On an imperfect preventive maintenance model

Presents two sequential preventive maintenance (PM) models. The first model can ^AcceP^{ted Se}P^{tember 1999} be viewed as an extension of Nakagawa's model where the age reduction of the system is assumed to depend on the level of PM activities. Linear and nonlinear relationships between age reduction and PM level have been considered. In the second model, a sequential PM model is developed in which PM intervals are defined such that the integrated hazard rate over each interval is thesamefor allintervals.Thisrestriction reducesthe number of decision variables from N + 2 to only three decision variables, where N is the number of intervals between PMs. The cost difference between these two models was very small for the examples solved. This provides evidence that the integrated hazard rate restriction provides a very good approximation of this sequential PM model. This suggests that the integrated hazard rate condition may be used to reduce greatly the number of decision variables at the expense of a reasonable increase in the expected total cost.