triaxial test

Submitted by Rahul Kumar on Fri, 11/01/2019 - 05:39

Dear all

I am doing triaxial test simulation, but I am facing some problem.

1. First, I applied six servo controlled wall using command to execute a confining pressure on a cube soil specimen, with the following command.

fix twall_servo all mesh/surface/stress/servo file meshes/sample_1/topwall.stl type 2 com 0.025 0.025 1.0 ctrlPV force axis 0.0 0.0 -1.0 target_val 100 vel_max 0.001
fix bwall_servo all mesh/surface/stress/servo file meshes/sample_1/bottomwall.stl type 2 com 0.025 0.025 0.0 ctrlPV force axis 0.0 0.0 1.0 target_val 100 vel_max 0.001
fix wall1_servo all mesh/surface/stress/servo file meshes/sample_1/sidewall1.stl type 2 com 0.05 0.025 0.06 ctrlPV force axis -1.0 0.0 0.0 target_val 200 vel_max 0.001
fix wall2_servo all mesh/surface/stress/servo file meshes/sample_1/sidewall2.stl type 2 com 0.025 0.0 0.06 ctrlPV force axis 0.0 1.0 0.0 target_val 200 vel_max 0.001
fix wall3_servo all mesh/surface/stress/servo file meshes/sample_1/sidewall3.stl type 2 com 0.0 0.025 0.06 ctrlPV force axis 1.0 0.0 0.0 target_val 200 vel_max 0.001
fix wall4_servo all mesh/surface/stress/servo file meshes/sample_1/sidewall4.stl type 2 com 0.025 0.05 0.06 ctrlPV force axis 0.0 -1.0 0.0 target_val 200 vel_max 0.001

2. After applying confining pressure I am modifying the servo command for top and bottom plate to apply additional axial pressure, with the following command

fix_modify twall_servo servo/target_val 250
fix_modify bwall_servo servo/target_val 250

But I am facing the following problem
1. I am not able to achieve constant wall force. The forces on the wall are constantly decreasing.
2. I am unable to obtain constant confining pressure

Forums:

southeast1012 | Thu, 11/14/2019 - 13:02

In my opinion, after consolidation, your bottom wall and topwall need to change to strain_controlled walls. and to get constant confining pressure you can try to decrease the vel_max.

Zhao

Rachel | Wed, 11/20/2019 - 03:54

Hi there,

In my mind, I think you should use the target pressure instead of target force for the consolidation process, because the contact area at each face will keep changing with the loading process. All you need is to keep modifying the target force value by calculating it using Force=pressure*Area. I hope this would help.

Rachel

wangxiukai | Sat, 04/24/2021 - 16:09

Dear Rachel,

I am a newer of liggghts and want to consult some questions.
How to calculating the area? Do you have a scripyt about the servo prolem?
Thank you a lot.

Wang xiukai