Moisture, Anisotropy, Stress State, and Strain Rate Effects on Bighorn Sheep Horn Keratin Mechanical Properties

Johnson, K. L., Trim, M. W., Francis, D.K., Whittington, W. R., Miller, J. A., Bennett, C. E., & Horstemeyer, M. (2017). Moisture, Anisotropy, Stress State, and Strain Rate Effects on Bighorn Sheep Horn Keratin Mechanical Properties. Acta biomaterialia. Elsevier. 48, 300-308. DOI:10.1016/j.actbio.2016.10.033.

Abstract

This paper investigates the effects of moisture, anisotropy, stress state, and strain rate on the mechanical properties of the bighorn sheep (Ovis Canadensis) horn keratin. The horns consist of fibrous keratin tubules extending along the length of the horn and are contained within an amorphous keratin matrix. Samples were tested in the rehydrated (35 wt% water) and ambient dry (10 wt% water) conditions along the longitudinal and radial directions under tension and compression. Increased moisture content was found to increase ductility and decrease strength, as well as alter the stress state dependent nature of the material. The horn keratin demonstrates a significant strain rate dependence in both tension and compression, and also showed increased energy absorption in the hydrated condition at high strain rates when compared to quasi-static data, with increases of 114% in tension and 192% in compression. Compressive failure occurred by lamellar buckling in the longitudinal orientation followed by shear delamination. Tensile failure in the longitudinal orientation occurred by lamellar delamination combined with tubule pullout and fracture. The structure-property relationships quantified here for bighorn sheep horn keratin can be used to help validate finite element simulations of ram’s impacting each other as well as being useful for other analysis regarding horn keratin on other animals.