Failure Of Silicon Nitride Ceramic Flotation Spheres At Critical State Of Implosion

Compared with the traditional buoyancy material,such as composite foam,hollow silicon nitride ceramic hollow flotation spheres have lower density and higher strength,which make it provide lift more effectively in the underwater environment.Therefore,silicon nitride ceramic flotation spheres have great potential for use in deep-sea exploration vehicles.However,the brittleness of silicon nitride ceramics and the special structure make hollow flotation sphere have a large risk of underwater implosion when it is submerged in the deep-sea.On the other hand,the process of implosion is usually accompanied with a sudden release of a large amount of energy in a short time,resulting in a strong shock wave,which is a great threat to the safety of surrounding structures.Based on the true catastrophe happened abroad and the needs of the development of flotation equipment in China,it is of great significance to study the failure of hollow silicon nitride ceramic flotation spheres at the critical state of implosion.Firstly,the research status of flotation spheres and underwater implosion is introduced,and the focus of this paper is confirmed as well.Then,the production,quality inspection and implosion test of hollow silicon nitride ceramic flotation sphere are reviewed to provide data support for the up-coming study.Next,the three-point bending test and compression test of silicon nitride ceramics are designed and conducted,and the material properties of silicon nitride ceramic is obtained.In addition,based on the finite element method,the first-order buckling mode of the structure is introduced into the explicit dynamic analysis as the initial geometric imperfection,and the implosion failure process of flotation sphere with eigenmode geometrical imperfections is analyzed.Then a real silicon nitride ceramic flotation sphere geometry,obtained by computed tomographic scanning,was imported into the finite element simulation.Finally,the effect of sphericity on the implosion results was investigated.The results indicate that the performance of silicon nitride ceramic flotation spheres is unstable to some degree.The ideal hollow sphere has the best pressure resistance.Local tension stress is the main reason for the failure of the structure.Since damage begins from the internal surface in the simulation,preload compression treatment of the inner surface might delay the failure of structure.