what material model is appropriate for polymer hydrogel

[trinhlee]

I am performing an analys of polymer hydrogel (PVA/PAA) using ANSYS software. This work is to calculate stress and strain of this material when it is swollen isotropically in solvent. PVA/PAA hydrogel is known as a crosslinked elastomer and nonlinear material. So, could you tell me what material model is appropriate and what type of load is used in this case?
Thank you beforehand,
Regards.

[Jorgen]

It sounds like you are working on an interesting project. I am very familiar with FEM of swollen elastomers. One approach that is often accurate is to represent the material as a hyperelastic material with a network response that depends on the swell strain (e.g. Boyce and Arruda, Swelling and Mechanical Stretching of Elastomeric Materials, Mathematics and Mechanics of Solids, 6: 641-659, 2001).

Appropriate material models are currently not available as built-in features of ANSYS, but can be implemented as a user material subroutine (I have done this). The load that is applied is a combination of the isotropical swelling and the externally applied loads.

[kd]

dr. bergstrom,

could i have the paper that you refer to in this post for modeling swelling in elastomeric materials. would greatly appreciate if it can be mailed to commando81 at yahoo dot com

thanks,

kd

[Polyurethane]

trinhlee,
Good to hear someone working on the same field. Here is my comments.
In general, there are two approaches to model the mechanical behavior of the hydrogels.
1. Physical and chemical approach, using thermodynamics to describe the swelling behavior as well as load deformation responses. This has been widely studied by Chemistry background people. If you search PNIPA gel, you will have a great chance to see those works.
2. Continuum mechanics way. Using mechanical constitutive model to describe the load-deformation responses. Two big category: single phase or Biphase. Single phase means you ignore the effect of the water/fluid in the gel. Then you might assume material is hyperelastic, viscoelastic or even more complicated. Biphasic models have been used by cartilage modeling community since 80s. However, it is quite recent to see some adoptions on hydrogels. In bipahsic model, you can use whatever constitutive model (elastic, viscoelatic, etc) to model the solid phase.
Hope this will help you out a little.