A review on auxetic structures: Applications, properties, classifications, finite element analysis, manufacturing methods, and selective laser melting process parameters

• Auxetic structures attract attention due to their extraordinary properties. • Auxetic structures are used in aerospace, defense, automotive, biomedical, and sports. • Selective laser melting technology produces complex metallic auxetic structures. • Future research is needed on the design and simulation of novel auxetic structures. • Research needs to focus on auxetic structures for elevated-temperature applications. Auxetic structures are a novel class of materials characterized by their unique internal geometric configuration at the micro/nano scale, resulting in unusual mechanical behavior. Specifically, auxetic structures exhibit transverse expansion under axial tension and transverse contraction under axial compression, which behavior called Negative Poisson's ratio (NPR). This manuscript focuses on the properties and classification based on the deformation mechanism of auxetic structures. Auxetic structures are mainly classified into re-entrant structures, rotational structures, chiral structures, and a lot of novel auxetic structures created by researchers. This article explores the finite element analysis (FEA) studies, as well as various manufacturing techniques of auxetic structures. In recent years, additive manufacturing (AM) has emerged as a promising approach for producing auxetic components. Among AM techniques, selective laser melting (SLM) or laser powder bed fusion (LPBF) is capable of manufacturing lightweight, strong, and complex metallic auxetic structures directly from computer-aided design (CAD) models by fusing metal powder layer upon layer using a laser energy source. This article discusses key SLM process parameters, including scanning speed, laser power, hatch spacing, and layer thickness. The SLM process parameters of auxetic structures have been discussed in the current review for the first time, as no prior researcher has addressed this subject. Finally, challenges and future perspectives related to SLM-based fabrication of auxetic structures are also addressed.