Periodic preventive maintenance policies following the expiration of warranty

Two types of replacement policies, following the expiration of warranty, have been discussed in the literature: 1) minimal repair is applied for a fixed length of time and the unit is replaced at the end of this period, and 2) the unit is replaced at first failure following the minimal repair period. This paper considers a periodic preventive maintenance (PM) policy after the warranty period is expired. We assume that each PM, following the expiration of warranty, slows the rate of system degradation while the failure rate of the system keeps increasing monotonically. In this paper we determine the optimal number and period for the periodic PM following the expiration of warranty which minimize the expected long-run maintenance cost per unit time. Explicit solutions for the optimal periodic PM are presented for illustrative purposes.