EXTENDED CONTINUAL MODEL FOR POWDERS AND POROUS MATERIALS 

Abstract

The work is dedicated to formulating a new behavioral model of porous and powdered bodies and aims to consider the internal structure features of the new material classes. Analysis of existing models shows that most of them rely on the hypothesis that the only parameter of the material is porosity. In the meantime, numerous structure observations of these materials indicate a significant impact of other types of imperfections on the properties, which may include crack-like defects. During deformation, they can facilitate the emergence of stratified cracks with the subsequent destruction of a product even at its manufacturing. Furthermore, such models are not sensitive to resistance in compression and tension. They also disregard the change in volume in the absence of hydrostatic pressure. To address these gaps, a new four-parameter plasticity theory is proposed. It describes the behaviour of powders and porous semi-finished products that include two new parameters in addition to porosity and mean deformation of the solid phase in porous body. They reflect the influence of resistance and the presence of dilatancy. Taking these into account, the expression for the dissipative potential and the load surface of such four-parametric material is formulated. The major difference between the proposed and existing models is that it describes a material, which can be both granular and porous. It is considered that the yield point of this material for total tensile strength in the mass state is zero. On the contrary, the yield strength in tension and compression in porous materials are equal to each other under conditions of perfect contact and full adhesion. Physical meaning of two new material parameters was clarified. Their influence on the development of delamination cracks in the conditions under which complex products are produced is established. The reasonableness of using the proposed model for the 3D printing process is outlined.