Periodic cellular metals (PCMs) can offer higher specific strengths and stiffnesses than conventional (i.e. stochastic) metallic foams. This study examines the effects of PCM microstructure and loading conditions on the mechanical performance.
PCM cores with 95% open porosity were constructed from perforated 6061 aluminium alloy sheets using a perforation-stretching method. This method places planar, periodically-perforated sheet metal in an alternating-pin jig. The pins apply force out-of-plane, plastically deforming the sheet metal into a truss-like array of struts (i.e. metal supports) and nodal peaks (i.e. strut intersections). Micro-hardness profiles were taken in the PCM struts to investigate microstructural evolution during fabrication and after heat treatment.
Truss cores were tested in two limiting uniaxial compression conditions. In the first, the PCM cores are placed between smooth compression platens where the nodes are laterally free and compressive forces are resisted through PCM node-bending (i.e. free compression). In the second, the PCM cores were placed between plates where the nodes are laterally confined and compressive forces are resisted through PCM beam-buckling (i.e. confined compression). Compression response was analyzed in terms of peak compressive strength, elastic modulus, and energy density absorbed upon densification; response values were used to illustrate the effect of compression test conditions. In addition, PCM cores were tested in the age-hardened state and annealed state to determine microstructural effects on compressive response.
Analysis of PCM response in free- and confined-compression conditions indicates a greater force resistance in beam-buckling over node-bending resistance mechanisms. The compressive strength, elastic modulus, and energy density of heat-treatable AA6061 PCMs are be found to respond: 1) over a wide range of value, dependent on the microstructure; 2) over a wide range of value, dependent on the PCM compression conditions; and 3) equally, if not more repeatable and with higher compressive strength-to-weight ratio than conventional metal foams.