Learning Forum

[javat33489]

Problems with the polymer.

Hi all.

I cut a piece of polymer into a cube and compressed it on a testing machine.

I received the graph: Power/Stroke of the machine:

 

Next, I translated all this into MPA and Strain:

 

Next I used this compression as biaxial tension and used Ogden model 1:

 

I also simulated this cube and squeezed it, but after applying force it does not show the same compression as in the test graph. Also, if you set the displacement and compress it, it does not show the forces that were during the test.

 

Why? This is fine?

[mrife]

Hi javat33489

There are several ways of addressing this but one often used is to change the Time of the analysis from the default 1 to the value of the applied Force.  That way these XY plots that default to value vs time become value vs appplied load.

Mike

[javat33489]

Thanks for your reply Sir. I didn't fully understand you. Could you tell us more?

[mrife]

javat33489

Perhaps I misunderstood what you are asking.  I thought you wanted a result force-displacement XY graph to compare to the test data.  Instead do you want a result stress-strain graph to compare to the material model?  In that case remember that the Hyperelastic material model inputs are 'engineering' stress-strain while the result are 'true' stress-strain (due to large deformation being turned on).  You can create a user defined result for the output that converts the stress and strain from true to engineering.  The use the Chart tool to plot them against each other and compare to the input.

[javat33489]

I tested and compressed the material on a testing machine, then I made a STRESS-STRAIN graph, it turns out that these are true stresses. Next, I created an Ogden model, and the Ogden model was obtained based on the true graph. Next, I made a 3D model of the tested sample and applied the same loads as in real tests, but the result is very different. Did I understand everything correctly?

[javat33489]

What do you say sir?