The effects of water and microstructure on the mechanical properties of bighorn sheep (Ovis canadensis) horn keratin

The function of the bighorn sheep horn prompted quantification of the various parametric effects important to the microstructure and mechanical property relationships of this horn. These parameters included analysis of the stress-state dependence with the horn keratin tested under tension and compression, the anisotropy of the material structure and mechanical behavior, the spatial location along the horn, and the wet-dry horn behavior. The mechanical properties of interest were the elastic moduli, yield strength, ultimate strength, failure strain and hardness. The results showed that water has a more significant effect on the mechanical behavior of ram horn more than the anisotropy, location along the horn and the type of loading state. All of these parametric effects showed that the horn microstructure and mechanical properties were similar to those of long-fiber composites. In the ambient dry condition (10 wt.% water), the longitudinal elastic modulus, yield strength and failure strain were measured to be 4.0 G Pa, 62 MPa and 4%, respectively, and the transverse elastic modulus, yield strength and failure strain were 2.9 GPa, 37 MPa and 2%, respectively. In the wet condition (35 wt.% water), horn behaves more like an isotropic material; the elastic modulus, yield strength and failure strain were determined to be 0.6G Pa, 10 MPa and 60%, respectively.