| In recent years,magnesium alloy has attracted much attention as a fixed implant material in human body.However,due to its chemical nature,the degradation rate in the body is too fast and does not match the bone healing cycle,which is a major reason that cannot be promoted and applied.This paper mainly studies the effect of three-point bending force on the degradation performance of magnesium alloy AZ31 bone plate.The finite element simulation combined with in vitro degradation experiments were used to quantitatively study the degradation process of magnesium alloy bone plates with different pore shapes.Through the comparison between the finite element simulation results and the in vitro degradation experiments,some conclusions are drawn,in order to provide a real and effective theoretical basis for the application of magnesium alloy as the bone material.The main research contents of the thesis are as follows:(1)The research status of medical magnesium alloys was expounded,and the necessity of research was put forward.Through the analysis of the research status,the research direction and research ideas of the thesis are further determined.(2)Two different hole-shaped magnesium alloy plate models(Model A and Model B)were designed in finite element simulation.Based on the "continuous damage theory",the two mechanisms of magnesium alloy corrosion were integrated into ABAQUS,and the degradation corrosion law under the load of 20 N,40N and 60 N was studied respectively.The hydrogen content and mass loss rate of the degradation process were recorded in real time.The results show that the fracture time and fracture location of the magnesium alloy plate are different: the greater the load,the earlier the fracture time appears;model A is the fracture of one of the two holes in the middle of the plate,and the model B is the fracture of the entire middle portion of the plate.(3)Four experimental models were designed in the in vitro degradation experiment: test pieces A,B,C and D,in which test pieces A and B were separate studies on magnesium alloy bone plates,test pieces C and D are studies on the fixation of fractured sheep's tibia with different pore-shaped magnesium alloy plates.The loads was 0N,20 N,40N and 60 N,of which 0N was the experimental control group.The hydrogen,mass loss rate,pH value and topography of the magnesium alloy plate were recorded at important time node.The results show that the corrosion rate of magnesium alloy plate increases with the increase of three-point bending force;the larger the load,the more obvious the pH fluctuation.(4)Through the comparison of finite element simulation results and in vitro degradation experiments,the results show that: The change in the amount of hydrogen leads to a change in the rate of loss,and the changes in the two are consistent;model A and test piece A are both of the two holes in the middle of the magnesium alloy plate,and one of them breaks,although there are numerical differences,the trend can reflect the entire degradation process of thebone plate;test piece B is broken in one of the two middle holes,and the break point is inconsistent with model B.The reason for this phenomenon is that the magnesium hydroxide formed in the middle position of the test piece B adheres to the middle part of the bone plate to form a protective shell,which hinders the corrosion of the middle part,but at this time the stress is redistributed to the vicinity of the middle hole of the bone plate,which in turn causes one of the two holes in the middle to break.It can be considered that the test piece B is a break of the intermediate part,the hole shape of the test piece B enables the stress to be effectively distributed,and the load is relatively uniform,which indirectly explains the rationality and practicability of the test piece B. |
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