Origami-inspired metamaterials have attracted remarkable research attention over the past years owing to their mechanical properties. In particular, Miura-ori and its derivatives have been used to achieve some characteristics that are difficult to attain in conventional designs. Also, the recent development of novel functionally graded materials has exhibited several advantages such as energy absorption efficiency that make them attractive for several applications. Nevertheless, despite the extensive research on origami structure and metamaterials, two main issues have not been fully explored. First, the commonly used design approach that involves tessellating identical units is still far from achieving the desired control over the structural stiffness. Secondly, the development of mechanical metamaterials with three-dimensional programmable stiffness has not been achieved due to inherent challenges.
To this note, a team of researchers from Tianjin University: Professor Lin Yuan, Huaping Dai, Jichao Song, Associate Professor Jiayao Ma and Professor Yan Chen developed a novel approach for the design and analysis of an origami structure based on Miura-ori pattern under quasi-static compression. This was a continuation of their previous research in which they observed that unidirectional geometric variation could be used to realize an out-of-plane graded stiffness and enhanced energy absorption. The main objective of the current study was to achieve mechanical metamaterial capable of providing three-dimensional graded stiffness and high energy absorption efficiency. Their research work is currently published in the journal, Materials and Design.
In their new approach, two designs: two-dimensional graded (2DG) and three-dimensional graded (3DG) were proposed. The two-dimensional graded design comprised of several tessellation layers with geometric variation in the x-direction only. In contrast, 3DG involved geometric variation in both x- and z-directions. The experiment involved three main steps, namely, development of a fabrication process based on Miura-ori pattern, stamping of sheets and heat treatment to release the desired residual stresses. Finally, the results obtained with the proposed design were compared to those for the conventional design to validate its feasibility.
Results showed that both the designs were capable of generating periodically graded stiffness and superior energy absorption. The sensitivity studies on the effects of sector angle designs and side length revealed that both in-plane and out-of-plane graded stiffness could be achieved with appropriate geometric gradients. For 2DG, an increase in the interval of the sector angle resulted in better-graded stiffness response and enhanced energy absorption. On the other hand, a sensitivity study of 3DG focused on the effect of sector angle gradient on both x- and z-directions. A reduction in the stress level and energy absorption was observed when the 3DG was compressed in the z-direction while the opposite was noted when compressed in the x-direction. Compared to the conventional design, the proposed design could achieve an increase in the specific energy absorption by 129.68%.
In summary, the study assessed the behavior of a functionally graded origami structure subjected to quasi-static compression. The proposed origami-structure based on Miura-ori proved feasible for generating graded in-plane and out of plane stiffness and enhanced energy absorption by tuning the geometric variation. According to the authors, their approach offers a viable alternative for mechanical metamaterials and would be useful in engineering applications, especially those that require a non-uniform response.
Yuan, L., Dai, H., Song, J., Ma, J., & Chen, Y. (2020). The behavior of a functionally graded origami structure subjected to quasi-static compression. Materials & Design, 189, 108494.