Elytra coupling of the ladybird Coccinella septempunctata functions as an energy absorber in intentional falls

Abstract

Some insects, such as bees, wasps, and bugs, have specialized coupling structures to synchronize the wing motions in flight. Some others, such as ladybirds, are equipped with coupling structures that work only at rest. By locking elytra into each other, such structures provide hindwings with a protective cover to prevent contamination. Here, we show that the coupling may play another significant role: contributing to energy absorption in falls, thereby protecting the abdomen against mechanical damage. In this combined experimental, numerical and theoretical study, we investigated free falls of ladybirds (Coccinella septempunctata), and discovered that upon collision to the ground, the coupling may fail and the elytra may unlock. This unlocking of the coupling increased the energy absorption by 33%, in comparison to when the elytra remain coupled. Using micro-computed tomography scanning, we developed comparative models that enabled us to simulate impact scenarios numerically. Our results showed that unlocking of the coupling, here called elytra splitting, reduces both the peak impact force and rebound velocity. We fabricated the insect-inspired coupling mechanism using 3D printing and demonstrated its application as a damage preventing on system for quadcopters in accidental collisions.

Performance of 3D-Printed Bionic Conch-Like Composite Plate under Low-Velocity Impact

“…The ratio of the energy release rate of the deflection crack on the left side of Equation (1) to the penetration crack was [ 35 ]: where D was a function related to the velocity, and D 1 and D 2 in the right-hand side of Equation (2) can be obtained by substituting and into D , respectively. and are the shear and expansion wave velocities of the matrix material, respectively.…”

“…The ratio on the right side of the Equation (1) was set to 1.5 [ 32 ] to determine the angle threshold of crack deflection or penetration. When the normalized energy release rate was greater than this value, the crack would traverse the interface, and vice versa, the crack was deflected into the interface [ 35 ].…”

“…Therefore, as shown in Figure 19 , a horizontal line with a normalized energy release rate of 1.5 was drawn, and the intersection point with the curve corresponded to about 0.87 rad (50°). Therefore, for the stiff/soft combination interface, according to Equation (2), it was considered that when was less than 50°, the crack would deflect into the interface, whereas the crack would propagate through the interface for > 50° [ 35 ]. Accordingly, the soft material determined the failure mode of the structure to a certain extent.…”

“…Here, the multilayer unit cell was repeated more than 15 times in each in-plane direction to eliminate the size effects and better capture the global anti-impact performance [32]. The Bio-B (Figure 2) was a composite plate, characterized with the tenon inserted in the mortise, as reported by Rivera et al [34] and Zhang et al [35]. Figure 4b showed the typical unit cell of Bio-B, where the 0 • layer was designed in the direction of 0 • section perpendicular to the suture line of carapace, rotated 90 • clockwise for 90 • layer, and rotated 180 • clockwise for 180 • layer.…”

“…The ratio of the energy release rate of the deflection crack on the left side of Equation (1) to the penetration crack was [35]: Linear elastic fracture mechanics were adopted to define the conditions under which fracture occurs. The crack strength factor or energy release rate was less than the fracture toughness of the given material, and the structure would not fracture [36].…”