Shear Band Formation in FLAC2D

1

Hello all,
I want to discuss shear band formation in FLAC2D for a UCS test done at different velocities. This is the code I used:
config
g 50 100
generate 0,0 0,.170 .08,.170 0.08,0
mo ss
mo null i=25,26 j=51,52 ;Forced failure from centre to form shear band
fix y j 1
fix y j 101
ini yvel -0.01e-5 j 101
prop den 1500 bulk 2.225e7 shear 1.027e7 coh 40e3 fric 30 ten 5e3 dil 0
pro ctab 2
table 2 0 40e3 0.0225 0e3
step 15000
The below figure is the shear band formed for the above code:

image
image369×781 11.1 KB

But when I decrease the velocity to let’s say 0.000625e-5, this is the shear band formed:
image
image371×782 7.58 KB

I just want to ask if this is a numerical instability which FLAC cannot control?
Or there is a way in which this can be controlled and as long as the model is symmetric, I can get double shear bands.

2

The applied velocity should be low enough to minimize the inertial effects, the first applied velocity is too high. Monitor the sratio velocity in the cycle window, ensure the value is not higher than 1e-2~1e–3. some more information can be found in the Users’ guide manual, that may help.
Section 3.2.4 Localization and Grid Dependence
Section 3.10.3 Localization, Physical Instability and Path-Dependence