## General Mechanical

#### Multi step analysis to simulate uniaxial tension and compression test

• marco.ballotta.2
Subscriber

Hello everyone,

I need to perform a simulation of a uniaxial tension and uniaxial compression test. This is because I want to obtain the stress - strain curve for the material, in the elastic and plastic zone. I am using the cast iron model and this analysis wants to make sure that Ansys follows the input data.

To create the curve, I need multiple points with stress and strain; to obtain them, I want to make a multi step analysis, in which the load is increased in every step to reach the maximum in the final step (ex. load 1000 N, first step 100 N applied, 2nd step another 100 N applied, etc, at the 10th step the last 100 N applied reach the 1000 N total, hope I made myself clear), so for every step I have the stress and the strain. Obviously I need to input a force that makes the material yield and go in the plastic region.

Do you know how to perform such analysis in Static Structural? Do you know if Ansys provides a tutorial video for this? Thank you for your help

• peteroznewman
Subscriber

Marco,

You say you will use the Ansys Cast Iron model, but that model requires inputs. What values will you use as input to that model?

I typically use a unit cube meshed with exactly one linear element to check that the material model is delivering as an output the numbers used as inputs to the material model.

The unit cube has a zero normal displacement on three adjacent sides, and a small positive or negative displacement on one other side. But I repeat myself, since I said this to you in your September 6 post where I provided a model that has a multistep analysis. https://forum.ansys.com/forums/topic/modeling-different-behaviour-in-tension-and-compression/

• marco.ballotta.2
Subscriber

Dear Peter,

yes you're right, you already told me this. I am using as input the following command:

/prep7

mp, ex, 1,3700  !Elastic modulus in MPa
mp,nuxy, 1,0.4  !Poisson ratio

!Define cast iron model
TB,CAST,1,,,ISOTROPIC
TBDATA,1,0.4  !Plastic poisson ratio

TB,CAST,1,1,7,TENSION !(stresses in MPa)
TBTEMP,20.
TBPT,,0,80.
TBPT,,0.007055167,82.24
TBPT,,0.00783981,84.93375
TBPT,,0.008905017,87.6605
TBPT,,0.009870315,90.3875
TBPT,,0.012339927,93.267
TBPT,,0.016915443,96.906

TB,CAST,1,1,6,COMPRESSION !(stresses in MPa)
TBTEMP,20.
TBPT,,0,40.
TBPT,,0.03855,40.95
TBPT,,0.077985,69.3
TBPT,,0.103,88.
TBPT,,0.1345,102.
TBPT,,0.155322,108.

I have another question, if you may help me. How does Ansys know when to apply the compression or tension data? I mean, how does Ansys know when the material is compressed and when it is in tension, so it can apply the correct material behaviour? I looked for this information in the Mechanical APDL help for cast iron, but they only talk about the yielding criterion used for compression and tension. The model I am working on is under a triaxial loading.

My idea was this: in a triaxial stress state, Ansys considers the principal stress with the higher magnitude, and if this principal stress is positive then that element is under tension, if the principal stress is negative there is compression. Can it be a possible explanation?

Thank you again