作为一种典型的生物复合材料，牛角具有复杂的多级结构和优异的力学性能，因而可以承受极其恶劣的力学环境。牛角由角蛋白外壳和松质骨骨芯组成，具备攻击和防御的生物学功能。研究牛角的力学性能与结构之间的关系，探索其强韧化机理，对于抗冲击工程结构和高韧轻质复合材料的仿生设计具有重要意义。因此，本文对牛角的多尺度结构、力学性能及其仿生进行了研究。 首先，研究了牛角结构的静态和动态力学性能。结果表明：牛角具有足够的承载能力，并且在静态加载时其失效模式为结构失稳而非断裂；牛角沿长度方向从顶端到底部，其静力学和冲击力学性能（如弹性模量和屈服强度）呈现明显的梯度变化；牛角试样在高应变率下具有相对较高的初始模量和屈服强度。牛角具有优化的多级结构，一方面其宏观结构满足等强度设计的原理，另一方面强韧的外壳可以防止裂纹的起裂和扩展，而疏松多孔的骨芯可以吸收能量。 研究了牛角角蛋白外壳的多尺度结构，并对其力学性能进行了实验表征。发现了牛角角蛋白外壳的波浪状界面以及表面迷宫形花纹的层状多级结构；研究了牛角角蛋白外壳的断裂力学性能，结果表明牛角外壳具有很高的断裂韧性（KIC=4.76 MPa m1/2）；角蛋白外壳的力学性能对水分含量具有敏感性，随着试样水分含量的增加，其弹性模量和强度显著减小，而断裂应变增加，有从脆性材料转变为塑性材料的趋势；从顶端到底部，角蛋白外壳的弯曲模量和屈服强度逐渐减小；沿厚度方向角蛋白外壳的微米硬度值在200~300 MPa范围内随机分布，没有明显的梯度变化；研究了牛角角蛋白外壳的强韧化机理，分析了影响裂纹扩展的多级结构和能量耗散机制。 基于牛角的多级结构提出了具有二级正弦波的仿生界面结构，并用粘聚区模型对具有仿生结构的界面裂纹的扩展进行了数值模拟。结果表明仿生结构具有很好的增韧效果，一级正弦波的存在对于在远场受到I型载荷的情况下的裂纹具有显著的增韧效果，而二级正弦波在远场受到II型载荷的情况下的裂纹具有更为显著的增韧效果。此外，界面摩擦也会明显提高多级结构裂纹在承受II型载荷情况下的界面断裂韧度。 最后，研究了具有仿生多级结构界面的超弹性薄膜在弹性基底的撕裂问题，结果表明仿生多级结构可以显著提高稳态撕裂力和稳态断裂功。

As a typical biological composite, the bovine horn possesses complicated hierarchical structures and superior mechanical properties, and thus is able to withstand harsh mechanical environments. The bovine horn, composed of a keratinous horn sheath overlying a bony core, has biological functions of defense and attack. The investigation of the relationship between the mechanical properties and the structures of bovine horn, as well as the strengthening and toughening mechanisms has important implications on designing bio-inspired anti-shock structures and light weight composite materials with high toughness. Therefore, the multi-scale structures, mechanical properties and biomimetics of bovine horns are investigated in the present thesis. First, the static and dynamic mechanical properties of the bovine horn structure are studied. It is indicated that the bovine horn has sufficient load bearing capacity, and during static loading the bovine horn shows a damage mode of structural instability instead of cracking. The static and dynamic mechanical properties of the bovine horn, such as the elastic modulus and yield strength, show an apparent declining trend from the distal to the proximal part along the length of the horn. The result shows that the bovine horn specimen has relatively higher initial modulus and yield strength under a higher loading rate. The bovine horn has optimized multi-scale structures for reasons as follows. Firstly, its geometric character meets the equal strength design. Secondly, the tough keratinous horn sheath can prevent crack initiation and propagation, while the porous bony core can absorb energy. Second, the multi-scale structure of the bovine horn sheath is investigated and the mechanical properties of the horn sheath are examined experimentally. The wavy layered structure and the maze-shaped surface of the keratinous horn sheath are found. The fracture mechanical properties of the horn sheath are studied. The result shows that the horn sheath has a very high toughness (KIC=4.76 MPa m1/2). The mechanical properties of the bovine horn sheath are sensitive to water content. As the water content increases, the horn sheath undergoes a transformation from a brittle material to a ductile material. In this process, the elastic modulus and the tensile strength decrease, while the strain at failure increases. The flexure modulus and yield strength of the keratinous horn sheath decrease from the distal to the proximal end. The micro hardness values of the horn sheath are in the range of 200–300 MPa along the horn thickness, with no apparent gradient. The strengthening and toughening mechanisms of the horn sheath are discussed. The factors affecting the crack propagation, such as multi-scale structures and energy dissipations, are analyzed. Third, based on the multi-scale structures of the bovine horn sheath, a bio-inspired two order hierarchical sinusoidal structure is proposed, and the propagation of the interfacial crack with the bio-inspired structure is numerically simulated using cohesive zone model. It is concluded that the bio-inspired structure has a superior toughening effect. The first order sinusoidal structure has a crucial toughening effect on a crack under far-field mode I load, while the second order sinusoidal structure has a prominent toughening effect on a crack under far-field mode II load. Moreover, it is found that the interfacial friction notably enhances the interfacial toughness of a crack with hierarchical structure under mode II load. Finally, the problem of a hyperelastic film peeling from an elastic substrate with an interface of bio-inspired hierarchical structure is studied. The result shows that the static peeling force and work of fracture are significantly enhanced due to the bio-inspired hierarchical structure.