Behaviour of 3D printed re-entrant chiral auxetic (RCA) geometries under in-plane and out-of-plane loadings

Abstract

Three-dimensional printing of auxetic materials is an emerging research field due to their intriguing negative Poisson's ratio (NPR) behaviour which enables improved load resistance than conventional materials for various applications. In this research, re-entrant chiral auxetic (RCA) structures of three different geometries were printed using polylactic acid (PLA) filament. The PLA material was also characterised in compression and tension. In total, 27 RCA specimens of varied cell sizes were designed, printed and tested under in-plane tension and compression and out-of-plane bending loads. Digital image correlation method was employed to study the failure modes, displacement profiles, load-displacement curves and ductility characteristics. Results showed that the samples with the smallest cell sizes exhibited the highest resistance against compression, tension and out-of-plane loading. The elastic modulus and Poisson's ratio was also higher for these geometries with the maximum NPR of −9 in compression and −5 in tension. In comparison, the larger cell geometries due to wider gaps between the cells showed higher deformability which resulted in high energy absorption characteristics in compression and tension. Whereas in out-of-plane bending, all designed geometries, irrespective of cell sizes exhibited similar deformability with the maximum ductility obtained for the RCA structures made of smaller cells.

Experimental Analysis of the Relationship between Textile Structure, Tensile Strength and Comfort in 3D Printed Structured Fabrics

“…According to the literature consulted, studies have been found that evaluate mechanical properties in 3D printed auxetic materials, which have geometrical and structural characteristics belonging to the group of mesh structures, i.e., structures composed of elements joined without linkage. The literature reports the maximum tensile stress of 1.5 MPa using PLA printed chiral auxetic geometries of various sizes, obtaining strains in the range from 1.5% to 7.5%; however, this higher strain of 7.5% is obtained by reducing the stress, since the maximum stress of 0.58 MPa was obtained for this type of structure [ 26 ]. Another study in auxetic materials reports tensile stresses of 1.6 to 2.7 MPa with strains in the range from 0.5% to 9.2% [ 27 ].…”

“…Small-scale samples were 3D printed and tested under compression and tension to ascertain their strength and deformation characteristics. The re-entrant chiral cell size has been shown to affect the mechanical properties of the re-entrant chiral auxetics [ 26 ]. Similarly, several geometries of re-entrant chiral auxetic (RCA) structures created using 3D printing have been evaluated.…”

Flexural behaviour of cementitious composites embedded with 3D printed re-entrant chiral auxetic meshes

“…It is well known that the re-entrant structure of auxetic materials results in NPR due to which these materials contract in all directions while compressed or stretched in all directions when extension is applied along one of their axes. These re-entrant auxetic topologies can be developed through thermo-mechanical, braiding, injection moulding and additive manufacturing methods, which is why the auxetic materials are also termed as auxetic metamaterials [5]. These auxetic metamaterials have been found suitable to develop composites of enhanced mechanical resistance for stress resistance, vibration damping and shock energy absorption [6].…”

A finite element analysis of auxetic composite fabric with rotating square structure

“…Auxetic materials are known for their exceptional deformation behavior under external forces, demonstrating a transverse enlargement or contraction when stretched or compressed longitudinally. Since the report of auxetic foams in 1987, 1 auxetic materials have experienced tremendous development, covering a series of materials such as fibers, [2][3][4] yarns, [5][6][7] knitted fabrics, [8][9][10] woven fabrics, [11][12][13] composites, [14][15][16][17] and metamaterials, [18][19][20][21] etc. Due to the unique deformation behavior and energy absorption ability, auxetic materials have demonstrated great potential applications in perfect-fitting clothing, protective equipment, high-performance footwear, high-sensitivity transducers, soft robots, wearable devices, and even aircraft components, etc.…”