# Symmetry Boundary Condition For Uniaxial Compression Of Cuboid Specimen

Hi,

I am trying to simulate homogeneous deformation of an uniaxial compression experiment with cuboid specimen (4mm x 4mm x 8mm). My questions are

1) Is the simulation result reliable if I only build a model which is 1/8 of true specimen based on symmetry condition (2mm x 2mm x 4m)?

2) If answer of 1st question is yes, should I assign 3 symmetry BC on 2mm x 2mm x 4mm models left face, back face and bottom face? Or 2 symmetry BC on models left & back face and a zero displacement BC on models bottom face? The reason I ask this is because during uniaxial compression, only specimen top face is pressed, symmetry BC on bottom face will assume specimen is being pressed on both top and bottom faces at the same time, which is not true for compression test. Another reason is because in similar upsetting modelling problem found in Abaqus example problem manual 1.3.1, a zero displacement BC is assign to a 1/4 axisymmetric upsetting model instead of a symmetry BC.

3) If I run the simulation model (2mm x 2mm x 4mm) which is 1/8 of the true specimen (4mm x 4mm x 8mm) and output the reaction force from simulation. How should I estimate the reaction force of true experiment (using true specimen)? Is it simply 8 times (value of reaction force from simulation)?

Thanks in advance for your opinions.

It is recommended to use symmetry if you can when creating a FE model. In your case it sounds like you can use 1/8 symmetry.

1) Yes, the results are reliable, and should be exactly the same.

2) You should apply symmetry boundary conditions on each of the cut faces.

3) Probably 4X multiplication since you have 1/4 of the area.

-Jorgen

Jorgen,

Thanks for your reply, I tried to run the simulation (using 1/8 specimen) using Abaqus Explicit, as I am using dynamic solver to analyze a static problem, the stable time increment is extremely small, about 1 x 10^(-8). It would take at least 2-3 days just to finish the computation of an simple uniaxial compression test (with 25 seconds time step). This is really too long for me as I need to run at least 10 different uniaxial compression simulation with different strain rate. I am thinking since my specimen is cuboid and its deformation is homogeneous, can I use 2D simulation like plane stress or plane strain simulation to conduct the analysis instead of 3D simulation, is it theoretical reasonable? Can you explain to me regarding this? If 2D simulation is not reasonable can you suggest me on how to speed up the simulation? Like choosing certain mesh option and so on.

PS: I have to use Abaqus Explicit because the next step is the implementation of a VUMAT

Thanks and regards

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