Abstract
We present in this work the manufacturing, modelling and testing of dome-shaped cellular structures with auxetic (negative Poisson's ratio) behaviour. The auxetic configurations allow the creation of structures with synclastic (i.e. dome-shaped) curvatures, and this feature is used to evaluate the performance of cellular metamaterials under quasi-static indentation conditions. We consider here different cellular geometries (re-entrant, arrow-head, tri-chiral, hexagonal) and the implications of their manufacturing using 3D printing techniques with PLA material. The dome-shaped configurations are modelled using full-scale non-linear explicit FE models that represent both the geometry and approximate constitutive models of the PLA filament material derived from tensile tests on dogbone specimens. The cellular metamaterials samples are subjected to indentation tests, with maps of strains obtained through DIC measurements. The correlation between experimental and numerical simulations is good, and shows the peculiar indentation behaviour of these cellular structures. We also perform a comparative analysis by simulation of the force/displacement, strain and fracture history during quasi-static loading, and discuss the performance of the different cellular topologies for these dome-shape metamaterial designs.
Highlights
A mechanical metamaterial is a multiscale system of materials with engineered mechanical properties that can vary dramatically from those of the base material
Lattice structures are a popular example of mechanical metamaterials because of their high strength to density ratio, compared to traditional structural materials (Ashby, 2006)
A subset of mechanical metamaterials is represented by auxetics
Summary
A mechanical metamaterial is a multiscale system of materials with engineered mechanical properties that can vary dramatically from those of the base material. Lattice structures are a popular example of mechanical metamaterials because of their high strength to density ratio, compared to traditional structural materials (Ashby, 2006). Another important aspect of lattice structures is their tailorable mechanical response, both at global and hierarchical scale (Sun and Pugno, 2013). A subset of mechanical metamaterials is represented by auxetics. While conventional cellular foams and rubber-like materials have a Poisson’s ratio varying from ν ≈ 0.5 (incompressible) to ν = 0 (e.g., cork) with decreasing density, auxetics possess instead a negative Poisson’s ratio. The auxetic material will shrink under compression. Perforated auxetic composite plates have been used in a hybrid flexible cushioning support for multiple sclerosis patients (Mohanraj et al, 2016)
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