Optimal Preventive Maintenance Policies for Repairable Systems

We study the problem of optimal preventive maintenance policies for repairable systems. After each repair the system improves but the failure rate function increases with the number of repairs carried out. Two types of preventive maintenance policies are considered. The criterion for optimal policies is to minimize the expected cost per unit time for an infinite time span. It is shown that under certain reasonable assumptions, both policies have unique solutions. An algorithm to compute the optimal solutions is described.