Investigations Of Multi-scale Structures And Mechanical Behaviors Of Deer Antler

Antlers are the bony protuberances that form on the heads of the deer and have been a weapon for deer to attack and defend.As a kind of natural biological composite material,antlers have high strength,stiffness,toughness and resistance to impact after several centuries of natural evolution.The excellent mechanical properties of antlers are closely related to its microstructure.The investigation on these excellent microstructures will provide beneficial guidance for synthetic high-performance composite materials.In this work,the relationship between the hierarchical microstructure and the excellent mechanical properties of compact bone of antler is investigated with the combined method of mechanical tests,observational experiments,model analyses and numerical simulations.The main work and contributions of this dissertation are listed as follows:(1)The macro/micro-mechanical properties of the specimens of the compact bone of antler in three different directions,such as elastic modulus,bending strength,work-offracture are tested by four-point bending experiment,and calculated by the stress-strain curve.Scanning electron microscopy(SEM)has been used to observe the crack propagation path along transversal,longitudinal and radial directions of antler,and the characteristics of the fracture surface was also observed.The experimental results show that the elastic modulus and bending strength of the transversal specimens of the antler bone are the largest,and the longitudinal specimens are the smallest in three kinds of specimens.Moreover,the work-of-fracture of the transversal specimen of the antler is the largest,followed by the radial specimen,and the longitudinal specimen is the smallest.The mechanical properties of antler bone are closely related to their unique microstructure,which is the main factors of the anisotropic mechanical properties of the bone.The effect of unique structure of osteon in the bone on crack deflection,is the main one of the factors.(2)Based on the observed results of the scanning electron microscopy(SEM)of the crack propagation route in three different orientations,the characteristics of the antler crack propagation path were analyzed.It is realized that the paths of the crack propagation of the bone have statistical self-similarity characteristics.The transversal fracture fractal model,longitudinal bridge fractal model and radial deflection fractal model are established.The fracture energy dissipated in the transversal,longitudinal and radial orientations of the antler bone was calculated,and the toughening mechanism of the specimens in three different orientations was analyzed.Based on the experimental results of four-point bending tests,the fractal dimensions of the fracture surfaces of the antler bone along three different orientations are calculated.It is shown that the fractal dimension of the transversal fracture surface of the antler bone is the largest,the one of the radial fracture surface is the minimal and the one of the longitudinal fracture surface is between them.The fractal dimension can reflect the roughness and complexity of the fracture surface.(3)Based on the characteristics of the microstructure of the osteons of the antler bone,three different finite element analytical models of the osteons were established.The progressive damage method has been adopted.In this calculation,the failure criteria and the strength parameters are inputed to ABAQUS 6.13 by means of its user subroutine USDFLD.The fracture criterion within the layer is Giner criterion,while the fracture criterion between layers is Brewer and Lagace criterion.The stress distribution and failure condition of the three models are obtained.Comparing the three different analytical models of the osteons,it is known that the arrangement and shape of the osteocyte lacunae in the osteons is a kind of optimized arrangement.It determines the location where the micro-cracks begin to formation,and the extension direction,compared with the other two kinds of model.Moreover,the damage is mostly within the layer,and there is less interlayer damage,which has positive effect on the integrity of the osteon structure.(4)The collagenous fibers in the antler bone compose a kind of periodic helical layer structure and the spiral angle is increasing by 30o.In order to study the effect of fiber helical angle on the compressive property of the multilayer bio-composite of the bone,the strength failure criterion of the composite was determined by progressive damage and the failure criterion of Tsai-Wu tensor.A model of the bi-composite with the fiber helix angle of 30o is established and the compression property of the model and the damage in its layers are studied.Analysis results show that in the model the angle between the layer is plus and minus 30o,the compression damage resistance of the composite are the largest.The results provide a useful guidance for the development of high-performance bionic composite materials.