Hi John, your help is greatly appreciated!

Yes: “weight mode” approach is a pressure load applied on the upper circular base of the cylinder: “SFL,3,PRES,9.8*Weight/(3.1415*Radius**2),

And, again, the “displace mode” approach is a direct displacement as you have noticed.

I have tried to change a lot of parameters, but none of them improve significantly the results (NEle from 5 to 100; Time_sim from 0,1 to 10; automatic or manual step size…)

Yes, I also tried switching to PLANE182 but no big improvements: It allows us to compress the material up to 37% instead of 31%.

Yesterday I read something that worried me in the ANSYS manual (Explicit Dynamics Analysis Guide). In the section "7.6. Hyperelasticity", it says that

"The different models are generally applicable over different ranges of strain as illustrated in the table below, however these numbers are not definitive and users should verify the applicability of the model chosen prior to use" .

The range they give for the Neo-Hookean is 30%. Does this mean that an element whose material is Neo-Hokean cannot have a deformation greater than 30% of its dimension at rest? If so, this would explain everything, wouldn't it?

Thanks, John (and any else who help in this issue!)