Fabrication And Mechanical Properties Of Pyramidal Lattice Truss Sandwich Structures Of Aluminium Alloy

A pyramidal lattice truss structure of 6061 aluminum alloy has been fabricated by assembly of slotted metal sheets, followed by air brazing to join the structure with aluminum plates on top-and-bottom making a sandwich structure. Structures with different cellular core relative densities ranging between 0.052 and 0.068 were obtained by changing the widths of the lattice truss. The static compressive mechanical behaviors and energy absorption performance of the fabricated pyramidal lattice truss sandwich samples were studied by the quasi-static compression tests. According to the results of the measured static compressive properties and theoretical estimates based on three mechanical analytical models, optimizing schemes were proposed to strengthen the mechanical properties of pyramid lattice truss sandwich structures from three aspects including shape optimization and topology optimization.The result shows that pyramidal lattice truss cores exhibited similar compressive stress strain to those of many cellular metals, their compression process included three stages:linear elastic stage, softening stage and densification stage. With the adding of core relative density, the measured peak compressive strengths have increased obviously. A model based on inelastic column-buckling theory incorporating strain hardening was able to predict the pyramidal lattice core's compressive peak strength over a range of relative densities, parent alloy yield strengths, and strain hardening capacities. The energy absorption capacity in the compression process increased monotonically with the adding of core relative density, while the energy absorption efficiency exhibited a rising and descending curve with a peak at the strain of 0.25. In a wide range of strain (varied from 0.15 to 0.35), the energy absorption efficiency of the pyramidal lattice truss sandwich structures maintained in 70% above. After decreasing the opening angle of the pyramid lattice cores from 30°to 15°, the mechanical properties of pyramidal lattice truss sandwich structures were well strengthened. The specific strength was enhanced about 25%, while the energy absorbed per unit mass was improved about 20%. An innovative topology structure provided a further strengthen of the pyramidal lattice truss sandwich structures. The value of their specific strength and energy absorbed per unit mass were both about twice of the pyramidal lattice truss sandwich structures without optimization, and higher than the shape-optimized sandwich structures also.