Study on the Super Viscoelastic Constitutive Theory for Saturated Porous Media
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摘要: 为了建立能考虑固体材料、多孔固体与流体可逆和不可逆变形的饱和多孔介质超粘弹性理论,以多孔固相为参考构型,以有效应力、材料真实应力和流相真实孔压作为状态变量,结合混合物均匀化响应原理获得各项均符合热力学功共轭特征的饱和多孔介质能量平衡方程,根据非平衡热力学熵分解理论求得熵流和熵产.结果表明,超弹塑性理论是该理论的一个特例;多孔固体的总变形可分为固相间隙和材料变形两部分,间隙应变与Terzaghi有效应力构成功共轭对,材料应变与材料真实应力构成功共轭对.饱和多孔介质的自由能可分为固相和流相两部分.当固相间隙和材料变形解耦时,固相所含的自由能又可分为间隙和材料两部分.证明了Skempton 有效应力不是饱和多孔介质的基本应力状态变量.Abstract: In order to establish the super viscoelastic constitutive framework for saturated porous media in view of the reversible and irreversible deformations of solids, porous solids and fluids, an energy balance equation of which all terms were in the thermodynamically power-conjugated form, was built for saturated porous media according to the principle of homogeneous mixture response, with the porous solid selected as the reference configuration and the effective stress tensor, the material’s real hydrostatic stress and the fluid’s real pore pressure chosen as the state variables. The entropy flux and entropy production of the saturated porous medium were derived based on the decomposing principle of entropy in the non-equilibrium thermodynamics. The work shows that the super elastoplastic constitutive theory is only a special case of the proposed theory. The deformation rate of a porous solid is composed of 2 parts: the solid-phase interstice and the material deformation, of which the former is power-conjugated with the Terzaghi effective stress tensor and the latter with the material’s real hydrostatic stress. The free energy of a saturated porous medium consists of 2 parts: the porous solid-phase part and the fluid-phase part. If the solid-phase interstice is decoupled from the material deformation, the free energy of the solid can be further divided into 2 parts: the material strain and the interstitial change. The Skempton-type effective stress is proved not to be a basic state variable for saturated porous media.
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