model clean all

model save ‘2p_contact’

;-----------Cycle----------------------
model restore ‘2p_contact’

model cycle 1

2

Hello Romaric,

Thank you for reporting this issue, and providing a minimal working example!
I am looking into the save/restore crash and will keep you informed of my progress on a solution.

  • May I ask you what exact version of PFC2D 9.00.VERSION you are using (Help / About / About pfc2d) ?

Regarding the contacts with rblocks and clumps, I am afraid there is confusion with the terminology.
A “PFC clump” refers to a “set of rigidly attached spherical pebbles”.
Although the command rblock clump create calculate from-rblocks range group ‘clumps’ uses that same word “clump”, it creates a “set of rigidly attached rblocks” but not a “PFC clump” as defined previously, i.e.:

  • your “set of rigidly attached rblocks” is not a “clump” and PFC commands for clump wont affect them.
  • the rblocks in your “set of rigidly attached rblocks” (purposely not calling it a “clump”) are not pebbles.

The PFC documentation does not currently make this distinction clear and we will update the terminology to reflect this issue and give a dedicated name to what I have called “set of rigidly attached rblocks” herein.

This is most likely why

PFC does not recognize clumps made of rigid blocks as being made of pebbles

and all contacts should be defined as rblock-rblock.

Can results obtained from simulations where contacts between rblocks and clumps made from rblocks be trusted given the issues I am encountering?

From the available information, I do not anticipate any issue with the underlying physics. If the model runs when the save/restore commands are not called and, per your engineering judgment and testing on this study, the results are correct, it may only be an issue with the save/restore when “set of rigidly attached rblocks” are present.

Please let me know if that helps.
Thank you,
Jibril B. Coulibaly

3

Hi Jibril,

Thank you for looking into the issue.

I am using PFC 2D 9.00.177

Please let me know if you were able to identify the root cause of the issue.

Thanks!