Fabrication, microstructure and mechanical properties of a 3D re-entrant anti-trichiral honeycomb structure with excellent auxeticity and mechanical performance

In this study, a 3D re-entrant anti-trichiral honeycomb (RATH) structure with the combination of various deformation mechanisms was proposed and formed through SLM additive manufacturing. It was found that the samples exhibited a good formability with less internal porosity and fine forming accuracy through the macroscopic and microscopic analyse. The microstructure of the fabricated sample present typical characteristics of the SLM-fabricated materials, which includes coarse grain zone, fine grain zone, and heat affected zone. The grains of the as-fabricated sample mainly exhibit the characteristics of columnar grains and the grains with a length up to 41∼86 μm grow from the boundary of one melt pool to another, which are predominantly oriented in the [001] direction and parallel to the forming direction. The quasi-static compression behavior, auxeticity and energy absorption capabilities of the 3D RATH structures with varied geometric parameters are comprehensively investigated through FEA method verified by the experimental results. The numerical results exhibited a good agreement with the experimental results with regard to stress strain behavior, deformation mode and Poisson's ratio. It was found that the compression performance and auxetic behavior of the 3D RATH structures can be tailored by varying the geometrical parameters. The 3D RATH structures exhibit the simultaneous re-entrant and rotating deformations throughout the whole compression process, thereby producing the auxeticity in large strain range. Moreover, the results exhibit that the proposed 3D RATH structures can significantly enhance the compression stress and auxetic behavior by the combination of different structures compared with conventional re-entrant honeycomb structures.