Research Of Interface Adhesive Strength Of Pyrolytic Carbon For Artificial Heart Valves

The article is about interface adhesive strength of Pyrolytic carbon coating and Graphite substrate which used in Artificial mechanical heart valve.Artificial heart valve includes Artificial mechanical heart valve and Bioprosthetic heart valve,the Artificial heart valve the article regards actually represents Artificial mechanical heart valve.Low temperature isotropic pyrolytic carbon is widely used in Artificial heart valve for its excellent strength,wear resistance,bending strength and low elastic modulus,it also has good chemical inertness and blood compatibility at the same time.Once the Artificial heart valve is planted in human body,it has to work for several decades, open and close for forty million to fifty million times and deliver about forty million tons of blood each year. The Artificial mechanical heart valve can not guarantee to be used for several decades right now,the failures due to abrasion,corrosion,fatigue and fracture often happen to the valve.The interface of Pyrolytic carbon and Graphite substrate is the weakness of the structure,so the failures are likely to happen in the interface. So improving the adhesive strength of Pyrolytic carbon and Graphite substrate has an important effect on the working life of Artificial heart valve.The article considered many methods to measure the value of interface adhesive strength of Pyrolytic carbon coating and Graphite substrate,then choose the improved shear test method after considering the material properties and preparation of samples.On the basis of the test,using ANSYS to analyze how the thickness,elastic modulus and residual stress of coating affect the adhesive strength of Pyrolytic carbon and Graphite when the sample was subjected to shear load.Due to the working condition of Artificial mechanical heart valve is quite complicated, so using ANSYS to modify the Hertz contact of spherical indenter and coating surface,then analyze the force situation of the whole system,also analyze the affection of coating thickness and elastic modulus on the adhesive strength of Pyrolytic carbon and Graphite substrate.The main research contents and results are as below:(1)According to the principle of improved shear test,the interface adhesive strength of Pyrolytic carbon and Graphite substrate was measured in the Reger3010universal material testing machine with a self-designed jigs,the measured value was5.535MPa.(2)Using finite element analysis software ANSYS to modify the load and bound condition of the improved shear test, it concluded that the maximum shear stress of the interface is10.23MPa,and the average value is5.98MPa,which means the model was correct. (3)Depending on the above model to analyze the influence factors of interface adhesive strength of Pyrolytic carbon coating and Graphite substrate,it concluded that thinner coating and coating with lower elastic modulus is good for interface adhesive strength as the system was subjected to shear stress.(4)Also using ANSYS to complete the thermal-structure coupling analysis of the above model,observe the differences of shear stress of the interface with different deposition temperatures,build a relationship between residual stress and adhesive strength through the deposition temperature,it concluded that the lower deposition temperature which leads to lower residual stress is good for interface adhesive strength.(5)Using ANSYS to modify the Hertz contact of spherical indenter and coating surface,according to the force situation concluded that the areas that most likely to invalid are the contact area of indenter and coating,and the interface of coating and substrate that below the contact area.(6)When the Artificial mechanical heart valve is subjected to Hertz contact,thinner coating and lower coating elastic modulus is good for interface adhesive strength.