An age-based inspection and replacement policy for heterogeneous components

This paper considers a hybrid maintenance policy for a simple system comprising a single component that arises from a heterogeneous population. This population of components consists of two sub-populations that possess different failure characteristics. There are a substantial number of papers that deal with appropriate mixture distributions for the lifetime of a component from such a population. However, the study of maintenance policies for a system with this type of component is limited. By supposing that a component may be in a defective but operating state, so that there exists a delay time between defect arrival and failure, we consider a novel maintenance policy that is a hybrid of inspection and replacement policies. There are similarities in this approach with the concept of “burn-in” maintenance. The policies are investigated in the context of traction motor bearing failures. Under certain circumstances, particularly when the mixture parameter is large and the distribution of lifetimes for the two component types are well separated, the hybrid policy has significant cost savings over the standard age-based replacement policy and over the pure inspection policy. In addition to the cost metric, the mean time between operational failures of the system under the hybrid policy can be used to guide decision-making. This maintenance policy metric is calculated using simulation, and using an approximation which assumes that operational failures occur according to a Poisson process with a rate that can be calculated in a straightforward way. The simulation and approximation results show good agreement.