Neo-Hookean Hyperelastic Material Simulation

[Anonymous]

I am new to Autodesk. 

I want to simulate a fibre re-inforced dog bone tensile test in Autodesk using Neo-hookean model. 

I have the tensile test of the specimen. 

Is it possible to find the coefficients of Neo-hookean model?

Do I have to create geometry with the fibres inside or simply a dog bone model (without fibres) can be used to simulate the hyperelastic model with the coefficents found?

Please let me know.

[John_Holtz]

Hi @Anonymous

Fusion does not have a neo-hookean material model, but you may be able to use the Mooney Rivlin material model to accomplish the same thing. Assuming that the measured material properties are based on the same fiber-filled-hyperelastic, you can enter the measured data into the material properties, and the software will calculate the coefficients. (Naturally, enter the coefficients if you have them.) You do not need to model the fibers (nor would you ever want to try to model and mesh the fibers).

See the article "How to set Mooney-Rivlin properties for a material in Fusion 360" for more details.

Note that for most analyses, you need more than simple tension data to fully characterize the hyperelastic material. You typically need simple tension and equibiaxial tension, volumetric compression, etc.

[Anonymous]

Thank you very much for your Email. I would consider using Mooney-Rivlin model. The other doubt I have is, after getting the coefficients, how can I compare the stress-strain data from uni-axial data and the model which we assumed?

For virtual simulation, should I model the fibers also or simply the dog bone without fiber would be okay? Please advice me.

Let me know if you have any examples like this in autocad tutorial. Thanks in advance.

[John_Holtz]

Hi,

For the simple tension test, the equation for a Mooney Rivlin material is as follows:

stress = 2*(C1+C2/stretch)*(stretch - 1/stretcth^2)

where

• stress is the engineering stress (force/original area)
• strain is the engineering strain (change in length/original length)
• stretch = 1+strain = length/original length
• C1 and C2 are the two constants. (In Fusion, these are A10 and A01.)

I assume that the fibers are small diameter, so I think it is impractical to model them and mesh them (using solid elements -- the only option in Fusion) as a separate part inside the hyperelastic. If this is true, then you are only going to model the dog bone, and the contribution of the fibers is assumed to be "present" in the measured material properties. (Maybe if the diameter of 1 fiber was 1/4 the thickness of the part, then it may be conceivable to model and mesh the individual fibers, and enter the material properties separately for the hyperelastic and the fiber.)

Also, the material models in Fusion assume that the properties are isotropic (the same in all directions). This may be reasonable if the fibers are randomly oriented throughout the volume. If the fibers are in some type of layup (like a composite would be), then the properties are orthotropic (different values in planes at 90 degree angles) or anisotropic (different in planes at some angle other than 90 degrees). I think that Fusion does not have orthotropic or anisotropic materials.

[Anonymous]

Thank you for your reply.


The thickness of the part-DogBone is 7mm. The fibre inside has a dianmeter 0.31 mm. But the tensile test is done with the fibres inside it in o degree and 90 degree to the loading. So, the data includes with fibres.


Should I still include the modelling of fibre during virtual simulation or a simple dog bone model (without fibre) is enough to get the desired output (experiment vs Simulation)?


Last question is, do you have any simple tension test problem in fusion 360 as I some have some doubts durinng the load setup. Thank you in advance.

[John_Holtz]

Hi @Anonymous

1. You want to model the dog bone only (without the fibers).
2. There are lots of example models in the software ("Data Panel > Simulation Samples > 1- Hands-On Exercises") and documentation (Fusion 360 Adoption Portal), and probably many other locations. Instead of looking at a sample/tutorial and trying to adapt it to your situation, why don't you start a new post and ask your questions directly? Attach an image, hand sketch, or the model ("File > Export > Archive Files (*.f3d)") and tell us what you have done and what your doubts are.

[Anonymous]

Thank you very much. I have added a new post as said by you and the link is,

https://forums.autodesk.com/t5/fusion-360-design-validate/fea-tensile-test-of-dog-bone-specimen/td-p...

Thank you.