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

Anja Mauko,Zoran Ren,Petr Zlámal,Petr Koudelka,Jan Falta,Michaela Neuhäuserová,Tomáš Fíla,Václav Rada,Matej Vesenjak,Ondřej Jiroušek

doi:10.3390/met11010052

Anja Mauko, Zoran Ren + Show 8 more

Open Access

https://doi.org/10.3390/met11010052

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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.

Highlights

There is an ever-increasing interest in the mechanical characterisation of cellular structures [1,2,3] for their use in modern, low-weight engineering structures
The compression deformation process of chiral auxetic structures can be characterised by three main regions [6,18,29]
The validity of digital image correlation (DIC) results was confirmed by comparing the strain-gauges results and calculation of the mean correlation coefficient, which was higher than 96% in all cases

Summary

Introduction

There is an ever-increasing interest in the mechanical characterisation of cellular structures [1,2,3] for their use in modern, low-weight engineering structures. Cellular materials usually have increased mechanical energy absorption properties due to extensive elastoplastic deformation of their internal structure, which is often characterised by long stress plateau at increasing strain [14,15]. Auxetic chiral cellular structures can exhibit even higher energy absorption due to predominant ligament bending deformation [12,16]. The response of the cellular structures can be strain-rate dependent, which necessitates the characterisation of their dynamic properties. Previous studies have shown a non-strain-rate dependency of some chiral structures with low stiffness [17], while the other study demonstrated stress enhancement of auxetic re-entrant honeycomb

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