Abstracts

This thesis investigates the microstructure and mechanical properties of horns from the bighorn sheep, domestic sheep, mountain goat and pronghorn, which are all composed of keratin. Microstructural similarity is found where disk-shaped keratin cells attach edge-to-edge along the tubule (medullary cavity) growth direction (longitudinal direction) forming a lamella, and the lamellae are layered face-to-face along the impact direction (radial direction), and forming a wavy pattern surrounding the tubules. Differences include the number and shape of the tubules, lamellae aligned direction and shape of keratin cells. Water absorption test reveals that the pronghorn horn has the largest water absorbing ability due to the presence of nanopores in the keratin cells. Stress direction and hydration dependent anisotropic mechanical behavior is found as common characteristics of horns. The differences in the mechanical properties between horns of different species can be explained as facilitating their different fighting behaviors. Fracture surface examination proves similar deformation and fracture mechanisms, with microbuckling and delamination mechanism under compressive stress and fiber breakage mechanism under tensile stress, while crack length and fiber-to-fiber adhesion affect strength of the horns.