| In biomedicine,the most widely used artificial mechanical heart valve coatings all use pyrolytic carbon materials.Pyrolytic carbon has compact structure,stable chemical properties,excellent anticoagulant performance,and excellent biocompatibility.However,pyrolytic charcoal is subjected to the cyclic impact of blood flow load for a long time in production and preparation,finished product processing and surgery,and in the heart.Due to cavitation and cavitation and the special environment inside the heart,the pyrolytic charcoal coating may be affected.Defects such as cracks are generated.In the long-term work of the artificial heart valve,the cracks may expand and even cause brittle fracture of the pyrolytic carbon coating,which poses a serious threat to the health of patients.Therefore,it is of great value to research the fracture properties of pyrolytic carbon materials for improving the stability of artificial mechanical heart valve.In this paper,the fracture properties of artificial heart valve pyrolytic carbon material were studied,the stress intensity factor of possible crack in pyrolytic carbon coating was calculated by ABAQUS software,and the propagation behavior of possible crack in pyrolytic carbon coating was studied by propagation finite element method.The fracture surfaces of compact tensile specimens of pyrolytic carbon and its composites were prepared by MTS electrodynamic testing system,and the morphology of the fracture was analyzed by optical microscope and scanning electron microscope.The specific research content is as follows:1.The ABAQUS software was used to simulate the edge cracks and central cracks stress intensity factor(SIFs)of the pyrolytic carbon coating.The results show that the relative error between the simulation value of the software and the theoretical value obtained through experiments is less than 4%.This reflects the reliability of the simulation calculation;keeping the number of cracks constant,the type I SIFs of the edge cracks and center cracks in the pyrolytic carbon coating increase with the increase of the crack inclination angle and length;the edge cracks and center cracks inclination angle is not 0° and 90°,the two kinds of type II SIFs cracks pyrolytic carbon coating increases with increasing length of the crack,the crack and reaches a maximum inclination angle is 45°.the type I and type II SIFs curves of edge cracks and center cracks coincide with each other and are smaller than those of type I and type II SIFs of single crack.2.The fracture surfaces of pyrolytic carbon and its composites were prepared by MTS electrodynamic test system.The results show that under optical microscope,the fracture of pyrolytic carbon coating is relatively smooth and fine,and the fracture of graphite is rough and uneven;By scanning electron microscope,the fracture of pyrolytic carbon is intergranular fracture,but the fracture of graphite is transgranular fracture;the mechanical properties of pyrolytic carbon and other ceramic materials are uncertain,which may be microscopic The mechanism can be divided into internal mechanism and external mechanism.3.Based on XFEM,the influence factors of crack propagation in pyrolytic carbon coating of artificial heart valve were researched.Within a certain range,Crack inclination angle,location,spacing and depth have no significant effect on the direction of crack propagation in pyrolytic carbon coating.Cracks propagate along straight lines with little fluctuation.Crack inclination angle,location and depth have significant influence on the rate of crack propagation.Crack propagation behavior of pyrolytic carbon coating is related to the internal structure of material,crack geometry parameters and energy. |
