Modeling repairable systems with failure rates that depend on age and maintenance

A general repairable system model that includes age and preventive maintenance (PM) dependent failure rates is proposed. This model introduces the concept of system availability as a random variable, leading to availability measures for individual realizations, rather than for the average over many trials. Thus this model generalizes the classical definition, and serves as a performance index for system design. A design scheme suggested to maximize the probability of achieving a specified stochastic cycle availability with respect to the duration of the operating interval between PMs. Numerical computations of the results for Weibull-like distributions illustrate the design criteria. Asymptotic behavior of the performance with no PM has been studied. Extension to other distributions is straightforward.>