Learning Forum

[hansenli]

Hi,

I encountered some issue with fitting the compressional stress-strain curve using MAT_HYPERELASTIC (#077). I have defined both compressive stress and strain to be negative based on the general sign convention. When the calculation starts, warnings keeps popping up and MAT_HYPERELASTIC failed to read in my defined curve properly. Does LS-DYNA support compressive data fitting for hyperelastic materials?

I have also tried to do the fitting my self and imput coefficient (C10, C20 ...), but it ends up with 0 time step. (It cannot be solved by defining initial timesteps.) Is there any methods to resolve this issue?

 

Thanks!

[Ram Gopisetti]

Hi

with define curve should have negative and positive side of the curve, i.e., from compression to tension and an 0,0 point

If you don’t have tension data, try to extrapolate it, assuming that you are working on compression loading only. 

Can you clarify on the second point 

cheers, ram 

 

 

 

[hansenli]

Thanks for your reply. For the fitting issues, this is what I got using MAT_077_HYPERELASTIC with positive stress strain values (which is not correct because the experiment result is from compression tests). You can see in the second picture that the fitting went terrible when switch both stress and strain value to negative.

When I manually fitted the negative stress-negative strain and input C10 C20 C30, LS-DYNA shows this error:

*** Error 40009 (SOL+9)
     The time step size is zero.

I have double checked that my timestep setup are correct. I don't know how to resolve this issue.

Is it normal that using an odgen/hyperelastic/rivlin model will make the simulation to be super slow?

Another question is that if I use MAT_024_PIECEWISE_LINEAR_PLASTICITY, where the input stree-strain curve is effective stress versus effective plastic strain, which are supposed to be positive, how can I import my compression test result to it?