PSI - Issue 56

Vasilica Ioana Cimpoies et al. / Procedia Structural Integrity 56 (2024) 49–57 Author name / Structural Integrity Procedia 00 (2019) 000–000

50

2

1. Introduction Metamaterials represent a class of materials characterized by the incorporation of structural components that induce alterations in the inherent physical characteristics of the constituent base material. Mechanical metamaterials possess unique and exceptional properties that arise from the relationship between their structural framework and mechanical properties and are able to modify their response to physical phenomena (Findeisen, 2017). These atypical properties may include negative stiffness, compressibility, thermal expansion, and auxeticity, that are rarely seen in nature (Fu, 2018). These characteristics result in advanced functionalities, thus making these materials ideal for a range of specialized applications. The most well-known group of mechanical metamaterials are auxetic systems, which include various geometries that have been established for authenticity (Mousanezhad, 2016). These comprise of re-entrant structure, rotating rigid unit systems, chiral honeycombs, origami/folding patterns, dilatational, and helical systems and have been replicated or detected in sizes that range from the nanoscale to the macroscale (Mizzi, 2021). By focusing on a particular direction of metamaterials inspired by art, in the last 10 years, has been developed an entire family of metamaterials originating from origami and kirigami (Tachi, 2013). These metamaterials are using the principals of the Japanese art of paper folding and are highly customizable. Their mechanical properties can be altered by changing the geometry and layout of the folded patterns. Researchers have developed a range of groundbreaking and practical origami-based metamaterials, including notable examples such as Ron Resch patterns, Miura-ori structures, and transformable origami metamaterials. (Kshad, 2018) (Zadpoor, 2016). These metamaterials have found applications in robotics, nano and micro mechanisms, aerospace, furniture, and medical devices (Tachi, 2013). In the context of paper quilling, this area remains relatively underexplored, offering a promising avenue for the development of self-sustaining structures. Paper quilling constitutes an artistic practice wherein strips of paper are meticulously shaped and adhered together to craft ornamental patterns. This process involves the rolling, looping, curling, twisting, and other forms of manipulation of paper strips to fashion various shapes that serve as the building blocks for decorative elements in greeting cards, artwork, containers, as well as in the creation of models, jewelry, figurines, and 3D miniatures, among other applications. Current research employs paper quilling as a source of inspiration for the development of novel metamaterials. The principal objective of this investigation is to gain insights into the mechanical response of a metamaterial inspired by quilling, particularly one characterized by nonlinear behaviour under deformation loads. The initial section of this paper introduces the structural configuration under scrutiny, elucidating its geometric parameters. A 3D-printed test specimen was employed to subject it to compressive forces while capturing the corresponding force-displacement relationship. The analysis of the inner structural displacements within the metamaterial was conducted using the optical technique known as Digital Image Correlation. Comparative assessments of both experimental datasets were performed in relation to numerical simulations executed via the Finite Element Method. The results convergence and the mechanical stiffness of the structure are presented in the subsequent sections, encompassing the results and conclusions. 2. Materials and Methods 2.1. Design Steps of the Metamaterial The creation of the metamaterial started from a conceptual design of paper, which was shaped using quilling techniques to create various forms, culminating in interconnected cellular structures comprised of linked spirals. Quilling as a modeling method frequently entails the use of curved, twisted, and spiral shapes, imbuing the model with a fluid quality and enabling the generation of limitless, repetitive patterns. The second step was the selection of the most suitable model, identified as a geometric configuration consisting of four-armed spirals, which were consistently arranged along both axes (XY). This arrangement led to the formation of layered metamaterial structures. The third stage of the process entailed the digital transposition of the model. The model was simplified and converted into a stylized digital format to facilitate its compatibility with 3D printing technology, resulting in their final cellular structure. Cellular materials are distinguished for their intrinsic lightweight properties and their exceptional ability to attenuate external forces. Within the domain of cellular materials, those exhibiting periodic