Mantis shrimp are aggressive marine crustaceans well known for their rapid and powerful hunting strategies. Less well known, however, is the ability of some species of mantis shrimp to defend themselves from the repeated blows of conspecifics during ritualized fighting using a shield-like segment of abdominal armor called the telson. Multiscale structure-mechanical property relationships of this damage-tolerant biological composite is examined in order to reveal strategies that nature uses for resisting failure from repeated high-energy impacts. The telson structures of the smashingtype species, Odontodactylus scyllarus, and the less aggressive spearing-type species, Lysiosquillina maculata, are compared in order to better understand the ecological pressures driving the formation and use of the telson as a biological shield. A higher bulk compressive stiffness is identified within the smasher telson, which is attributed to its concave macromorphology, thicker cuticle, and higher degree of mineralization within its exocuticle. The presence of ridges at the dorsal surface suggests a role in imparting compliance for energy absorption. Fracture analysis identifies an enhanced toughening mechanism of crack twisting within the smasher telson, attributed to its well-defined pitch-graded helicoidal fibrous micro-architecture. Such findings may prove useful for the design of lightweight composite materials with potential flexibility and improved damage tolerance.
Beetles typically use their protective wing coverings or elytra to shield their membranous hindwings from the environment. Elytra in some terrestrial species have evolved a greater protective role capable of shielding the organism from powerful antagonistic predators. The structure-function relationships of these biological composites identify how architectural and chemical variations of the cuticle are tuned to create light-weight, impact resistant composites. Specifically, the elytral structures of a tree dwelling beetle capable of flight, Trypoxylus dichotomus, and a terrestrial beetle incapable of flight, Phloeodes diabolicus, are compared to understand how their varied environmental needs forged the elytra to facilitate fight or resist fatal predator strikes. Mechanical and microstructural analysis reveals P. diabolicus has a harder, stiffer elytra that incorporate through-thickness fibers to resist greater mechanical stresses imposed by bending and puncture. Conversely, the elytra of T. dichotomus have a compliant structure with large voids that facilitates localized deformation. Variations in flexural strength and puncture resistance remain attributed to P. diabolicus possessing a thicker cuticle with a greater degree of cross-linking and an increased amount of endocuticular layers. These findings may provide useful insight into the design and manufacturing of composite materials for use in light-weight or energy-absorbing applications.
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