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Dynamic crushing behavior of closed-cell aluminum foams based on different space-filling unit cells

Talebi S., Hedayati R., Sadighi M.

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 3

231--245

Closed-cell metal foams are cellular solids that show unique properties such as high strength to weight ratio, high energy absorption capacity, and low thermal conductivity. Due to being computation and cost effective, modeling the behavior of closed-cell foams using regular unit cells has attracted a lot of attention in this regard. Recent developments in additive manufacturing techniques which have made the production of rationally designed porous structures feasible has also contributed to recent increasing interest in studying the mechanical behavior of regular lattice structures. In this study, five different topologies namely Kelvin, Weaire–Phelan, rhombicuboctahedron, octahedral, and truncated cube are considered for constructing lattice structures. The effects of foam density and impact velocity on the stress–strain curves, first peak stress, and energy absorption capacity are investigated. The results showed that unit cell topology has a very significant effect on the stiffness, first peak stress, failure mode, and energy absorption capacity. Among all the unit cell types, the Kelvin unit cell demonstrated the most similar behavior to experimental test results. The Weaire–Phelan unit cell, while showing promising results in low and medium densities, demonstrated unstable behavior at high impact velocity. The lattice structures with high fractions of vertical walls (truncated cube and rhombicuboctahedron) showed higher stiffness and first peak stress values as compared to lattice structures with high ratio of oblique walls (Weaire–Phelan and Kelvin). However, as for the energy absorption capacity, other factors were important. The lattice structures with high cell wall surface area had higher energy absorption capacities as compared to lattice structures with low surface area. The results of this study are not only beneficial in determining the proper unit cell type in numerical modeling of dynamic behavior of closed-cell foams, but they are also advantageous in studying the dynamic behavior of additively manufactured lattice structures with different topologies.

Analysing effective thermal conductivity of 2D closed-cell foam based on shrunk Voronoi tessellations

Wang H., Liu B., Kang Y.-X., Qin Q.-H.

Archives of Mechanics

2017

Vol. 69, nr 6

451--470

Two-dimensional foam is a type of cellular solid materials containing a high volume fraction of pores. The thermal behavior of foam depends strongly on its microscopic structure. In this study, a two-dimensional closed-cell foam model containing randomly distributed air voids and solid walls is designed via a Voronoi diagram enhanced by the shrinking technique to approximately represent the real foam structure. The porosity, pore size and solid wall thickness of the established random foam structure is examined by introducing the so-called shrinking ratio. Subsequently, the effective thermal conductivity of the rebuilt foam model is numerically presented through the finite element analysis. The numerical results obtained are verified by comparison with the available theoretical and experimental results. In the analysis, the effects of porosity, number of pores and thermal conductivity of solid phase in foam structures are investigated respectively to reveal the relationship of geometric parameters and thermal properties of solid phase with effective thermal conductivity of the foam.