A simulation approach to auxetic and non-auxetic behavior of 3D composites produced with multi-cell flat-knitted spacer fabrics

Abstract

The paper aims to simulate the auxetic and non-auxetic behavior of 3D composites reinforced with multi-cell flat-knitted spacer fabrics. Spacer weft knitted preforms were fabricated on an electronic flat knitting machine. 3D knitted composite samples with re-entrant, regular hexagonal and spear-head geometries, were prepared via vacuumed assisted resin transfer molding method. Using a cross-over geometrical model surrounded by a rigid resin cube, the composite unit-cell was designed in Abaqus software’s environment. Chamis micromechanical model was then used to determine the elastic constants of composite unit-cell. Meso-macro finite element analysis was used to simulate the response of the 3D composites to compressive loading. The results revealed that the Poisson’s ratio of re-entrant and hexagonal 3D knitted composite varied between −6 and −1 and 1.6 to 3.8, respectively. Also, the Poisson’s ratio of spear-head knitted composite was measured as zero. The proposed model was used to verify the predicted compressive behavior and Poisson’s ratio of the prepared composite samples. For hexagonal knitted composite, the proposed model demonstrated a good agreement with the experimental results. The Poisson’s ratio-strain curve obtained for 3D re-entrant knitted composite is highly compatible to those due to modelling results in strain range of about 5.8 to 22.5%. Also, for 3D spear-head knitted composite, the modelling results are not compatible to experimental method at strain values over 6%.