Experimental study on the mechanical properties of the horn sheaths from cattle.

Bovine horn is composed of a sheath of keratin overlying a bony core. Previous studies of the bovine horn sheath have focused mainly on its morphology and compositions. In the present paper, we performed a series of uniaxial tension, three-point bending, and fracture tests to investigate the structural and mechanical properties of the horn sheaths from subadult cattle, Bos taurus. The effects of hydration on the mechanical properties were examined and their variations along the longitudinal direction of the horn sheath were addressed. Scanning electron microscopy of the fracture surfaces showed that the horn sheath has a layered structure and, more interestingly, the laminae have a rippled appearance. The Young's modulus and tensile strength increase from 850 MPa and 40 MPa at 19% water content to 2.3 GPa and 154 MPa at 0% water content, respectively. The Poisson's ratio of the horn sheath was about 0.38. The critical stress intensity factor was about 4.76 MPa m1/2 at an intermediate hydration (8% water content), greater than that at 0% water content (3.86 MPa m1/2) and 19% water content (2.56 MPa m1/2). The bending properties of the samples varied along the length of the horn. The mean flexural moduli of the specimens in the distal, middle and proximal parts were about 6.26 GPa, 5.93 GPa and 4.98 GPa, respectively; whereas the mean yield strength in the distal segment was about 152.4 MPa, distinctly higher than that in the middle (135.7 MPa) and proximal parts (116.4 MPa). This study deepens our understanding of the relationships among optimal structure, property and function of cattle horn sheaths.