Abstract
Deer antlers have a primary function in intraspecific combat and have been designed for sustaining high impact loading and bending moment without fracture. Antlers have a similar microstructure as mammalian long bones, composed primarily of type-I collagen fibrils and carbonated apatite crystals, arranged in osteons in the compact bone and a lamellar structure in the cancellous bone. Antlers have much higher work to fracture and fracture toughness compare to other mammalian bones. It is important to understand the fracture behavior and toughening mechanisms of antler at high strain rate. In this study, quasi-static and dynamic (split-Hopkinson bar) bending tests (ASTM C1421) were performed on single-notched North American elk (Cervus canadensis) antler and bovine femur samples to measure the fracture toughness. Tests were conducted in the transverse (breaking) and the longitudinal (splitting) directions in both dry and re-hydrated conditions to study the effects of fiber orientation and hydration. Fracture toughness results in the transverse direction were much higher than that in the longitudinal direction and increased with degree of hydration for both antler and bovine femur. The fracture toughness of elk antler is ~ 50% higher than that of bovine femur. The double-notched samples were prepared and tested in quasi-static and dynamic modes. Fracture paths were then examined using scanning electron microscopy. Toughening mechanisms, including crack deflection by osteons, uncracked ligament bridging, and microcracks formation, were observed and discussed. Comparisons between antler and bone were made. This research is supported by the National Science Foundation grant DMR 0510138.