Learning Forum

[Mansoureh]

Hi.

I am trying to model the compression test for verification of my own result. this structure was chosen from an academic paper and they wrote the Ansys non-linear mechanical solver was used to simulate the structural behavior. But they did not mention that they sued static structural or quasi-static(Explicite Dynamic) process, so I chose static structural, I do not know how to understand which module of Ansys should I use?

I will put the image from my structures and explain everything here.

The top and Bottom plates: solid.

Top plates are coming down in the 19.6 mm in 100 steps. (uy = -19.6 mm) and ux = uz = 0.

Bottom plate: fixed.

Scaffold: deformable with these material properties.

Biliear isotropic hardening , E = 104.8 GPa , Density = 4428.78 , yiels stress = 860 MPa and poisson's ratio 0.3.

and they wrote For computational efficiency, the contact between the right body and scaffold was modeled frictionless.

I used static structural and input my material properties. I defined the Boundary condition and define frictionless contact between the top and bottom plates and my scaffold surfaces.

[salmarzooqi]

Hi Mansoureh

can you give me your email, I have some questions regarding the compression analysis

[Erik Kostson]

Hi
Assuming the structure is quarter symmetric can you model only quarter as that will be much faster to run and the model will be more stable and it will not slide anywhere (we do not want sliding here).
Also set 1 sec and end time, set the auto time stepping to on, and have initial and minimum sub steps to 100 and maximum steps 10000, that will ramp the displacement.
Al the best

Erik

PS: see this for more info on sub steps

[Mansoureh]

Dear Thank you so much for your prompt answer. yes, my model is symmetric, I did not use symmetric, but you are right. I will try it. I started the new simulation and it is still going and not finished yet , every thing is the same as before just I turned on Auto time step and I put this value for time steps:
Up to now, convergence is going very well
but in the middle of simulation process still, it shows me these warnings:
I read in another post about "Matrix coefficient ratio exceeds 1.0e8..." and SandeepMedikonda wrote that this is because of ill-conditioned that can occur due to multiple reasons such as rigid body motion, highly distorted elements, high frictional contacts, units that may result in numbers too big/small, or even unstable material models.
but SandeepMedikonda also said this is just a warning and it can be ignored, but I am confused!!! Should I be worried about that in my simulation or not?(/forum/discussion/9716/matrix-coefficient-ratio-exceeds-1e8), It means sth is wrong in my model but I can not understand what.
BUT right now, I used the frictional contact to prevent moving my model and I could not use frictionless contact.
Do you mean if I use one quarter on my model, can I use frictionless contact and my scaffold won't move?
Do you know if I want to use frictionless contact, what should I do for preventing sliding my model? it seems i can not use frictionless contact and use some constraint for the scaffold. it can change the result if i use any constraint for the scaffolds.
Any recommendation will be appreciated...
Best, Mansoureh

[Mansoureh]

Dear As I am not very expert in Ansys, Maybe I can not guide you very well. I still have so many problems with Ansys and compression test, I can guide you but not very professional. And if you ask your questions here in the ANSYS forum, there is ANSYS employees to guide you or other members also that can guide you very well and help you.
Best, Mansoureh