The specification of permitted usable lives, or as they are frequently called “life limits,” is an F.A.A. requirement for critical aviation gas turbine rotating components in commercial use (1). To establish these life limits in a consistent conservative manner, a statistical analysis is necessary to assimilate the many variables involved. The most important parameters are the expected component deterioration with use, the characteristics of this use and the chosen overhaul times and maintenance procedures. Considerable effort has been expended in the aircraft engine industry to obtain better recordings of actual engine operation and environment. A paper by Hohenburg (2) which was principally concerned with such monitoring devices did, however, state “Users of engines must make decisions on when to perform maintenance, to overhaul, or to retire engines from service …. There is a substantial requirement for rational determination of maintenance and retirement intervals.” This paper demonstrates such a rational approach in the form of computer program SMILE (Statistical, Maintenance, Inspection and Life Evaluation). It compares, on the basis of estimated risk, alternative choices of life limits by including all the principal parameters involved. An example makes a comparison of a component with early crack initiation and substantial propagation before failure with an alternative design having late crack initiation but virtually infinitely fast propagation. It shows how a life limit may be considered redundant but necessary in the first case and essential in the second. The alternative risks with specified permitted usable lives will be estimated for each design.
Інтелектуальний регулятор запасу газодинамічної стійкості компресора авіаційного ГТД
