An Adaptive Hybrid Maintenance Policy for a Gamma Deteriorating Unit in The Presence of Random Effect

In this paper, we propose an adaptive hybrid age/condition-based maintenance policy for units whose degradation paths can be modelled via a gamma process with random effect. The maintenance policy consists in measuring the degradation level of the unit at a first (age-based) inspection time, and in using a condition-based rule to decide whether to immediately replace the unit or to postpone its replacement to a future time that is determined, unit by unit, based on the outcome of the inspection. The optimal maintenance policy is defined by minimizing the long-run average cost rate. After each replacement the unit is considered as good as new. The lifetime of the unit is defined by using a failure threshold model. Maintenance costs are computed accounting for preventive replacement cost, corrective replacement cost, inspection cost, logistic cost, and downtime cost (which depends on the time spent in a failed state).