An imperfect maintenance model with block replacements

We consider a model in which when a device fails it is either repaired to its condition prior to failure or replaced. Moreover, the device is replaced at times kT, k = 1, 2, … The decision to repair or replace the device at failure depends on the age of the device at failure. We find the optimal block time, T 0 , that minimizes the long‐run average cost of maintenance per unit time. Our results are shown to extend many of the well known results for block replacement policies.