Abstract
The design and production of multifunctional materials possessing tailored mechanical properties and specialized characteristics is a major theme in modern materials science, particularly for implementation in high-end applications in the biomedical and electronics industry. In this work, a number of metamaterials with perforated architectures possessing the ability to exhibit a plethora of 2D auxetic responses with negative Poisson's ratios ranging from quasi-zero to large negative values (lower than −3.5), stiffnesses, stretchability and surface coverage properties were manufactured. These systems were produced through the introduction of microstructural cuts in a rubber sheet using direct laser cutting, and analysed using a dual approach involving experimental tests and Finite Element Analysis. In addition to examining the mechanical properties of the perforated metamaterials, the influence of edge effects and material thickness on the deformation behaviour of these systems were investigated, with re-entrant systems shown to possess anomalous deformation profiles which are heavily dominated by the boundary regions. These findings highlight the effectiveness of this method for the fabrication of auxetic metamaterial sheets as well as the large variety of mechanical properties, deformation mechanisms and load responses which may be obtained through what may be effectively described as simply the introduction of patterned cuts in a thin sheet.
Highlights
Auxetic mechanical metamaterials are systems which possess the unusual property of having a negative Poisson’s ratio[1]
We explore the effectiveness and viability of using direct laser cutting as a method for the design of thin sheetlike 2D perforated auxetic metamaterials
This behaviour was extremely surprising and is probably the result of the decreasing Young’s modulus of this geometry upon increasing strain (see Figure 7b(ii) and Supplementary Information Section 6). This deformation pattern suggests that simulating such systems in the form of periodic unit cells will only give an indication of the localized deformation of the repeating unit within the deformation ‘vein’ rather than a mean picture of the overall deformation. These results indicate that by analysing the stress-strain plots obtained from simulations using periodic boundary conditions one may possibly be able to predict whether a finite system behaves in this manner or else in the ‘normal’ form such as that shown for the other architectures, where the Young’s modulus increases upon increasing strain
Summary
Auxetic mechanical metamaterials are systems which possess the unusual property of having a negative Poisson’s ratio[1]. A number of rapid prototyping techniques have been suggested and implemented for the manufacture of auxetic metamaterials ranging from additive manufacturing methods such as extrusion-based and stereolithography 3D printing [13][14][15][16][17], to molding[18] and laser lithography[19][20][21] These methods allow for the production of mechanical metamaterials on a wide range of scales with their suitability for the specific fabrication of different metamaterial types depends on a variety of factors such as desired resolution, material type, scale, geometric characteristics and required properties. This solution is inadmissible for thin sheet-like systems requiring large in-plane auxetic behaviour and in these cases it is imperative to counteract this problem through smart design of the metamaterial system
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