Compressive and flexural behaviour of engineered cementitious composites based auxetic structures: An experimental and numerical study

This paper presents a systematic experimental and numerical study on the compressive and flexural behaviour of engineered cementitious composites (ECC) based auxetic structures fabricated through 3D printing. ECC was adopted to tackle the cracking problem and inherent brittleness of plain concrete. Uniaxial compressive and flexural tests on 2D re-entrant, cross-chiral and buckling-induced auxetic structures were conducted to examine the effect of auxetic type on the mechanical response of ECC based auxetics. Results indicate that the studied auxetics exhibit obvious auxetic behaviour under compressive loading, while no obvious auxetic behaviour occur on these auxetics under flexural loading. The compressive strength of buckling-induced auxetic structure is 5.1 MPa that is about 750% and 264% higher than that of re-entrant and cross-chiral structures, respectively. The flexural strength of buckling-induced auxetic structure is around and 163% higher than that of re-entrant and cross-chiral structures, respectively. The cross-section uniformity of buckling-induced auxetic structure was much more superior to that of other structures, leading to stronger shear resistance compared with other auxetic structures in four-point flexural test. The parametric study indicates that with the increase of relative density from 32.5% to 52.5%, the compressive peak stress and plateau stress of re-entrant, cross-chiral and buckling-induced ECC at the same strain both go up. The buckling-induced auxetic structures possess higher compressive strength, energy absorption capacity, flexural strength and toughness compared with equivalent re-entrant and cross-chiral structures. Overall, it is feasible to incorporate ECC material into auxetic structures.