I'm trying to simulate the material NBR as a hyperelastic material in ABAQUS by using the coefficients using the Neo-Hooke model as I cannot obtain the stress-strain data values for the material.
I am using C1 = 1.38 MPa and D1 = 0.08431. I am simulating a seal, that is why I cannot assume incompressibility and write D1 = 0.
I'm getting the following error: Initial poissons ratio (pr0) for the hyperelastic material is zero or negative: pr0 = -0.99998. It is generally recommended that single element models be used to verify that the chosen material constants lead to a well defined hyperelastic material.
How can I fix it?
Hello Julia,
what type of part and elements do you use? I have try to use your material properties with 3D-deformable part which is meshed using C3D8RH elements type (An 8-node linear brick, hybrid, constant pressure, reduced integration, hourglass control), and the simulation runs successfully for me.
Could you also please provide the input file in order to check if there some problems?
Sincerely,
Pavlo
This may be due to the material constants you have specified for the Neo-Hooke model.
In the Neo-Hooke model, the initial Poisson's ratio (pr0) is calculated as:
pr0 = -D1 / (2*C1)
If the value of pr0 is negative or zero, it means that the material constants you have specified are not valid for the Neo-Hooke model.
Pavlo Pavliuchenko , you're using D1=0 in your simulation, that's likely why your simulation is working and Julia Fibla 's one is not.
Julia Fibla , the problem may be that your resulting Poisson's ratio is extremely close to -1, i.e. the lower extreme of admissible values. Try to modify the values of C1 and D1 to get pr0 ~ -0.5. Try also D1=0 (i.e. incompressible). That should rule out other problems in the model (elements, contact,...).
Suganth Velumani , a negative Poisson's ratio is the most common case in materials: if the material is pulled in one direction, the materials shrinks in the transverse direction. A value of 0 is less common, but still admissible: the material does not shrink in the direction transverse to the applied stretch.
Luca Di Stasio, my bad, thanks for pointing out the mistake. I didn't quite get the material parameters right away.
Despite this, I attempted to use the model with the same parameters as Julia Fibla (C1 = 1.38 MPa and D1 = 0.08431) and it still performed well. I attempted to alter the material properties in various ways, but I was unable to reproduce the error that Julia mentioned.This is why I am requesting the inp-file again in order to try to identify any issues with the model.
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