The sandwich structure consists of two-face sheets sandwiching the core material. A honeycomb core is widely used as one of the core materials \cite{he2019effect}. However, the manufacture of honeycomb cores is complex and costly. Therefore, extensive research has been conducted on honeycomb cores based on the origami technique \cite{saito2014manufacture}. In this regard, the origami technique enables the manufacturing of honeycomb cores without considerable processing. Folded cores based on origami are currently developed as alternative core materials. Examples include Miura-ori, which is commonly used to shape folded cores \cite{miura2009science}, and creases similar to Ron Resch patterns \cite{resch1968self}. Folded cores can be manufactured from various sheet materials by a simple process and tailored into various shapes that meet specific functional requirements \cite{zhou2017thermal}. Thus, the origami technique has been applied to core materials for sandwich structures.
On the contrary, corrugated cores are stiff, perpendicular to the corrugation, flexible in the parallel direction, and the structures exhibit anisotropy \cite{yokozeki2006mechanical}. This property is leveraged in load-bearing applications such as corrugated cardboards, roofs, and walls, in addition to morphing wings \cite{dayyani2015mechanics}. In contrast, the folded core is stiff in the perpendicular and parallel directions. The stiff direction of a corrugated core with linear creases is stiffer than that of the folded core by a factor greater than 75 \cite{woodruff2021curved} \cite{gilewski2014comparativea} . The closed-cell structures lead to problems of air and humidity retention, which can increase the total weight and degrade core properties \cite{katzman2008moisture}. Conversely, corrugated cores have open channels in one direction, which minimizes these problems.
Corrugated, honeycomb, and folded cores can be readily fabricated using the origami technique. Origami structures can be fabricated by manual folding or by using robotic devices \cite{balkcom2008robotic} . However, these methods are not efficient for mass production at small or large scales and for remote applications. Mass production can be realized using manufacturing equipment; however, large machines require space allocation and initial investment, and the compression process consumes large amounts of energy. Moreover, it compromises the specialized feature of creating structures with desired mechanical properties within a short time.
To overcome these shortcomings, self-folding techniques have been studied for the automatic fabrication of origami structures \cite{peraza2014origami}. Self-folding generally uses smart materials that respond to external stimuli, such as shape memory alloy (SMA) \cite{peraza2013design}, shape memory polymer (SMP) \cite{ge2016multimaterial}, and hydrogel\cite{an2016predicting}. The crease pattern is pre-defined for these smart materials, and the application of heat or light triggers automatic folding. Given that external stimuli automatically form the origami structure, rapid manufacture and autonomous assembly at remote sites can be achieved without human intervention. Moreover, given that 3D structures can be constructed by changing the 2D crease patterns, a variety of origami structures can be created. Liu et al. proposed self-folding SMP sheets using light. They defined crease patterns to fold SMP sheets by 90° and fabricated a rectangular shape. By changing the crease patterns, the fold angle was adjusted to 60°, and a tetrahedron structure was formed \cite{liu2012self}.
Besides the origami technique, core materials for sandwich structures are manufactured by compression molding \cite{rejab2013mechanical}, hot-press molding \cite{du2018fabrication}, and embossing with rollers, among other methods \cite{heimbs2013foldcore}. However, these manufacturing methods require molds and rollers for each design requirement, which increases the cost, time, and energy required to form the structure. Therefore, core materials fabricated with 3D printing technology, which can be used to design complex structures at low cost, have been developed\cite{li2017bending}\cite{goh2021quasi}\cite{meng2020inverse}. Furthermore, the development of core sandwich structures using smart active materials, which are referred to as smart cores, was investigated \cite{feng2020creative}. Tolley et al. fabricated a self-folding origami consisting of a three-layer shape memory composite with SMP as the intermediate layer to form a Miura-ori structure \cite{tolley2014self}. Evans et al. fabricated a micro-scale self-folding origami structure consisting of three layers of photo-cross-linkable copolymers with a thermosensitive hydrogel as the intermediate layer. They realized a Miura-ori structure by controlling the fold angle \cite{na2015programming}. However, limited studies were conducted on the mechanical properties of the smart core sandwich structures. Hubbard et al. fabricated corrugated structures with rectangular, square, trapezoidal, and triangular waveforms using stimuli-responsive thermoplastic sheets \cite{hubbard2021stiff}. They conducted compression and tensile tests by varying the wavenumbers of the fabricated corrugated structures, and investigated the effects of the wavenumbers on the compressive and tensile properties of the structures. However, mechanical properties were not investigated with respect to the amplitude and wavelength, which are important structural parameters of the corrugated structure when using the tailor-made feature of the self-folding methods. By investigating the mechanical properties with respect to the amplitude and wavelength, the desired mechanical properties can be imparted to the structure and specialized characteristics can be realized. Therefore, we conducted experiments to investigate the mechanical properties of corrugated structures with respect to the amplitude and half-wavelength, which are the two most important structural parameters of the corrugated structure.