Abstract
The stiffness, anisotropy and structural deformation of three gyroid-based lattices was investigated, with particular focus on a newly proposed honeycomb gyroid. This honeycomb is based on a modified triply periodic minimal surface (TPMS) equation with reduced periodicity. Using the numerical homogenisation method, the anisotropy of the gyroid lattice types was found to differ greatly, as was the dependence of this anisotropy on the volume fraction. From compression testing of laser sintered polyamide PA2200 specimens, the honeycomb gyroid was found to possess extremely high anisotropy, with Emax*/Emin*, the ratio of the highest to the lowest direction-dependent modulus, ∼250 at low volume fraction. The stiffness and anisotropy of the honeycomb gyroid are compared to equivalent results from the square honeycomb, the closest analogue in the set of conventional honeycomb types. The honeycomb gyroid lattice exhibited novel deformation and post-yield stiffening under in-plane loading; it underwent reorientation into a second, stiffer geometry following plastic bending and contact of its cell walls. The unique deformation behaviour and extremely high anisotropy of the honeycomb gyroid provide strong motivation for further investigations into this new family of reduced periodicity TPMS-based honeycombs.
Highlights
Lattice structure performance has become an important element of design for additive manufacturing (DfAM)
The network and matrix gyroid lattices exhibited the fairly typical stress-strain curves of cellular structures composed of elastic–plastic material; they showed an initial elastic response followed by long plastic plateaux and eventual densification, where the lattice struts or walls are forced into direct contact
The deformation of the honeycomb gyroid lattice under [001] loading was similar, but is marked by a significant reduction in strength following the onset of plastic collapse at ε ≈ 0.05, and a further strength reduction at ε ≈ 0.2
Summary
Lattice structure performance has become an important element of design for additive manufacturing (DfAM). This is because AM lattices are an example of cellular structures, a class of materials known to possess high specific mechanical properties [1,2]. One overlooked aspect of lattice performance is mechanical anisotropy, which has been observed in materials made using a range of AM processes [16,17,18,19], and is often associated with the layer-by-layer fabrication process and part orientation during fabrication [20,21,22,23,24]. Cutolo et al [27] found that the mechanical properties and failure modes of the triply periodic minimal surface (TPMS) diamond lattice were significantly affected by the loading direction with respect to the lattice orientation
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