本文提出的多孔材料质量不变条件是一个塑性变形与致密的协调方程。经典的体积不变条件是在材料密度变化不显著时对质量不变条件的近似应用。文中提出塑变致密与压实致密两类致密机理,描述了颗粒塑变的致密模型,探讨了烧结体宏观受静水压时颗粒产生塑变的应力分解数学模型。最后,本文分解了应力张量第二不变量,指出多孔体屈服与静水压有关。 In this paper, the condition of constant mass of porous material is a plastic deformation and compact coordination equation. The classical volume invariant condition is an approximation of the mass-invariant condition where the material density changes insignificantly. In this paper, two types of densification mechanisms, compact densification and compact densification, are proposed, and the compact model of particle plastic deformation is described. The mathematical model of stress decomposition of the particles is also discussed. Finally, this paper decomposes the second invariant of stress tensor, and points out that the yield of porous body is related to hydrostatic pressure.