Research On Multi-field Coupling Thermodynamic Constitutive Model And Finite Element Analysis For Multi-phase Porous Materials

Porous materials have long been neglected in civil engineering design and structural analysis.Or they have been improperly simplified to the theoretical system of soil mechanics.These practices would likely result in calculation errors that lead to potential security risks in construction projects.The purpose of this study is to establish constitutive models of porous elastic materials under isothermal saturated,non-isothermal,and isothermal unsaturated conditions through thermodynamic methods to create a more comprehensive research.On this basis,by means of numerical simulation,the finite element calculation program of plane strain is developed on the basis of the constitutive model under variable temperature and saturation conditions,and the research is carried out for temperature stress and other problems.Here is an overview of the research contents.First of all,our research establishes a constitutive model of saturated porous materials and compares it with the existing constitutive model of saturated porous materials based on the thermodynamic framework.Our analysis shows the physical significance of the new material parameters is caused by the change of the compressibility and porosity of each phase.Secondly,to set up the constitutive model of saturated porous material under variable temperature,we utilize the constitutive model of saturated porous material under constant temperature.On the basis of this theoretical work,the plane strain program is compiled to calculate for cases of engineering energy tunnels.The results are then compared with the general finite element program to analyze energy piles and energy tunnels.Finally,three typical deformation mechanisms of unsaturated porous materials are summarized by the characteristics of unsaturated porous materials.Each deformation mechanism introduces respectively its intrinsic free energy,elastic potential energy and associated pore water potential energy.This forms the overall free energy model of unsaturated porous materials.The total stress composition of unsaturated porous materials was obtained by computing the thermodynamic pressure and elastic skeleton stress.By combining the strain coordination equation,we achieve a constitutive model for unsaturated porous materials.Characterized by its universality and versatility,this constitutive model fully considers the volumetric deformation of each phase under uniform pressure,the elastic deformation of the skeleton and the deformation caused by capillary action and adsorption action.The validity of the model is proven by comparing saturation and suction of unsaturated porous material and soil-water characteristic curve of unsaturated soil.It is also further verified by combining the existing test data of loose sand and glass beads.