Residue strenth is too small when using Smoothjoint model to simulate grain boundary

PFC
,
1

Hello
I use a grain based model in PFC to simulate the granite behavior in unconfined and confined conditions. The grain boudary is simulated with smooth jointed model and the grain is simulated with flat jointed model. The residue strenth and volumetic strain in unconfined conditon is good. However, in confined conditon, the residue strenth is significantly low than the experimental data and dilation volumetic strain tend to reduce at the residue stage.
Please see the results: the confined stress is 60MPa, the residue strenth should be around 270MPa.

1
11117×837 132 KB

2
2956×620 105 KB

2

Hello Xiongyu,

It’s difficult to speak to calibrating a model that contains both smooth joints and flat joints. However, in my experience the best place to start would be to follow guidelines given by @dpotyondy in Calibration of a Flat-Joint Material. This guideline can be found in the Material Modeling Support package, in the Documentation folder → Calibration_FJmaterial[Apr13_2018].pdf

There are additional documents in the Documentation folder that also discuss FJ models. I would recommend looking at those as well.

Thanks,
Derrick

3

Hello Derrick
Thank you very much for this informaiton. As i am doing a grain based mode, the grain boundary is usually simulated with smooth jointed model in PFC, while the grain is usually suggested simulated with flat-joint model. In this conditon, i found that the residue strength of the confined specimen is very low, especially at high confining stress. I also find that there are many particles overlapped at the shear band. I wondering if this is caused by the smooth joint, which means there will be some problems in the residue strength when using the smooth joint to simulate the grain boundary???
Thanks
Xiongyu

4

Hello Derrick
Thank you very much for this informaiton. As i am doing a grain based mode, the grain boundary is usually simulated with smooth jointed model in PFC, while the grain is usually suggested simulated with flat-joint model. In this conditon, i found that the residue strength of the confined specimen is very low, especially at high confining stress. I also find that there are many particles overlapped at the shear band. I wondering if this is caused by the smooth joint, which means there will be some problems in the residue strength when using the smooth joint to simulate the grain boundary???
Thanks
Xiongyu

5

Hello Xiongyu,

I am not sure what the answer to this question is, nor do I think this forum may be the best place to determine the answer (although perhaps someone with more expertise in this subject can aid us). That being said, I rounded up a few resources that may be helpful:

  1. A good recent paper on the subject - Novel grain-based model for simulation of brittle failure of Alxa porphyritic granite - ScienceDirect
  2. A list of good papers provided by one of Itasca’s engineers -
    breakageModeling.pdf (2.3 MB)

If you still have questions, I’d suggest reaching out to PFCsupport@itascacg.com, we may be able to provide more insight that way.

6

Hello Derrick
Thank you very much for your help. I really appreciate.

Best regards
Xiongyu