| Nowadays common fracture fixation repair material adopts more inert ones in orthopedic clinical stage,such as stainless steel,titanium,etc.,which high strength but much larger than the elastic modulus of human bone are bound to result in stress shielding effect in the healing process,which furthermore in the healed bone presence does not be absorbed,biodegradable,need reoperation.In contrast the magnesium alloy material repairing fractures can reduce the stress-shielding effect in fracture healing process and prevent patients from suffering a second surgery.With previous studies showing that the mechanical environment has some influence on the degradation behavior of magnesium alloy and mostly qualitative researches,so the study with the aim of quantitative analysis adopts in finite element analysis software ABAQUS\ EXPLICIT 13.1 the VUSDFLD short for user-defined field variables subroutine written to achieve the degradation process simulation of the magnesium alloy in the mechanical environment,with whose simulation results the in vitro degradation experiments were compared.Screening a better overall performance of magnesium alloy AZ31,then magnesium alloy designed and manufactured specimens,as well as experimental device,bone plates and screws could be used in the uniaxial compression loads in vitro degradation research prior to which its finite element simulation had been done to explore the laws of magnesium alloy degradation under different mechanical environments.The main contents are as follows specifically:(1)The research status of degradable magnesium alloys at home and abroad is described,and the significance and importance of the research are put forward.(2)The theory of continuous damage is described.The subroutine of user defined field variable(VUSDFLD)in ABAQUS \ EXPLICIT 6.13.1 software is written to realize the quantitative output of hydrogen volume,mass loss and effective stress during the degradation process.The finite element analysis model was established,including three models of magnesium alloy specimen and the model of the middle segment of the tibia of the sheep fixed with magnesium alloy plate as well as their numerical simulation in ABAQUS \ EXPICITE software.(3)The numerical simulation results are studied and analyzed.The results show that the volume and quality of hydrogen in the degradation process of the magnesium alloy specimens in different groups have the same change rule.The load size plays an important role in regulating the surface topography,effective stress distribution,failure mode and failure time.The degradation of magnesium alloy in the model is gentle.(4)The degradation behavior of magnesium alloy was studied under the single axial pressure.The results showed that the degradation behavior of magnesium alloy including volume of hydrogen,mass loss and pH,maximum compressive displacement,and the maximum pressure and compression time are related to the load value.The axial load will accelerate the degradation of the magnesium alloy.In some certain,the larger the axial load,the larger the pH fluctuation.In the axial compression experiment,the maximum compressive strength of the specimen has a regulatory role.(5)The simulation results and experimental results are compared and analyzed.The results showed that the volume of evolved hydrogen in the simulated body fluid was larger than that of the simulation results because the solubility of air in simulated body fluid at room temperature(25 ?)was greater than that of body temperature(37 ?),but all of them could explain the degradation rate of magnesium alloy will be accelerated to certain load size.From the simulation results the experimental ones of the mass loss and,it can be concluded that the degradation products of inorganic salts can strengthen the surface of the alloy,and the uniaxial load can control the attachment and detachment of degradation products to regulate the degradation behavior of magnesium alloys. |
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