The objective of this paper is to unveil a novel damping mechanism exhibited by 3D woven lattice materials (3DW), with emphasis on response to high-frequency excitations. Conventional bulk damping materials, such as rubber, exhibit relatively low stiffness, while stiff metals and ceramics typically have negligible damping. Here we demonstrate that high damping and structural stiffness can be simultaneously achieved in 3D woven lattice materials by brazing only select lattice joints, resulting in a load-bearing lattice frame intertwined with free, ‘floating’ lattice members to generate damping. The produced material samples are comparable to polymers in terms of damping coefficient, but are porous and have much higher maximum use temperature. We shed light on a novel damping mechanism enabled by an interplay between the forcing frequency imposed onto a load-bearing lattice frame and the motion of the embedded, free-moving lattice members. This novel class of damping metamaterials has potential use in a broad range of weight sensitive applications that require vibration attenuation at high frequencies.
We have created a new architected material, which is both highly deformable and ultra‐resistant to dynamic point loads. The bio-inspired metallic cellular structure (with an internal grid of large ceramic segments) is non-cuttable by an angle grinder and a power drill, and it has only 15% steel density. Our architecture derives its extreme hardness from the local resonance between the embedded ceramics in a flexible cellular matrix and the attacking tool, which produces high-frequency vibrations at the interface. The incomplete consolidation of the ceramic grains during the manufacturing also promoted fragmentation of the ceramic spheres into micron-size particulate matter, which provided an abrasive interface with increasing resistance at higher loading rates. The contrast between the ceramic segments and cellular material was also effective against a waterjet cutter because the convex geometry of the ceramic spheres widened the waterjet and reduced its velocity by two orders of magnitude. Shifting the design paradigm from static resistance to dynamic interactions between the material phases and the applied load could inspire novel, metamorphic materials with pre-programmed mechanisms across different length scales.
Materials with periodic architectures exhibit many beneficial characteristics such as high specific stiffness thanks to the material placement along the stress paths and the nano-scale strength amplification achieved through the use of hierarchical architectures. Recently, the porosity of architectured materials was leveraged to increase the efficiency of compact heat exchangers, and their internal aerodynamics was studied. However, their performance on external aerodynamics applications is generally assumed to be detrimental. Here, we demonstrate that exposing 3D lattice material to the external flow reduced the drag of a circular cylinder when placed at carefully selected angular locations. We tested two configurations with the lattice material installed at the windward and leeward regions. On the one hand, the windward configuration showed a strong Re dependency, with a drag reduction of up to 45% at Re=11E4. On the other hand, the lattice material in the leeward region reduced the drag by 25% with weak Re dependency. Alterations of the lattice material topology had a noticeable effect on the drag reduction in both cases. Adding aerodynamic features to the already 1
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
There has been much recent interest in the combined structural and aerodynamic properties of porous metal foams, but there does not yet appear to be a consensus on the aerodynamic behaviour of these foam materials. A comprehensive analytical and experimental study with special attention to scaling was carried out in order to examine the flow around cylinders coated with porous metal foam and characterize the effects upon the mechanisms governing shear layer separation, vortex shedding and wake formation. Results have yielded a correlation between the distance separating the detaching shear layers and the vorticity losses in the near-wake. It seems that it is the coating configuration, rather than geometry, that influences vortex shedding, and therefore foams affect the flow in a similar way as shrouds or bleeding systems.
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