Research On Mechanical Behavior Of The Skull Bone With Porous Microstructure And Design Of The Replacement Structure

Skull bone belongs to a typical lightweight cellular lattice structure.As an external protection of the human brain,it plays a significantly important role in sustaining life safety.According to the statistics,the probability of occurrence of traumatic brain injury accounts for 10%~20% in the damage of all human body parts.Many fields put forward an urgent need on craniocerebral injuries.Considering multiple threats faced by the skull in the exterior environment,it is necessary to analyze mechanical properties of the skull,and to reveal its mechanical behaviors and failure mechanism.Establishing precise theoretical and numerical models,designing and preparing bionic skull structures that meet human needs has become an urgent scientific problem.Firstly,the research progress of morphological characteristics and mechanical properties of bone materials at home and broad are reviewed,and a brief overview of micro-computer tomography and reconstruction technique are given.Then,the theoretical prediction model of sandwich structures under impact and bending loads,as well as important achievements of the skull bone in mechanical experiments and numerical simulations are narrated.Finally,the research overview of bionic bone structures is analyzed.Compared with the study of human femoral implants,very little work is involved in the design and preparation of bionic replacement structures of human skull bones.Therefore,the purpose of this paper is to establish theoretical and numerical models of the cranium under impact and bending loads,and to lay the foundation for revealing mechanical behaviors and failure mechanism of the human skull.In view of the advantage of hierarchical structures with high specific stiffness and high specific strength,the multi-level thought is adopted to design the unit cell configuration of the cranium in order to provide a reference for the clinical application of cranial bone implants.Then,the energy absorption and failure mechanism of 2D porous cranial cross sections subjected to medium and low velocity impact loads are systematically studied through numerical methods.The non-destructive 3D imaging technology and reverse engineering software were used to obtain the cranial numerical model,and the feasibility of numerical models was verified by existing experimental results.In addition,several typical structural parameters(such as impact velocity,impact angle,the density and shape of impactors,cranial reconstructed sections and the size of impactors)that may affect impact behaviors of the human cranial bone were analyzed,and the impact resistance and energy absorption characteristics of the skull were summarized.Next,the impact resistance of the 3D cranial porous sandwich structure with internal pores in a gradient distribution is studied using theoretical and numerical methods.The skull is equivalent to a multi-layer sandwich structure,and the analytical solution of the residual velocity of the impactor,contact force and energy absorption of the skull bone is obtained,and the influence of the equivalent layer on the impact resistance of the structure is theoretically analyzed.The skull model was reconstructed,and three sets of cranial bone sections with different thicknesses and porosity were used as geometrical models for finite element analysis.At the same time,based on the theoretical method,the influence of typical structural parameters(the size and shape of impactors and the thickness ratio between the panel and the core layer in equivalent sandwich structures)on the impact resistance of the porous skull bone was studied.The theoretical results of energy absorption of the skull bone are in good agreement with experimental results in the existing literature.After that,quasi-static bending properties and failure mechanism of the 3D skull bone are investigated based on theoretical and numerical methods.A three-point bending numerical model of the skull bone is established and the structural failure process is analyzed.The skull bone is equivalent to a sandwich curved beam and the theoretical prediction model of the curved beam under three-point bending load is built.The analytical expression for cranial deflection is obtained.Through numerical simulation,the effect of the model width,the length of the span and the different bending load types on cranium bending behaviors,and the relationship between bending properties of skull bones composed of different cross sections and their internal morphological characteristics are systematically investigated.The corresponding failure mechanism of the structure is summarized.In addition,failure modes of the cranial model are verified by existing experimental results.Finally,the multi-layered idea is adopted to design the cranial bionic replacement structure.Firstly,the theoretical and numerical analysis of the out-of-plane compression performance of hierarchical sandwich structures is carried out.The evaluation indicator of the ultra-light structure is proposed.Theoretical prediction formulas of ultra-light lattice sandwich structures under various failure modes are obtained,and the corresponding 3D failure mechanism maps are drawn.From the comparison,the “pyramidal-pyramidal” hierarchical lattice structure with the highest load mass efficiency has the best out-of-plane compression performance,and it can be identified as the unit cell configuration of the cranium replacement structure.Then,three-point bending properties of “pyramidal-pyramidal” hierarchical lattice structure are investigated through theoretical analysis.Finally,several post-treatment methods for the preparation of cranial implants are analyzed,and the processing technique and prospect of microlattice structures are forecasted.