Mechanical characterization of compact region of red deer antler under static and dynamic loadings

In this study, static three-point bending, tensile, compression (Brazilian) and dynamic (Split Hopkinson Pressure Bar test device) compression tests were performed on compact regions of Cervus Elaphus Red Deer antler having superior mechanical properties. In static three-point bending experiments, change in mechanical strength of deer antlers with age was observed. The fracture surfaces and crack propagation of the damaged samples were captured by Scanning Electron Microscopy. Furthermore, the effects of the dimensions of the cross-linking fibers connecting the osteons on the mechanical strength were investigated. EDS analyses were performed on five different locations of these damaged cross-linked fibers. Some toxic elements, such as lead, mercury, and cadmium, leading to high brittleness were detected on the cracked regions of the fibers. In the static tensile tests, the tensile strength and elastic modulus were found to be 178 - 221 MPa and 13 - 22 GPa, respectively. Static tensile tests were also verified with an analytical model considering effects of mineral and collagen content in the structure on mechanical strength. From quasi-static Brazilian tests, it was observed that the compact region of the deer antlers has an anisotropic structure and has an average indirect tensile strength i.e., 43.8 MPa in the longitudinal direction, 44.5 MPa in the transverse direction, and 31.5 MPa in the radial direction. Furthermore, the mechanical strength is approximately two times higher in dynamic loading compared to static loading (average 83.2 MPa in the longitudinal direction), that is, the mechanical strength depends on the loading rate of the material. The fracture strength of the samples tested by this method was also investigated by the Weibull survival probability, and the samples in the transverse direction exhibited more brittle fracture behavior than in the longitudinal direction. Finally, in the dynamic tests, a global crushing occurred in loadings transverse to osteon directions while a longitudinal fracture conforming to the Brazilian method was observed. This global crushing is thought to be due to the denaturation of collagen fibrils and the weakening of adhesion between collagen particles at high strain rate tests.