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Visco-hyperelastic model

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Hi,
I need to implement a viscoelastic material model in Comsol for a Stretch Blow Molding simulation.
The model is a modified Christensen-Yang Visco-Hyperelastic constitutive law.

It should be possible to implement it (basing on my limited knowledeges on the software). It should be easy to implement the hyperelastic part, but I have some doubts on the viscous part of the equation.

There is the Viscous part of the 2nd Piola Kirckhoff Stress tensor (Sv) with the equation:

Sv= Integral (from 0 to t)([M4+M5*I2(tau)]exp(-(t-tau)/M6)*Et(tau)dtau)

with M4, M5 and M6 model parameters, I2 second invariant of the Cauchy-Green tensor and Et the Strain rate tensor.

I know I have to use a PDE to evaluate the integral (transforming I=intergral(u*dt) in dI/dt=u) but I don't know how to specify the difference between t and tau. t is the time variable which is incremented after each iteration. But how do I insert the tau (the "material memory") since the inegral is in dtau?

Also, for what concern the strain rate tensor, can I simply create 6 variables and write d(E11,t), d(E22,t) ecc ecc?

Thank you very much

Regards

0 Replies Last Post 05.04.2013, 12:09 GMT-4
COMSOL Moderator

Hello Giampaolo Pileggi

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