28 September 2020 at 19 h 07 min #17224Pasquale94Participant
- Vrije Universiteit Brussel
I am implementing Soft robotic design models with Neo-hookean constituve laws.
I derived the model data, from experimental data ( tension and compression test) in Abaqus, and I deriverd from curve fitting the constitutive parameters, and the constitutive law result a Neo-hookean one.
So i tried with the same parameters, and the same pressure inside the cavity, a simulation of a pneumatic soft finger. I made it both in Abaqus and SOFA.
In Abaqus, the bending angle result overcome 200 degree.
In Sofa, the bending angle is about 110 degree.
So, at beginning, i thought that was a meshing problem in SOFA, but playing a lot with the parameters for meshing (facet angle, cell ratio, cell size, facet size) I obtain the same results.
In the End, for curiosity, I checked how it is expressed the NeoHookean strain energy function (NeoHookean.h) In SOFA and in Abaqus, and they seems two different equations.
in particular, in Sofa you have :
in Abaqus is implemeted this one:
U= C10*(I1−3)+(1/D1)*(Jeℓ−1)^2(this is also the common one that I know for Neohookean behaviour, for uncompressible assumption)
Anyway, the formulation that i found for compressiblr material is:
U = C10*(I1-2-2*log(J))+(1/D1)*(J-1)^2(from Wikipedia, maybe is wrong)
so, I understand that your mu is the Lame’ constant and D1=2/K0, but, the two equation for Abaqus and Sofa are different ( because abaqus assume incompressible material), and this can be the cause of such a difference in bending angle.
Anyway, your equation for Neo-hookean compressible material, seems not equal and have the lack of some terms, respect the equation that i found.
I am not an expert on Hyperelastic constitutive models, so a clarification would be appreciated, because maybe Wikipedia formula is wrong, but I am in doubt right now.
Thank you in advance.5 October 2020 at 22 h 30 min #17283
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