Hyperelasticity + Viscoelasticity
Hyperelasticity + Viscoelasticity
(OP)
I intend to use a model where the instantanous response is nonlinear elastic (hyperelastic - Neo Hooke potential) and is followed with a viscoleastic response (linear model - Prony series).
It doesn't calculate a single increment and I get information about "negative eigenvalues" and heavily distorted elements.
I've tried with a finer mesh (Hex). I've tried various element types. I've lowered the inintial increment value and trid with various values of strain tolerance (for viscoelasticity). Still error.
Step type is visco.
Thanks in advance.
It doesn't calculate a single increment and I get information about "negative eigenvalues" and heavily distorted elements.
I've tried with a finer mesh (Hex). I've tried various element types. I've lowered the inintial increment value and trid with various values of strain tolerance (for viscoelasticity). Still error.
Step type is visco.
Thanks in advance.





RE: Hyperelasticity + Viscoelasticity
Also, I would start with a one element model and pull it in tension or compression at a reasonably slow rate during a visco step. Make sure the stress/strain response seems correct. If no errors, then move on to using this material in your big model.
RE: Hyperelasticity + Viscoelasticity
there might be something wrong with those hyperelestic constans as D is relatively high, which means that the Poissons ratio should be close to zero (and I get a warning message that the Poissons ratio is negative or close to zero.
I've tried with a purely hyperelastic model in a static step and it's alright. It completes the analysis.
RE: Hyperelasticity + Viscoelasticity
http://img18.imageshack.us/img18/6562/creepn.gif
I think that probably it's alright but the creeping has been seriously linearized (I don't know - maybe it's due to the plot scale etc).
I've evaluated both hyperelastic and viscoelastic models and Abaqus says that they are stable for all cases.
I get a warning about a negative eigenvalue (1). One negative eigenvalue for one-element analysis. For a more complicated part there is much more of them and that's the reason why the analysis crashes. Still, I don't know what causes those negative eigenvalues.
RE: Hyperelasticity + Viscoelasticity
It looks like your creep time constant is really really small, which is why you see the initial spike and then the flattening out. Try to increase your time constant, or decrease your time scale.