Investigations Of Micro-Structures And Mechanical Behaviors Of Biological Corner Material

In the development of composite materials,nature has always played an important role.As a representative of natural composite materials,horn sheath has excellent mechanical properties.The excellent macro-mechanical properties of the horn sheath are closely related to its special micro-internal structure.Therefore,investigating the relationship between the properties and structure can provide an important guidance for the design and optimization of bionic composite materials.In this paper,the horn sheath of an adult bovine is taken as research object.Firstly,three-point bending experiment,the nano indentation experiment and the scanning electron microscope are carried out.Then,the theoretical analysis models and finite element numerical models are established based on the results of the scanning electron microscope observation.The relationships between the special microstructure of the horn sheath and its excellent mechanical properties are discussed.The research result has guiding significance for the design of bionic composite materials.The main work of this dissertation is summarized as follows:(1)Through three-point bending experiments of the lateral,longitudinal,and radial specimens of the horn sheath,the mechanical parameters such as elastic modulus,bending strength,and crack propagation force of the three specimens were measured and calculated.Through the comparison of the data,it is found that all the mechanical parameters of the transverse specimen of the horn sheath were larger than those of the other two specimens,and the radial specimen had the worst mechanical properties,and the longitudinal specimen was between the other two specimens.Scanning electron microscopy observations of the fracture surfaces of three-point curved specimens in three different directions revealed that the difference in mechanical properties is closely related to the microstructure of the horn sheath.The crack propagation patterns of the specimens in different directions have their own unique laws,which results in different energy consumption during their crack initiations and propagations,resulting in the anisotropy of the macro-mechanical properties.(2)By analyzing and summarizing the observation results of the scanning electron microscope experiments of the horn sheath,the fractal models of the crack propagation paths of the horn sheath in the horizontal,longitudinal and radial directions are established.Based on the calculation results of the crack propagation forces of the three models,it is found that the order of the magnitude of the crack propagation forces is:lateral>longitudinal>radial.The results discussed in the model are in good agreement with the three-point bending test results of the horn sheath specimen.(3)Based on the characteristics of the fracture surfaces of the specimens observed in the experiments of the scanning electron microscope,three finite element models were established:elliptical annular cavity model,elliptical radial cavity model,and circular cavity model.The USDFLD user subroutines were written in FORTRAN language,and progressive failure analyses were performed on the three finite element models.Based on the results of the finite element calculations,it was found that the cracks in the elliptical toroidal cavity finite element model and elliptical radial cavity finite element model mainly originate at the two ends of the long axis of the elliptical cavity,and are affected by the orientation of the cavity.In the ring-shaped cavity-finite finite element model,cracks propagate in the circumferential direction of the haval tube,and in the elliptical ring-shaped cavity-finite finite element model,the crack is radial expansion.Because the circular cavity in the circular cavity finite element model is circular,the crack generation and propagation of the circular cavity is random.By comparing the three models,it is also observed that the damage of the elliptical annular cavity finite element model mostly occurs in the layer,which is of great significance to ensure that the horned sheath unit does not cause global damage of the horn sheath.(4)Based on the spiral laminate structure existing in the horn sheath,the finite element impact models of the spiral laminate structure were established.Considering the complexity of natural bio-composites,the finite element impact models of the spiral laminate structures were optimized.For comparision,four finite element models were established.They include:spiral recursive configuration(HR),spiral exponential configuration(HE)and spiral semicircular configuration(HS),quasi-isotropic contrast configuration(LR).The Tsai-Wu tensor strength theory was selected as the failure criterion,and the user subroutines were written.The finite element calculation software was used to calculate the impact response of the four finite element impact models.From the results of the finite element calculations,it is found that the F_max of the finite element models of the three spiral structures are greater than that of the finite element model of the linear-structure,and that with the increase of the spiral angle,the impact resistance of the model is gradually enhanced.And the research results has guiding significance for the design and optimization of bionic composite materials.