Deformation behaviour of hexagonal- and circular-patterned Ni single-crystal 2D micro-lattices via in situ micro-tensile testing and computational analysis

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Springer Nature Limited
The effects of hole shape and orientation on the mechanical properties of micro-scale 2D honeycomb structures, fabricated using a focused ion beam equipment, have been investigated using an in situ micro-mechanical testing machine inside the scanning electron microscope . The material used was single-crystal Ni oriented in the < 100 > direction, with the plane of the 2D micro-lattice having a {001} normal direction. The hole shapes explored were hexagonal and circular, while two different orientations of the hexagonal holes were also compared. One of these orientations had a horizontal arm (designated 0° orientation), while the other had a vertical arm (30° orientation) in each hexagon. The results indicate that there is substantial change in strength and ductility depending on the orientation and shape of the holes with respect to the tensile axis. The samples with 30° oriented hexagonal holes had the lowest strength and highest ductility, while the samples with circular holes showed the greatest yield and tensile strength. The samples with the 0° orientated hexagonal holes had much higher strength and lower ductility than the 30° orientated ones. Moreover, the samples with 0° orientated hexagonal holes, which had a similar hole pattern arrangement to the ones with circular holes, had a similar strength to those of the latter type. Thus, it is apparent from this study that the orientation or arrangement of the holes is more important in determining the properties of the 2D microlattice than the shape of the holes. Finite element simulation of the lattice structures utilised the GTN (Gurson, Tvergaard and Needleman) model to evaluate the failure modes under uniaxial tension. The lattice structure has been shown, in a previous paper by the authors, to exhibit composite like behaviour with strength differences in various parts arising from size effects. These size effect variations were incorporated into the model, and a generalised formulation for the GTN parameters was proposed on the basis of one of the experimental configurations and subsequently applied to the other geometries. The models were in good quantitative agreement with the experimental results with accurate representation of the flows stress and failure modes. © 2022, The Author(s), under exclusive licence to Springer Science Business Media, LLC, part of Springer Nature
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Deformation, Hexagonal lattices, Crystals, Crystal lattices, Tensile properties, Nickel, Electron microscopy, Orientation
Xu, A., Saleh, M., & Bhattacharyya, D. (2022). Deformation behaviour of hexagonal- and circular-patterned Ni single-crystal 2D micro-lattices via in situ micro-tensile testing and computational analysis. Journal of Materials Science, 57(17), 8276-8297. doi:10.1007/s10853-022-07164-1