Plastic Beam for simple tensile test

[dxvn818]

Hi all,

I have tried to use Plastic Beam model for a simple tensile test which includes only 2 discrete elements. In order to use that, I must set the value for "MaxElasticElongation" which is sensitive to get the plastic behavior.

Based on the elastic stress-strain diagram, I set MaElasticElongation to a value lower than the critical value (0.01), then it results in a plastic stress-strain. For specifically, in this case, MaxElasticElongation (0.009, 0.008,...) < 0.01:



However, when I set it equal or bigger to 0.01, it results in elastic, and not plastic at all:



So, my question is: Is it right that we must perform the elastic simulation to get the value of critical MaxElasticElongation, then we put that value into the setting for PlasticBeam model ? Is it possible to estimate or calculate that value without elastic simulation to start directly with the PlasticBeam ?

Thank you in advance.

Vinh

[Damien André]

Hello Vinh,
Can you share with us your input files (*.inp and *.agdd). I would like to test myself for giving you the correct answer.

Thank you, Damien.

[dxvn818]

Hello Damien,

I am sorry for forgetting uploading the case. Here is the link:

https://uowmailedu-my.sharepoint.com/:u:/g/personal/dxvn818_uowmail_edu_au/EZe2VIPYIFZPoIsy1ZEq7KUBx_1wkY4xDo9oknQTT7F_ow?e=b2bVqK

The model includes only 2 discrete elements. This is my first simple test, so I may make some basic mistakes in setting.

Thank you very much for your help, Vinh

[Damien André]

Hello Vinh, If you use this in your input file, it should work :

<PlugIn Id="_Convert" What="ElementPair" To="PlasticBeam"
	    YoungModulus="50.e8" RadiusRatio="0.8" PoissonRatio="0.3" DampingFactor="0."
	    MaxElasticElongation="0.01" MaxElongation="0.02"/>

Note that I remove the MaxStress="50.e6" because, in fact you reach this criterion. Best regards, Damien.

[dxvn818]

Hello Damien,

Thanks so much for your answer. It works. When I use your input file, it gives me the results like this:



Does it mean that the plastic region will last up to the maximum strain 0.02 then damage occurs ?

I have a question: the yield stress is often selected as the input for determining the yield point - the beginning of the plastic phase, however, in this plastic model we must set the MaxElasticElongation and MaxElongation. Do we always have to set these two values when using plastic model ? Is there any example that the plastic model also works when we set the MaxStress value ?

Vinh

[Damien André]

Hello,

dxvn818 wrote

Does it mean that the plastic region will last up to the maximum strain 0.02 then damage occurs ?

Yes, because of the

MaxElongation="0.02"

 in the input file. This is the maximal strain when the fracture occurs.

dxvn818 wrote

I have a question: the yield stress is often selected as the input for determining the yield point - the beginning of the plastic phase, however, in this plastic model we must set the MaxElasticElongation and MaxElongation. Do we always have to set these two values when using plastic model ? Is there any example that the plastic model also works when we set the MaxStress value ?

No, but the relation is really simple :

YieldStress = Young's modulus / MaxElasticElongation

.
Note that the beam that you use here is not the same as inigo terrerros' work.

Best regards, Damien.

[dxvn818]

Hello Damien,

Many thanks for your help.

Best Regards,
Vinh