Kamyar Malakpoor

Swelling driven cracking in large deformation in porous media

Ionized porous media, such as hydrogels, soft tissues, are considered as a saturated two-phase mixture, consist of a charged deformable solid skeleton and an interstitial fluid of opposite charge. Hydrogels subjected to changes of salt concentrations often develop cracks during swelling or shrinking. In return, the presence of discontinuities influences the swelling mechanics of the porous media, like swelling capacity. Therefore, it is strongly desirable to study the coupling between the fluid pressure and crack propagation. In biomedical engineering, hydrogel is a common physical model for soft tissues and consists of cross-linked ionized polymers. In this paper, we present a swelling driven fracture model for porous media in large deformation. Flow of fluid within the crack, within the medium and between the crack and the medium are accounted for. The partition of unity method is used to describe the displacement field and chemical potential field respectively. In order to capture the chemical potential gradient between the gel and the crack, an enhanced local pressure model is applied. A crack opening example is used to test the accuracy of the current model without the influence of the complexity of the crack propagation.

A Full 3D Mixed Hybrid Finite Element Model of Superabsorbent Polymers

Superabsorbent polymers (SAPs) are cross-linked polymer networks with large negatively charged ion groups attached to the solid matrix (polymer chains). By the presence of these large negatively charged ion groups, Donnan osmotic pressure difference rises in and outside of the gel. The Donnan osmotic pressure difference is, as a matter of fact, the main cause for the exceptional swelling ability of SAPs. In this study, we present a dynamic mixed hybrid finite element (MHFE) model in three dimensional setting for the simulation of the finite swelling of SAPs. In this model, the normal flux is approximated using Raviart-Thomas elements, which conserve mass both locally and globally. The solid part is assumed to be isotropic and hyperelastic under isothermal conditions. The transient simulation results are verified with a semi-analytical solution in one dimension; while the 3D equilibrium results in the case of a spherical geometry are verified against the analytical solutions.