Using I, the stiffness of the SCS can be evaluated. The distance between the fulcrums l was 280 mm, and Young’s modulus of the paper E derived from the tensile test was 5.32 GPa (Figure S1). We fabricated three of each 12 types of SCSs as samples and conducted a total of 36 tests. The three test results obtained for each structure were averaged.
Figure 8b presents a sample result of a load-deflection curve obtained from a three-point bending test. In this section, an area of up to 10 mm of the entire 30 mm stroke was excerpted to better understand the analysis method. To derive the second area moment from the load-deflection curve, an explanation of the three stages (i)–(iii) shown in Figure 8b is presented. The load bar descends in the first stage; however, it is not in contact with the SCS (Figure 8b(i)). Then, as the load bar continues to descend, it contacts the SCS (Figure 8b(ii)). This point is regarded as the starting point of the three-point bending test, and is the origin of the load-deflection curve. In this study, the starting point was located within the stroke range of 0–5 mm for all structures tested; however, there was variation among the structures. Therefore, the test was conducted up to a stroke of 30 mm, and the deflection δ was unified in the range of 0–25 mm in the load-deflection curve. In the final stage, the mountain fold parts collapsed as the load was applied to the SCS until its peak was reached (Figure 8b(iii)). The stiffness k can be calculated from the slope of the initial stage in the range from the test start point to the peak. In this experiment, the increase in the deflection δ from 0 mm to 2 mm was defined as the slope of the initial stage.