EFFECT OF REPETITIVE IMPACT ON THE MECHANICAL STRENGTH OF PYROLYTIC CARBON

Impact loading is experienced by mechanical heart valve components whe n the leaflet comes into contact with the housing orifice as the valve opens and closes during the cardiac cycle. Since the human heart beat s approximately 40 million times per year, a large number of impact lo ading cycles are imposed on the carbon valve components. Contact loadi ng can produce high mechanical stress at the contact area, leading to potential material damage and fracture. This paper describes a procedu re for characterizing the effect of repetitive impact on the mechanica l strength of pyrolytic carbon. The results shed light on the basic un derstanding of the damage formation and its strength degradation effec t. In particular, fatigue crack growth was identified as the primary m echanism which causes the observed strength degradation. Design proced ures based on fracture mechanics and contact mechanics are used in mec hanical heart valve design to prevent structural failure associated wi th impact fatigue.