Experimental investigations on microstructures and mechanical properties of white yak horns sheath

The horns of male bovines often show excellent mechanical properties due to the hierarchical microstructures. In this paper, the mechanical properties of white yak horn sheaths were studied by tensile and compressive tests, the moisture effect on the fracture toughness of the yak horn sheaths was explored through the three-point bending test. Meanwhile, in order to reveal the relation between the microstructure damages and the macroscopic mechanical properties of yak horn sheaths, the fracture surface of the tensile specimens was observed by scanning electron microscope (SEM). From the experimental results, it follows that the yak horn sheath was found to have a multiscale damage mode, including delamination of lamellae (macroscale), shear deformation of the scales and distortion of the hollow cavities (mesoscale), and matrix cracking and fiber filaments pull-out (microcosmic). Besides, the horn sheath was observed to have a typical laminated structure with interlaminar cavities extending along the growth direction of the horn. The laminated structures and cavities have the potential of energy absorption and can lead to higher energy dissipation, which helps toughen the horn sheath.