Study On The Mechanism Of Strength And Toughness Of Hierarchical Microstructure Of Teeth

Natural biological materials have particular structure and function which man-made material can't rival.They are composed of basic component that form kinds of structure.These inner structures make natural biological materials fit the environment well,and fulfill them with good mechanical properties.Human teeth have the performance of excellent mechanical properties in the long evolutionary process.The structure of human teeth have been optimized whether in macro or in micro.Human teeth are composed of hydroxyapatite,protein,water and a small amount of other things.These basic materials form micro structure in human teeth which have the influence on the mechanical properties.It's important to research the micro structure of human teeth to develop bionic and serve engineers as guidance in the designs of structure and materials for engineering applications.Natural biological material human teeth are researched in this paper.Mechanical experiment and scanning electron microscope and numerical simulation are used to research the properties of teeth.Fracture strength and ultimate strain and elastic modulus and fracture energy are measured.Numerical simulation is used to research the relationship between the micro structure and the excellent mechanical properties of teeth.The aim of this paper is to reveal the micro structure's influence on the toughness of the teeth.The main work and contributions of this dissertation are listed as follows:(1)Axial tensile experiment and three-point bending experiment are carried out to test the ultimate strength,ultimate strain,fracture energy and elastic modulus in transverse and longitudinal direction.The conclusions are listed as follows: through axial tensile experiment,it can be found that the ultimate strength and ultimate strain in transverse direction is smaller than those in longitudinal direction which means the ability of resisting fracture in longitudinal direction is better.The elastic modulus of longitudinal direction is larger than that of transverse direction.Through three-point bending experiment,it can be found that the ultimate strength,ultimate strain and fracture energy in longitudinal direction is larger than those in transverse direction.There are differences in mechanical properties between the transverse direction and longitudinal direction.(2)Based on the hole structure of the internal of teeth through the scanning electron microscope,two different models are built.The one contains only one hole in the structure and compare whether there is the peritubular dentin or not,the other contains multiple hole and compare whether there is the peritubular dentin.Linear elastic fracture mechanics theory and extended Finite Element Method are used to simulate the crack propagation in the two different models.The conclusions are listed as follows: there is a big difference between the one hole model containing only peritubular dentin and the one hole model containing both the peritubular dentin and intertubular dentin when the crack propagated at initial.The biggest stress and strain are found in the bottom of the crack.The biggest stress and strain are obviously larger in the one hole model containing only peritubular dentin than those in the one hole model containing both peritubular dentin and intertubular dentin.The path of crack propagation in the one hole and two phase model is more complicated than that in the one hole and one phase model.The ability of resisting fracture of one hole and two phase model is more excellent than one hole and one phase model.The crack propagation in the multiple hole is similar to that in the one hole.The multiple hole can protect structure from damage through longer path of crack propagation and consuming more fracture energy.(3)According to the microstructure of teeth observed on the scanning electron microscope,three 2-D microstructure models are established.They are circumferential ellipse pore,circular pore and radial elliptical pore.The approach of the progressive damage has been applied.In this calculation,the failure criteria and the strength parameters are input to ABAQUS 6.13 by means of its user subroutine USDFLD to simulate.The conclusions are listed as follows: under compression,the stress in the circumferential ellipse pore which is establish based on the real situation is the smallest,which means it can't be damaged easily.The damage element in the circumferential ellipse pore is along the circumference direction while the damage element of the other two models is along the radial direction.The circumferential ellipse pore in teeth is more benefit to resist crack.