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M. Priewasser:
"Experimental and Computational Study of the Cheliceral Fang of Cupiennius salei";
Betreuer/in(nen): F. G. Rammerstorfer, D. H. Pahr; Institut für Leichtbau und Struktur-Biomechanik, TU Wien, 2012.

Cuticle, a combination of chitin and proteins, is one of the most flexible and versatile among nature´s structural materials. The cuticular exoskeleton of arthropods (animals with exoskeleton and jointed appendages, including insects, arachnids and crustceans) has to be hard or soft, stiff or compliant, sometimes even in adjacent areas, depending on the biological requirements. This multifunctionality is what makes arthropod cuticle such an interesting object for material research.

I examined the structural characteristics of the chelicerae, the biting apparatus of the spider Cupiennius salei, and its fang in detail using various physical methods. The original idea behind this thesis has been a description and modelling of the microstructure of this material and its relation to its behavior under biologically relevant loads. It has been shown that a simple macroscopic and isotropic model sufficient describes many qualities of the fang like the minimization of local stress concentrations.

The success of the spider's bite relies on a variety of qualities its fangs have to have. These must be able to penetrate another cuticular shell without being damaged, which requires a degree of hardening of the fang that can hardly be achieved by sclerotization alone. It was shown that a zinc-fortificat ion of the tip of the fang results in significantly increased material properties, e.g. a maximum elastic modulus of 23GPa, which is remarkable for a cuticular material. The velocity of the fang's movement has been measured using a high-speed camera setup, while the maximum occurring force under natural loading conditions was obtained by strain gauge measurements. The typical arachnid layering of the cuticle including a mesocuticle was shown using Mallory´s triple stain method.

According to finite element analysis the distribution of elastic modulus and hardness across the fang has proven to approximate a fully stressed design. It exhibits a topologically optimized structure comparable to the tiger claw, which reduces the occurring stress concentrations to a minimum. The distribution of material properties is correlated with the stress distribution along the structure, at the same time a high resistance to fracture has been recorded. The outstanding mechanical properties of the load-bearing tip in combination with the quick movement and the curvature of the fang make it a precise, tough and powerful hunting device.