Mesoscopic Finite Element Modeling And Mechanical Properties Prediction Of Boron Nitride Fibers

A large number of studies have shown that the mechanical properties of materials are not only related to the properties of the material itself,but also have an important relationship with the microstructure.Therefore,with the wide application of boron nitride fibers in the fields of aviation,aerospace,electronics,nuclear industry and composite materials,further understanding of the relationship between the macroscopic mechanical properties of boron nitride fibers and their internal microstructure has become the top priority.There are three main phases in the boron nitride fiber,which can be expressed as amorphous boron nitride(a-BN),Turbostratic boron nitride,(t-BN)and Hexagonal boron nitride(h-BN).Microscopically,they exhibit amorphous,semi-crystalline,and crystalline states,respectively.The distribution,size,and proportion of the three phases will affect the macroscopic mechanical properties of boron nitride fibers.Therefore,studying the relationship between the macroscopic and microscopic mechanical properties of boron nitride fibers has become the focus of this article.(1)Ignoring the effect of a-BN,boron nitride fiber can be regarded as a polycrystalline material composed of two-phase particles.Among them,h-BN is an anisotropic crystal grain,and t-BN is an isotropic inclusion.Set the direction of the grains and establish the elastic constitutive equation of each phase under small deformation.Then,the homogenization method was used to study the relationship between the macroscopic mechanical properties and the microstructure of the fiber.But because the homogenization method has many ideal assumptions,so the result of Voigt-Hill-Reuss method is not accurate.In this paper,the results of Voigt-Hill-Reuss method will be used as the upper and lower limits of the material performance parameters to verify the finite element model.(2)In order to improve the accuracy of the calculation results of the material's macroscopic performance parameters,this paper builds a two-dimensional microscopic finite element model of boron nitride fiber based on Voronoi diagram.And use MATLAB,Python and ABAQUS mixed programming and joint use to achieve a simple tensile simulation of fibers.Subsequently,the comparison between the solution results and the Voigt-Hill-Reuss method shows that the effective elastic modulus of the boron nitride fiber obtained by the finite element method is within the upper and lower limits of Voigt-Reuss.Therefore,it is effective to introduce the Voronoi diagram to the establishment of microstructure inside the boron nitride fiber.(3)On the basis of verifying the effectiveness of the finite element model,this article further discusses the effect of the microstructure inside the fiber,such as bubbles,crystallinity,and grain size to the macroscopic mechanical properties.This research will provide a reasonable reference for the design of boron nitride fiber mechanical properties,the setting of processing conditions and the guidance of production.