عنوان مقاله [English]
This paper proposes a mathematical model to determine optimal sequence of preventive maintenance (PM) activities for a repairable multi-component series system. The structure of system is series, i.e., if a component of system fails, the system stops. The occurrence of each components failure is modeled by a non-homogeneous Poisson process (NHPP) with an increasing failure rate. It is assumed that maintenance planning horizon has been divided into equal time periods, and at the end of each period, four possible actions for each component (mechanical service, repair, replacement or do nothing) have been considered. If mechanical service or repair is performed, the age of component is reduced. In this situation, the age of component is returned somewhere between the current age of it and the state of as-good-as-new. However, repair reduces the age of component more than mechanical service. If the component is replaced, it is returned to a state of as-good-as-new. If no action is performed, the age of component is not changed. If the system is suddenly stopped before the end of each period, corrective maintenance (CM) is performed. The objective is to determine optimal preventive maintenance activity for each component of system at the end of each period. In other words, it must be decided about each component of system at the end of each period to perform which kind of PM activities. The optimal actions for each component at the end of each period are derived, such that the availability of the system subject to a constraint on system costs over maintenance planning horizon is maximized. The total maintenance cost of the system includes the cost of performing PM, cost of performing CM, system stopping cost due to performing PM, and system stopping cost due to performing CM. A numerical example is given to illustrate the proposed model.