Shape Memory Polymer

**Michel** · 2012-03-29, 20:11

Hi everybody !

I'm trying to modeling a SMP on Ansys. This kind of polymer can recover his shape after deformation under a stimuli (like temperature). Hence, I would like to know if somebody has some knowledges about this subject.

My problem :
My polymer sample doesn't recover his original shape. Example : a polymer tube deformed with an angle of 60°, should recover his linear shape after an increase of temperature beyond the Tg. Note : I'm using the element type "solid227".

Someone has an idea ?

Thank you very much,
Michel

**Jorgen** · 2012-03-29, 22:03

I have experience simulating the response of shape memory polymers. In my experience, to accurately capture the thermomechanical response requires a suitable non-linear viscoplastic material model. What material model are you currently using?

Thanks,
Jorgen

**Michel** · 2012-03-30, 11:49

Thank you for your response.

I'm using an elastic linear isotropic material. In input I have the evolution of storage modulus function of temperature.
What kind of non lienar viscoplastic material model should I use ?

Thank you,
Michel

Originally Posted by Jorgen

I have experience simulating the response of shape memory polymers. In my experience, to accurately capture the thermomechanical response requires a suitable non-linear viscoplastic material model. What material model are you currently using?

Thanks,
Jorgen

**Michel** · 2012-03-30, 13:31

I have also the loss modulus because I have tan(delta) versus temperature of my polymer.

**Jorgen** · 2012-04-26, 21:22

The most appropriate material model will depend on what you are trying to do. If you need accurate predictions then you need an accurate (and advanced) material model. The Parallel Network Model is an example of an accurate material model for SMP.

-Jorgen

**Michel** · 2012-04-26, 23:57

My plan is to apply the parallel model.
Should I use prony series to characterize the viscoelastic behaviour of the polymer ? I will do a DMA next week.

**Jorgen** · 2012-04-29, 21:40

A Prony series is useful, but I recommend that you also perform tests at different strain amplitudes to evaluate if your material is linear viscoelastic.

-Jorgen

**Michel** · 2012-06-01, 12:59

Hello,

The material is assumed to be linear viscoelastic according to the test.

The mechanical behavior of the polymer follows Zener model. Thus, I have choosen PNM with :
Network1: neo-hookean with power-law temperature dependence (important feature for the SMP)
Network2: neo-hookean + linear-viscoelastic flow with power law temperature dependence.

The calibration provided by this PNM doesn't fit with the DMA results. Could you please tell me what can I improve in the model ?

Thank you very much,