| The content of this paper is to study artificial heart valves isotropic pyrolytic carbon fractureproperties. Isotropic pyrolytic carbon was prepared by using a fluidized bed chemical vapordeposition method, pyrolytic carbon chemical vapor deposition refers to the chemical cleavage ofhydrocarbons in the conditions of gaseous in the reaction apparatus, the carbon atomsre-deposited on the heating solid substrate surface, and finally get pyrolytic carbon. If adding acertain amount of silicon in the deposition process, it called silicon-containing pyrolytic carbon.Both isotropic pyrolytic carbon and silicon-containing pyrolytic carbon have excellent resistanceto anti-clotting and biocompatibility and high strength, wear resistance, it is be widely applicationin biomedical science and medical range, become the most important material of artificialmechanical heart valve. Since the preparation technology of the material is not mature enough anditself brittle, there are pores, cracks and delimitation and other defects in the artificial heart valvespyrolytic carbon, prone to fatigue fracture under sustained effect of the load in vivo, it can resultin structural failure, affect the lives of heart valve replacement patients eventually. Therefore, itplays a very important role to clear fracture properties and fatigue crack growth of pyrolyticcarbon material to improve the reliability of artificial mechanical heart valve structure. In thispaper, we do some study for pyrolytic carbon’s properties, focusing on material fracture analysis,the purpose is to improve the structure reliability and prolong its service life. The main contentsare as follows:(1) Using the finite element software ABAQUS with the fracture analysis softwareFRANC3D V6.0,to calculate I-mode stress intensity factors of semi-elliptical crack of artificialmechanical heart valves pyrolytic carbon center crack tension specimen, contrast to the theoreticalvalues based on the experiment, and discussed the influence of the initial crack size、position andshape. The results indicate that: maximum relative error less than3.0%, verified the effectivenessof the software to calculate stress intensity factors; the value increases with the initial crack size;the initial crack located at the middle or edge almost no effect on the value; elliptical crack semimajor and semi minor axis ratio is more close to1, the result become more stable.(2) Brief overview the importance of fatigue crack propagation threshold value, and itsmeasuring principle and measuring method. According to the author’s research of pyrolyticcarbon’s fracture properties,a method and equipment for test pyrolytic carbon fracture toughnesswas designed.(3) Analyzing the effect of corrosion caused by cavitation bubbles in the surface of the artificial heart valve, the water pressure formula on the surface of artificial prosthetic heart wasgiven. According to the first strength theory, using the finite element software to verify theartificial heart prosthetic pieces maximum endurance position, it’s in the intersection region of theflap and the ear flap.(4) Use the online software eFatigue to count the fatigue crack life of artificial mechanicalheart valve, come to the conclusions that: the initial crack size of artificial heart valves impact’s isvery large, control the initial crack size can greatly improve fatigue crack propagation life; theeffect of critical crack size on the fatigue crack propagation life is small; with the cyclic stressratio decline, the crack growth is reduced, the corresponding crack propagation life extension. |
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