EFFECTIVE PLASTIC PROPERTIES OF POROUS MATERIALS WITH AN INVERSE OPAL STRUCTURE 

Abstract

The study focuses on theoretical evaluation of the mechanical properties of porous materials with an inverse opal structure, which is important for their application in various technological fields. The study focuses on a porous nickel-based material produced by a sequential multistep process that includes the self-assembly of polystyrene spheres, sintering, electrolytic deposition, and subsequent removal of polystyrene to achieve the desired structure. The study covers the process of transition from elastic to irreversible deformation. The objective of this study is to apply the finite element method to model this transition process to reveal the relationship between the structural characteristics of materials, such as porosity and coating thickness, and their mechanical properties. The yield surface was constructed by computational modelling on a representative cell with a number of points in the (p, τ) plane for two cases of opal structure: a highly porous uncoated structure and a structure with an additional layer. One of the results included approximation of the yield surface’s numerical representation with a Deshpande–Fleck crushable foam model available in finite element modelling packages. The conclusions show that the effective plastic properties of materials with an inverse opal structure significantly depend on their porosity level and the presence of additional coatings. The yield curve plotted for a porosity of 0.9 is close to the associated plastic flow law, allowing the material’s behavior under loading to be assessed from the uniaxial stress state. However, for a structure with medium porosity and an additional coating layer, the surface becomes significantly unassociated, with a discrepancy of almost 30%. The application of the Deshpande–Fleck model for crushable foam in the approximation of the numerical data from the study demonstrates its relevance in describing the plastic behavior of this structure only at high porosity values.