Additive manufacturing of re-entrant structures: Well-tailored structures, unique properties, modelling approaches and real applications
Wendy Triadji Nugroho, Yu Dong, Alokesh Pramanik, Chithirai Pon Selvan, Zhixiao Zhang, Seeram Ramakrishna
Abstract
Re-entrant (RE) structures arise from unique construction enabling them to yield a negative Poisson’s ratio (NPR) under tension or compression loading, which is required in various applications such as pressure garments for hypertrophic scar treatment, impact absorbers for automobiles, wing fillers for aircrafts and strain sensors. Conventional manufacturing techniques, namely extrusion and injection moulding, cannot be applied to fabricate RE structures since they contain lattice structures typically with complex geometries. This issue has been tackled by additive manufacturing (AM), which enables the creation of RE structures from various materials including polymers and metals. This paper provides a comprehensive review on structural design, manufacturing techniques and unique properties that are crucial for sophisticated development of novel metamaterials. Modelling approaches including an optimisation method to obtain the best structure and desired properties are also discussed. Finally, real applications of RE structures in medical engineering, automobiles, aerospace and strain sensing are reported, along with a summary and future challenges for these unique structures.