Dynamic Deformation Behaviour of Chiral Auxetic Lattices at Low and High Strain-Rates

Abstract

The mechanical behaviour of three different auxetic cellular structures, hexa-chiral 2D, tetra-chiral 2D and tetra-chiral 3D, was experimentally investigated in this study. The structures were produced with the powder bed fusion method (PBF) from an austenitic stainless steel alloy. The fundamental material mechanical properties of the sample structures were determined with classic quasi-static compressive tests, where the deformation process was captured by a high-resolution digital camera. The Split Hopkinson Pressure Bar (SHPB) apparatus was used for dynamic impact testing at two impact velocities to study the strain-rate dependency of the structures. Two synchronised high-speed cameras were used to observe the impact tests. The captured images from both quasi-static and dynamic experiments were processed using a custom digital image correlation (DIC) algorithm to evaluate the displacement/strain fields and the Poisson’s ratio. Predominant auxetic behaviour was observed in all three structures throughout most of the deformation process both under quasi-static and impact loading regimes. The tetra-chiral 2D structure showed the most significant auxetic behaviour. Significant stress enhancement in all tested structures was observed in dynamic testing. The Poisson’s ratio strain-rate dependency was confirmed for all three auxetic structures.

Compressive Behaviour of Additively Manufactured Periodical Re-Entrant Tetrakaidecahedral Lattices at Low and High Strain-Rates

“…Auxetic behaviour of lattice structures is typically assessed by the evaluation of Poisson's ratio, which is supposed to gain negative values for auxetic materials [21,22]. However, this property was not evaluated in this study due to the geometry of the investigated specimens.…”

“…Regarding the impact energy absorption capability of auxetic structures, resulting from a stress enhancement occurring under dynamic loading conditions, a significant number of recent studies have focused on investigation into this property [17][18][19]. While some of the authors demonstrated the strain-rate sensitivity of auxetic structures [20][21][22], others indicated rather non-strain-rate-dependent behaviour for specific structures [23]. Thus, further investigation into the possible strain-rate sensitivity of auxetic lattices is still necessary.…”

Strain Rate-Dependent Compressive Properties of Bulk Cylindrical 3D-Printed Samples from 316L Stainless Steel

“…In this field, the strain rate-dependency of such porous solids is given by the architecture of the lattice and the base material used for its production. Here, we have already shown that a split Hopkinson pressure bar (SHPB) instrumented with a high-speed camera can be used to assess the dynamic compressive response of various auxetic lattices manufactured by LPBF from 316L powdered austenitic steel [ 15 , 16 , 17 ]. The SHPB apparatus has also been used to evaluate the influence of elevated and reduced temperatures on the deformation response of steel auxetic lattices [ 18 ].…”

2D Numerical Simulation of Auxetic Metamaterials Based on Force and Deformation Consistency

“…Materials 2022, 15, 4490 2 of 19 structures, metallic auxetic metamaterials exhibit increased yield strength, energy absorption [2], and energy dissipation [3], especially at high rates of strain. The extensive elastoplastic deformation of the internal structure yields a characteristic stress plateau at increasing strains and, therefore, enhanced energy absorption capabilities [4][5][6]. Predominant bending deformation, as seen in chiral structures specifically, provides an even higher energy absorption potential [7,8].…”