A Parametric Study of Hertzian Contact Stresses in Pyrolytic Carbon/Graphite Composite.

A mechanical heart valve (MHV) prosthesis made of pyrolytic carbon (PyC) coated graphite is a long-term implant that operates continuously for lifetime in patient's body. The ceramic-like PyC coating is brittle and is prone to contact damages. The high-level local contact stress may lead to the initiation of microcracks, as well as accelerated propagation of preexisting cracks. In this paper, the effect of changing coating parameters on Hertzian contact stresses is investigated for a trilayer PyC/graphite laminate undergoing a spherical indentation test, by means of a finite element analysis. It is shown that by suitably changing Young's modulus, Poisson's ratio, and the thickness of the coating material, the stress levels at critical locations can be greatly modified. This can be accomplished effectively within a small range of variations of the coating parameters. Low Young's modulus, large Poisson's ratio, and relatively thick coating are found to be beneficial in general. The results obtained may be useful in the design of MHV components for improving resistance against contact-induced damages by elaborately controlling the deposition process of PyC coating. [ABSTRACT FROM AUTHOR]