Research On Theory And Numerical Simulations Of Multi-Phase Media

Multi-phase medium are known as these materials which include some different substance. For example, the polymer gel includes the polymer network, interstitial water and mobile salt ion. Because of the complexity of the micorstructure, the multi-phase materials behave the complex macroscopical properties that include some multiphysics field coupling effect, such as the fluid-solid coupling effect, the chemo-mechanical coupling effect and so on. This paper was based on the mixture theory under the thermodynamics frame and developed the multi-phase coupling theory of multi-phase mediums. In this paper the main studies are shown as follow:(1) The theory model of biphasic media which describes the fluid-solid coupling effect was built. The biphasic medium includes the solid phase and the interstitial fluid phase. The solid phase is known as porous media which can't be modeled directly for its complex geometry configure. The fluid phase is the fluid which fills the interspace of the solid phase. Based on the hypothesis of mixture theory, the biphasic media is treated as the two kinds of continuous media which are uniformly distributed in the whole material space. According to mixture theory, the constitutive equations of biphasic medium were deduced and simplified by using the infintesimal strain theory and the hypothesis that the solid phase is incompressible elastic and the fluid phase is incompressible and inviscous.(2) The finite element equations of the biphasic medium were deduced. And then this biphasic medium model was applied on the intervertebral disc. When a uniform press was loaded on the disc, the results of the numerical simulation can be obtained. At the beginning of the simulation, the stress was shared by solid phase and fluid phase. As time elapsed, the fluid phase was ejected out of the disc. At last the stress of solid phase reaches the uniform press.(3) The chemo-mechanical coupling model of triphase medium including solid phase, fluid phase and ion phase was developed according to the mixture theory. This model considered the chemo-mechanical coupling effect of triphase medium deduced by the change of ion concentration. In this paper the constitutive equations of triphase medium model were derived and the finite element equations of this model were also given.(4) The chemo-mechanical coupling model of triphasic medium was applied to the polymer gel. The numerical simulation of polymer gel show that the material stress was composed by stress of solid phase, the fluid press and the swelling stress caused by ion.In this paper the fluid-solid coupling model of biphasic medium and the chemo-mechanical coupling model of triphasic medium were built by using mixture theory. The research shows that the two models can describe the mechanics behaviors of the materials considering the fluid-solid coupling effect and chemo-mechanical coupling effect.