Effective Plastic Properties of Porous Materials with an Inverse Opal Structure

The paper presents a 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 the 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 modeling 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 solid phase layer. One of the results included approximation of the yield surface with a phenomenological Deshpande–Fleck crushable foam model available in finite element modeling 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.