Effect of repetitive impact on the mechanical strength of pyrolytic carbon.

Impact loading is experienced by mechanical heart valve components when the leaflet comes into contact with the housing orifice as the valve opens and closes during the cardiac cycle. Since the human heart beats approximately 40 million times per year, a large number of impact loading cycles are imposed on the carbon valve components. Contact loading can produce high mechanical stress at the contact area, leading to potential material damage and fracture. This paper describes a procedure for characterizing the effect of repetitive impact on the mechanical strength of pyrolytic carbon. The results shed light on the basic understanding of the damage formation and its strength degradation effect. In particular, fatigue crack growth was identified as the primary mechanism which causes the observed strength degradation. Design procedures based on fracture mechanics and contact mechanics are used in mechanical heart valve design to prevent structural failure associated with impact fatigue.