| Attributed to the degradability,excellent biocompatibility and biosecurity,biomedical magnesium alloy becomes a promising material that used for making bone screw.However,comparing with the traditional non-degradable metal bone screws,the strength of the screws that made from biomedical magnesium alloy is lower.Besides,the stress concentration condition can affect the degradation rateof magnesium bone screw.Thus,the structure of non-degradable screw is not suitable for degradable magnesium screw,andthe structure optimization is to be conducted in biomedical magnesium bone screw,which can help it to meet the requirement of clinical application.At present,few studies have been reported at home and abroad.In order to solve the problems of low strength and local stress concentration in biomedical magnesium bone screw,three-dimensional structure model of femoral bone screw was constructed in reference of titanium alloy and stainless steel pharmaceutical industry standards.The finite element analysis of mechanical properties by ANSYS was carried out,including simulation of three-point bending experiment,torsion experiment and axial pulling-out experiment.The stress,strain and deformation distribution was discussed.At first,the structure characteristics of the screws were changed,including the shape and hollow structure of the screw,and the mechanical properties before and after the change were compared.Secondly,the structure parameters of the bone screws were changed,including pitch,inner diameter and thread angle,and the corresponding models were established respectively,and the influence of various size parameters on mechanical properties and the results were explored.Finally,based on the simulation results,the coupling effect of various factors is analyzed by orthogonal test,the optimal screw size parameters are determined and processed,and the actual mechanical properties of the real screws are characterized and the simulation results are verified.The main results were shown as below:The asymmetric thread is better than the symmetrical thread on prevention of prolapse,and the stress concentration is significantly reduced;The simulation results of bending and torsion shows that the force of the center of the screw is smaller,so there is no obvious difference between solid and hollow diameter 1 mm structure.The supportability of bending,torsional are raised by the increase of the inner diameter,but the bite force of bone and thread will reduce;The effect of pitch on the mechanical properties is not obvious;The addition of thread angle increased the loading capacity of screws first and then decreased.The influence of the parameters on the bending load is obtained by the orthogonal test.The order is the diameter,pitch,tooth angle ? and tooth angle ? from large to small.;The order of the torque is the inner diameter,the pitch,the tooth angle ? and the tooth angle ?;The order of the axial pullout force is the pitch,the inner diameter,the tooth angle ? and the tooth angle ?.Analysis of single factor variables and range analysis,the screw pitch was 1.45,the inner diameter was 3.2mm,the tooth angle ? was 2°,and the tooth angle ? was 35°,which was the optimal group parameter.The experimental results and the simulation results of the bone screws are in good agreement with each other,and the correctness of the finite element analysis is verified.The results show that the bending load of the bone screw is improved by 83.5% and the torque is increased by 24.2%,but the axial pulling-out force is not improved obviously.In this thesis,the mechanical load carrying capacity of the Mg-Zn-Y-Nd biomedical magnesium bone screwwas improved by the structure optimization.The basic parametersystem of the biomedical magnesium bone screw was established,which can provide the data reference for the clinical bone implantation. |
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